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Stokes, Jason R. "Swirling flow of viscoelastic fluids /". Connect to thesis, 1998. http://eprints.unimelb.edu.au/archive/00000686.
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Ferguson, John William James. "Swirling flows in conical vessels". Thesis, University of Leeds, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.329778.
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Davidson, P. A. "Magnetohydrodynamics of swirling, recirculating flow". Thesis, University of Cambridge, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.383052.
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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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Lucca-Negro, Oona. "Modelling of swirling flow instabilities". Thesis, Cardiff University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310677.
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This research concentrates on the swirl motion, and in particular the flow structure which develops under its action, in swirl burner/furnace systems. Although the Reynolds numbers for such systems are usually large and well into the turbulent regime, periodic oscillations and associated instabilities are still prevalent. The predominant coherent structure is the so-called precessing vortex core (PVC) which is a three-dimensional, time-dependent phenomenon. It is helical in shape, twisted against the flow, and precesses around the geometric centre of the system, in the sense of the flow. The aim of this work was to numerically model this instability in a 2MW industrial-size system, under isothermal conditions. A fully three-dimensional, time-dependent model was developed using the CFD (Computational Fluid Dynamics) software FLUENT. This study first presents an overview of publications on vortex breakdown, a similar phenomenon observed initially on delta wings, in order to highlight its significant features. A summary was also made of various recent studies, experimental and theoretical, carried out at Cardiff University, in the same equipment as used in the present work. This review allows a better understanding of the phenomenon and constitutes a basis for further validation of the mathematical model. Numerous flow pattern characteristics have- been predicted, which agree qualitatively with different published studies, such as crescent shaped regions of maximum axial and tangential velocities, off-centred reverse flow zone, and spiralling vortex core. Quantitatively, the agreement is good, in terms of range of velocities and frequency. However, the predicted flow pattern could. not be maintained in time and tended back to axisymmetry, possibly due to numerical diffusion. Grid refinement could not, however, be envisaged due to the practical limits of the available machines. Nevertheless, these results are encouraging and prove that mathematical modelling of these complex flows is a realistic objective.
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Heaton, Christopher James. "Acoustics and stability in swirling flow". Thesis, University of Cambridge, 2006. https://www.repository.cam.ac.uk/handle/1810/272161.
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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 performancesThis 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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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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Tarr, Stephen John. "The mathematical modelling multiple swirling burner flows". Thesis, University of Nottingham, 1997. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.243506.
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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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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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Hatziapostolou, Antonis. "Swirling flows in direct-injection diesel engines". Thesis, Imperial College London, 1991. http://hdl.handle.net/10044/1/8661.
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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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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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Nygaard, Thor Isak. "Two phase swirling flow in a cylindrical reactor". Thesis, Georgia Institute of Technology, 1986. http://hdl.handle.net/1853/10192.
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IJzermans, Rutgerus Henricus Anthonius. "Dynamics of dispersed heavy particles in swirling flow". Enschede : University of Twente [Host], 2007. http://doc.utwente.nl/57886.
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Short, David James. "Swirling flow induced by a rotating magnetic field". Thesis, Imperial College London, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.338644.
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Dunham, David. "Unsteady fluid mechanics of annular swirling shear layers". Thesis, Loughborough University, 2011. https://dspace.lboro.ac.uk/2134/8483.
