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1
Hatta, N., R. Ishii, and H. Fujimoto. "Numerical Analysis of Gas-Particle Two-Phase Subsonic Freejets." Journal of Fluids Engineering 114, no. 3 (September 1, 1992): 420–29. http://dx.doi.org/10.1115/1.2910048.
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This paper describes a numerical analysis of gas-droplet two-phase subsonic free jets in the axisymmetric system. Thermal coupling through heat transfer to droplets, as well as momentum coupling through aerodynamic drag responsible for droplet motion, is taken into account in the present numerical model. The Navier-Stokes equations for a gas-phase interacting with particle phase are solved by a time-dependent difference technique and the particle-phase is solved by a discrete particle cloud model. The jet flow structures of mixture composed of air and water-droplets with 1 μm, 5 μm, and 30 μm, respectively, in diameter are calculated with a single particle size. Some of significant characteristics for the two-phase subsonic free jets are pointed out, in particular, focusing upon the effect of particle size on the flow structure.
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Li, Songqi, and Lawrence S. Ukeiley. "Experimental investigation of the fluctuating static pressure in a subsonic axisymmetric jet." International Journal of Aeroacoustics 20, no. 3-4 (April 13, 2021): 196–220. http://dx.doi.org/10.1177/1475472x211004854.
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Measuring the fluctuating static pressure within a jet has the potential to depict in-flow sources of the jet noise. In this work, the fluctuating static pressure of a subsonic axisymmetric jet was experimentally investigated using a 1/8” microphone with an aerodynamically shaped nose cone. The power spectra of the fluctuating pressure are found to follow the -7/3 scaling law at the jet centerline with the decay rate varying as the probe approaches the acoustic near field. Profiles of skewness and kurtosis reveal strong intermittency inside the jet shear layer. By applying a continuous wavelet transform (CWT), time-localized footprints of the acoustic sources were detected from the pressure fluctuations. To decompose the fluctuating pressure into the hydrodynamic component and its acoustic counterpart, two techniques based on the CWT are adopted. In the first method the hydrodynamic pressure is isolated by maximizing the correlation with the synchronously measured turbulent velocity, while the second method originates from the Gaussian nature of the acoustic pressure where the separation threshold is determined empirically. Similar results are obtained from both separation techniques, and each pressure component dominates a certain frequency band compared to the global spectrum. Furthermore, cross-spectra between the fluctuating pressure and the turbulent velocity were calculated, and spectral peaks appearing around Strouhal number of 0.4 are indicative of the footprint of the convecting coherent structures inside the jet mixing layer.
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Saxer-Felici, H. M., A. P. Saxer, A. Inderbitzin, and G. Gyarmathy. "Prediction and Measurement of Rotating Stall Cells in an Axial Compressor." Journal of Turbomachinery 121, no. 2 (April 1, 1999): 365–75. http://dx.doi.org/10.1115/1.2841323.
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This paper presents a parallel numerical and experimental study of rotating stall cells in an axial compressor. Based on previous theoretical and experimental studies stressing the importance of fluid inertia and momentum exchange mechanisms in rotating stall, a numerical simulation using the Euler equations is conducted. Unsteady two-dimensional solutions of rotating stall behavior are obtained in a one-stage low subsonic axial compressor. The structure and speed of propagation of one fully developed rotating stall cell together with its associated unsteady static pressure and throughflow field distributions are presented. The numerical capture of a stalled flow region starting from a stable high-flow operating point with an axisymmetric flow distribution and evolving at a reduced mass flow operating point into a rotating stall pattern is also discussed. The experimental data (flow visualization, time-averaged and unsteady row-by-row static pressure measurements) acquired in a four-stage water model of a subsonic axial compressor cover a complete characteristic line ranging from high mass flow in the stable regime to zero throughflow. Stall inception is presented together with clearly marked different operating zones within the unstable regime. For one operating point in the unstable regime, the speed of propagation of the cell as well as the static pressure spikes at the front and rear boundaries of the rotating stall cell are compared between computations, measurements, and an idealized theory based on momentum exchange between blade rows entering and leaving the stalled cell. In addition, the time evolution of the pressure trace at the rotor/stator interface is presented. This study seems to support the assumption that the cell structure and general mechanism of full-span rotating stall propagation are essentially governed by inertial effects and momentum exchange between the sound and stalled flow at the cell edges.
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Afsar, Mohammed Z., Adrian Sescu, and Stewart J. Leib. "Modelling and prediction of the peak-radiated sound in subsonic axisymmetric air jets using acoustic analogy-based asymptotic analysis." Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 377, no. 2159 (October 14, 2019): 20190073. http://dx.doi.org/10.1098/rsta.2019.0073.
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This paper uses asymptotic analysis within the generalized acoustic analogy formulation (Goldstein 2003 JFM 488 , 315–333. ( doi:10.1017/S0022112003004890 )) to develop a noise prediction model for the peak sound of axisymmetric round jets at subsonic acoustic Mach numbers (Ma). The analogy shows that the exact formula for the acoustic pressure is given by a convolution product of a propagator tensor (determined by the vector Green's function of the adjoint linearized Euler equations for a given jet mean flow) and a generalized source term representing the jet turbulence field. Using a low-frequency/small spread rate asymptotic expansion of the propagator, mean flow non-parallelism enters the lowest order Green's function solution via the streamwise component of the mean flow advection vector in a hyperbolic partial differential equation. We then address the predictive capability of the solution to this partial differential equation when used in the analogy through first-of-its-kind numerical calculations when an experimentally verified model of the turbulence source structure is used together with Reynolds-averaged Navier–Stokes solutions for the jet mean flow. Our noise predictions show a reasonable level of accuracy in the peak noise direction at Ma = 0.9, for Strouhal numbers up to about 0.6, and at Ma = 0.5 using modified source coefficients. Possible reasons for this are discussed. Moreover, the prediction range can be extended beyond unity Strouhal number by using an approximate composite asymptotic formula for the vector Green's function that reduces to the locally parallel flow limit at high frequencies. This article is part of the theme issue ‘Frontiers of aeroacoustics research: theory, computation and experiment’.
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Pokora, C. D., and J. J. McGuirk. "Stereo-PIV measurements of spatio-temporal turbulence correlations in an axisymmetric jet." Journal of Fluid Mechanics 778 (July 30, 2015): 216–52. http://dx.doi.org/10.1017/jfm.2015.362.
