Bulletin of the American Physical Society
70th Annual Meeting of the APS Division of Fluid Dynamics
Volume 62, Number 14
Sunday–Tuesday, November 19–21, 2017; Denver, Colorado
Session A21: Aeroacoustics IAcoustics
|
Hide Abstracts |
Chair: Meng Wang, University of Notre Dame Room: 706 |
Sunday, November 19, 2017 8:00AM - 8:13AM |
A21.00001: A numerical study of self-sustained oscillations in wind instruments Pablo L. Rendon, Roberto Velasco-Segura The study of sustained notes in wind musical instruments in realistic conditions requires consideration of both excitation and propagation mechanisms, and the manner in which these two interact. Further, to model adequately acoustic propagation inside the instrument, a variety of competing effects must be taken into account, such as nonlinearity, thermoviscous attenuation and radiation at the open end. Physical solutions also involve some degree of feedback at the excitation end, and here we propose the simplest boundary conditions possible at this end, given by a simple harmonic oscillator with fixed stiffness. By feeding single-frequency acoustic waves into the system we are able to study the formation of self-sustained oscillations, which are stationary states associated with resonance frequencies, and also to observe transitory states. Visualizations are presented of waves traveling in both directions. As expected, resonance frequencies are dependent on the stiffness parameter, and this dependence is examined. The full-wave simulation is performed in the time domain over a 2D spatial domain assuming axial symmetry, and it is based on a previously validated open source code, using a finite volume method (FiVoNAGI) implemented in a GPU [Velasco-Segura & Rendón, 2015]. [Preview Abstract] |
Sunday, November 19, 2017 8:13AM - 8:26AM |
A21.00002: Near acoustic field of a high aspect ratio supersonic Single Expansion Ramp Nozzle Ephraim Gutmark, Bhupatindra Malla, Kailas Kailasanath, Andrew Corrigan, Ryan Johnson, Kamal Viswanath The near acoustic field of a supersonic jet issued from a high aspect ratio Single Expansion Ramp Nozzle (SERN) is characterized. The impact of extended expansion ramps with different lengths past the exit of the nozzle is determined. The nozzle under study has throat aspect ratio (AR) of 9 and the lengths of the extension ramps range from 2.1 inches to 9 inches. The design Mach number of the nozzle is 1.5. The study is performed in the over-expanded flow regime, at two nozzle pressure ratios (NPRs) of 2.5 and 3.0. For a nozzle without a ramp the jet starts to screech at NPR 2.5 and its amplitude increases until it reaches its maximum at NPR=3.0. This study shows that expansion ramps can completely mitigate the flapping instabilities along with a significant reduction in the Broad-band Shock associated Noise (BBSN) and in the turbulent mixing noise. The current study focuses on the near-field of the jet and aims to identify the locations of the acoustic sources, their directivity patterns, and changes in those characteristics when extended expansion ramps of different lengths are added. [Preview Abstract] |
Sunday, November 19, 2017 8:26AM - 8:39AM |
A21.00003: Numerical Simulations of Noise Generated by High Aspect Ratio Supersonic Rectangular Jets - Validation Kamal Viswanath, Ryan Johnson, Kailas Kailasanath, Bhupatindra Malla, Ephraim Gutmark The noise from high performance jet engines of both civilian and military aircraft is an area of active concern. Asymmetric exhaust nozzle configurations, in particular rectangular, potentially offer a passive way of modulating the farfield noise and are likely to become more important in the future. High aspect ratio nozzles offer the further benefit of easier airframe integration. In this study we validate the far field noise for ideally and over expanded supersonic jets issuing from a high aspect ratio rectangular nozzle geometry. Validation of the acoustic data is performed against experimentally recorded sound pressure level (SPL) spectra for a host of observer locations around the asymmetric nozzle. Data is presented for a slightly heated jet case for both nozzle pressure ratios. The contrast in the noise profile from low aspect ratio rectangular and circular nozzle jets are highlighted, especially the variation in the azimuthal direction that shows ``quiet'' and ``loud'' planes in the farfield in the peak noise direction. This variation is analyzed in the context of the effect of mixing at the sharp corners, the sense of the vortex pairs setup in the exit plane, and the evolution of the high aspect ratio exit cross-section as it propagates downstream including possible axis-switching. [Preview Abstract] |