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The vast majority of gas turbine combustor systems employ swirl injectors to produce a central toroidal recirculation zone (CTRZ) which entrains and recirculates a portion of the hot combustion gases to provide continuous ignition to the incoming air-fuel mix. In addition to these primary functions, swirl injectors often generate multiple aerodynamic instability modes which are helical in nature with characteristic frequencies that can differ by many orders of magnitude. If any of these frequencies are consistent with prevalent acoustic modes within the combustor there is a potential for flow-acoustic coupling which may reinforce acoustic oscillations and drive combustion instabilities via the Rayleigh criterion. The aerodynamic performance of the swirl injector is thus of great practical importance to the design and development of combustion systems and there is a strong desire within industry for reliable computational methods that can predict this highly unsteady behaviour. This assessment can be made under isothermal conditions which avoids the complex interactions that occur in reacting flow. The goal of the present work was to compare and contrast the performance of Unsteady Reynolds- Averaged Navier-Stokes (URANS) and Large-Eddy Simulation (LES) CFD methodologies for a combustion system equipped with a derivative of an industrial Turbomeca swirl injector as this exhibits similar unsteady aerodynamic behaviour under reacting and isothermal conditions. The influence of the level of swirl, SN = 0.51−0.8, was first investigated experimentally using Particle Image Velocimetry (PIV) by varying the inlet swirl vane angle. Based on a qualitative assessment of instantaneous velocity data, and a range of coherent structure eduction techniques, it was found that ®1 = 30± (SN ¼ 0.8) would be the most challenging test case for LES and URANS as this contained near and far-field instability modes that differ in frequency by around two orders of magnitude and the highest levels of normal Reynolds-stress anisotropy. Based on extensive simulations performed with both in-house (LULES and Delta) and commercial (Fluent) CFD codes it was found that, despite the relative modest computational cost of URANS which is between one-third (RST) to an order of magnitude (k−²) less than that demanded by LES, only LES captures the all-important frequency content in accordance with experimental evidence and, thus, only LES can be recommended for use in swirl injector flows. The increased cost is believed to be an absolutely worthwhile expense because of the high fidelity of the predicted results in the important area of flow instabilities.
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Valenciano, Rubio Jose L. "Adaptive spectral element methods for swirling Newtonian flows". Thesis, Edinburgh Napier University, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.285227.
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Ahmadi, Abolfazl. "The swirling orifice plate independent of inlet conditions". Thesis, University of Sheffield, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.427248.
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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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Willey, Donald. "Application of small swirling jets in fluidised beds". Thesis, University of Sheffield, 2016. http://etheses.whiterose.ac.uk/15259/.
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This thesis provides an analysis of the effects of introducing a novel flow regime into fluidised beds, where swirling structures interact with particles of a similar scale. The motivation behind the work is to investigate the potential of increasing the efficiency of a widespread industrial process by a system that is readily scaled up and possible to retrofit. It begins by providing a review of the scientific literature around swirl flows and fluidised beds, explaining the reasoning behind the research hypothesis and the flow mechanisms in the inventive principle. This covers the background and utilisation of swirling and helical flow structures, followed by the principles of fluidised beds. The research hypothesis was tested empirically on a specially constructed pilot scale rig designed to provide a range of different flow regimes. The apparatus required advanced manufacturing methods and design was guided by Finite Element Analysis to ensure the desired flow regimes were achieved. The empirical studies with the apparatus were backed up through numerical modelling of the pseudo one dimensional fluidised bed, that is, the interaction between one jet and one particle. The empirical studies indicate a significant change in the behaviour of the fluidised bed between the novel flow regime and the standard design control. It was found that the novel flow resulted in improved gas distribution and the creation of smaller bubbles, improving the gas-solid interaction demonstrated by 2% lower bed expansion, 18% shorter drying times, 29% increased bubble frequency and minimal difference in total bubble volume. The numerical model shows change in the direction of momentum transfer and reduced heat transfer rate as the intensity of novel flow conditioning increases. This results in the particle being drawn towards an individual jet by a recirculation zone and a more even spread of heat throughout the gaseous phase. The evidence presented shows that by the introduction of a novel flow conditioning to fluidised beds results in significantly improved gas distribution across the system, leading to improved mixing between the gas and solid phases and resultantly a more efficient process.
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Zhang, Qingguo. "Lean blowoff characteristics of swirling H2/CO/CH4 Flames". Diss., Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/22641.
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This thesis describes an experimental investigation of lean blowoff for H2/CO/CH4 mixtures in a swirling combustor. This investigation consisted of three thrusts. The first thrust focused on correlations of the lean blowoff limits of H2/CO/CH4 mixtures under different test conditions. It was found that a classical Damköhler number approach with a diffusion correction could correlate blowoff sensitivities to fuel composition over a range of conditions.
The second part of this thesis describes the qualitative flame dynamics near blowoff by systematically characterizing the blowoff phenomenology as a function of hydrogen level in the fuel. These near blowoff dynamics are very complex, and are influenced by both fluid mechanics and chemical kinetics; in particular, the role of thermal expansion across the flame and extinction strain rate were suggested to be critical in describing these influences.