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Stereoscopic three-component particle image velocimetry (3C-PIV) measurements have been made in a turbulent round jet to investigate the spatio-temporal correlations that are the origin of aerodynamic noise. Restricting attention to subsonic, isothermal jets, measurements were taken in a water flow experiment where, for the same Reynolds number and nozzle size, the shortest time scale of the dynamically important turbulent structures is more than an order of magnitude greater that in equivalent airflow experiments, greatly facilitating time-resolved PIV measurements. Results obtained (for a jet nozzle diameter and velocity of 40 mm and $1~\text{m}~\text{s}^{-1}$, giving $\mathit{Re}=4\times 10^{4}$) show that, on the basis of both single-point statistics and two-point quantities (correlation functions, integral length scales) the present incompressible flow data are in excellent agreement with published compressible, subsonic airflow measurements. The 3C-PIV data are first compared to higher-spatial-resolution 2C-PIV data and observed to be in good agreement, although some deterioration in quality for higher-order correlations caused by high-frequency noise in the 3C-PIV data is noted. A filter method to correct for this is proposed, based on proper orthogonal decomposition (POD) of the 3C-PIV data. The corrected data are then used to construct correlation maps at the second- and fourth-order level for all velocity components. The present data are in accordance with existing hot-wire measurements, but provide significantly more detailed information on correlation components than has previously been available. The measured relative magnitudes of various components of the two-point fourth-order turbulence correlation coefficient ($R_{ij,kl}$) – the fundamental building block for free shear flow aerodynamic noise sources – are presented and represent a valuable source of validation data for acoustic source modelling. The relationship between fourth-order and second-order velocity correlations is also examined, based on an assumption of a quasi-Gaussian nearly normal p.d.f. for the velocity fluctuations. The present results indicate that this approximation shows reasonable agreement for the measured relative magnitudes of several correlation components; however, areas of discrepancy are identified, indicating the need for work on alternative models such as the shell turbulence concept of Afsar (Eur. J. Mech. (B/Fluids), vol. 31, 2012, pp. 129–139).
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Schmidt, Oliver T., Aaron Towne, Georgios Rigas, Tim Colonius, and Guillaume A. Brès. "Spectral analysis of jet turbulence." Journal of Fluid Mechanics 855 (September 21, 2018): 953–82. http://dx.doi.org/10.1017/jfm.2018.675.
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Informed by large-eddy simulation (LES) data and resolvent analysis of the mean flow, we examine the structure of turbulence in jets in the subsonic, transonic and supersonic regimes. Spectral (frequency-space) proper orthogonal decomposition is used to extract energy spectra and decompose the flow into energy-ranked coherent structures. The educed structures are generally well predicted by the resolvent analysis. Over a range of low frequencies and the first few azimuthal mode numbers, these jets exhibit a low-rank response characterized by Kelvin–Helmholtz (KH) type wavepackets associated with the annular shear layer up to the end of the potential core and that are excited by forcing in the very-near-nozzle shear layer. These modes too have been experimentally observed before and predicted by quasi-parallel stability theory and other approximations – they comprise a considerable portion of the total turbulent energy. At still lower frequencies, particularly for the axisymmetric mode, and again at high frequencies for all azimuthal wavenumbers, the response is not low-rank, but consists of a family of similarly amplified modes. These modes, which are primarily active downstream of the potential core, are associated with the Orr mechanism. They occur also as subdominant modes in the range of frequencies dominated by the KH response. Our global analysis helps tie together previous observations based on local spatial stability theory, and explains why quasi-parallel predictions were successful at some frequencies and azimuthal wavenumbers, but failed at others.
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SIMON, FRANCK, SEBASTIEN DECK, PHILIPPE GUILLEN, PIERRE SAGAUT, and ALAIN MERLEN. "Numerical simulation of the compressible mixing layer past an axisymmetric trailing edge." Journal of Fluid Mechanics 591 (October 30, 2007): 215–53. http://dx.doi.org/10.1017/s0022112007008129.
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Numerical simulation of a compressible mixing layer past an axisymmetric trailing edge is carried out for a Reynolds number based on the diameter of the trailing edge approximately equal to 2.9 × 106. The free-stream Mach number at separation is equal to 2.46, which corresponds to experiments and leads to high levels of compressibility. The present work focuses on the evolution of the turbulence field through extra strain rates and on the unsteady features of the annular shear layer. Both time-averaged and instantaneous data are used to obtain further insight into the dynamics of the flow. An investigation of the time-averaged flow field reveals an important shear-layer growth rate in its initial stage and a strong anisotropy of the turbulent field. The convection velocity of the vortices is found to be somewhat higher than the estimated isentropic value. This corroborates findings on the domination of the supersonic mode in planar supersonic/subsonic mixing layers. The development of the shear layer leads to a rapid decrease of the anisotropy until the onset of streamline realignment with the axis. Due to the increase of the axisymmetric constraints, an adverse pressure gradient originates from the change in streamline curvature. This recompression is found to slow down the eddy convection. The foot shock pattern features several convected shocks emanating from the upper side of the vortices, which merge into a recompression shock in the free stream. Then, the flow accelerates and the compressibility levels quickly drop in the turbulent developing wake. Some evidence of the existence of large-scale structures in the near wake is found through the domination of the azimuthal mode m = 1 for a Strouhal number based on trailing-edge diameter equal to 0.26.
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Baqui, Yamin B., Anurag Agarwal, André V. G. Cavalieri, and Samuel Sinayoko. "A coherence-matched linear source mechanism for subsonic jet noise." Journal of Fluid Mechanics 776 (July 6, 2015): 235–67. http://dx.doi.org/10.1017/jfm.2015.322.
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We investigate source mechanisms for subsonic jet noise using experimentally obtained datasets of high-Reynolds-number Mach 0.4 and 0.6 turbulent jets. The focus is on the axisymmetric mode which dominates downstream sound radiation for low polar angles and the frequency range at which peak noise occurs. A linearized Euler equation (LEE) solver with an inflow boundary condition is used to generate single-frequency hydrodynamic instability waves, and the resulting near-field fluctuations and far-field acoustics are compared with those from experiments and linear parabolized stability equation (LPSE) computations. It is found that the near-field velocity fluctuations closely agree with experiments and LPSE computations up to the end of the potential core, downstream of which deviations occur, but the LEE results match experiments better than the LPSE results. Both the near-field wavepackets and the sound field are observed directly from LEE computations, but the far-field sound pressure levels (SPLs) obtained are more than an order of magnitude lower than experimental values despite close statistical agreement of the near hydrodynamic field up to the potential core region. We explore the possibility that this discrepancy is due to the mismatch between the decay of two-point coherence with increasing distance in experimental flow fluctuations and the perfect coherence in linear models. To match the near-field coherence, experimentally obtained coherence profiles are imposed on the two-point cross-spectral density (CSD) at cylindrical and conical surfaces that enclose near-field structures generated with LEEs. The surface pressure is propagated to the far field using boundary value formulations based on the linear wave equation. Coherence matching yields far-field SPLs which show improved agreement with experimental results, indicating that coherence decay is the main missing component in linear models. The CSD on the enclosing surfaces reveals that the application of a decaying coherence profile spreads the hydrodynamic component of the linear wavepacket source on to acoustic wavenumbers, resulting in a more efficient acoustic source.