Sunday, November 19, 2017 8:39AM - 8:52AM |
A21.00004: Sound radiated by the interaction of non-homogeneous turbulence on a transversely sheared flow with leading and trailing edges of semi-infinite flat plate Mohammed Afsar, Vasilis Sassanis The small amplitude unsteady motion on a transversely sheared mean flow is determined by two arbitrary convected quantities with a particular choice of gauge in which the Fourier transform of the pressure is linearly-related to a scalar potential whose integral solution can be written in terms of one of these convected quantities. This formulation becomes very useful for studying Rapid-distortion theory problems involving solid surface interaction. Recent work by Goldstein et al. (JFM, 2017) has shown that the convected quantities are related to the turbulence by exact conservation laws, which allow the upstream boundary conditions for interaction of a turbulent shear flow with a solid-surface (for example) to be derived self-consistently with appropriate asymptotic separation of scales. This result requires the imposition of causality on an intermediate variable within the conservation laws that represents the local particle displacement. In this talk, we use the model derived in Goldstein et al. for trailing edge noise and compare it to leading edge noise on a semi-infinite flat plate positioned parallel to the level curves of the mean flow. Since the latter represents the leading order solution for the aerofoil interaction problem, these results are expected to be generic. [Preview Abstract] |
Sunday, November 19, 2017 8:52AM - 9:05AM |
A21.00005: Near-field acoustic radiation by high-speed turbulence: amplitude, structure, gas-stiffness, and dilatational dissipation David Buchta, Jonathan Freund High-speed (supersonic) turbulent shear flows are well-known to radiate pressure-wave patterns that have higher positive peaks than negative valleys, which yields a notable skewness, usually with $S_k>0.4$. Direct numerical simulations (DNS) of planar turbulent mixing layers at different Mach numbers ($M$) are used to examine this. The baseline simulations, of an air-like gas at speeds up to $M=3.5$, reproduced the observed behavior of jets. Simulations initialized with corresponding instability modes show that $S_k$ increases linearly with the velocity amplitude ($M_t=\sqrt{\overline{u_i'u_i'}}/c_o$), reflecting the $M$ dependence of the DNS, which can be related to simpler gas dynamic flows. Simulations with a stiffened-gas equation of state (often used to model liquids) show essentially the same Mach-number dependence, despite the nominally greater resistance to compressibility. Turbulence simulations with an artificial energy reallocation mechanism, imposed to alter its structure, show little change in $S_k$. Finally, we also consider significantly increased bulk viscosity to suppress dilatation. In this case, $S_k$ diminishes along with the sound-field intensity, though the turbulence stresses themselves are nearly unchanged. [Preview Abstract] |
Sunday, November 19, 2017 9:05AM - 9:18AM |
A21.00006: Evaluating the far-field sound of a turbulent jet with one-way Navier-Stokes equations Ethan Pickering, Georgios Rigas, Aaron Towne, Tim Colonius The one-way Navier-Stokes (OWNS) method has shown promising ability to predict both near field coherent structures (i.e. wave packets) and far field acoustics of turbulent jets while remaining computationally efficient through implementation of a spatial marching scheme. Considering the speed and relative accuracy of OWNS, a predictive model for various jet configurations may be conceived and applied for noise control. However, there still remain discrepancies between OWNS and large eddy simulation (LES) databases which may be linked to the previous neglect of nonlinear forcing. Therefore, to better predict wave packets and far field acoustics, this study investigates the effect of nonlinear forcing terms derived from high-fidelity LES databases. The results of the nonlinear forcings are evaluated for several azimuthal modes and frequencies, as well as compared to LES derived acoustics using spectral proper orthogonal decomposition (SPOD). [Preview Abstract] |
Sunday, November 19, 2017 9:18AM - 9:31AM |