The third part of this thesis quantitatively analyzed strain characteristics in the vicinity of the attachment point of stable and near blowoff flames. Surprisingly, it was found that in this shear layer stabilized flame, flow deceleration is the key contributor to flame strain, with flow shear playing a relatively negligible role. Near the premixer exit, due to strong flow deceleration, the flame is negatively strained i.e., compressed. Moving downstream, the strain rate increases towards zero and then becomes positive, where flames are stretched. As the flame moves toward blowoff, holes begin to form in the flame sheet, with a progressively higher probability of occurrence as one moves downstream. It is suggested that new holes form with a more uniform probability, but that this behavior reflects the convection of flame holes downstream by the flow.
It has been shown in prior studies, and affirmed in this work, that flames approach blowoff by first passing through a transient phase manifested by local extinction events and the appearance of holes on the flame. A key conclusion of this work is that the onset of this boundary occurs at a nearly constant extinction strain rate. As such, it is suggested that Damköhler number scalings do not describe blowoff itself, but rather the occurrence of this first stage of blowoff. Given the correspondence between this first stage and the actual blowoff event, this explains the success of classical Damköhler number scalings in describing blowoff, such as shown in the first thrust of this thesis. The physics process associated with the actual blowoff event is still unclear and remains a key task for future work.
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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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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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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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Feyedelem, Michael S. "Interaction of a swirling jet with a free surface". Thesis, Monterey, California. Naval Postgraduate School, 1996. http://hdl.handle.net/10945/8548.
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Approved for public release; distribution is unlimitedThe turbulent flow field of a swirling jet issuing from a nozzle, beneath and parallel to a free surface has been studied in as much detail as possible using a three-component laser Doppler velocimeter and flow visualization. The results have shown that the swirl leads to the faster spreading and quicker mixing of the jet. For strongly swirling jets (S = 0.522), the similarity is not reached within ten diameters downstream. The results have also shown that both the acial and tangential velocity components decrease outward from the jet axis, naturall leading to centrifugal instabilities. This, in turn, leads to the creation of large scale coherent structures at the periphery of the jet, particularly when it is in the vicinity of the free surface. The turbulent shear stresses exhibit anisotropic behavior, the largest always being in the plane passing through the jet axis. The change of TKE with S is not monotonic. It is maximum for S - 0.265, smallest for S = 0.50, and has an intermediate value for S - 0.522. This is due to the occurrence of vortex breakdown and the resulting intensification of the turbulence within the jet prior to its exit from the nozzle.
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Tonkin, Ruth Julie Jane. "Swirling pipeflow of non-Newtonian and particle-laden fluids". Thesis, University of Nottingham, 2005. http://eprints.nottingham.ac.uk/11673/.
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This thesis describes the application of novel swirl inducing pipe to various pipe configurations, when pumping a range of fluids and fluid / particle mixtures. An extensive experimental programme, incorporating particle image velocimetry and photography, was implemented using a pipe flow loop designed specifically for the purpose. Experimental data was obtained on the effect of a 4-lobe near-optimal swirl pipe on coal-water, sand-water and magnetite-water slurries of various particle size. Results indicated that swirl induction produced greater benefit for denser slurries and higher concentrations, and that swirl induced into slurries containing larger and denser particles decayed more rapidly. At low velocity, experimental data highlighted a reduction in the total pressure drop experienced across a 3.0m horizontal pipe section, a downward sloping section and vertical pipe bends, when the swirl-inducing pipe was present. PIV was used to measure the axial and tangential velocity of swirling flows downstream of a near-optimal swirl-inducing pipe. It was confirmed that a significant tangential velocity was generated when pumping water in the turbulent regime, however, when the fluid viscosity was increased, leading to laminar flow, no significant tangential velocity was detected.
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Gatti, Marco. "Combustion dynamics of premixed swirling flames with different injectors". Thesis, Université Paris-Saclay (ComUE), 2019. http://www.theses.fr/2019SACLC070/document.