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Chen, Li-Wei, Guo-Lei Wang, and Xi-Yun Lu. "Numerical investigation of a jet from a blunt body opposing a supersonic flow." Journal of Fluid Mechanics 684 (August 30, 2011): 85–110. http://dx.doi.org/10.1017/jfm.2011.276.
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AbstractNumerical investigation of a sonic jet from a blunt body opposing a supersonic flow with a free stream Mach number ${M}_{\infty } = 2. 5$ was carried out using large-eddy simulation for two total pressure ratios of the jet to the free stream, i.e. $\mathscr{P}= 0. 816$ and 1.633. Results have been validated carefully against experimental data. Various fundamental mechanisms dictating the flow phenomena, including shock/jet interaction, shock/shear-layer interaction, turbulent shear-layer evolution and coherent structures, have been studied systematically. Based on the analysis of the flow structures and features, two typical flow states, i.e. unstable and stable states corresponding to the two values of $\mathscr{P}$, are identified and the behaviours relevant to the flow states are discussed. Small-scale vortical structures mainly occur in the jet column, and large-scale vortices develop gradually in a recirculation region when the jet terminates through a Mach disk and reverses its orientation as a conical free shear layer. The turbulent fluctuations are enhanced by the rapid deviation of the shear layer and the interaction with shock waves. Moreover, the coherent structures of the flow motion are analysed using the proper orthogonal decomposition technique. It is found that the dominant mode in the cross-section plane exhibits an antisymmetric character for the unstable state and an axisymmetric one for the stable state, while statistical analysis of unsteady loads indicates that the side loads can be seen as a rotating vector uniformly distributed in the azimuthal direction. Further, we clarify a feedback mechanism whereby the unsteady motion is sustained by the upstream-propagating disturbance to the Mach disk through the recirculation subsonic region and downstream propagation in the conical shear layer. Feedback models are then proposed which can reasonably well predict the dominant frequencies of the two flow states. The results obtained in this study provide physical insight into the understanding of the mechanisms relevant to the opposing jet/supersonic flow interaction.
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Bogey, Christophe. "On noise generation in low Reynolds number temporal round jets at a Mach number of 0.9." Journal of Fluid Mechanics 859 (November 27, 2018): 1022–56. http://dx.doi.org/10.1017/jfm.2018.864.
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Two temporally developing isothermal round jets at a Mach number of 0.9 and Reynolds numbers of 3125 and 12 500 are simulated in order to investigate noise generation in high-subsonic jet flows. Snapshots and statistical properties of the flow and sound fields, including mean, root-mean-square and skewness values, spectra and auto- and cross-correlations of velocity and pressure, are presented. The jet at a Reynolds number of 12 500 develops more rapidly, exhibits more fine turbulent scales and generates more high-frequency acoustic waves than the other. In both cases, however, when the jet potential core closes, mixing-layer turbulent structures intermittently intrude on the jet axis and strong low-frequency acoustic waves are emitted in the downstream direction. These waves are dominated by the axisymmetric mode and are significantly correlated with centreline flow fluctuations. These results are similar to those obtained at the end of the potential core of spatially developing jets. They suggest that the mechanism responsible for the downstream noise component of these jets also occurs in temporal jets, regardless of the Reynolds number. This mechanism is revealed by averaging the flow and pressure fields of the present jets using a sample synchronization with the minimum values of centreline velocity at potential-core closing. A spot characterized by a lower velocity and a higher level of vorticity relative to the background flow field is found to develop in the interfacial region between the mixing layer and the potential core, to strengthen rapidly and reach a peak intensity when arriving on the jet axis, and then to break down. This is accompanied by the growth and decay of a hydrodynamic pressure wave, propagating at a velocity which, initially, is close to 65 per cent of the jet velocity and slightly increases, but quickly decreases after the collapse of the high-vorticity spot in the flow. During that process, sound waves are radiated in the downstream direction.
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TINNEY, C. E., M. N. GLAUSER, and L. S. UKEILEY. "Low-dimensional characteristics of a transonic jet. Part 1. Proper orthogonal decomposition." Journal of Fluid Mechanics 612 (October 10, 2008): 107–41. http://dx.doi.org/10.1017/s0022112008002978.
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An experimental investigation concerning the most energetic turbulent features of the flow exiting from an axisymmetric converging nozzle at Mach 0.85 and ambient temperature is discussed using planar optical measurement techniques. The arrangement of the particle image velocimetry (PIV) system allows for all three components of the velocity field to be captured along the (r, θ)-plane of the jet at discrete streamwise locations between x/D=3.0 and 8.0 in 0.25 diameter increments. The ensemble-averaged (time-suppressed) two-point full Reynolds stress matrix is constructed from which the integral eigenvalue problem of the proper orthogonal decomposition (POD) is applied using both scalar and vector forms of the technique. A grid sensitivity study indicates that the POD eigenvalues converge safely to within 1% of their expected value when the discretization of the spatial grid is less than 30% of the integral length scale or 10% of the shear-layer width. The first POD eigenvalue from the scalar decomposition of the streamwise component is shown to agree with previous investigations for a range of Reynolds numbers and Mach numbers with a peak in azimuthal mode 5 at x/D=3.0, and a gradual shift to azimuthal mode 2 by x/D=8.0. The eigenvalues from the scalar POD of the radial and azimuthal components are shown to be much lower-dimensional with most of their energy residing in the first few azimuthal modes, that is modes 0, 1 and 2, with little change in the relative energies along the streamwise direction. From the vector decomposition, the azimuthal eigenspectra of the first two POD modes shift from a peak in azimuthal mode 5 at x/D=3.0, followed by a gradual decay to azimuthal mode 2 at x/D=8.0, the differences in the peak energies being very subtle. The conclusion from these findings is that when the Mach number is subsonic and the Reynolds number sufficiently large, the structure of the turbulent jet behaves independently of these factors.
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Vasin, A. D. "Thin axisymmetric cavities in a subsonic compressible flow." Fluid Dynamics 22, no. 5 (1988): 808–11. http://dx.doi.org/10.1007/bf01051708.
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Baskaran, Kabilan, and K. Srinivasan. "Aeroacoustic characteristics of subsonic flow from axisymmetric pipe-cavities." Physics of Fluids 31, no. 10 (October 1, 2019): 106107. http://dx.doi.org/10.1063/1.5123661.
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Broze, George, and Fazle Hussain. "Nonlinear dynamics of forced transitional jets: periodic and chaotic attractors." Journal of Fluid Mechanics 263 (March 25, 1994): 93–132. http://dx.doi.org/10.1017/s0022112094004040.
