Дисертації: "Turbulent swirling"

1

Jones, Lee Nicholas. "Modelling of turbulent swirling flows." Thesis, University of Leeds, 2004. http://etheses.whiterose.ac.uk/1192/.

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This thesis investigates the predictability of non-reacting and reacting anistropic turbulent, swirling flows using popular turbulence models with a robust numrical procedure. The performance of these turbulence models is assessed and compared against experimental data for anisotropic, turbulent swirling flow in a cylindrical pipe and non-reacting and reacting combustion chambers. The transport equations for title k -e and k - w two-equation turbulence models are presented along with the LRR and SSG second-moment closure models for isothermal and variable density flows. The effect of anisotropy in the Reynolds stress dissipation rate tensor is accounted for by the inclusion of an algebraic model for the dissipation anistropy tensor dependent 0n the mean strain and vorticity of the flow. The implementation of the SMART and CUBISTA boundedness preserving, high order accurate convective discretisation schemes is shown to yield superior predictive accuracy compared to previous methods such as Upwinding. The PISO and SIMPLE solution algorithms are employed to provide a robust calculation procedure. The second moment closure models are found to provide increased predictive accuracy compared to those of the two-equation models. Mean flow properties are predicted well, capturing the effects of the swirl in the experimental flow field. The LRR model shows a premature decay of swirl downstream compared to the more accurate predictions of the other models. The effect of dissipation anistropy on the SSG model shows an over-prediction of the turbulent properties in the upstream region followed by premature decay downstream. In the near field of the non-reacting combustion chamber flow, the anisotropic dissipation model corrects the SSG model over-prediction of the veloocities at the central axis. A combined CMC flamelet combustion model is employed alongside the anisotropic dissipation Reynolds stress model to predict the flow field and combustion related properties of the TECFLAM swirl burner. The species mass fractions are conditioned on the mixture fraction to provide an accurate model for the determination of the probability density functions governing the reactions within the turbulent flamelet. The turbulent model shows an ability to provide accurate predictinS for the aerodynamic properties of the flow whilst providing accurate determination of combustion related phenomena alongside the combnstion model. A limitation of the flamelet assumption was identified with the over-prediction of CO due to the larger lengthscales of the oxidation reactions present in such flows.

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2

Zhang, Huangwei. "Extinction in turbulent swirling non-premixed flames." Thesis, University of Cambridge, 2015. https://www.repository.cam.ac.uk/handle/1810/254974.

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This thesis investigates the localized and global extinction in turbulent swirling non-premixed flames with Large Eddy Simulation (LES) and sub-grid scale Conditional Moment Closure (CMC) model. The first part of this thesis describes the derivations of the three dimensional conservative CMC governing equations and their finite volume discretization for unstructured mesh. The parallel performance of the newly developed CMC code is assessed. The runtime data coupling interface between the 3D-CMC and LES solvers is designed and the different solvers developed during the course of this research are detailed. The aerodynamics of two swirling non-reacting flows from the Sydney and Cambridge burners are first simulated. The main ow structures (e.g. the recirculating zones) in both cases are correctly predicted. The sensitivity analysis about the influences of turbulent inlet boundary, computational domain and mesh refinement on velocity statistics is conducted. This analysis acts as the preparatory investigation for the following flame simulations. The Sydney swirl diluted methane flame, SMA2, is then simulated for validating the LES/3D-CMC solvers. Excellent agreements are achieved in terms of velocity and mixture fraction statistics, averaged reactive scalars in both physical and mixture fraction space. The local extinction level from the increased central fuel velocity is reasonably predicted. At the experimental blow-off point, the LES/3D-CMC modelling does not obtain the occurrence of complete extinction, but severe extinction occurs at the flame base, qualitatively in line with experimental observations. Localized extinction features of a non-premixed methane flame in the Cambridge swirl burner are investigated and it is found that the occurrence of local extinction is typically manifested by low heat release rate and hydroxyl mass fraction, as well as low or medium temperature. It is also accompanied by high scalar dissipation rates. In mixture fraction space, the CMC cells undergoing local extinction have relatively wide scatter between inert and fully burning solutions. The PDFs of reactedness at the stoichiometric mixture fraction demonstrate some extent of bimodality, showing the events of local extinction and reignition and their relative occurrence frequency. Local extinction near the bluff body in the Cambridge swirl burner is also studied. The convective wall heat loss is included as a source term in the conditionally filtered total enthalpy equation. It shows a significant influence on the mean flame structures, directly linked to the changes of the conditional scalar dissipation near the wall. Furthermore, the degree of local extinction near the bluff body surface is intensified because of the wall heat loss. However, the wall heat loss shows a relatively small influence on the statistics of lift-off height. Finally, the blow-off conditions and dynamics in the Cambridge swirl burner are investigated. The blow-off critical air bulk velocity from LES/3D-CMC is over-predicted, greater than the experimental one by at most 25%. The predicted blow-off transient lasts finitely long duration quantified by the blow-off time, in good agreement with the experimental results. The reactive scalars in both physical and mixture fraction space demonstrate different transient behaviors during blow-off process. When the current swirling flame is close to blow-off, high-frequency and high-amplitude fluctuations of the conditionally filtered stoichiometric scalar dissipation rate on the iso-surfaces of the filtered stoichiometric mixture fraction are evident. The blow-off time from the computations is found to vary with different operating conditions.

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3

Riahi, Ardeshir. "Turbulent swirling flow in short cylindrical chambers." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/30810.

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The effects of aspect ratio (L/D) on the rate of decay of swirl in a cylindrical chamber were experimentally studied using the Laser-Doppler-Anemometry technique. Preliminary measurements revealed that water should be used as working fluid; the results pertaining to air were inferred from Reynolds number similarity. The steady-state measurements revealed that a solid body type of rotation can be generated by a disc whose surface has been uniformly roughened. The effect of aspect ratio on the rate of decay of such flow field was studied in three chambers with aspect ratios in the range of interest to engine combustion. Experimental results showed a faster decay rate in the shorter chamber (i.e. smaller aspect ratio). This was attributed to the stronger swirl driven secondary flow pattern in the shorter chamber. A mathematical model describing axi-symmetric, decaying, turbulent swirling flow inside a short cylindrical chamber was also developed. The model was numerically solved, using the control-volume analysis, to provide insight on swirl decay in engines. The model validation was based on experimental observations. Turbulence parameters were represented by a two-equation turbulence model, modified for streamline curvature effects. The ad-hoc curvature modification of the standard k-e model proposed by Launder et al. and the mixing energy model developed by Saffman-Wilcox-Traci (SWT) were used to account for curvature effects. The analysis of steady flow between two long concentric cylinders, established the superiority of the latter over the former method. The SWT model was also successfully used in reproducing previously published experimental results, pertaining to decaying swirling flow field (mean velocity and turbulence intensity) in a short cylinder. The calculated turbulence intensity profile revealed that swirl promotes anisotropic turbulence. The validated numerical model was used to predict the effect of aspect ratio on the rate of decay of the flow field observed by the experimental measurements in the present study. The overall prediction of decay rate was successful, leading to the conclusion that Wilcox and Chambers model can be used in predicting the behaviour of two-dimensional transient turbulent swirling flows.
Applied Science, Faculty of
Mechanical Engineering, Department of
Graduate

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4

García-Villalba, Navaridas Manuel. "Large eddy simulation of turbulent swirling jets." Karlsruhe : Univ.-Verl. Karlsruhe, 2006. http://deposit.d-nb.de/cgi-bin/dokserv?idn=979664586.

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5

Ranga-Dinesh, K. K. J. "Large eddy simulation of turbulent swirling flames." Thesis, Loughborough University, 2007. https://dspace.lboro.ac.uk/2134/21086.

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Large eddy simulation (LES) is attractive as it provides a reasonable compromise between accuracy and cost, and is rapidly evolving as a practical approach for many engineering applications. This thesis is concerned with the application of large eddy simulation to unconfined swirl in turbulent non-premixed flames and isothermal flows. The LES methodology has been applied for the prediction of turbulent swirling reacting and non-reacting flows based on laboratory scale swirl burner known as the Sydney swirl burner, which has been a target flame of the workshop series of turbulent non-premixed flames (TNF). For that purpose a LES code was developed that can run wide range of applications. An algorithm was developed for LES of variable density reacting flow calculations. Particular attention was given to primitive conservation (mass, momentum and scalar) and kinetic energy of the flow and mixing field. The algorithm uses the primitive variables, which are staggered in both space and time. A steady laminar flamelet model which includes the detailed chemical kinetics and multi component mass diffusion, has been implemented in the LES code. An artificial inlet boundary condition method was implemented to generate instantaneous turbulent velocity fields that are imposed on the inflow boundary of the Cartesian grid. To improve the applicability of the code, various approaches were developed to improve stability and efficiency. LES calculations for isothermal turbulent swirling jets were successful in predicting experimentally measured mean velocities, their rms fluctuations and Reynolds shear stresses. The phenomenon of vortex breakdown (VB) and recirculation flow structures at different swirl and Reynolds numbers were successfully reproduced by the present large eddy simulations indicating that LES is capable of predicting VB phenomena which occurs only at certain conditions. For swirling flames, the LES predictions were able to capture the unsteady flow field, flame dynamics and showed good agreement with experimental measurements. The LES predictions for the mean temperature and major species were also successful.

