Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Fluid Dynamics
Volume 57, Number 17
Sunday–Tuesday, November 18–20, 2012; San Diego, California
Session D24: Acoustics II: Jets and Cavities |
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Chair: Meng Wang, University of Notre Dame Room: 30E |
Sunday, November 18, 2012 2:15PM - 2:28PM |
D24.00001: Near and Far Field Acoustic Pressure Skewness in a Heated Supersonic Jet Ephraim Gutmark, Pablo Mora, Jeff Kastner, Nick Heeb, Kailas Kailasanath, Junhui Liu The dominant component of turbulent mixing noise in high speed jets is the Mach wave radiation generated by large turbulent structures in the shear layer The Over-All Sound Pressure Level (OASPL) in the far field peaks in a direction near the Mach wave angle. ``Crackle'' is another important component of high speed jet noise. Crackle cannot be recognized in the spectrum of the acoustic pressure signal, but it appears in the temporal waveform of the pressure as sharply rising peaks. Skewness levels of the pressure and dP/dt have been used as a measure of crackle in high specific thrust engines and rockets. In this paper, we focus on recognizing a technique that identifies the impact of different test conditions on the near-field and far-field statistics of the pressure and dP/dt signals of a supersonic jet with a design Mach number of Md=1.5 produced by a C-D conical nozzle. Cold and hot jets, T0=300K and 600K, are tested at over, design, and under-expanded conditions, with NPRs=2.5, 3.671, 4.5, respectively. Second, Third and Forth order statistics are examined in the near and far fields. Rms, skewness and kurtosis intensity levels and propagation are better identified in the dP/dt than in the pressure signal. Statistics of the dP/dt demonstrate to be a better measure for crackle. [Preview Abstract] |
Sunday, November 18, 2012 2:28PM - 2:41PM |
D24.00002: The Sudden Onset of Acoustic Effects with Increasing Nozzle-Chevron Length In a Mach 0.9 Jet Ryan A. Fontaine, Joanna M. Austin, Gregory S. Elliott, Jonathan B. Freund The addition of chevrons to the exit of a jet has been found to reduce far-field noise, making it an effective passive noise reduction technique. The selection of specific designs, however, is challenging since mechanics models provide insufficient guidance and computations remain far too expensive for trial-and-error parameter exploration. To assess the design optimization problem, we have experimentally evaluated parametric dependence of sound on chevron geometry. Specifically, rapid prototyping is used to change the model geometries and study the relationship between chevron length and the far-field jet noise. We show that the effect of the chevron starts relatively abruptly for lengths less than 4 mm, which is well less than the 16 mm length selected as a starting point from previous studies. Thus a small increase in the chevron length can produce a large change in the far-field sound. However, for longer chevrons the sound is insensitive to the length, which has important implications for design optimization. Additionally, other flow diagnostics are performed to better understand the flow characteristics resulting in the observed changes in jet noise. [Preview Abstract] |
Sunday, November 18, 2012 2:41PM - 2:54PM |
D24.00003: Far-field noise predictions of imperfectly expanded jet flows Junhui Liu, Kailas Kailasanath, Nicholas Heeb, Dave Munday, Ephraim Gutmark The far-field noise levels of imperfectly expanded jet flows are predicted using the Ffowcs Williams {\&} Hawkings (FW-H) surface integral approach, where the information on the integral surfaces are generated from large-eddy simulations. Three FW-H surfaces are used to test the dependence of the far-field noise prediction on the location of the integral surfaces. The near-field pressure distributions on these FW-H surfaces are first examined to see if those surfaces are located in the acoustic propagation region. The variations of the monopole and dipole sources on the integral surfaces are also examined. The contribution of the shock-associated noise to the far-field noise level is well predicted. The difference between numerical predictions and measurements is within 1.0dB, whereas the contribution of the mixing noise is within 2.0dB. The contribution of the end cap is found to be small, but this contribution is sensitive to the mesh size used in the integration. [Preview Abstract] |
Sunday, November 18, 2012 2:54PM - 3:07PM |