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Conclusive experimental evidence is presented for the existence of a low-dimensional temporal dynamical system in an open flow, namely the near field of an axisymmetric, subsonic free jet. An initially laminar jet (4 cm air jet in the Reynolds number range 1.1 × 104 [Lt ] ReD × 9.1 × 104) with a top-hat profile was studied using single-frequency, longitudinal, bulk excitation. Two non-dimensional control parameters – forcing frequency StD (≡fexD/Ue, where fez is the excitation frequency, D is the jet exit diameter and Ue is the exit velocity) and forcing amplitude af (≡ u’f/Ue, where u’f is the jet exit r.m.s. longitudinal velocity fluctuation at the excitation frequency) – were varied over the ranges 10-4 < af < 0.3 and 0.3 < StD < 3.0 in order to construct a phase diagram. Periodic and chaotic states were found over large domains of the parameter space. The periodic attractors correspond to stable pairing (SP) and stable double pairing (SDP) of rolled-up vortices. One chaotic attractor, near SP in the parameter space, results from nearly periodic modulations of pairing (NPMP) of vortices. At large scales (i.e. approximately the size of the attractor) in phase space, NPMP exhibits approximately quasi-periodic behaviour, including modulation sidebands around ½fex in u-spectra, large closed loops in its Poincaré sections, correlation dimension v ∼ 2 and largest Lyapunov exponent λ1 ∼ 0. But investigations at smaller scales (i.e. distances greater than, but of the order of, trajectory separation) in phase space reveal chaos, as shown by v > 2 and λ1 > 0. The other chaotic attractor, near SDP, results from nearly periodic modulations of the first vortex pairing but chaotic modulations of the second pairing and has a broadband spectrum, a dimension 2.5 [Lt ] v [Lt ] 3 and the largest Lyapunov exponent 0.2 [Lt ] λ1 [Lt ] 0.7 bits per orbit (depending on measurement locations in physical and parameter spaces).A definition that distinguishes between physically and dynamically open flows is proposed and justified by our experimental results. The most important conclusion of this study is that a physically open flow, even one that is apparently dynamically open due to convective instability, can exhibit dynamically closed behaviour as a result of feedback. A conceptual model for transitional jets is proposed based on twodimensional instabilities, subharmonic resonance and feedback from downstream vortical structures to the nozzle lip. Feedback was quantified and shown to affect the exit fundamental–subharmonic phase difference ϕ – a crucial variable in subharmonic resonance and, hence, vortex pairing. The effect of feedback, the sensitivity of pairings to ϕ, the phase diagram, and the documented periodic and chaotic attractors demonstrate the validity of the proposed conceptual model.
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Busse, C. A., and R. I. Loehrke. "Subsonic Pressure Recovery in Cylindrical Condensers." Journal of Heat Transfer 111, no. 2 (May 1, 1989): 533–37. http://dx.doi.org/10.1115/1.3250710.
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A method is presented for predicting laminar, subsonic flow in axisymmetric cylindrical heat pipe condensers. The method involves the use of the boundary layer approximation and a noncontinuous power series to describe the velocity profile under conditions including strong axial flow reversal. A comparison between laminar predictions and measurements indicates that transition to turbulent flow in the condenser begins when the absolute value of the radial Reynolds number exceeds 6. The condenser pressure recovery in the turbulent regime can be calculated from the momentum flow at the condenser inlet and an empirical wall-friction parameter.
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Porteiro, J. L. F., and V. Perez-Villar. "Wake development in turbulent subsonic axisymmetric flows." Experiments in Fluids 21, no. 3 (July 1996): 145–50. http://dx.doi.org/10.1007/bf00191685.
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Peskova, E. E. "Numerical modeling of subsonic axisymmetric reacting gas flows." Journal of Physics: Conference Series 2057, no. 1 (October 1, 2021): 012071. http://dx.doi.org/10.1088/1742-6596/2057/1/012071.
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Abstract A numerical algorithm is developed and implemented for modelling axisymmetric subsonic reacting gas flows based on a previously created program for plane flows. The system of Navier-Stokes equations in the low Mach number limit is used as a mathematical model. Calculations of ethane pyrolysis for axisymmetric and plane flow of mixture at heat supply from the reactor’s walls are carried out. Through the interplay of the developed code and the code for plane flows it becomes possible to identify the geometric factor role at the presence of a large number of nonlinear physicochemical processes. We found that diffusion of synthesized molecular hydrogen mainly influences heat supply from the reactor’s walls to gas and pyrolysis products distribution along its length.
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Samanta, Arnab. "On the axisymmetric stability of heated supersonic round jets." Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences 472, no. 2188 (April 2016): 20150817. http://dx.doi.org/10.1098/rspa.2015.0817.
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We perform an inviscid, spatial stability analysis of supersonic, heated round jets with the mean properties assumed uniform on either side of the jet shear layer, modelled here via a cylindrical vortex sheet. Apart from the hydrodynamic Kelvin–Helmholtz (K–H) wave, the spatial growth rates of the acoustically coupled supersonic and subsonic instability waves are computed for axisymmetric conditions ( m =0) to analyse their role on the jet stability, under increased heating and compressibility. With the ambient stationary, supersonic instability waves may exist for any jet Mach number M j ≥2, whereas the subsonic instability waves, in addition, require the core-to-ambient flow temperature ratio T j / T o >1. We show, for moderately heated jets at T j / T o >2, the acoustically coupled instability modes, once cut on, to govern the overall jet stability with the K–H wave having disappeared into the cluster of acoustic modes. Sufficiently high heating makes the subsonic modes dominate the jet near-field dynamics, whereas the supersonic instability modes form the primary Mach radiation at far field.
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Tran The Hung. "AERODYNAMIC CHARACTERISTICS OF FLOW OVER BOAT-TAIL MODELS AT SUBSONIC AND SUPERSONIC CONDITIONS." Journal of Military Science and Technology, no. 75A (November 11, 2021): 60–69. http://dx.doi.org/10.54939/1859-1043.j.mst.75a.2021.60-69.
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In this study, the flow behavior and drag of the axisymmetric model at subsonic and supersonic speeds were investigated by a numerical approach. The numerical results were validated with previous experimental results to determine the model's accuracy. The numerical results showed that the optimal angles reduce from 14° at subsonic conditions to 6° ÷ 8° at supersonic conditions. At the supersonic speeds, shock waves occur at the head and boat-tail of the model, which leads to changes in the pressure distribution and drag of the model. The flow behavior and velocity distribution around the model were investigated and presented in detail in this study.
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Naser, J. A., and A. D. Gosman. "Prediction of Compressible Subsonic Flow through an Axisymmetric Exhaust Valve-port Assembly." Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 209, no. 4 (October 1995): 289–95. http://dx.doi.org/10.1243/pime_proc_1995_209_216_02.