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6

Vondál, Jiří. "Computational Modeling of Turbulent Swirling Diffusion Flames." Doctoral thesis, Vysoké učení technické v Brně. Fakulta strojního inženýrství, 2012. http://www.nusl.cz/ntk/nusl-234149.

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Schopnost predikovat tepelné toky do stěn v oblasti spalování, konstrukce pecí a procesního průmyslu je velmi důležitá pro návrh těchto zařízení. Je to často klíčový požadavek pro pevnostní výpočty. Cílem této práce je proto získat kvalitní naměřená data na experimentálním zařízení a využít je pro validaci standardně využívaných modelů počítačového modelování turbulentního vířivého difúzního spalování zemního plynu. Experimentální měření bylo provedeno na vodou chlazené spalovací komoře průmyslových parametrů. Byly provedeny měření se pro dva výkony hořáku – 745 kW a 1120 kW. Z měření byla vyhodnocena data a odvozeno nastavení okrajových podmínek pro počítačovou simulaci. Některé okrajové podmínky bylo nutné získat prostřednictvím dalšího měření, nebo separátní počítačové simulace tak jako například pro emisivitu, a nebo teplotu stěny. Práce zahrnuje několik vlastnoručně vytvořených počítačových programů pro zpracování dat. Velmi dobrých výsledků bylo dosaženo při predikci tepelných toků pro nižší výkon hořáku, kde odchylky od naměřených hodnot nepřesáhly 0.2 % pro celkové odvedené teplo a 16 % pro lokální tepelný tok stěnou komory. Vyšší tepelný výkon však přinesl snížení přesnosti těchto predikcí z důvodů chybně určené turbulence. Proto se v závěru práce zaměřuje na predikce vířivého proudění za vířičem a identifikuje několik problematických míst v použitých modelech využívaných i v komerčních aplikacích.

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7

Müller, Sebastian. "Numerical investigations of compressible turbulent swirling jet flows." kostenfrei, 2007. http://e-collection.ethbib.ethz.ch/view/eth:30052.

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8

Regunath, Gavita Shamuna. "Measurements and Investigation of Helicity in Turbulent Swirling Flow." Thesis, University of Sheffield, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.489741.

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9

Chang, T. H. "An investigation of turbulent swirling flow with heat transfer." Thesis, Swansea University, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.636228.

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A detailed investigation of swirling flow in an axisymmetric pipe has been undertaken and the findings from both an experimental and analytical research programme have been reported in this thesis. The study was divided into two sections, firstly that concerning isothermal flow, before extending it to account for heat transfer resulting from swirling flow within a heated pipe. An experimental test-rig was manufactured to permit a detailed interrogation of all flow variables. The rig incorporated a specially designed swirl generator, fitted to the inlet of a perspex circular pipe, enabling varying intensities of swirl flow to be stimulated over a Reynolds number range of 20-60 x 10³. An identical pipe, manufactured out of copper, enabled a constant heat flux to be applied at its outer surface, thereby permitting a corresponding investigation of the heat transfer phenomena. An analysis of the above flow regimes was undertaken through the solution of the equations of flow and the one-equation (k-1) model together with corresponding boundary conditions, for depicting isothermal turbulent flow with swirl. For the heat transfer analysis, a solution of the energy equation with its appropriate boundary conditions was included. The solution of the mathematical model was effected by using the finite element method and discretising in three dimensions over the domain. The effect of increasing the swirl intensity results in a migration of the locus of the points of maximum axial and tangential velocity towards the pipe wall. This is accompanied by higher heat transfer rates for a constant surface heat flux. The analysis has provided a viable technique for predicting turbulent flow with low swirl intensities, exhibiting good comparisons with the experimental results over much of the flow field. The main discrepancy occurred in the region of flow reversal, where the analysis is underpredictive, a consequence of the limitation of the one-equation model in accounting for momentum transport across the boundary of zero velocity.

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10

Croft, Thomas Nicholas. "Unstructured mesh : finite volume algorithms for swirling, turbulent, reacting flows." Thesis, University of Greenwich, 1998. http://gala.gre.ac.uk/6371/.

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The work presented in this thesis develops techniques, employing the Finite Volume discretisation method, which allow the numerical simulation of three dimensional heat transfer and fluid flow problems using unstructured meshes. The method solves and stores all variables at the element centres which lowers storage requirements and generally shortens run times compared with the Control Volume-Finite Element approach. Correction terms are formulated which address two of the main forms of errors caused by mesh skewness. To allow a generic handling of any unstructured mesh the Cartesian components of velocity are solved under all circumstances. This leads to the requirement to adjust the discretisation of the momentum equations when there is significant flow curvature. The changes are presented in this study both when the position of the flow axis is known prior to the simulation and when its position is known only as a result of the simulation, this being the case when there is more than one source of swirling flow. These original features contribute to a Computational Fluid Dynamics code which is capable of solving swirling, turbulent fluid flow and reactive, radiative heat transfer on highly complex geometries. Specifically the techniques are applied to the simulation of processes occurring in the direct smelting of iron. The use of the Finite Volume method makes it relatively easy to employ many techniques and physical models developed for structured codes. The evaluation of the face convective fluxes is effected through the Rhie - Chow interpolation method. The SIMPLE algorithm is used in the pressure - velocity coupling. In the simulation of swirling flows it is shown that both the standard and ReNormalisation Group k-e models fail to accurately predict turbulent effects. An anisotropic hybrid (k-e and mixing length) model is developed which produces excellent numerical results for the flows of interest. The Simple Chemical Reaction Scheme is used to evaluate the transport of the various chemical species. Radiation effects are simulated through the use of the radiosity model. A series of simulation results are presented which show the capabilities of the methods in test cases ranging from simple heat transfer problems through to the simulation of two swirling jets in a three dimensional unstructured mesh.

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11

Fu, Song. "Computational modelling of turbulent swirling flows with second-moment closures." Thesis, University of Manchester, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.267917.

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This work focuses on the simulation of turbulent swirling flows within the framework of second-moment closure. The main objectives are to assess the performance of currently available turbulence models in predicting such flows, and to develop new closure models which would further enhance current predictive ability, and hence, to provide a reliable turbulence model for engineering applications that would help the design process and reduce the development costs of industrial combustion systems. Attention is confined to isothermal flows, and predictions have been carried out for three major swirling cases: a weakly and a strongly swirling free jet and a confined strongly swirling flow in which an annular swirling stream is discharged together with a non-swirling central jet into a suddenly enlarging circular chamber. In the last case, mass transfer has also been examined by predicting the behaviour of an inert scalar tracer with which the central jet has been laced. The existing turbulence models examined are the standard versions of the k — e Boussinesq-viscosity model, the algebraic stress closure and the differential stress closure (BVM, ASM and DSM, respectively), as well as modified ASM and DSM variants. One outcome of this study is that neither the standard versions of the BVM, ASM and DSM nor their previously modified forms examined here predict adequately swirling-flow behaviour. An important conclusion emerging from preliminary efforts has been that the algebraic approximation of stress transport in terms of the transport of turbulence energy—which is a widely used practice—is fundamentally flawed in the presence of swirl. Specifically, the method returns a physically unrealistic behaviour of the normal stresses. It is this conclusion which eventually led to the ASM methodology being discarded and to the exclusive use of the differential methodology. Within the framework of differential closures, two new pressure-strain models have been proposed, namely the Isotropization of Production and Convection Model (IPCM) and the Cubic Quasi-Isotropic Model (CQIM). The former emerged as an extension of the standard DSM approach with the inclusion of the convection tensor into the turbulence isotropization mechanism, whereas the latter follows from a more rational and fundamental approach in which non-linear anisotropy effects have been incorporated, with the resulting model made to satisfy the limit of two-dimensional turbulence. Comparisons between predicted solutions and measurements for swirling flow show that the IPCM produces a marked improvement over all the other models considered, while it does not significantly alter the behaviour of the standard stress closure in non-swirling conditions. Only very limited improvement is achieved by the CQIM, however, despite its success in predicting nearly homogeneous shear flows. The merits and weaknesses of all the models examined are discussed in detail, and the IPCM is recommended as the best approach for predictions of swirling flows. Within the study of the confined case, considerations were extended to the modelling of scalar transport by a second-moment flux closure, and comparisons are made between eddy-diffusivity and flux-closure calculations and experimental data. Computational results show that the distribution of the scalar field is primarily governed by aero-dynamic features. There are indications, however, that the flux model is superior to the eddy-diffusivity model.

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12

Armfield, S. (Steve) 1956. "Numerical simulation of incompressible turbulent swirling flow in conical diffusers." Phd thesis, Department of Mechanical Engineering, 1988. http://hdl.handle.net/2123/8074.

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13

Cho, Nam-Hyo. "Computation of turbulent swirling flows in conical diffusers with tailpipes." Phd thesis, Department of Mechanical Engineering, 1990. http://hdl.handle.net/2123/7998.

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14

García-Villalba, Navaridas Manuel [Verfasser]. "Large eddy simulation of turbulent swirling jets / Manuel García-Villalba Navaridas." Karlsruhe : Univ.-Verl. Karlsruhe, 2006. http://d-nb.info/979664586/34.