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Les systèmes de combustion à prémélange pauvre (PP) sont l’une des technologies les mieux adaptées pour la réduction des émissions de polluants, mais ils sont très sensibles aux phénomènes d’extinction, aux retours de flamme (flashback) dans l’injecteur et aux instabilités de combustion. La plupart des chambres de combustion des turbines à gaz utilisent de swirleurs pour stabiliser des flammes compactes et permettre une combustion efficace et propre avec des densités de puissance élevée. Une meilleure connaissance des mécanismes de la dynamique de la combustion d’écoulements swirlés PP présente un intérêt aussi bien pratique que fondamental. Ce travail est une contribution pour atteindre ce but. Le brûleur Noisedyn, avec une geometrie modifiable, a été spécialement conçu pour répondre à cet objectif. Une analyse expérimentale a etait conduite pour examiner les paramètres qui reduisent la sensibilité des systèmes PP aux phénomènes dynamiques. Mesures de fonction de transfert de flamme (FTF), diagnostiques laser (LDV et PIV) et imagerie des flammes sont les principaux techniques utilisé dans ce travail. Large eddy simulation sont aussi utilisé pour expliquer les mécanismes derrière les observations experimentauxLean premixed (LPM) combustion systems achieve low pollutant emission levels, with compact flames and high power densities, but are highly sensitive to dynamic phenomena, e.g, flashback, blowout and thermoacoustic instabilities, that hinder their practical application. Most LPM gas turbine combustors use swirling flows to stabilize compact flames for efficient and clean combustion. A better knowledge of the mechanisms of steady and unsteady combustion of lean premixed swirled mixtures is then of practical, as well as fundamental interest. This thesis is a contribute towards the achievement of this goal. A burner, made of several components with variable geometry, was specifically designed for this scope. An experimental analysis was conducted to investigate the main parameters leading to a reduction of the sensitivity of LPM systems to dynamic phenomena. The diagnostics applied include flame transfer function (FTF) measurements, laser diagnostics (LDV and PIV) and flame imaging. Large eddy simulations were also exploited to elucidate the mechanisms behind the experimental observations
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Carrara, Mark David. "Hydrodynamic Stability of Periodically Unsteady Axisymmetric and Swirling Jets". Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/10139.
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Axisymmetric and swirling jets are generic flows that characterize many natural and man-made flows. These include cylindrical shear layer/mixing layer flows, aircraft jets and wakes, shedding of leading edge and wing tip vortices, tornadoes, astrophysical plasma flows and flows in mechanical devices such as supersonic combustion chambers and cyclone separators. These and other applications have resulted in a high level of interest in the stability of axisymmetric and swirling jets. To date, the majority of studies on stability of axisymmetric and swirling jets have been completed under the assumption of steady flow in both axial and azimuthal (swirl) directions. Yet, flows such as the ones mentioned above can have an inherent unsteadiness. Moreover, such unsteadiness can be used to control stability and thus flow characteristics in axisymmetric and swirling jets. In this work effects of periodic variations on the temporal stability of axisymmetric and swirling jets is examined. The unsteadiness is introduced in the former as a periodic variation of the axial velocity component of the flow, and in the latter as a periodic variation of the azimuthal (swirl) velocity component of the flow.
The temporal linear hydrodynamic stability of both steady inviscid axisymmetric and swirling jets is reviewed. An analytical dispersion relation is obtained in both cases and solved numerically. In the case of the steady axisymmetric jet, growth rate and celerity of unstable axisymmetric and helicalmodes are determined as functions of axial wavenumber. Results show that the inviscid axisymmetric jet is unstable to all values of axisymmetric and helical modes. In the case of the steady swirling jet, growth rate and celerity of axisymmetric modes are determined as functions of the axial wavenumber and swirl number. Results show that the inviscid swirling jet is unstable to all values of axial and azimuthal wavenumber, however, it is shown that increasing the swirl decreases the growth rate and increases the celerity of axisymmetric disturbances. The effects of periodic variations on the stability of a mixing layer is also reviewed. Results show that when the instability time scale is much smaller than the mean time scale a transformation of the time variable may be taken that, when the quasi-steady approach works, will reduce the unsteady field to that of the corresponding steady field in the new time scale. The price paid for this transformation, however, is a modulation of the amplitude and phase of the unsteady modes.