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Flow details through an axisymmetric exhaust valve-port assembly have been investigated numerically. Computations were performed for steady compressible subsonic air flow at different valve lifts. The numerical procedure used for this purpose solves the governing equations using the SIMPLE algorithm. The governing equations are expressed in a general curvilinear coordinate system and are discretized in a finite volume fashion. The time-averaged governing equations are closed using the k–e. turbulence model. The predictions are assessed by comparing with the available experimental flow field data. Good agreement is observed between the predictions and the experiment.
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Miller, P., J. Agrell, J. Olsson, and K. Sjörs. "Axisymmetric afterbody experiments for CFD validation." Aeronautical Journal 98, no. 974 (April 1994): 137–46. http://dx.doi.org/10.1017/s0001924000049988.
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Summary An experiment is described which was undertaken specifically to provide CFD validation data for the case of transonic flow over nozzle afterbodies. The tests were undertaken with the AGARD standard 10° and 15° axisymmetric boat-tail geometries. Onset Mach numbers in the range 0·80-0·99 and subsonic and under-expanded jet plumes were employed in the tests. Test conditions were selected which provided a range of afterbody flow features from largely attached to shock-induced separated flows. A uniquely detailed set of surface pressure and flowfield data are presented. The flow data were acquired with a two-component laser Doppler anemometer (LDA) and define the mean and fluctuating flow components at about 500 spatial locations for each of these complex transonic flowfields. Additional information was recorded which fully defines the required computational boundary conditions. Also presented is a detailed study of the necessary attributes of windtunnel CFD validation data. It is demonstrated that relatively high blockage experiments using cost-effective windtunnels can be used to generate CFD validation data if proper account is taken of the model/tunnel interference.
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Vasin, A. D. "Calculation of axisymmetric cavities downstream of a disk in subsonic compressible fluid flow." Fluid Dynamics 31, no. 2 (March 1996): 240–48. http://dx.doi.org/10.1007/bf02029683.
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Du, Yanfeng, Cong Wang, and Yan Zhou. "A study on supercavitation in axisymmetric subsonic liquid flow past slender conical body." European Journal of Mechanics - B/Fluids 72 (November 2018): 264–74. http://dx.doi.org/10.1016/j.euromechflu.2018.06.004.
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Benard, N., J. Jolibois, M. Forte, G. Touchard, and E. Moreau. "Control of an axisymmetric subsonic air jet by plasma actuator." Experiments in Fluids 43, no. 4 (July 10, 2007): 603–16. http://dx.doi.org/10.1007/s00348-007-0344-9.
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Ziwan, Li, and V. L. Varsegov. "Computational Study of Interaction of Transverse Subsonic and Supersonic Axisymmetric Jets with Main Flow." Russian Aeronautics 62, no. 3 (July 2019): 438–47. http://dx.doi.org/10.3103/s1068799819030115.
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Sandberg, R. D., and B. J. Tester. "Mach-number scaling of individual azimuthal modes of subsonic co-flowing jets." Journal of Fluid Mechanics 793 (March 14, 2016): 209–28. http://dx.doi.org/10.1017/jfm.2016.133.
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The Mach-number scaling of the individual azimuthal modes of jet mixing noise was studied for jets in flight conditions, i.e. with co-flow. The data were obtained via a series of direct numerical simulations (DNS), performed of fully turbulent jets with a target Reynolds number, based on nozzle diameter, of $Re_{jet}=8000$. The DNS included a pipe 25 diameters in length in order to ensure that the flow developed to a fully turbulent state before exiting into a laminar co-flow, and to account for all possible noise generation mechanisms. To allow for a detailed study of the jet mixing noise component of the combined pipe–jet configuration, acoustic liner boundary conditions on the inside of the pipe and a modification to the synthetic turbulent inlet boundary condition of the pipe were applied to minimize internal noise in the pipe. Despite these measures, the use of a phased-array source breakdown technique was essential in order to isolate the sources associated with jet noise mechanisms from additional noise sources that could be attributed to internal noise or unsteady flow past the nozzle lip, in particular for the axisymmetric mode. Decomposing the sound radiation from the pipe–jet configuration into its azimuthal Fourier modes, and accounting for the co-flow effects, it was found that at $90^{\circ }$ the individual azimuthal Fourier modes of far-field pressure for the jet mixing noise component exhibit the same $M^{8}$ scaling with the centreline jet Mach number as that experimentally documented for the overall noise field. Applying the phased-array source breakdown code to the DNS data at smaller angles to the jet axis, an increase of the velocity exponent of the jet noise source was found, approaching 10 at $30^{\circ }$. At this smaller angle the higher azimuthal modes again showed the same behaviour as the axisymmetric mode.
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Guslyakova, E. V. "Instability and structure of axisymmetric rotating flow." Fluid Dynamics 28, no. 5 (1994): 638–43. http://dx.doi.org/10.1007/bf01050046.
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Zhang, X., X. X. Chen, and C. L. Morfey. "Acoustic Radiation from a Semi-Infinite Duct With a Subsonic Jet." International Journal of Aeroacoustics 4, no. 1-2 (January 2005): 169–84. http://dx.doi.org/10.1260/1475472053730075.
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The radiation of high-order spinning modes from a semi-infinite exhaust duct is studied numerically. The issues involved have applications to noise radiation from the exhaust duct of an aircraft engine. The numerical method is based on solutions of linearised Euler equations (LEE) for propagation in the duct and near field, and the acoustic analogy for far field radiation. A 2.5D formulation of a linearised Euler equation model is employed to accommodate a single spinning mode propagating over an axisymmetric mean flow field. In the solution process, acoustic waves are admitted into the propagation area surrounding the exit of an axisymmetric duct and its immediate downstream area. The wave admission is realised through an absorbing non-reflecting boundary treatment, which admits incoming waves and damps spurious waves generated by the numerical solutions. The wave propagation is calculated through solutions of linearised Euler equations, using an optimised prefactored compact scheme for spatial discretisation. Far field directivity is estimated by solving the Ffowcs Williams-Hawkings equations. The far field prediction is compared with analytic solutions with good agreement.
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Yan, Dongfeng, Zhijun Wei, Kan Xie, Changchao Guo, Wan Tang, and Ningfei Wang. "Study of the vortex structure of a subsonic jet in an axisymmetric transonic nozzle." Physics of Fluids 32, no. 7 (July 1, 2020): 076109. http://dx.doi.org/10.1063/5.0008796.
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Hu, Shuzhen, Xingen Lu, Hongwu Zhang, Junqiang Zhu, and Qiang Xu. "Numerical investigation of a high-subsonic axial-flow compressor rotor with non-axisymmetric hub endwall." Journal of Thermal Science 19, no. 1 (January 29, 2010): 14–20. http://dx.doi.org/10.1007/s11630-010-0014-8.
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Jelínek, Tomáš, Erik Flídr, Martin Němec, and Jan Šimák. "Test Facility for High-Speed Probe Calibration." EPJ Web of Conferences 213 (2019): 02033. http://dx.doi.org/10.1051/epjconf/201921302033.