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15

Kong, L. "Finite element analysis to confined turbulent swirling flow with heat transfer." Thesis, Swansea University, 1993. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.637821.

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A finite element based numerical method has been developed in order to model the isothermal and heat tranfer aspects of turbulent swirling flows. A number of turbulent modelling techniques, such as the one-equation (K - L) model, the two-equation (K - ε) model, and the Reynolds stress models have been investigated. Numerical results indicate that better turbulence models can produce higher accurate predictions. In the present study, the two-equation model gives much better flow field predictions than the one-equation model, and the Algebraic Stress model produces predictions even closer to the experimental results. The universal law of wall is adopted as the main techniques in modelling the near wall zone, whilst other near wall modelling is investigated. it is found that boundary conditions, especially the inlet boundary conditions play important roles in the development of the downstream flow field. Unrealistic inlet conditions for any of the flow variables can be lead to erroneous prediction downstream.

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16

Ikhlaq, Muhammad. "Flow and heat transfer characteristics of turbulent swirling impinging jets [thesis]." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2021. https://ro.ecu.edu.au/theses/2389.

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Numerous industrial applications rely on impinging jets to impart convective heat and mass transfer in processes ranging from the cooling of electronic devices and gas turbine blades to drying of paper and food products. Conventionally, non-swirling impinging jets have been employed, but some studies have shown that inducing swirl allows better control of uniformity and improved convective fluxes. A better understanding of the underlying physical mechanisms that lead to such behaviour warrants deeper insights into the flow and heat transfer characteristics of impinging jets, both swirling and non-swirling. Whilst important to achieve, the flow field of an impinging jet is already quite complex even before the addition of swirl which, in free (not impinging) jets, induces vortex breakdown and other instability modes. The addition of swirl to impinging jets thus has the potential to affect the transient and steady-state convective behaviour, both of which are crucial in industrial applications. This study features experimental and numerical investigations of incompressible turbulent impinging air jets that utilize aerodynamically generated swirl. The research focuses on the velocity field, upstream near the nozzle exit plane as well as further downstream, and the way in which it affects heat transfer at the impingement plane, both under transient and steady-state conditions. Boundary conditions at the nozzle exit were measured using Constant Temperature Anemometry. The surface temperature distribution of a thin foil heater, which forms the impingement surface cooled by the ambient temperature jet, was measured using infrared thermography for a range of Reynolds numbers (Re=11,600-35,000), swirl numbers (S=01.05), and impingement distances (H/D=2-6). The effects of different inflow conditions for non-swirling and weakly swirling impinging jets were also simulated (numerically) using ANSYS Fluent (version 16.2). Particle Image Velocity was utilized to resolve the flow field, over low (S=0.30) and higher (S=0.74) swirl over a range of Reynolds numbers (Re=11,60035,000) and nozzle-to-plate distance (H/D=2 and 4). Whilst the use of non-intrusive infrared thermography has been widely reported in studies of the steady-state heat transfer behaviour of impinging jets, an image processing methodology to resolve the time-dependant (transient) convective heat transfer behaviour was lacking. In this context, a MATLAB based method was developed to quantify the role of various impinging jet parameters on the time to reach steady-state. The effect of spatial discretization, image resolution, and the threshold value of time-dependent Nusselt number, on the time to reach steady-state, was also analysed. The role of various operating (Re, S) and geometric conditions (H/D) on the temporal evolution of turbulent impinging jets was also resolved. By applying the innovative image processing methodology developed, results show that for non-swirling jets, transient heat transfer characteristics at some conditions (H/D=4) are distinct if compared to others (H/D=2 and 6) and that the heat transfer distribution over the impingement plate changes significantly over a small interval of time. For swirling jets, the peak Nusselt number shifts to the wall jet region as the intensity of the swirl increases. Two correlations (no-to-low swirl, moderate-to-high swirl) are proposed to predict the time needed to reach a steady-state for Re=35,000. Computational Fluid Dynamics was then used to resolve the role of various (upstream) nozzle exist conditions (velocity profiles) on the emerging heat transfer characteristics at the impingement plane. Results showed that under some conditions (S=0.31, uniform velocity profile) a small recirculation zone, stabilised on the impingement plane, affects the heat transfer compared to other tested velocity profiles. This study also gave valuable insights on the impact of using (simple) geometric inserts to generate for swirl into impinging jets, a method widely used for its simplicity. Results showed that this can fundamentally perturb the results unlike the use of aerodynamic swirl which relies on tangential air ports. For the experimentally measured flow field, vortex breakdown is observed for two of conditions (Re=11,600 and 24,600 at S=0.74) out of the six tested. Impingement affects the position, shape, and strength of the vortex breakdown. For Re=24,600, impingement significantly affects (shape and position) the recirculation bubble when compared to impingement at Re=11,600. Heat transfer characteristics at high swirl are compared with low swirling impinging jets. The vortex breakdown (at high swirl) affects the impingment heat transfer and showed comparatively uniform heat transfer distribution in contrast to low swirling impinging jets. Vortex breakdown significantly deteriorates stagnation zone heat transfer and the Nusselt number peak occurs in the wall jet region. Benefits derived from this study include identifying impingement conditions that allow quicker stabilisation of heat transfer (shorter transients) as well as an improved understanding for the role of impingement on the upstream and downstream velocity field and heat transfer characteristics.

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17

Haber, Ludwig Christian. "Investigation of Dynamics in Turbulent Swirling Flows Aided by Linear Stability Analysis." Diss., Virginia Tech, 2003. http://hdl.handle.net/10919/11076.

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Turbulent swirling flows are important in many applications including gas turbines, furnaces and cyclone dust separators among others. Although the mean flow fields have been relatively well studied, a complete understanding of the flow field including its dynamics has not been achieved. The work contained in this dissertation attempts to shed further light on the behavior of turbulent swirling flows, especially focused on the dynamic behavior of a turbulent swirling flow encountering a sudden expansion. Experiments were performed in a new isothermal turbulent swirling flow test facility. Two geometrical nozzle configurations were studied. The \cb\ nozzle configuration exhibits a cylindrical \cb\ in the center of the nozzle. The free vortex nozzle configuration is obtained when the cylindrical \cb\ is removed. Detailed laser velocimeter measurements were performed to map out the flow field near the sudden expansion of the 2.9" (ID) nozzle leading to the 7.4" (ID) downstream section. In addition to presenting detailed flow profiles for both nozzle and downstream flow fields, representative frequency spectra of the flow dynamics are presented. Along with the flow time histories and histograms, the wide variety of dynamic behavior was thus described in great detail. The dynamics observed in the experiment can be classified into three main categories: coherent and large scale motion, intermittent motion and coherent periodic motion. Free vortex geometry flows, in the parameter space of the experiments (Swirl number = 0 - 0.21), exhibited mostly coherent and large scale motion. The spectra in these cases were broadband with very light concentration of spectral energy observed in some specific cases. Center--body geometry flows exhibited all three categories of flows as swirl strength was increased from zero. Flows with little or no swirl exhibited broad--band spectra similar to those for the free vortex geometry. Intermediate swirl levels resulted in a large amount of low frequency energy which, with the aid of the time histories, was identified as a large scale intermittence associated with radial movement of the annular jet as it enters the sudden expansion. Large swirl levels resulted in high magnitude coherent oscillations concentrated largely just downstream of the sudden expansion. Linear stability analysis was used to help in the interpretation of the observed dynamics. Although, as implemented here (using the parallel flow assumption), the analysis was not successful in quantitatively matching the experimentally observed dynamics, significant insight into the physical mechanisms of the observed dynamics was obtained from the analysis. Specifically, the coherent oscillations observed for larger swirl levels were able to be described in terms of the interaction between the inner and outer shear layers of the flow field.
Ph. D.

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18

Ahmed, Zahir Uddin. "An experimental and numerical study of surface interactions in turbulent swirling jets." Thesis, Edith Cowan University, Research Online, Perth, Western Australia, 2016. https://ro.ecu.edu.au/theses/1790.