Extending the results from the unsteady mixing layer, the stability of a periodically unsteady inviscid axisymmetric jet is considered. An analytical dispersion relation is obtained and results show that for the unsteady inviscid axisymmetric jet, the quasi-steady approach works. Following this, the stability of a periodically unsteady swirling jet is considered and an analytical dispersion relation is obtained. It is shown that for the unsteady inviscid swirling jet, the quasi-steady approach does not work. Resulting modulations of unsteady modes are shown via a numerical solution to the unsteady dispersion relation. In both cases, using established results for unsteady mixing layers, these results are substantiated analytically by showing that the unsteady axisymmetric jet can be reduced the the exact equational form of the steady axisymmetric jet in a new time scale, whereas the unsteady swirling jet cannot.Master of Science
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Baej, Hesham. "Effects of geometry and gas composition on swirling flow". Thesis, Cardiff University, 2015. http://orca.cf.ac.uk/86536/.
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Lean premixed swirl stabilised combustion is regarded as one of the most successful technologies for flame control and NOx reduction in gas turbines. Important characteristics of these flows are good mixing, flame stability through the formation of a Central Recirculation Zone, and low emissions at lean conditions as a consequence of the low operating temperature. This project presents a series of experiments and numerical simulations using commercial software (ANSYS) to determine the behaviour and impact on the blowoff process at various swirl numbers, nozzle geometries and gas compositions at same power outputs using confined and open conditions. Experiments were performed using a generic premixed swirl burner. The Central Recirculation Zone and the associated turbulent structure contained within it were obtained through CFD analyses providing details of the structures and the Damkölher Number (Da) close to blowoff limits. The results show how the strength and size of the recirculation zone are highly influenced by the blend and nozzle geometry, with a shift of Da and turbulence based on carbon-hydrogen ratio, shearing flows and Reynolds number. The Central Recirculation Zone was also measured and correlated to the blowoff phenomenon. A trend was found between the CRZ size/strength, the different compositions of gases used and the burner nozzle. Chemical kinetic analyses were carried out using PRO-CHEMKIN to determine flame speeds and chemical properties needed for CFD calculations. Experiments were performed using Phase Locked PIV and High Speed Photography. The Central Recirculation Zone and its turbulence were measured and correlated providing details of the structure close to blowoff. It was found that the nozzle angle has a small effect on the LBO at low flow rates using all mixtures. During the tests, the Coanda effect was observed with some geometries, thus further research was carried out regarding the transition of this phenomenon. It was found that the process occurs at a particular geometry and step size, with a shift in frequency produced by the leading structure due to the entrainment of air and strength of the latter. Stability of the flow occurs after a Coanda Vortex Breakdown (COVB) has occurred, a process similar to the one observed in the central region of the flow under regular swirling open flames. As the step size is increased, the COVB will evolve into a slower Trapped Vortex (TV).
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Qadri, Ubaid Ali. "Global stability and control of swirling jets and flames". Thesis, University of Cambridge, 2014. https://www.repository.cam.ac.uk/handle/1810/245143.
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Large-scale unsteady flow structures play an influential role in the dynamics of many practical flows, such as those found in gas turbine combustion chambers. This thesis is concerned primarily with large-scale unsteady structures that arise due to self-sustained hydrodynamic oscillations, also known as global hydrodynamic instability. Direct numerical simulation (DNS) of the Navier--Stokes equations in the low Mach number limit is used to obtain a steady base flow, and the most unstable direct and adjoint global modes. These are combined, using a structural sensitivity framework, to identify the region of the flow and the feedback mechanisms that are responsible for causing the global instability. Using a Lagrangian framework, the direct and adjoint global modes are also used to identify the regions of the flow where steady and unsteady control, such as a drag force or heat input, can suppress or promote the global instability. These tools are used to study a variety of reacting and non-reacting flows to build an understanding of the physical mechanisms that are responsible for global hydrodynamic instability in swirling diffusion flames. In a non-swirling lifted jet diffusion flame, two modes of global instability are found. The first mode is a high-frequency mode caused by the instability of the low-density jet shear layer in the premixing zone. The second mode is a low-frequency mode caused by an instability of the outer shear layer of the flame. Two types of swirling diffusion flames with vortex breakdown bubbles are considered. They show qualitatively similar behaviour to the lifted jet diffusion flames. The first type of flame is unstable to a low-frequency mode, with wavemaker located at the flame base. The second type of flame is unstable to a high-frequency mode, with wavemaker located at the upstream edge of the vortex breakdown bubble. Feedback from density perturbations is found to have a strong influence on the unstable modes in the reacting flows. The wavemaker of the high-frequency mode in the reacting flows is very similar to its non-reacting counterpart. The low-frequency mode, however, is only observed in the reacting flows. The presence of reaction increases the influence of changes in the base flow mixture fraction profiles on the eigenmode. This increased influence acts through the heat release term. These results emphasize the possibility that non-reacting simulations and experiments may not always capture the important instability mechanisms of reacting flows, and highlight the importance of including heat release terms in stability analyses of reacting flows.