D24.00004: Noise source detection and measurement in a supersonic air jet using Ultra-high Speed Rainbow Schlieren Deflectometry Manik Rajora, Ajay Agrawal, William Mitchell, Pankaj Kolhe Supersonic jets emit noise from various regions including the shear layer containing vortical structures, various shock cell structures in the near field and the downstream jet core breakdown region. Sound waves emitted from these various regions interact with each other and produce distinct noise spectra away from the jet, which depends upon the measurement location. Typically sound is detected by intrusive probes that provide measurements at a specific location, which makes it difficult to identify the origination point of such noise in a supersonic jet. In this study, an ultra-high speed Rainbow Schlieren Deflectometry (RSD) technique has been developed to optically visualize not only the supersonic jet flow but also the sound waves emanating from it in real time. Color schlieren images are acquired at up to 250,000 frames per second to capture the sound wave propagation with adequate spatial resolution. Optical components of the system were optimized to improve the spatial and temporal resolutions and hence, the schlieren video quality. To the best of our knowledge, this is the first time sound wave propagation from supersonic jets has been recorded in real time on a schlieren video. Acquired color schlieren images are amenable to quantitative analysis, and can provide data on sound power and sound wave frequency across the whole field. [Preview Abstract] |
Sunday, November 18, 2012 3:07PM - 3:20PM |
D24.00005: Unstructured Large Eddy Simulations of Hot Supersonic Jets from a Chevron Nozzle Guillaume Br\`es, Joseph Nichols, Sanjiva Lele, Frank Ham Large eddy simulations (LES) are performed for heated supersonic turbulent jets issued from a converging-diverging round nozzle with chevrons. The unsteady flow processes and shock/turbulence interactions are investigated with the unstructured compressible flow solver ``Charles'' developed at Cascade Technologies. In this study, the complex geometry of the nozzle and chevrons ($12$ counts, $6^\circ$ penetration) are explicitly included in the computational domain using unstructured body-fitted mesh and adaptive grid refinement. Sound radiation from the jet is computed using an efficient frequency-domain implementation of the Ffowcs Williams--Hawkings equation. Noise predictions are compared to experimental measurements carried out at the United Technologies Research Center for the same nozzle and operating conditions. The initial blind comparisons show good agreement in terms of spectra shape and levels for both the near-field and far-field noise. The current results show that the simulations accurately capture the main flow and noise features, including the shock cells, broadband shock-associated noise and turbulent mixing noise. Additional analysis of the large database generated by the LES is ongoing, to further investigate jet noise sources and chevron effects. [Preview Abstract] |
Sunday, November 18, 2012 3:20PM - 3:33PM |
D24.00006: Acoustic response of heated jets to nozzle-upstream perturbations Matthias Ihme, Yee Chee See, Ghobad Amini Effects of nozzle-upstream entropy perturbations on the acoustic radiation from heated jets are investigated. For this, a model problem is considered, in which a gas-turbine combustor discharges reaction products through a converging nozzle into the ambient environment. The turbulent reacting flow field in the combustor is computed using large-eddy simulation, and the unsteady flow-field at the combustor exit is extracted to provide realistic inflow conditions to the jet-flow simulation. To study the indirect coupling process, arising from the interaction of the combustion-generated entropy fluctuations with the adverse pressure gradient through the nozzle, a linearized Euler formulation is employed. Parametric studies are performed to investigate effects of frequency and amplitude of the nozzle-upstream entropy perturbations on the jet instability and the jet noise directivity. It is shown that the excitation near the preferred shear-layer instability leads to strong acoustic radiation in the jet-forward direction, and the radiation angle decreases with decreasing excitation frequency. [Preview Abstract] |
Sunday, November 18, 2012 3:33PM - 3:46PM |