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Convective heat transfer and drying processes are found in industrial applications from gas turbine blade cooling to drying of food products and paper. In many instances, these processes rely on either a single or an array of fluid jets which impinge onto a surface. Traditionally, non-swirling impinging jets have been used, but interest surrounds possible advantages from imposing swirl into these jets to further promote heat and mass transfer at the surface. The challenge of resolving this question is that including swirl further complicates fluid-surface interactions. Studies are faced with the complexity of flow behaviour, the need for intricate measurement techniques and jets which seamlessly transition from non-swirling to swirling with well-defined boundary conditions. To better understand the nature of turbulent jet impingement with, and without, swirl requires carefully designed experiments covering parameters believed to affect the magnitude and uniformity of heat transfer. This research investigated, experimentally and numerically, incompressible turbulent impinging air jets using aerodynamically derived swirl. The aim was to elucidate the effects of different parameters on fluid flow and surface heat transfer characteristics. Measurements of mean velocity and turbulence, surface pressure and temperatures were done using Constant Temperature Anemometry, integrating micro-manometer (pressure) tappings and steady-state heated thin foil technique via infrared thermography. Imaging for flow visualisations was also done. Numerical simulations were performed using ANSYS Fluent (version 14.5). Test conditions investigated encompassed a range of Reynolds numbers (Re = 11,600 – 35,000), swirl numbers (S = 0 – 1.05) and nozzle-to-plate distances (H = 1D – 6D). Results show that the use of low-to-medium swirl numbers (S = 0.27 – 0.45) is found to improve heat transfer (Nu) in the impingement region compared to non-swirling (S = 0) jets over H ≤ 4D, with little improvement in spatial Nu uniformity. When S further increases, significant enhancement in Nu occurs only at near-field impingement (H ≤ 2D), regardless of the impingement area (footprint). At H ≥ 4D, a significantly low but more uniform radial profile of Nu is obtained. Results conclude the effect of swirl on the heat transfer characteristics is a complex relationship, which depends on the Reynolds number and nozzleto- plate distance. Whilst high swirl can lead to significant improvements in heat transfer, this is not necessarily always the case. It appears that there exist a threshold impingement distance and a transitional swirl number (dependent on Re) over which the effect of swirl on field and turbulence at different swirl numbers and nozzle-to-plate distances, with flow recirculation in near-field impingement (H = 2D) and non-swirl like at far-field (H = 6D). The occurrence of peak heat transfers at different swirl numbers is largely correlated with swirl induced turbulence characteristics near the impingement surface. Increase in Reynolds number augments the magnitude of Cp and heat transfer. For a given S, flow field and heat transfer distributions are found to be largely independent of Re.

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19

Karasu, Tahir. "Numerical prediction of incompressible turbulent swirling flows in circular sectioned ducts and annuli." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/8804.

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20

Lin, Chao-An. "Three-dimensional computations of injection into swirling cross-flow using second-moment closure." Thesis, University of Manchester, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.280543.

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21

Oberleithner, Kilian [Verfasser], and Christian Oliver [Akademischer Betreuer] Paschereit. "On Turbulent Swirling Jets:Vortex Breakdown, Coherent Structures,and their Control / Kilian Oberleithner. Betreuer: Christian Oliver Paschereit." Berlin : Universitätsbibliothek der Technischen Universität Berlin, 2012. http://d-nb.info/1024771504/34.

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22

Francia, Garcia Victor. "Spray drying of detergents in counter current towers : a study of turbulent swirling flows, fouling and agglomeration." Thesis, University of Birmingham, 2015. http://etheses.bham.ac.uk//id/eprint/5646/.

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This thesis is concerned with the manufacture of granular laundry detergents in counter-current spray dryers making use of turbulent swirling flows. It contributes to a comprehensive description of this process by providing a) an experimental study of the swirling fluid dynamics in various scales and designs, introducing the use of sonic anemometry to this context, b) the description of a complex fouling dynamics at the walls, quantified by rates of deposition and re-entrainment of material, and c) the analysis of the sources of particle-droplet agglomeration in different sections of the dryer, under the operation of one or multiple sprays. This thesis demonstrates that the interaction with the walls is a central part of the process. In the one hand, friction affects the structure of the flow: it reduces its angular momentum and destabilizes the swirl, which causes recirculation in the dryer and the production of turbulence. In the other, particles deposit at the walls forming a multi-layer that continuously builds and breaks up. A tracer experiment has revealed that this equilibrium in part governs the product residence time, and ultimately how particles dry and aggregate. The data provided here constitute the first evidence of such a behavior in spray dryers.

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23

Taamallah, Soufien. "Impact of fuel and oxidizer composition on premixed flame stabilization in turbulent swirling flows : dynamics and scaling." Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/103437.

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Thesis: Ph. D., Massachusetts Institute of Technology, Department of Mechanical Engineering, 2016.
This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 205-214).
The world relies on fossil fuels as its main energy source (86.7% in 1973, 81.7% in 2012). Several factors including the abundance of resources and the existing infrastructure suggest that this is likely to continue in the near future (potentially 75% in 2040). Meanwhile climate change continues to be a pressing concern that calls for the development of low CO2 energy systems. Among the most promising approaches are pre-combustion capture technologies, e.g., coal gasification and natural gas reforming that produce hydrogen-rich fuels. Another approach is oxy-combustion in which air is replaced by a mixture of O2/CO2/H2O as the oxidizer stream. However, modern gas turbines have been optimized to operate on methane-air combustion and several challenges, notably thermo-acoustic instability, arise when using other fuels or oxidizers because of their different thermochemical and transport properties. While these phenomena constitute a major challenge under conventional operations, using hydrogen-rich fuels or CO2-rich oxidizer exacerbates the problem by modifying the combustor stability map in ways that are not well understood. In this thesis, we identify combustion modes most prone to dynamics, predict the onset of thermo-acoustic instability over a wide range of fuel and oxidizer compositions, and define parameters that can scale the data. To this end, a combination of experimental and numerical tools were deployed. We carried out a series of experiments in an optically accessible laboratory-scale swirl-stabilized combustor typical of those found in modern gas turbines, using high-speed chemiluminescence to examine the flame macrostructure; high-speed Particle Image Velocimetry and OH Planar Laser Induced Fluorescence to probe the flow and flame microstructure. Numerical simulations were used to complement experiments and examine the complex three-dimensional two-way interaction between the flame and the turbulent swirling flow. Experimental data were used to construct the stability maps for different CH4-H2 mixtures and analyze the dynamic flame macrostructures and their transitions. A comparison with acoustically uncoupled combustion shows that the onset of thermo-acoustic instability is concomitant with a specific transition associated with the intermittent appearance of the flame in the outer recirculation zone (ORZ) and stabilization along the outer shear layer (forming between the swirling jet and the ORZ, as revealed by the PIV-PLIF data). The sudden onset of large amplitude limit cycle oscillations and the observed hysteresis suggest the existence of a sub-critical Hopf bifurcation typically characterized by a bistable or "triggering" zone; the flame intermittency in the ORZ can potentially provide the disturbance required to trigger these oscillations. Using a dual-camera method to track chemiluminescence in space and time, this flame transition was found to originate from a reacting kernel that detaches from the inner shear layer flame (forming between the jet and the vortex breakdown zone), reaching the ORZ and spinning at a specific frequency; its characteristic Strouhal number is independent of the Reynolds number and the fuel/oxidizer, only a function of the swirl strength. We propose a new Karlovitz number based criterion that defines the transition on a flow time - flame time space, the former being the inverse of the spinning frequency and the latter being the flame extinction strain rate. According to this scaling, the flame survives in the ORZ if and when it can overcome the region's bulk strain rate. This criterion is valid over a wide range of operating, fuel and oxidizer composition, covering a wide range of fast to slow chemistry scenarios. Given the role of this flame transition in triggering the instability, the same criterion is applicable to predicting the onset of thermo-acoustics. The interaction of the turbulent swirling flow with the flame is further examined using large eddy simulations. Numerical simulations show that the experimentally observed large scale flame structures along the inner shear layer are due to a helical vortex core that originates at the swirler's centerbody. This vortical structure stays aligned with the centerline in the combustor upstream section, but bends and reaches the inner shear layer-stabilized flame around the sudden expansion where it causes the flame wrinkling. We propose that the flame kernel igniting the ORZ/ OSL observed in the experiment may be related to the interaction between the helical vortical structure and the outer shear layer.
by Soufien Taamallah.
Ph. D.

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24

Roussillo, Mathieu. "Development of optical diagnostics for soot particles measurements and application to confined swirling premixed sooting flames under rich conditions." Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLC060/document.