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A new test facility was built up as a part of a closed-loop transonic wind tunnel in VZLU´s High-speed Aerodynamics Department. The wind tunnel is driven by a twelve stage radial compressor and Mach and Reynolds numbers can be changed by the compressor speed and by the total pressure in the wind tunnel loop by a set of vacuum pumps, respectively. The facility consists of an axisymmetric subsonic nozzle with an exit diameter de = 100 mm. The subsonic nozzle is designed for regimes up to M = 1 at the nozzle outlet. At the nozzle inlet there is a set of a honeycomb and screens to ensure the flow stream laminar at the outlet of the nozzle. The subsonic nozzle can be supplemented with a transonic slotted nozzle or a supersonic rigid nozzle for transonic and supersonic outlet Mach numbers. The probe is fixed in a probe manipulator situated downstream of the nozzle and it ensures a set of two perpendicular angles in a wide range (±90°). The outlet flow field was measured through in several axial distances downstream the subsonic nozzle outlet. The total pressure and static pressure was measured in the centreline and the total pressure distribution in the vertical and horizontal plane was measured as well. Total pressure fluctuations in the nozzle centreline were detected by a FRAP probe. From the initial flow measurement in a wide range of Mach numbers the best location for probe calibration was chosen. The flow field was found to be suitable for probe calibration.
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Legras, Guillaume, Isabelle Trébinjac, Nicolas Gourdain, Xavier Ottavy, and Lionel Castillon. "A Novel Approach to Evaluate the Benefits of Casing Treatment in Axial Compressors." International Journal of Rotating Machinery 2012 (2012): 1–19. http://dx.doi.org/10.1155/2012/975407.
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Passive control devices based on casing treatments have already shown their capability to improve the flow stability in axial compressors. However, their optimization remains complex due to a partial understanding of the related physical mechanisms. In order to quantitatively assess the interaction between slots and the blade tip flow, the present paper develops a novel analysis methodology based on a control-volume approach located in the rotor tip region. This methodology may be used for analyzing the casing treatment based on both axi- and non-axisymmetric slots design. The second issue of the paper focuses on the application of the current approach to better understand the effects of axi- and non-axisymmetric grooves in three different axial compressors which differ by the flow regime (subsonic/transonic) and the smooth casing shape (cylindrical/concave). Numerical simulations are performed, and results of the current approach with and without casing treatments are compared.
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MIYATA, Masafumi. "Axisymmetric Annular Jet : Flow Structure Near Nozzle Exit." Proceedings of the JSME annual meeting 2003.2 (2003): 151–52. http://dx.doi.org/10.1299/jsmemecjo.2003.2.0_151.
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Lyubimov, Dmitriy, and Alena Fedorenko. "External flow velocity and synthetic jets parameters influence on cavity flow structure and acoustics characteristics using RANS/ILES." International Journal of Aeroacoustics 17, no. 3 (March 14, 2018): 259–74. http://dx.doi.org/10.1177/1475472x18763858.
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An influence of synthetic jets on the flow in a three-dimensional cavity M219 was studied using RANS/ILES method. Calculations were performed for Mach numbers M0 = 0.85 and M0 = 1.5. Synthetic jets’ operating parameters such as their position, number, frequency, and amplitude were varied. An impact of these parameters and M0 on flow in the cavity, distributions, and levels of pressure fluctuations on the cavity walls as well as the narrowband spectra of pressure fluctuations were obtained. Synthetic jets located in front of a cavity may reduce peak pressure pulsations on the cavity back wall by 37% for a subsonic external flow. Moreover, it was found that synthetic jets may decrease the second and the third modes of pressure fluctuations on the back wall both for subsonic flow and supersonic case.
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Yang, Hai-Hua, Lin Zhou, Xing-Chen Zhang, Zhen-Hua Wan, and De-Jun Sun. "Nonlinear interaction of instability waves and vortex-pairing noise in axisymmetric subsonic jets." Fluid Dynamics Research 48, no. 5 (August 25, 2016): 055502. http://dx.doi.org/10.1088/0169-5983/48/5/055502.
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Madaliev, Murodil Erkinjon oglu, and Dilshod Primkulovich Navruzov. "RESEARCH OF RESEARCH OF νt-92 TURBULENCE MODEL FOR CALCULATING AN AXISYMMETRIC SOUND JET." Scientific Reports of Bukhara State University 4, no. 2 (April 27, 2020): 82–90. http://dx.doi.org/10.52297/2181-1466/2020/4/2/1.
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A comparative analysis of the use of the turbulence model is carried out: the one-parameter Secundov νt-92 model on the problem of an axisymmetric subsonic jet. The calculation results are compared with experimental results on the propagation of speed, voltage, and temperature. The flow is turbulent, therefore, as a mathematical model, the system of Navier-Stokes equations averaged by Reynolds (RANS) is used. For the posed problem, a generalized stream function ψ is introduced. A comparison was made of the results of the νt-92 model with experimental data from [5] the dimensionless axial velocity from the distance to the nozzle
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Симашов, Р. Р., and С. В. Чехранов. "Determination of mass flow characteristics of supersonic axisymmetric nozzle diaphragms in modeling variable duties of low-consumption turbines." MORSKIE INTELLEKTUAL`NYE TEHNOLOGII), no. 4(50) (December 17, 2020): 39–43. http://dx.doi.org/10.37220/mit.2020.50.4.070.
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В работе приводятся обобщающие зависимости коэффициентов расхода сопловых аппаратов со сверхзвуковыми осесимметричными соплами в широком диапазоне изменения определяющих геометрических и режимных параметров. Предложена двухпараметрическая функция, учитывающая влияние расположения сопел в сопловом аппарате и степени конфузорности дозвуковой части осесимметричного сопла на коэффициент расхода. Показано слабое влияние на коэффициент расхода относительного радиуса закругления стенки в узкой части сопла и относительной длины дозвуковой части сопла в области их оптимальных значений определенных по минимуму потерь кинетической энергии. Переменные режимы работы сопла учитываются зависимостью относительного коэффициента расхода в функции от числа Рейнольдса в критическом сечении сопла. Полученные в работе эмпирические зависимости позволяют использовать их при моделировании переменных режимов и многорежимной оптимизации малорасходных турбин. The research presents generalizing dependences of mass flow rates in supersonic axisymmetric nozzle diaphragms n a wide range of variation of the governing geometric and operating parameters. A two-parameter function is proposed that takes into account the influence of the location of the nozzles in the nozzle apparatus and the degree of compression of the flow of the subsonic part of the nozzle on the mass flow rate. It is shown that the relative radius of rounding of the nozzle wall in the vicinity of the throat section and the relative length of the subsonic part of the nozzle in the region of their optimal values determined by the minimum of kinetic energy losses have a weak effect on the flow rate. Variable duties of nozzle operation are taken into account by the dependence of the relative flow rate as a function of the Reynolds number in the throat of the nozzle. The empirical dependencies obtained in this work make it possible to use them in modeling variable modes and multi-mode optimization of low-consumption turbines.