D24.00007: Active Control of Jet Noise Using Observable Inferred Decomposition and Large Window PIV Zachary Berger, Matthew Berry, Kerwin Low, Laurent Cordier, Bernd Noack, Sivaram Gogineni, Mark Glauser In this investigation, we seek to find sources of noise created in the near-region of a highly subsonic jet, with a nozzle diameter of 2''. Using large window PIV alongside simultaneous hydrodynamic and acoustic pressure, we focus on observing flow structures created in the collapse of the potential core. Correlations can be made between the low-dimensional velocity field (using POD) and the far-field acoustics in an effort to identify loud modes in the flow. An advanced reduced order model known as Observable Inferred Decomposition (OID) is used to form closed-loop controllers for noise reduction in the far-field. With this technique, we find low-dimensional representations of near-field velocity and far-field pressure -- finding a linear mapping between the two fields. Then, we obtain acoustically optimized modes in the flow field and seek to drive these modes to zero using active control strategies. For flow control, synthetic jet actuators are used as shear layer excitation. A large range of tests are explored, varying Mach number and flow control configurations. Finally, large PIV windows will allow us to investigate several diameters of the flow field in the streamwise plane. [Preview Abstract] |
Sunday, November 18, 2012 3:46PM - 3:59PM |
D24.00008: Scaling model for nonlinear supersonic jet noise Woutijn Baars, Charles Tinney Numerous endeavors have been undertaken to investigate nonlinear propagation of sound from jet flows in range-restricted environments. However, only weak observations of cumulative nonlinear effects have been made using these laboratory-scale setups, all the while being observed under full-scale conditions. The inconsistency is caused by the lack of rigor in understanding what the appropriate scaling parameters should be for producing measurable cumulative nonlinearities in laboratory-scale environments. A scaling model will be presented that one could use to guide future studies aimed at investigating this unique component of turbulent mixing noise. At first, the important length-scales for cumulative nonlinear waveform distortion -- the shock formation distance and the acoustic absorption length -- are written in terms of jet exit parameters. Their ratio, expressed as the effective Gol'dberg number, is a measure of the strength of nonlinear distortion relative to that of dissipation. By computing the individual length-scales and this dimensionless ratio for an experiment that is being designed, one can estimate the presence of cumulative nonlinear distortion beforehand. [Preview Abstract] |
Sunday, November 18, 2012 3:59PM - 4:12PM |
D24.00009: Large-eddy simulation of crackle in heated supersonic jets Joseph W. Nichols, Sanjiva K. Lele, Frank E. Ham, Steve Martens, John T. Spyropoulos Crackle noise from heated supersonic jets is characterized by the presence of strong positive pressure impulses resulting in a strongly skewed far-field pressure signal (Ffowcs Williams et al., 1975). These strong positive pressure impulses are associated with N-shaped waveforms involving a shock-like compression, and thus is very annoying to observers when it occurs. In this talk, the origins of these N-shaped waveforms is investigated through high-fidelity large-eddy simulations (LES) applied to an over-expanded supersonic jet issuing from a faceted military-style nozzle. Two different levels of heating are considered. From the LES, we observe N-shaped waves associated with crackle to emerge directly from the jet turbulence. Furthermore, even at this extreme near-field location, we find that the emergent waves are already well-organized, having correlation over significant azimuthal distances. [Preview Abstract] |
Sunday, November 18, 2012 4:12PM - 4:25PM |
D24.00010: Predicting Acoustic Wave Generation and Amplification inside a Rectangular Cavity Ryan Schmit, James Grove Empirical and theoretical solutions to predict acoustic tones inside a rectangular cavity have been proposed throughout the years. A new theoretical understand is being developed that can now explain at the minimum the cavity tonal frequency response and possibly the self amplification of the acoustic tones. Current simulated results based on acoustic wave motion inside a cavity utilizing this theoretical understanding have produced results that compare well with experimental data all ready taken. [Preview Abstract] |
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