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Le contrôle de la production des particules de suies est aujourd'hui un enjeu industriel majeur en raison de leur impact néfaste tant sur le climat que sur la santé humaine et de leur forte contribution aux transferts radiatifs. Pour mieux comprendre et contrôler la production de ces polluants dans les foyers industriels, il est primordial d’améliorer nos connaissances à ce sujet dans un brûleur turbulent. L’objectif de cette thèse est donc de mettre en place des diagnostics optiques pour l’étude des flammes suitées turbulentes et pour caractérise la production de suies dans une nouvelle configuration de combustion prémélangée,confinée, swirlée turbulente académique tout en se rapprochant des configurations industrielles. Une première configuration expérimentale laminaire est donc considérée afin de valider la mise en place de la technique d’Incandescence Induite par Laser (LII) pour mesurer la fraction volumique de suies fv. Il s’agit d’un brûleur conçu à l’université de Yale qui permet la stabilisation d’une flamme laminaire de diffusion éthylène/air. Ce brûleur a été largement étudié dans la littérature nous permettant ainsi de comparer nos mesures aux résultats de différentes équipes internationales. La calibration du signal LII avec la technique MAE (Modulated Absorption Emission) a été effectuée via une collaboration avec l’UPMC, permettant de mesurer quantitativement fv et de comparer les techniques MAE et LII. Le brûleur a ensuite été équipé d’un haut-parleur afin de moduler l’écoulement et de pouvoir étudier les effets d’une perturbation contrôlée sur la production de suies, se rapprochant ainsi des phénomènes instationnaires caractéristiques des écoulements turbulents. Enfin, les effets d’élargissement de la nappe laser sur les résultats de la LII sont examinés afin de pouvoir appliquer ce diagnostic optique dans une configuration turbulente innovante caractérisée par de grandes dimensions. Ce brûleur (EM2Soot) a été développé pour mesurer la production de suies dans une flamme turbulente swirlée riche confinée prémélangée. Il permet de quantifier indépendamment les effets de la richesse, de la puissance et de l’environnement thermique sur la production de suies. Un point de fonctionnement représentatif a alors été étudié et, en parallèle avec la LII, les techniques de vélocimétrie par images de particules (PIV), et de mesure de température des parois par phosphorescence induite par laser (LIP) ont été employées afin de caractériser l’effet de la turbulence sur la production des suies et d’établir une base de données pour la validation de futures simulations numériques. Enfin, la géométrie du brûleur a été modifiée permettant une stabilisation différente de la flamme (en forme d’un V). Un nouveau point de fonctionnement a alors été étudié afin de mettre en évidence le rôle de la géométrie de l’injecteur sur la stabilisation de la flamme et, par conséquent, la production totale de suies
The control of soot particles production represents today a major industrial issue because of their harmful impact on both the climate and the human health and their strong contribution to the radiative transfers. To better understand and control the production of these polluting emissions, it is essential to improve our knowledge on this subject in a turbulent burner. The objective of this Ph.D. is to set up optical diagnostics for the study of turbulent flames and to experimentally characterize soot production in a new academic turbulent premixed combustion configuration while approaching industrial configurations, generally confined and swirled flows. For this, a laminar experimental configuration is first considered to validate the implementation of the Laser Induced Incandescence (LII) technique to measure the soot volume fraction fv. This burner designed at Yale University allows the stabilization of a laminar ethylene/air diffusion flame. This burner has been widely studied in the literature, so that it is possible to compare the quality of our measurements with the results of different international teams. Through collaborations with the UPMC, we calibrated the LII signal with the MAE (Modulated Absorption Emission) technique, making it possible to quantitatively measure fv and to compare the MAE and LII techniques. Finally, the burner was equipped with a loudspeaker to modulate the flow and to study the effects of a controlled perturbation on the soot production, thus approaching the unsteady phenomena characteristics of turbulent flows. Finally, the effects of the enlargement of the laser sheet on LII results were also investigated in order to be able to apply this diagnostic technique in an innovative large turbulent configuration. This experimental configuration, called EM2Soot, was developed to measure the production of soot in a turbulent swirled rich confined premixed ethylene/air flame. This burner makes it possible to independently quantify the effects of the equivalence ratio, the total flame power and the thermal environment on the total soot production. A representative operating point was then characterized, in parallel with LII measurements, Particle Image Velocimetry (PIV) and Laser Induced Phosphorescence (LIP) techniques have been employed in order to characterize the effect of the turbulence on soot production and to establish a database for the validation of future numerical simulations. Finally, the geometry of the burner has been modified allowing a different stabilization of the flame (V flame shape). A new operating point is then studied in order to highlight the role of the injector geometry on the stabilization of the flame and, consequently, on the total soot production

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25

Nabhani, Nader. "Hot-wire anemometry study of confined turbulent swirling flow : development of a hot-wire technique for measurement in confined turbulent swirling flow and an investigation of the effect of inlet flow rate and geometrical conditions on the velocity field." Thesis, University of Bradford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.256901.

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26

Kalpakli, Vester Athanasia. "Vortices in turbulent curved pipe flow-rocking, rolling and pulsating motions." Doctoral thesis, KTH, Mekanik, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-145311.

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This thesis is motivated by the necessity to understand the flow structure of turbulent flows in bends encountered in many technical applications such as heat exchangers, nuclear reactors and internal combustion engines. Flows in bends are characterised by strong secondary motions in terms of counter-rotating vortices (Dean cells) set up by a centrifugal instability. Specifically the thesis deals with turbulent flows in 90° curved pipes of circular cross-section with and without an additional motion, swirling or pulsatile, superposed on the primary flow. The aim of the present thesis is to study these complex flows in detail by using time-resolved stereoscopic particle image velocimetry to obtain the three-dimensional velocity field, with complementary hot-wire anemometry and laser Doppler velocimetry measurements. In order to analyse the vortical flow field proper orthogonal decomposition (POD) is used. The so called ``swirl-switching'' is identified and it is shown that the vortices instantaneously, ``rock'' between three states, viz. a pair of symmetric vortices or a dominant clockwise or counter-clockwise Dean cell. The most energetic mode exhibits a single cell spanning the whole cross-section and ``rolling'' (counter-)clockwise in time. However, when a honeycomb is mounted at the inlet of the bend, the Dean vortices break down and there is strong indication that the ``swirl-switching'' is hindered. When a swirling motion is superimposed on the incoming flow, the Dean vortices show a tendency to merge into a single cell with increasing swirl intensity. POD analysis show vortices which closely resemble the Dean cells, indicating that these structures co-exist with the swirling motion. In highly pulsating turbulent flow at the exit of a curved pipe, the vortical pattern is diminished or even eliminated during the acceleration phase and then re-established during the deceleration. In order to investigate the effect of pulsations and curvature on the performance of a turbocharger turbine, highly pulsating turbulent flow through a sharp bend is fed into the turbine. Time-resolved pressure and mass-flow rate measurements show that the hysteresis loop in the pressure-ratio-mass-flow plane, may differ significantly between straight and curved inlets, however the mean operating point is only slightly affected.

QC 20140523

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27

Hilares, Luis Roberto Tay Wo Chong [Verfasser], Wolfgang H. [Akademischer Betreuer] Polifke, and Thierry [Akademischer Betreuer] Schuller. "Numerical Simulation of the Dynamics of Turbulent Swirling Flames / Luis Roberto Tay Wo Chong Hilares. Gutachter: Thierry Schuller. Betreuer: Wolfgang H. Polifke." München : Universitätsbibliothek der TU München, 2012. http://d-nb.info/1020915129/34.

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28

Örlü, Ramis. "Experimental studies in jet ﬂows and zero pressure-gradient turbulent boundary layers". Doctoral thesis, KTH, Mekanik, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-10448.

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This thesis deals with the description and development of two classical turbulent shear flows, namely free jet and flat plate turbulent boundary layer flows. In both cases new experimental data has been obtained and in the latter case comparisons are also made with data obtained from data bases, both of experimental and numerical origin. The jet flow studies comprise three parts, made in three different experimental facilities, each dealing with a specific aspect of jet flows. The first part is devoted to the effect of swirl on the mixing characteristics of a passive scalar in the near-field region of a moderately swirling jet. Instantaneous streamwise and azimuthal velocity components as well as the temperature were simultaneously accessed by means of combined X-wire and cold-wire anemometry. The results indicate a modification of the turbulence structures to that effect that the swirling jet spreads, mixes and evolves faster compared to its non-swirling counterpart. The high correlation between streamwise velocity and temperature fluctuations as well as the streamwise passive scalar flux are even more enhanced due to the addition of swirl, which in turn shortens the distance and hence time needed to mix the jet with the ambient air. The second jet flow part was set out to test the hypothesis put forward by Talamelli & Gavarini (Flow, Turbul. & Combust. 76), who proposed that the wake behind a separation wall between two streams of a coaxial jet creates the condition for an absolute instability. The experiments confirm the hypothesis and show that the instability, by means of the induced vortex shedding, provides a continuous forcing mechanism for the control of the flow field. The potential of this passive mechanism as an easy, effective and practical way to control the near-field of interacting shear layers as well as its effect towards increased turbulence activity has been shown. The third part of the jet flow studies deals with the hypothesis that so called oblique transition may play a role in the breakdown to turbulence for an axisymmetric jet.For wall bounded flows oblique transition gives rise to steady streamwise streaks that break down to turbulence, as for instance documented by Elofsson & Alfredsson (J. Fluid Mech. 358). The scenario of oblique transition has so far not been considered for jet flows and the aim was to study the effect of two oblique modes on the transition scenario as well as on the flow dynamics. For certain frequencies the turbulence intensity was surprisingly found to be reduced, however it was not possible to detect the presence of streamwise streaks. This aspect must be furher investigated in the future in order to understand the connection between the turbulence reduction and the azimuthal forcing. The boundary layer part of the thesis is also threefold, and uses both new data as well as data from various data bases to investigate the effect of certain limitations of hot-wire measurements near the wall on the mean velocity but also on the fluctuating streamwise velocity component. In the first part a new set of experimental data from a zero pressure-gradient turbulent boundary layer, supplemented by direct and independent skin friction measurements, are presented. The Reynolds number range of the data is between 2300 and 18700 when based on the free stream velocity and the momentum loss thickness. Data both for the mean and fluctuating streamwise velocity component are presented. The data are validated against the composite profile by Chauhan et al. (Fluid Dyn. Res. 41) and are found to fulfil recently established equilibrium criteria. The problem of accurately locating the wall position of a hot-wire probe and the errors this can result in is thoroughly discussed in part 2 of the boundary layer study. It is shown that the expanded law of the wall to forth and fifth order with calibration constants determined from recent high Reynolds number DNS can be used to fix the wall position to an accuracy of 0.1 and 0.25 l_ * (l_* is the viscous length scale) when accurately determined measurements reaching y+=5 and 10, respectively, are available. In the absence of data below the above given limits, commonly employed analytical functions and their log law constants, have been found to affect the the determination of wall position to a high degree. It has been shown, that near-wall measurements below y+=10 or preferable 5 are essential in order to ensure a correctly measured or deduced absolute wall position. A number of peculiarities in concurrent wall-bounded turbulent flow studies, was found to be associated with a erroneously deduced wall position. The effect of poor spatial resolution using hot-wire anemometry on the measurements of the streamwise velocity is dealt with in the last part. The viscous scaled hot-wire length, L+, has been found to exert a strong impact on the probability density distribution (pdf) of the streamwise velocity, and hence its higher order moments, over the entire buffer region and also the lower region of the log region. For varying Reynolds numbers spatial resolution effects act against the trend imposed by the Reynolds number. A systematic reduction of the mean velocity with increasing L+ over the entire classical buffer region and beyond has been found. A reduction of around 0.3 uƬ, where uƬ is the friction velocity, has been deduced for L+=60 compared to L+=15. Neglecting this effect can lead to a seemingly Reynolds number dependent buffer or log region. This should be taken into consideration, for instance, in the debate, regarding the prevailing influence of viscosity above the buffer region at high Reynolds numbers. We also conclude that the debate concerning the universality of the pdf within the overlap region has been artificially complicated due to the ignorance of spatial resolution effects beyond the classical buffer region on the velocity fluctuations.
QC 20100820