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Lewis, Jonathan. "The behaviour of swirling flames under variable fuel composition". Thesis, Cardiff University, 2014. http://orca.cf.ac.uk/66162/.
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This thesis is concerned with the swirl stabilised combustion of gases with variable composition, primarily those derived from the gasification of carbonaceous material, and secondarily those that occur naturally, such as shale gas. During the course of this research the temporal composition of producer gas, derived from the gasification of biomass, was studied in order to ascertain the effect its variable fuel composition had on its combustion properties. Its variation was highly dependent on gasifier operation, and despite the stoichiometric air-to-fuel ratio and Wobbe Index of the fuel being consistent, high throat temperatures resulted in high hydrogen content and laminar flame speeds. Alterations in flame speed are linked to thermo-acoustic instabilities, flame extinction and damaging flame propagation. Acoustic response under combustion conditions was investigated, to determine how it altered over a flames stability range. Indicators of impending flame flashback and blowoff were found, which could be utilised to prevent such events from occurring in an appropriate control system, without the need for real time gas analysis. Flames with high hydrogen content display a propensity for flashback, especially in high turbulence burners, such as those found in gas turbines, where thermo-acoustics are also a significant problem. Variation in fuel composition, particularly in the proportion on hydrogen, exacerbates these problems. The diffusive injection effects of three gases on reacting flow structures were investigated as a method of improving the stability of pre-mixed flames. Carbon dioxide was found to improve flame stability, whilst reducing emissions during the combustion of syngas mixtures in a development gas turbine combustor. Monitoring acoustic response and diffusive injection are thus suggested as additional stabilisation methods for the combustion of gases with variable composition.
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WANG, DEXIN. "STRONGLY SWIRLING FLOW STUDY ON PRESSURE-SWIRL ATOMIZER AND CYCLONE COMBUSTOR". University of Cincinnati / OhioLINK, 2002. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1032210020.
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Yazdabadi, Paul Adi. "A study of the precessing vortex core in cyclone dust separators and a method of prevention". Thesis, Cardiff University, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.297246.
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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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Facciolo, Luca. "A study on axially rotating pipe and swirling jet flows". Doctoral thesis, Stockholm : Royal Institute of Technology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-3862.
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Örlü, Ramis. "Experimental study of passive scalar mixing in swirling jet flows /". Stockholm : KTH Mechanics, Royal Institute of technology, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-4142.
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Yehia, Mohamed Ahmed Aly. "Modelling of pulverised coal swirling flames in axi-symmetric furnaces". Thesis, Imperial College London, 1992. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.245761.
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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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Mobed, Darius Darayes. "Experimental aero-acoustic assessment of swirling flows for drag applications". Thesis, Massachusetts Institute of Technology, 2007. http://hdl.handle.net/1721.1/38650.
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Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2007.Includes bibliographical references (p. 131-133).
The need for quiet drag technologies stems from stricter requirements for and growing demand of low-noise aircraft. The research presented in this thesis regards the use of swirling exhaust flows capable of generating pressure drag quietly by establishing a steady streamwise vortex. The simple concept of a so called swirl tube, a ducted set of stationary turning vanes, was implemented to experimentally assess the aerodynamic and aero-acoustic behavior of swirling flows. A modular design was chosen for the model-scale wind-tunnel test article based on a full-scale diameter of 1.2 m to allow for the wind-tunnel testing of different swirl angles, including both stable swirling configurations and cases exhibiting vortex breakdown. Analyses of both aerodynamic and aero-acoustic test results indicate that highly swirling stable flows obtain maximum drag coefficients greater than 0.8 +0.04 referenced to inlet area with full-scale overall sound pressure level (OASPL) of 42 dBA ±2 dBA, validating the working hypothesis that swirling flows can generate drag quietly. An advanced deconvolution approach for the mapping of acoustic sources (DAMAS), previously developed at the NASA Langley Research Center, was used to identify and to quantify quadrupole- and turbulent scattering-type noise sources in stable swirling flow cases, radiating from the downstream exhaust core and nacelle trailing edge regions, respectively.