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Masud, J. "Flow field and performance analysis of an integrated diverterless supersonic inlet." Aeronautical Journal 115, no. 1170 (August 2011): 471–80. http://dx.doi.org/10.1017/s0001924000006114.
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Abstract In this paper the computed flow and performance characteristics at low angle-of-attack (AOA) of an integrated diverterless supersonic inlet (DSI) are presented. The subsonic characteristics are evaluated at M∞ = 0·8 while the supersonic characteristics are evaluated at M∞= 1·7, which is near the design Mach number for the intake. In addition to the external flow features, the internal intake duct flow behaviour is also evaluated. The results of this study indicate effective boundary layer diversion due to the ‘bump’ compression surface in both subsonic and supersonic regimes. At M∞ = 1·7, the shockwave structure (oblique/normal shockwave) on the ‘bump’ compression surface and intake inlet is satisfactory at design (critical) mass flow rate. The intake duct flow behaviour at subsonic and supersonic conditions is generally consistent with ‘Y’ shaped intake duct of the present configuration. The secondary flow structure inside the duct has been effectively captured by present computations. The computed intake total pressure recovery at M∞ = 1·7 exhibits higher-than-conventional behaviour at low mass flow ratios, which is attributed to unique inlet design. Overall computed subsonic and supersonic total pressure recovery characteristics are satisfactory under the evaluated conditions and are also in agreement with wind tunnel test data.
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Chandola, Gaurav, Xin Huang, and David Estruch-Samper. "Highly separated axisymmetric step shock-wave/turbulent-boundary-layer interaction." Journal of Fluid Mechanics 828 (September 6, 2017): 236–70. http://dx.doi.org/10.1017/jfm.2017.522.
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The unsteadiness of a shock-wave/turbulent-boundary-layer interaction induced by an axisymmetric step (cylinder/$90^{\circ }$-disk) is investigated experimentally at Mach 3.9. A large-scale separation of the order of previously reported incoming turbulent superstructures is induced ahead of the step ${\sim}30\unicode[STIX]{x1D6FF}_{o}$ and followed by a downstream separation of ${\sim}10\unicode[STIX]{x1D6FF}_{o}$ behind it, where $\unicode[STIX]{x1D6FF}_{o}$ is the incoming boundary-layer thickness. Narrowband high-frequency instabilities shift gradually to more moderate frequencies along the upstream separation region exhibiting a strong predominance of shear-induced disturbance levels – arising between the outer high-speed flow and the subsonic bubble. Through spectral/time-resolved analysis of this high Reynolds number and large-scale separation, results offer new insights into the shear layer’s inception and evolution (convection, growth and instability) and its influence on interaction unsteadiness.
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da Silva, A. R., G. P. Scavone, and A. Lefebvre. "Sound reflection at the open end of axisymmetric ducts issuing a subsonic mean flow: A numerical study." Journal of Sound and Vibration 327, no. 3-5 (November 2009): 507–28. http://dx.doi.org/10.1016/j.jsv.2009.06.027.
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Starikov, O. Yu. "The study of the induction of subsonic wind tunnels with an axisymmetric working part." Fluid Dynamics 20, no. 1 (1985): 130–33. http://dx.doi.org/10.1007/bf01097375.
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Hyhlík, Tomáš. "Method of Vortex Structure Identification in Axisymmetric Flow Field." Manufacturing Technology 15, no. 5 (November 1, 2015): 842–45. http://dx.doi.org/10.21062/ujep/x.2015/a/1213-2489/mt/15/5/842.
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Singh, Rakesh K., and Ram S. Azad. "Structure of Turbulence in an Incipient-Separating Axisymmetric Flow." Journal of Fluids Engineering 117, no. 3 (September 1, 1995): 433–38. http://dx.doi.org/10.1115/1.2817280.
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The relative intensity, skewness, and flatness of fluctuating streamwise velocity along the centerline of an 8 deg included angle conical diffuser show dramatic rapid growth in the final stages of the flow under the increasing influence of growing instantaneous reversals in the wall-layer. Pulsed-wire anemometry was effectively used for the measurement of quantitative instantaneous reversals and the turbulent flow field. In the severe adverse pressure gradient of the diffuser flow, the maxima of the streamwise and transverse fluctuating velocities, Reynolds shear stress, and turbulent energy production coincide and move away from their near-wall position in the pipe, also the velocity triple products show completely opposite nature as compared to the pipe flow. These measurements reveal the strong influence of instantaneous backflow on the structure of turbulence. The present results further corroborate the ability of the “structural” turbulence model of Nagano and Tagawa (1990) to predict velocity triple products in an axisymmetric diffuser flow.
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Damle, S. V., T. Q. Dang, and D. R. Reddy. "Throughflow Method for Turbomachines Applicable for All Flow Regimes." Journal of Turbomachinery 119, no. 2 (April 1, 1997): 256–62. http://dx.doi.org/10.1115/1.2841108.
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A new axisymmetric throughflow method for analyzing and designing turbomachines is proposed. This method utilizes body-force terms to represent blade forces and viscous losses. The resulting equations of motion, which include these body-force terms, are cast in terms of conservative variables and are solved using a finite-volume time-stepping scheme. In the inverse mode, the swirl schedule in the bladed regions (i.e., the radius times the tangential velocity rVθ) is the primary specified flow quantity, and the corresponding blade shape is sought after. In the analysis mode, the blade geometry is specified and the flow solution is computed. The advantages of this throughflow method compared to the current family of streamline curvature and matrix methods are that the same code can be used for subsonic/transonic/supersonic throughflow velocities, and the proposed method has a shock capturing capability. This method is demonstrated for designing a supersonic throughflow fan stage and a transonic throughflow turbine stage.
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Jung, Seo Yoon, and Hyung Jin Sung. "Flow structure and flow-induced noise in an axisymmetric cavity with lids." Journal of Mechanical Science and Technology 30, no. 7 (July 2016): 3229–41. http://dx.doi.org/10.1007/s12206-016-0631-6.
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Yaman, Kemal. "Subsonic Flutter of Cantilever Rectangular PC Plate Structure." International Journal of Aerospace Engineering 2016 (2016): 1–10. http://dx.doi.org/10.1155/2016/9212364.
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Flutter characteristics of cantilever rectangular flexible plate structure under incompressible flow regime are investigated by comparing the results of commercial flutter analysis program ZAERO©with wind tunnel tests conducted in Ankara Wind Tunnel (ART). A rectangular polycarbonate (PC) plate, 5 × 125 × 1000 mm in dimension, is used for both numerical and experimental investigations. Analysis and test results are very compatible with each other. A comparison between two different solution methods (g-methodandk-method) of ZAERO©is also done. It is seen that thek-methodgives a closer result than the other one. However,g-method results are on a conservative side and it is better to use conservative results, namely,g-method results. Even if the modal analysis results are used for the flutter analysis for this simple structure, a modal test should be conducted in order to validate the modal analysis results to have accurate flutter analysis results for more complicated structures.