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29

VERFAILLIE, SWANN. "CORRELATIVE STUDIES AND COHERENT STRUCTURES EDUCTION BASED ON PROPER ORTHOGONAL DECOMPOSITION AND LINEAR STOCHASTIC ESTIMATION." University of Cincinnati / OhioLINK, 2004. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1099519886.

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30

Barre, David. "Numerical simulation of ignition in aeronautical combustion chambers." Thesis, Toulouse, INPT, 2014. http://www.theses.fr/2014INPT0004/document.

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Pour des raisons évidentes d’opération et de sécurité, l’allumage est un problème essentiel dans les moteurs aéronautiques. La conception d’une chambre de combustion de turbine à gaz intègre de multiples objectifs contradictoires, l’un d’entre eux étant un allumage ou ré-allumage efficace des brûleurs. Parmi les paramètres dont disposent les ingénieurs dans la phase d’optimisation du design, le nombre de systèmes d’injection de carburant et leur espacement sont des points cruciaux qui doivent être fixés dès le début. En effet, de tels choix ont non seulement un impact sur le coût de fabrication et la taille de la chambre mais ils affectent aussi l’efficacité d’un moteur ainsi que ses caractéristiques d’allumage. Afin d’améliorer les connaissances relatives au processus l’allumage dans des moteurs réels, la recherche actuelle combine des expériences fondamentales de plus en plus complexes et des simulations numériques de haute fidélité. Ces actions se concentrent d’une part sur les premiers instants où le noyau de flamme apparaît et d’autre part sur la phase de propagation entre les différents brûleurs. Ces deux phases sont capitales mais restent difficiles à étudier simultanément. Le premier objectif de cette thèse vise à évaluer les modèles SGE sur un seul brûleur expérimental situé au CORIA (France) pour mettre en place une méthodologie fiable afin de réaliser numériquement une séquence d’allumage dans des conditions d’opération réelles et équivalentes aux premiers instants. Une telle étude met en jeu plusieurs phénomènes tels que les écoulement swirlés, l’allumage, l’extinction, la propagation de flamme et les interactions flamme/turbulence. Tous ces processus et mécanismes interagissent et augmentent de façon significative le niveau de difficulté, notamment pour modéliser la combustion turbulente d’un tel allumage. Ces modèles requièrent donc d’être évalués précisément. Ensuite, ce travail examine par la simulation numérique la phase de propagation en utilisant les expériences réalisées sur une chambre composée de plusieurs injecteurs. La comparaison des séquences d’allumage obtenues numériquement avec celles des données expérimentales montre que la SGE reproduit les bonnes tendances et s’avère prédictive. D’un point de vue global, les caractéristiques de propagation du front de flamme en direction des injecteurs voisins sont bien capturées par le numériquemontrant desmodes de propagation identiques à ceux obtenus expérimentalement (radial ou axial) et des temps d’allumage similaires. Pour finir, l’analyse détaillée de ces données numériques a permis d’identifier les mécanismes principaux qui sont à l’origine des différents modes de propagation
For evident operational and safety reasons, ignition is a key feature of aeronautical gas turbine applications. In fact the design of a gas turbine combustion chamber imposes multiple contradicting objectives one of them being efficient ignition or re-ignition. Among all the parameters available to the engineers, the number of fuel injection systems and their spacing are crucial elements, that must be fixed early on in the design phase. Such choices however not only impact the manufacturing cost and size of the combustor but they also affect the operability of the engine as well as its ignition. To improve knowledge of the ignition process occurring in real engines, current research combines fundamental and increasingly complex experiments complemented by high fidelity numerical simulations. These actions focus on the one hand on the initial instants where the first flame kernel appears as well as the follow-on instants corresponding to the light-around phase or burner to burner flame propagation phase. Both phases are clearly important but are difficult to study simultaneously. The first purpose of this thesis aims at assessing LES models on a single experimental burner located at CORIA (France) to provide a reliable numerical methodology to achieve an ignition sequence in real engines. Indeed, various phenomena are involved in such numerical studies dedicated to real aeronautical combustion chambers and all need to be reproduced by numerics: swirling flows, ignition, quenching, flame propagation, flame/turbulence interactions. All of these processes interact and clearly raise the level of difficulty notably in terms of turbulent combustion modeling of an ignition transient. Having assessed the method on a single burner configuration, the work then investigates the second phase, using a multi-injector experiment simulated by LES to study the flame propagation during ignition. The comparison of numerical fully transient ignition sequences with experimental data shows that LES recovers features found in the experiment. Global events such as the propagation of the flame front to neighboring swirlers are well captured and correct propagation modes (radial or axial) as well as correct overall ignition time delay are obtained. Finally the detailed analysis of LES data allows to identify the driving mechanisms governing each of these propagation modes

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31

Stone, Christopher. "Large-Eddy simulation of combustion dynamics in swirling flows." Diss., Georgia Institute of Technology, 2003. http://hdl.handle.net/1853/13430.

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32

Pascau, Benito Antonio. "The application of second order turbulence closures to isothermal and combusting swirling flows." Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/46491.

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33

Quaranta, Hugo. "Instabilities in a swirling rotor wake." Thesis, Aix-Marseille, 2017. http://www.theses.fr/2017AIXM0052.

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Cette thèse est consacrée à l'étude des instabilités du sillage tourbillonnaire des rotors, largement utilisés dans l'industrie pour la conversion d'énergie mécanique. Leur sillage peut être modélisé par un ensemble de vortex hélicoïdaux entrelacés, au sein duquel de nombreuses instabilités peuvent émerger. Ces mécanismes ont un impact significatif sur l'évolution intermédiaire du sillage et peuvent influencer les performances du rotor. Ce travail, plus particulièrement dédié aux hélicoptères, s'est tout d'abord attaché à caractériser expérimentalement l'écoulement derrière trois rotors conçus pour des régimes de vols différents. Ces conditions de bases ont ensuite servi à étudier les différents modes instables de grande longueur d'onde pouvant apparaître dans le sillage. Une bonne correspondance est trouvée entre les prédictions théoriques et les mesures expérimentales des taux de croissance associés. Une rapide analyse de l'évolution spatio-temporelle de ces perturbations a permis d'étudier la propagation d'une perturbation localisée dans le plan rotor. Il est en effet envisagé que dans certaines configurations de vol de descente, les instabilités provoquent la transition du sillage vers un état spécifique connu sous le nom d'état d'anneau tourbillonnaire, potentiellement dangereux pour l'appareil. Il se caractérise par une stagnation du sillage au voisinage du plan rotor qui en dégrade les performances
This work studies the instabilities associated with the wake of a rotor. These devices are used in many applications such as energy harvesting or propulsion,and their optimisation is crucial for both industry and the environment. The wakebehind a rotor is broadly defined as a system of interlaced helical vortices, whose dynamics governs the transition from the near-wake to the far-wake regime. In our first study, we investigate the wake behind different small-scale rotors in their design operating condition. We use the resulting flows in a subsequent linear stability analysis, aiming at predicting long-wavelength instability modes in the helical vortex. We find that the theoretical prediction of the modes growth-rates matches our experimental measurements. We also show that the dynamics of helical vortex filaments can be predicted from simple two-dimensional theory. In more critical flow configurations, instabilities are suspected to promote the transition to hazardous regimes such as the so called Vortex-Ring State, characterised by large-scale recirculating structures.The second part of this work is thus dedicated to the spatio-temporal evolution of localised perturbations in the rotor plane, and their potential tendency to propagate upstream in the flow

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34

Salhi, Abdelaziz. "Etude de l'ecoulement couette poiseuille, liquide et liquide-gaz, dans un espace annulaire reduit." Nantes, 1986. http://www.theses.fr/1986NANT2066.

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Etude experimentale d'un ecoulement force dans un labyrinthe tournant. Interpretation des resultats en fonction des diverses compositions de regimes laminaire-turbulent-tourbillonnaire. Proposition d'une correlation semi-analytique. Essais en ecoulements diphasiques

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35

Örlü, Ramis. "Experimental study of passive scalar mixing in swirling jet flows." Licentiate thesis, KTH, Mechanics, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4142.