A21.00007: Aeroacoustic directivity via wave-packet analysis of mean or base flows Adam Edstrand, Peter Schmid, Louis Cattafesta Noise pollution is an ever-increasing problem in society, and knowledge of the directivity patterns of the sound radiation is required for prediction and control. Directivity is frequently determined through costly numerical simulations of the flow field combined with an acoustic analogy. We introduce a new computationally efficient method of finding directivity for a given mean or base flow field using wave-packet analysis (Trefethen, PRSA 2005). Wave-packet analysis approximates the eigenvalue spectrum with spectral accuracy by modeling the eigenfunctions as wave packets. With the wave packets determined, we then follow the method of Obrist (JFM, 2009), which uses Lighthill's acoustic analogy to determine the far-field sound radiation and directivity of wave-packet modes. We apply this method to a canonical jet flow (Gudmundsson and Colonius, JFM 2011) and determine the directivity of potentially unstable wave packets. Furthermore, we generalize the method to consider a three-dimensional flow field of a trailing vortex wake. In summary, we approximate the disturbances as wave packets and extract the directivity from the wave-packet approximation in a fraction of the time of standard aeroacoustic solvers. [Preview Abstract] |
Sunday, November 19, 2017 9:31AM - 9:44AM |
A21.00008: Thermoviscous analysis of open photoacoustic cells Madhusoodanan Mannoor, Sangmo Kang Open photoacoustic cells, apart from the conventional spectroscopic applications, are increasingly useful in bio medical applications such as in vivo blood sugar measurement. Maximising the acoustic pressure amplitude and the quality factor are major design considerations associated with open cells.Conventionaly, resonant photoacoustic cells are analyzed by either transmission line analogy or Eigen mode expansion method. In this study, we conducted a more comprehensive thermo viscous analysis of open photoacoustic cells. A Helmholtz cell and a T-shaped cell, which are acoustically different, are considered for analysis. Effect of geometrical dimensions on the acoustic pressure, quality factor and the intrusion of noise are analyzed and compared between these cells. Specific attention is given to the sizing of the opening and fixtures on it to minimize the radiational losses and the intrusion of noise. Our results are useful for proper selection of the type of open photoacoustic cells for in vivo blood sugar measurement and the optimization of geometric variables of such cells. [Preview Abstract] |
Sunday, November 19, 2017 9:44AM - 9:57AM |
A21.00009: Prediction of broadband trailing edge noise from a NACA0012 airfoil using wall-modeled large-eddy simulation Mohammad Mehrabadi, Daniel Bodony In modern high-bypass ratio turbofan engines, the reduction of jet exhaust noise through engine design has increased the acoustic importance of the main fan to the point where it can be the primary source of noise in the fight direction of an airplane. While fan noise has been reduced by improved fan designs, its broadband component, originating from the interaction of turbulent flow with a solid surface, still remains an issue. Broadband fan noise is generated by several mechanisms, usually involving a turbulent boundary layer interacting with a solid surface. To prepare for a wall modeled large eddy simulation (WMLES) of the NASA/GE source diagnostic test fan, we study the broadband noise due to the turbulent flow on a NACA0012 airfoil at zero degree angle-of-attack, a chord-based Reynolds number of 408,000, and a Mach number of 0.115 using WMLES. We investigate the prediction of transition-to-turbulence and sound generation from the WMLES and examine its predictability compared with available experimental and DNS datasets for the same flow conditions. Verification of WMLES for such a canonical problem is crucial since it provides useful insight about the WMLES approach before using it for broadband fan noise prediction. [Preview Abstract] |
Follow Us |
Engage
Become an APS Member |
My APS
Renew Membership |
Information for |
About APSThe American Physical Society (APS) is a non-profit membership organization working to advance the knowledge of physics. |
© 2024 American Physical Society
| All rights reserved | Terms of Use
| Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 20740-3844
(301) 209-3200
Editorial Office
100 Motor Pkwy, Suite 110, Hauppauge, NY 11788
(631) 591-4000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 20045-2001
(202) 662-8700