(cont.) Cases exhibiting vortex breakdown, found to occur at swirl angle settings exceeding -50', demonstrated noise signatures 10 to 15 dB louder than the stable swirling flows, attributable to the increased scattering noise due to the turbulence of the burst vortex near swirl tube rear surfaces and edges. The practical integration of swirl tubes into aircraft design was assessed based on the conceptual silent aircraft design SAX-40. Integrating swirl vanes into the fan bypass or mixing ducts of aircraft engines is suggested to be capable of generating effective drag at minimal weight cost, benefiting from increased mass flow through the device due to fan pumping. The effects of non-uniform inlet flows on the generation of drag and noise were assessed experimentally and showed a reduction in drag by less than 17% with virtually no noise penalty. The experimental assessment of the swirl tube combined with theoretical engine and airframe integration studies suggest that swirling exhaust flows are capable of generating drag for quiet transport aircraft.
by Darius Darayes Mobed.
S.M.
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Kharraz, Adel Omar. "Stability of Swirling Flow in Passive Cyclonic Separator in Microgravity". Case Western Reserve University School of Graduate Studies / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=case150257066154572.
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Ghulam, Mohamad. "Characterization of Swirling Flow in a Gas Turbine Fuel Injector". University of Cincinnati / OhioLINK, 2019. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1563877023803877.
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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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Wang, Xionghui. "Experimental Investigation of Self-Excited Instabilities in Liquid-Fueled Swirl Combustion". University of Cincinnati / OhioLINK, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1516361245616083.
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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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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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Quaranta, Erika. "Noise radiation from a ducted rotor in a swirling-translating flow". Thesis, Cranfield University, 2009. http://dspace.lib.cranfield.ac.uk/handle/1826/4577.
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This PhD dissertation investigates the noise radiation produced by a rotor inside a
duct, which is convected by a swirling-translating mean
flow. The study is based
on an extension of Gennaretti's and Morino's boundary element method to the
frequency domain for scattering problems in conjunction with a spinning rotor source
model in the presence of a swirling-translating
flow. Firstly, two different source
models of the rotor are analyzed in absence of mean
flow. The parametric study of
the two dipole components distributed over a ring or a disc shows that the source
radius is a crucial parameter. The scattered pressure directivity patterns of the ring
and disc source models are in perfect agreement when a particular ratio between the
two model radii is adopted. Therefore, the present analysis justifies the preference
for the ring source model due to its simplicity. The proposed formulation is validated
by means of exact solutions and used to investigate the effects of the translating
flow
Mach number and swirling
flow angular velocity on noise radiation both in the far
and in the near field. The scattered sound is highly affected by the convecting
mean
flow. The modal content of the scattered field increases when increasing the
translating
flow Mach number, while a swirling
flow leads to a reduction of the mode
propagation, if co-rotating with respect to the azimuthal order of the spinning source,
or an increase of the modal content, if counter-rotating with respect to the source.
This is clearly confirmed by the scattered pressure patterns and levels both in the far
and in the near field for all the source frequencies. In general, the mean translating
flow moves the main lobes of the directivity patterns downstream, whereas in some
cases the mean swirling
flow appears to neglect this effect and the downstream
lobe is completely shifted. However, the investigation on the in-duct propagation
shows that the main effect of the convecting mean
flow is to change the modal
duct characteristics, more than the pattern itself. This results in turn in the strong
modification of the patterns noted in the far field.
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Terdalkar, Rahul J. "Direct numerical simulation of swirling flows using the front tracking method". Worcester, Mass. : Worcester Polytechnic Institute, 2007. http://www.wpi.edu/Pubs/ETD/Available/etd-122007-233351/.
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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.