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Despite its importance in various industrial applications there is still a lack of experimental studies on the dynamic and thermal field of swirling jets in the near-field region. The present study is an attempt to close this lack and provide new insights on the effect of rotation on the turbulent mixing of a passive scalar, on turbulence (joint) statistics as well as the turbulence structure.

Swirl is known to increase the spreading of free turbulent jets and hence to entrain more ambient fluid. Contrary to previous experiments, which leave traces of the swirl generating method especially in the near-field, the swirl was imparted by discharging a slightly heated air flow from an axially rotating and thermally insulated pipe (6 m long, diameter 60 mm). This gives well-defined axisymmetric streamwise and azimuthal velocity distributions as well as a well-defined temperature profile at the jet outlet. The experiments were performed at a Reynolds number of 24000 and a swirl number (ratio between the angular velocity of the pipe wall and the bulk velocity in the pipe) of 0.5.

By means of a specially designed combined X-wire and cold-wire probe it was possible to simultaneously acquire the instantaneous axial and azimuthal velocity components as well as the temperature and compensate the former against temperature variations. The comparison of the swirling and non-swirling cases clearly indicates a modification of the turbulence structure to that effect that the swirling jet spreads and mixes faster than its non-swirling counterpart. It is also shown that the streamwise velocity and temperature fluctuations are highly correlated and that the addition of swirl drastically increases the streamwise passive scalar flux in the near field.

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36

Ko, Jordan. "Numerical modelling of highly swirling flows in a cylindrical through-flow hydrocyclone." Licentiate thesis, Stockholm, 2005. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-293.

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37

Cazan, Radu. "Dynamics of swirling flows induced by twisted tapes in circular pipes." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/33944.

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The present study describes the flow characteristics of swirling flows induced by twisted tape inserts in circular pipes. The study is focused on the secondary flow which is investigated experimentally and with numerical models. The results are expected to improve the paper manufacturing process by identifying and removing the detrimental secondary flow. Experimental tests show for the first time the existence of two co-rotating helical vortices superimposed over the main swirling flow, downstream of twisted tapes. The close proximity of the two co-rotating vortices creates a local counter-rotating flow at the pipe centerline. The flow is analyzed using LDV measurements and high speed camera visualization with fine air bubbles seeding which confirm that the helical vortices are stable. After extracting the characteristic tangential velocity profiles of the main vortex and of the two secondary vortices, it was observed that the maximum tangential velocity of all three vortices is the same, approximately half of the bulk velocity. The winding of the helical vortices is in the swirl direction and the pitch of the helical vortices is found to be independent of the inlet velocity. The experimental findings are confirmed by numerical simulations. The numerical results show that the helical vortices originate inside the swirler and evolve from single co-rotating vortices on each side of the tape. The flow characteristics are analyzed in detail. Swirlers with multiple twists and multiple chambers are shown to have less stable secondary motion and could be employed in applications were the secondary motion is detrimental.

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38

Capiaux, Sylvie. "Application et développement de la vélocimétrie par images de particules pour l'étude de la phase d'admission dans les moteurs à allumage commandé." Rouen, 1997. http://www.theses.fr/1997ROUES068.

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Le présent travail, effectué dans l'entreprise PSA, en collaboration avec le CORIA par le biais d'une convention CIFRE, vise à implanter la technique de vélocimétrie par images de particules, PIV, à la DRAS (PSA, Vélizy 78). La PIV est une technique bidimensionnelle de mesure de vitesse, qui fournit des champs instantanés de vecteurs vitesse dans un plan matérialisé par une nappe laser. Elle apporte ainsi une vision d'ensemble des structures de l'écoulement que les techniques ponctuelles ne permettent pas d'obtenir. Deux expériences sont mises en œuvre afin de tester la technique d'une part et d'obtenir des informations intéressantes sur l'écoulement en aval d'une culasse de série. La première est un banc statique : un plateau plat doté d'une soupape de série à levée variable, sous lequel est monté un cylindre transparent permettant de visualiser l'écoulement ensemencé de micro gouttelettes d'huile. L'écoulement autour de la soupape et dans le cylindre est créé à l'aide d'une aspiration. La seconde est constituée d'une culasse de série PSA, entrainée par un moteur électrique. La PIV s'avère être un bon outil de diagnostic pour les applications moteur et permet grâce à une méthode de filtrage spatial des champs instantanés d'évaluer les grandes échelles de l'écoulement (>= 7 mm) et la part des fluctuations cycliques. Pour ce faire on utilisera des traitements à l'aide de maillages de taille moyenne (64p*64p) et un taux de recouvrement des mailles de traitement assez élevé (75%). Les images obtenues ici ont l'inconvénient d'être moyennement résolues car les CCD sur le marché il y a 3 ans étaient de petite taille (768 pixels*512 pixels). Elles nécessitent un travail de mise au point conséquent à cause du confinement des cylindres, mais avec l'augmentation des cadences d'acquisition, la dégradation dans le temps d'expérience des images ne sera bientôt plus un problème. L'accès aux plus petites échelles sera possible dans l'avenir avec l'utilisation de cameras plus résolues (Kodak 1000*1000 par ex. ). Nous avons réalisé une étude théorique permettant de quantifier les biais de mesure. Les erreurs sont majoritairement liées à une répartition hétérogène des particules dans les mailles de traitement (mailles moyennes ou grandes et gradients locaux de vitesse au sein des mailles).

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39

Buntine, James D. Saffman P. G. "Part 1. Inviscid, swirling flows and vortex breakdown. : Part 2. A numerical investigation of the Lundgren turbulence model /." Diss., Pasadena, Calif. : California Institute of Technology, 1994. http://resolver.caltech.edu/CaltechETD:etd-10182005-082716.

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40

Bai, Haitong. "A Study of the Swirling Flow Pattern when Using TurboSwirl in the Casting Process." Doctoral thesis, KTH, Tillämpad processmetallurgi, 2016. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-196806.

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The use of a swirling flow can provide a more uniform velocity distribution and a calmer filling condition according to previous studies of both ingot and continuous casting processes of steel. However, the existing swirling flow generation methods developed in last decades all have some limitations. Recently, a new swirling flow generator, the TurboSwirl device, was proposed. In this work, the convergent nozzle was studied with different angles. The maximum wall shear stress can be reduced by changing the convergent angle between 40º and 60º to obtain a higher swirl intensity. Also, a lower maximum axial velocity can be obtained with a smaller convergent angle. Furthermore, the maximum axial velocity and wall shear stress can also be affected by moving the location of the vertical runner. A water model experiment was carried out to verify the simulation results of the effect of the convergent angle on the swirling flow pattern. The shape of the air-core vortex in the water model experiment could only be accurately simulated by using the Reynolds Stress Model (RSM). The simulation results were also validated by the measured radial velocity in the vertical runner by the ultrasonic velocity profiler (UVP). The TurboSwirl was reversed and connected to a traditional SEN to generate the swirling flow. The periodic characteristic of the swirling flow and asymmetry flow pattern were observed in both the simulated and measured results. The detached eddy simulation (DES) turbulence model was used to catch the time-dependent flow pattern and the predicted results agree well with measured axial and tangential velocities. This new design of the SEN with the reverse TurboSwirl could provide an almost equivalent strength of the swirling flow generated by an electromagnetic swirling flow generator. It can also reduce the downward axial velocities in the center of the SEN outlet and obtain a calmer meniscus and internal flow in the mold.
Tidigare studier visar att ett roterande flöde kan ge en mer likformig hastighetsfördelning och en lugnare fyllning i både göt- och stränggjutning av stål. De befintliga metoderna för att generera ett roterande flöde har vissa begränsningar. En ny metod för att generera det roterande flödet, en så kallad TurboSwirl, föreslogs nyligen. I detta arbete undersöktes ett konvergent munstycke med olika vinklar för att se hur detta påverkade det roterande flödet som genererades i anordningen. Resultaten visar att skjuvspänningen i systemet kan reduceras genom att ändra munstyckets vinkel mellan 40º till 60º. En lägre maximal axiell hastighet kan också uppnås med en mindre konvergent vinkel på munstycket. Det är även möjligt att påverka den maximala axiella hastigheten och skjuvspänningen i systemet genom att förflytta den vertikala kanalen i anordningen. Vattenmodellexperiment har utförts för att validera simuleringsresultaten. Det kraftigt roterande flödet kunde endast beskrivas väl av Reynolds Stress Model (RSM). Validering utfördes också genom att mäta den radiella hastigheten i den vertikala kanalen med en Ultrasonic Velocity Profiler (UVP). TurboSwirl-anordningen vändes och kopplades till gjutröret för att generera det roterande flödet. Detta studerades både med numeriska modeller och med vattenmodellering. Ett periodiskt asymmetriskt roterande flöde observerades både i numeriska modellerna och i vattenmodellerna. För att modellera detta periodiska flöde så användes detached eddy simulation (DES) modellen. Resultaten då denna modell användes stämmer väl med de experimentella mätningarna. Denna nya design med TurboSwirl kan uppnå liknande styrka på det roterande flödet som när elektromagnetisk omrörning användes. Det resulterande roterande flödet leder till en lägre axiell hastighet i gjutröret samt en lugnare yta och ett lugnare flöde i kokillen.

