Bulletin of the American Physical Society
61st Annual Meeting of the APS Division of Fluid Dynamics
Volume 53, Number 15
Sunday–Tuesday, November 23–25, 2008; San Antonio, Texas
Session LF: Jet and Cavity Flows |
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Chair: Xiaofeng Liu, Johns Hopkins University Room: 003B |
Monday, November 24, 2008 3:35PM - 3:48PM |
LF.00001: Investigation of the Near-Field Acoustic Properties of Imperfectly Expanded Supersonic Jets using Large-Eddy Simulations Junhui Liu, Kailas Kailasanath, Ravi Ramamurti, David Munday, Ephraim Gutmark Numerical simulations of Imperfectly Expanded Supersonic Jets from a CD nozzle representative of those used in military engines have been carried out. A MILES (Monotonically Integrated Large Eddy Simulations) approach with a finite element version of Flux-Corrected Transport algorithm (FEM-FCT) is used. FEM-FCT is able to accurately implement nozzle geometries and is ideal for simulating shock-containing flows. We have simulated a wide range of under-and over-expanded flow conditions as well as the design condition. The distributions of the centerline static pressure and noise spectra are in good agreement with the corresponding experimental data. It is found that this type of nozzle is not shock free even at the design condition due to the sharp change of the geometry in the throat area. The near-field acoustics is investigated, and screech tones are observed in all cases except in an over-expanded case with a low total pressure ratio. The frequencies of the screech tones are in good agreement with both the theoretical prediction and the measurement. The noise source locations are investigated by studying the noise distributions at peak frequencies and the correlations between pressure and other flow quantities. [Preview Abstract] |
Monday, November 24, 2008 3:48PM - 4:01PM |
LF.00002: Nonlinear Parabolized Stability Equation Models for Turbulent Jets and their Radiated Sound Kristjan Gudmundsson, Tim Colonius We investigate the nonlinear and non-parallel stability characteristics of round jets using the Nonlinear Parabolized Stability Equations (NPSE) supplemented with a turbulence model. We adopt an approach where both the meanflow and Reynolds-averaged stresses from a RANS simulation serve as input to the NPSE. We compare our predictions to measurements in the both the near and far fields of a turbulent round jet. We also compare our methodology to previous NPSE calculations for planar mixing layers and jets. [Preview Abstract] |
Monday, November 24, 2008 4:01PM - 4:14PM |
LF.00003: Investigation of the Near-Field Acoustic and Flow Properties of Imperfectly Expanded Supersonic Jets using Particle Image Velocimetry Ephraim Gutmark, David Munday, Junhui Liu, K. Kailasanath The flow fields of imperfectly Expanded Supersonic Jets from conical CD nozzles are investigated by Particle Image Velocimetry. This nozzle geometry represents the exhaust nozzles on high-performance military engines. The results are compared with shadowgraph to bring out the details of the highly accelerated regions where seed particles may lag behind the flow, viz. the shocks and Prandtl-Meyer fans. Nozzles with three area ratios are examined over a wide range of under- and over-expanded conditions as well as the design conditions for each nozzle. It is found that this type of nozzle is not shock free at the design condition due to the sharp change of the geometry in the throat area. Both near-field and far-field acoustic measurements are presented. Flow-field and near-field acoustic measurements are compared with Numerical simulations in the accompanying presentation by Liu, Kailasanath and Ramamurti. The distributions of the centerline static pressure and noise spectra are in good agreement with the corresponding experimental data. [Preview Abstract] |
Monday, November 24, 2008 4:14PM - 4:27PM |
LF.00004: Propagation of Ultrasound Waves inside a Supersonic Jet Catalina Stern, Cesar Aguilar, Jose Manuel Alvarado We use a Rayleigh scattering technique to detect density fluctuations in a supersonic air jet. The technique gives the spatial Fourier transform of the density fluctuations for a wave vector given by the experimental set-up. The method works as a nonintrusive microphone that can measure inside the flow. We measure at different locations inside and outside the flow to determine the emission pattern. We can determine the propagation inside the flow, the diffraction through the mixing layer and the propagation outside the jet. [Preview Abstract] |