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Cavalieri, André V. G., Daniel Rodríguez, Peter Jordan, Tim Colonius, and Yves Gervais. "Wavepackets in the velocity field of turbulent jets." Journal of Fluid Mechanics 730 (August 2, 2013): 559–92. http://dx.doi.org/10.1017/jfm.2013.346.
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AbstractWe study the velocity fields of unforced, high Reynolds number, subsonic jets, issuing from round nozzles with turbulent boundary layers. The objective of the study is to educe wavepackets in such flows and to explore their relationship with the radiated sound. The velocity field is measured using a hot-wire anemometer and a stereoscopic, time-resolved PIV system. The field can be decomposed into frequency and azimuthal Fourier modes. The low-angle sound radiation is measured synchronously with a microphone ring array. Consistent with previous observations, the azimuthal wavenumber spectra of the velocity and acoustic pressure fields are distinct. The velocity spectrum of the initial mixing layer exhibits a peak at azimuthal wavenumbers $m$ ranging from 4 to 11, and the peak is found to scale with the local momentum thickness of the mixing layer. The acoustic pressure field is, on the other hand, predominantly axisymmetric, suggesting an increased relative acoustic efficiency of the axisymmetric mode of the velocity field, a characteristic that can be shown theoretically to be caused by the radial compactness of the sound source. This is confirmed by significant correlations, as high as 10 %, between the axisymmetric modes of the velocity and acoustic pressure fields, these values being significantly higher than those reported for two-point flow–acoustic correlations in subsonic jets. The axisymmetric and first helical modes of the velocity field are then compared with solutions of linear parabolized stability equations (PSE) to ascertain if these modes correspond to linear wavepackets. For all but the lowest frequencies close agreement is obtained for the spatial amplification, up to the end of the potential core. The radial shapes of the linear PSE solutions also agree with the experimental results over the same region. The results suggests that, despite the broadband character of the turbulence, the evolution of Strouhal numbers $0. 3\leq St\leq 0. 9$ and azimuthal modes 0 and 1 can be modelled as linear wavepackets, and these are associated with the sound radiated to low polar angles.
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Miao, Junjie, and Yuxin Fan. "Influence of struts on cavity at subsonic speeds: Flow characteristics." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 233, no. 14 (April 18, 2019): 5369–79. http://dx.doi.org/10.1177/0954410019843726.
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Cavity–strut combined flame holder is a promising choice for turbine-based combined cycle engines with its excellent fuel distribution and flame stabilization. In this paper, the effects of the strut structure parameters on the flow characteristics in the cavity were investigated by using particle image velocimetry and numerical simulation. Experimental and numerical results show that the struts induce complex three-dimensional flow patterns, which have a significant influence on the cavity transverse vortex. The relative position between the cavity and the strut influences the critical length-to-depth ratio of the open cavity reverting to the closed cavity. The mass exchange rate of the cavity decreases with the increase in the space between the cavity and the struts, while it increases with the strut inclination angle increases. The variation law of mean cavity residence time with the structure parameters is exactly opposite to that of the mass exchange rate. Compared with a single cavity, at a high subsonic speed, the cavity–strut combined structure has the advantage of increasing the mass exchange rate and cavity residence time simultaneously.
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MELIGA, P., D. SIPP, and J. M. CHOMAZ. "Effect of compressibility on the global stability of axisymmetric wake flows." Journal of Fluid Mechanics 660 (August 19, 2010): 499–526. http://dx.doi.org/10.1017/s002211201000279x.
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We study the linear dynamics of global eigenmodes in compressible axisymmetric wake flows, up to the high subsonic regime. We consider both an afterbody flow at zero angle of attack and a sphere, and find that the sequence of bifurcations destabilizing the axisymmetric steady flow is independent of the Mach number and reminiscent of that documented in the incompressible wake past a sphere and a disk (Natarajan & Acrivos, J. Fluid Mech., vol. 254, 1993, p. 323), hence suggesting that the onset of unsteadiness in this class of flows results from a global instability. We determine the boundary separating the stable and unstable domains in the (M, Re) plane, and show that an increase in the Mach number yields a stabilization of the afterbody flow, but a destabilization of the sphere flow. These compressible effects are further investigated by means of adjoint-based sensitivity analyses relying on the computation of gradients or sensitivity functions. Using this theoretical formalism, we show that they do not act through specific compressibility effects at the disturbance level but mainly through implicit base flow modifications, an effect that had not been taken into consideration by previous studies based on prescribed parallel base flow profiles. We propose a physical interpretation for the observed compressible effects, based on the competition between advection and production of disturbances, and provide evidence linking the stabilizing/destabilizing effect observed when varying the Mach number to a strengthening/weakening of the disturbance advection mechanism. We show, in particular, that the destabilizing effect of compressibility observed in the case of the sphere results from a significant increase of the backflow velocity in the whole recirculating bubble, which opposes the downstream advection of disturbances.
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Rusak, Zvi, Jung J. Choi, Nicholas Bourquard, and Shixiao Wang. "Vortex breakdown of compressible subsonic swirling flows in a finite-length straight circular pipe." Journal of Fluid Mechanics 781 (September 16, 2015): 3–27. http://dx.doi.org/10.1017/jfm.2015.482.
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A global analysis of steady states of inviscid compressible subsonic swirling flows in a finite-length straight circular pipe is developed. A nonlinear partial differential equation for the solution of the flow stream function is derived in terms of the inlet flow specific total enthalpy, specific entropy and circulation functions. The equation reflects the complicated thermo–physical interactions in the flows. Several types of solutions of the resulting nonlinear ordinary differential equation for the columnar case together with a flow force condition describe the outlet state of the flow in the pipe. These solutions are used to form the bifurcation diagram of steady compressible flows with swirl as the inlet swirl level is increased at a fixed inlet Mach number. The approach is applied to two profiles of inlet flows, solid-body rotation and the Lamb–Oseen vortex, both with a uniform axial velocity and temperature. The computed results provide for each inlet flow profile theoretical predictions of the critical swirl levels for the appearance of vortex breakdown states as a function of the inlet Mach number, suggesting that the results are robust for a variety of inlet swirling flows. The analysis sheds light on the dynamics of compressible flows with swirl and vortex breakdown, and shows the delay in the appearance of breakdown with increase of the inlet axial flow Mach number in the subsonic range of operation. The present theory is limited to axisymmetric dynamics of swirling flows in pipes where the wall boundary layer is thin and attached and does not interact with the flow in the bulk.