QC 20161123

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41

Kucukal, Erdem. "EXPERIMENTAL AND CFD INVESTIGATIONS OF THE FLUID FLOW INSIDE A HYDROCYCLONE SEPARATOR WITHOUT AN AIR CORE." Case Western Reserve University School of Graduate Studies / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=case1424174590.

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42

Kelson, Neil. "Study of industrially relevant boundary layer and axisymmetric flows, including swirl and turbulence." Thesis, Queensland University of Technology, 2000. https://eprints.qut.edu.au/37083/1/37083_Digitised%20Thesis.pdf.

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Micropolar and RNG-based modelling of industrially relevant boundary layer and recirculating swirling flows is described. Both models contain a number of adjustable parameters and auxiliary conditions that must be either modelled or experimentally determined, and the effects of varying these on the resulting flow solutions is quantified. To these ends, the behaviour of the micropolar model for self-similar flow over a surface that is both stretching and transpiring is explored in depth. The simplified governing equations permit both analytic and numerical approaches to be adopted, and a number of closed form solutions (both exact and approximate) are obtained using perturbation and order of magnitude analyses. Results are compared with the corresponding Newtonian flow solution in order to highlight the differences between the micropolar and classical models, and significant new insights into the behaviour of the micropolar model are revealed for this flow. The behaviour of the RNG-bas based models for swirling flow with vortex breakdown zones is explored in depth via computational modelling of two experimental data sets and an idealised breakdown flow configuration. Meticulous modeling of upstream auxillary conditions is required to correctly assess the behavior of the models studied in this work. The novel concept of using the results to infer the role of turbulence in the onset and topology of the breakdown zone is employed.

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43

Hamma, Laurence. "Etude de la diffusion de la chaleur en aval d'un cylindre chauffé à faible nombre de Reynolds (40." Rouen, 1988. http://www.theses.fr/1988ROUES031.

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Etude expérimentale. On utilise le chauffage du cylindre pour modifier les propriétés du fluide et contrôler ainsi le phénomène tourbillonnaire. Analyse du champ thermique. La température effective contrôlant le développement de la double allée de Von Karman est très inférieure à la température de film. Etude du couplage entre un écoulement amont turbulent et le sillage en aval du cylindre

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44

Rangwala, Aliasgar H. "Structure of Turbulent, Swirling Round Jets." Thesis, 2022. https://etd.iisc.ac.in/handle/2005/6008.

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The present study deals with the numerical analysis of the effect of the swirl in the self-preservation region of the turbulent round jet. However, a large number of literature exists for the analysis of near-exit regions—very few deals with the self-preservation region of the jets far downstream. The present study attempts to provide insights into the effect of swirl on the turbulent mixing and jet spread rate by examining the self-similar solution in the far-field region of the jet. The study is divided into two main portions: a comparison of the turbulent swirling and non- swirling jets and the comparison between the turbulent jets having low to moderate values of swirls. A standard computation for a non-swirling jet is used to validate the flow solver. Simulations are carried out at a Reynolds number of 2,400 for the top-hat velocity profile at the inlet. All flow characteristics are computed in detail and compare the results with existing DNS data. Velocity profiles at different streamwise locations collapse on a single curve and closely match the available data. The jet decay and spread rates also align with the standard computed data. Large eddy simulation has been performed for non-swirl (S = 0), weak swirls (S = 0.3, 0.5) and moderate swirl (S = 0.7) at a Reynolds number of 11,000. In both the non-swirling and swirling cases, special care is taken to ensure that the computational domain is large enough to study the jet’s behaviour in a self-similar region. The research presents the effects of the swirl on a turbulent flow and compares the simulation results with available experimental data. Comparing the swirling and non-swirling cases indicates a changed turbulence structure to the effect that the swirling jet spreads and mixes faster than the non-swirling. With increasing degrees of swirl, the angle of spread of the jets is increased, and correspondingly, the decay of the maximum values of velocity components along the lengths of the jets is faster. Flow entrainment shows that the entrainment increases with swirls. The numerical simulations showed that the flow quickly achieved a self-similarity for the mean axial velocity. In contrast, the radial and azimuthal mean velocities reached a self-similar state after a longer period of jet development. Results of the decay of velocity and jet spread rate in the self-similar region of the swirling jet without vortex breakdown were found to vary linearly with the streamwise direction of the jet irrespective of the magnitude of swirl number, which is in line with the findings from experiments of Rose (1962), Chigier & Chervinsky (1967) & Pratte & Keffer (1972). In contrast, Craya & Darrigol (1967) has theoretically shown that axial velocity decay varies as three halves along the length of the jet. Additionally, mass flux shows higher mixing in swirling jets compared with non-swirling. The integrated axial fluxes of linear and angular momentums were conserved along the jet’s axis in the self-preserving region.

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45

紀丕鴻. "Numerical simulation and analysis of the swirling turbulent combustor." Thesis, 1987. http://ndltd.ncl.edu.tw/handle/12596785457982922469.

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46

Zhang, Dehong. "Turbulent swirling combustion of premixed natural gas and air." Thesis, 1995. http://hdl.handle.net/2429/8828.

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Constant-volume combustion of a stoichiometric homogenous mixture of natural gas and air with global rotational motion (swirl) in a short cylindrical chamber has been studied experimentally and simulated numerically. Swirl was generated by a rotating disc in the combustion chamber with variable intensity. Turbulence intensity was varied by changing the swirl level as well as changing the size of roughness on the rotating disc. Combustion was initiated at the centre of the cylindrical combustion chamber. Combustion pressure signals were used to determine the combustion rate at different swirl levels. High-speed laser schlieren photography was used to obtain schlieren images of flame kernel development at different swirling levels. Combustion pressure measurements showed that: (i) at given turbulence intensity, there is a swirl level limit, below which swirl enhances the burning rate; above which swirl reduces the burning rate; (ii) the turbulence intensity has greater effect on combustion duration at high swirl than at low swirl; (iii) increased swirl leads to increased heat transfer rate; at the intermediate swirl, the total heat loss during combustion was the minimum. High-speed laser schlieren pictures showed some evidence of small flame kernel elongation along the rotating axis of swirl. Multi-dimensional numerical modeling, which was based on the KIVA II code, was applied to simulate combustion. A combustion model with a two-step chemical reaction scheme, in which the fuel was treated as a mixture of a number of simple chemical components, was developed to evaluate the burning rate with, and without, swirl. The numerical results show that (i) at the zero, low, and intermediate swirl levels, the predicted combustion rates were closely consistent with the measured combustion rates; at the high swirl level, the combustion rates were over predicted; (ii) the numerical simulation is consistent with the observed effect of swirl on the flame kernel development.

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47

Khademi, Shamami Keivan. "Performance of RANS models for simulating turbulent swirling and free jet flows." 2008. http://hdl.handle.net/1993/21292.

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48

Iyogun, Christopher Omokhowa. "Effect of nozzle geometry on the stability of a turbulent jet flame with and without swirling co-flow." 2009. http://hdl.handle.net/1993/21452.

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49

Chen, Jian Chou, and 陳建州. "Modelling confined swirling flow field by nonlinear pressure- strain turbulence model." Thesis, 1996. http://ndltd.ncl.edu.tw/handle/45770267151017905489.

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50

Buntine, James D. "Part I: Inviscid, swirling flows and vortex breakdown. Part II: A numerical investigation of the Lundgren turbulence model." Thesis, 1994. https://thesis.library.caltech.edu/4155/1/Buntine_jd_1994.pdf.

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NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Abstract for part I A study of the behaviour of an inviscid, swirling fluid is performed. This flow can be described by the Squire-Long equation if the constraints of time-independence and axisymmetry are invoked. The particular case of flow through a diverging pipe is selected and a study is conducted to determine over what range of parameters (both pipe inlet conditions and geometry) does a (unique) solution exist. The work is performed with a view to understanding how the phenomenon of vortex breakdown develops. Experiments and previous numerical studies have indicated that the flow is sensitive to boundary conditions particularly at the pipe inlet. A "quasi-cylindrical" simplification of the Squire-Long equation is compared with the more complete model and shown to be able to account for most of its behaviour. An advantage of this latter representation is the relatively undetailed description of the flow geometry it requires in order to calculate a solution. "Criticality" or the ability of small disturbances to propagate upstream is related to results of the quasi-cylindrical and axisymmetric flow models. This leads to an examination of claims made by researchers such as Benjamin and Hall concerning the interrelationship between "failure" of the quasi-cylindrical model and the occurrence of a "critical" flow state. Other criteria for predicting the onset of vortex breakdown are considered in the context of the model employed, particularly those of Brown & Lopez and Spall, Gatski & Grosch. Abstract for part II Lundgren (1982) developed an analytical model for homogeneous turbulence based on a collection of contracting spiral vortices each embedded in an axisymmetric strain field. Using asymptotic approximations he was able to deduce the Kolmogorov [...] behaviour for inertial scales in the turbulence energy spectrum. Pullin & Saffman have enlarged upon his work to make a number of predictions about the behaviour of turbulence described by the model. This work investigates the model numerically. The first part considers how the flow description compares with numerical simulations using the Navier-Stokes equations. Integration of the full expressions proposed by Lundgren for the energy spectrum is also performed to determine how the various parameters available affect the behaviour and validity of the result.

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