Monday, November 24, 2008 4:27PM - 4:40PM |
LF.00005: An Asymptotic Description of Supersonic Jet Modes Luis Parras, St\'ephane Le Diz\`es We present a large-axial-wavenumber asymptotic analysis of inviscid normal modes in supersonic jets. A complete map of inviscid instabilities is obtained for different perturbation azimuthal wavenumbers. We demonstrate the existence of four kinds of modes according to their convective Mach number, defined as the ratio of their phase velocity by the speed of sound: counterflow subsonic waves, subsonic waves, radiating waves (supersonic waves) and Kelvin-Helmholtz instabilities. We provide the general conditions for each kind of this modes to exist, and by means of WKBJ analysis, the dispersion relation and an explanation for the physical mechanism of instability. Finally, we explore the limit of large Mach numbers (hypersonic flows), in which the dominant unstable modes are the radiating waves. [Preview Abstract] |
Monday, November 24, 2008 4:40PM - 4:53PM |
LF.00006: ABSTRACT WITHDRAWN |
Monday, November 24, 2008 4:53PM - 5:06PM |
LF.00007: Performance Results for the Optical Turbulence Reduction Cavity Ryan Schmit, Chris McGaha, John Tekell, Jim Grove, Michael Stanek The testing of a new optical turbulence reduction cavity model from Mach 0.3 to 1.5 in the Trisonic Gasdynamics Facility (TGF) has occurred. The current model has optical quality fused silica windows that will allow non-intrusive flow field measure to be made. The results presented will compare the current optical turbulence reduction cavity model with the historic data from the old turbulence reduction cavity model that was built in the mid 1970s. Various flow control techniques to reduce the sound pressure level and overal sound pressure level inside the cavity were also exmanied and thier preformance results will be shown. [Preview Abstract] |
Monday, November 24, 2008 5:06PM - 5:19PM |
LF.00008: Development and Calibration of a Reduced Order Modelling for subsonic cavity flows Kaushik Kumar Nagarajan, Christophe Airiau, Azeddine Kourta, Laurent Cordier In this study we propose a new calibration technique for the development of a Reduced Order Model (ROM) for a compressible cavity. A DNS is performed for a 2D rectangular cavity at a Mach number of 0.6 and a Reynolds number of 52 (based on the mometum thickness) which corresponds to a shear mode of the cavity oscillations. The technique of Proper Orthogonal Decomposition (POD) is utilised to get the most dominant flow dynamics, a ROM based on the isentropic equations is developped by projecting the governing equations on the subspace spanned by the POD modes resulting in a dynamical system. The dynamical system is then utilised to predict the flow dynamics, but the main disadvantage of the ROM is that the system fails to predict the large time temporal dynamics. In this work we propose a way to stabilise the dynamical system to predict accurately the flow dynamics. This enhances the usefulness of the ROM for control applications. [Preview Abstract] |
Monday, November 24, 2008 5:19PM - 5:32PM |
LF.00009: Effect of Cavity Width on the Self-sustained Oscillation in a Low-Mach-number Cavity Flow Ke Zhang, Ahmed Naguib Recent unsteady-wall-pressure and velocity measurements (Zhang and Naguib, AIAA paper 4376-2008) in finite-width and azimuthally-uniform cavities showed that a low-Mach-number ($M <$ 0.1) cavity has distinct behavior with different width-to-length ($W/L)$ ratios and a turbulent boundary layer at separation. The cavity was defined as a \textit{narrow cavity} if $W/L<$1 and a \textit{wide cavity} if $W/L>$1. In the latter case, the self-sustained oscillation was attenuated \textit{and}, instead, low-frequency disturbances became dominant. This effect was more pronounced with increasing Reynolds number. This interesting finding is believed to relate to the recently uncovered three-dimensional instability of the cavity and its interaction with the shear layer (Bres and Colonius \textit{JFM} \textbf{599}, 2008). To explore this idea further, the distribution of the unsteady wall pressure along the azimuthal direction and the flow velocity are measured simultaneously. The results give better understanding of the nature of the low-frequency unsteadiness, the three dimensionality of the flow in the cavity and the effect of cavity width on them. [Preview Abstract] |
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