Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session A05: Acoustics: General |
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Chair: Vincenzo Armenio, University of Trieste Room: Georgia World Congress Center B207 |
Sunday, November 18, 2018 8:00AM - 8:13AM |
A05.00001: Viscosity, surface tension, and gravity effects on acoustic reflection and refraction Rouslan Krechetnikov The idea of the present work is to study the effects of viscosity, surface tension, and gravity on Snell's law of reflection and refraction of an acoustic field from an interface between two fluids. The analysis leads to a number of non-trivial phenomena and corrections to Snell's law. While all these effects can be considered individually due to separation of the associated time scales, the contributions of surface tension to the gravity and viscosity cases are treated as well. |
Sunday, November 18, 2018 8:13AM - 8:26AM |
A05.00002: New model for acoustic waves propagating through a vortical flow Jim Thomas I will present a new amplitude equation derived for high-frequency acoustic waves propagating through an incompressible vortical flow using multi-time-scale asymptotic analysis. The reduced model is derived without an explicit spatial-scale separation ansatz between the wave and vortical fields. As a consequence, the model is seen to capture very well the features of the wave field in the regime where the spatial scales of the wave and vortical fields are comparable, a regime for which an optimal reduced model was not available. |
Sunday, November 18, 2018 8:26AM - 8:39AM |
A05.00003: A sensitivity-based Bayesian hierarchical process for calibrating reduced-order wave-propagation models Christophe Millet Model calibration is viewed in the sense of adapting the full set of model parameters in order to get better ressemblance between observations and major end-predictions. In this study, we present a new probabilistic method to calibrate normal-mode-based propagation models using some observed data and sources of uncertainties. The unknown parameters are estimated using a multiple parallel Markov Chain Monte-Carlo (MCMC) method. Using a few normal modes allows to rapidly estimate the statistical distributions of the arrival characteristics, on a mode-by-mode basis. In a sense, the unknown inputs "propagate" through the plausible waveguides with each mode and alters its amplitude and phase structure. The resulting waveform is obtained as a combination of individual wavepackets so that the likelihood is a continuous function of input parameters. Further, once the maximum likelihood has been identified, the reduced model can be extended to higher dimensions to better refine the calibration process. Numerical results are obtained using a spectral numerical method and realistic representations of atmospheric disturbances. The method is used to revisit the infrasound signals recorded during campaigns of ammunition destruction explosions. |
Sunday, November 18, 2018 8:39AM - 8:52AM |
A05.00004: An Equation of State for Compressible Liquid Water for CFD Applications Jared A. Carnes, Ethan A. Vogel, James G. Coder Computational fluid dynamics simulations of water typically assume the fluid to be truly incompressible; however, resolving acoustic behaviors such as turbulent boundary layer self-noise in simulations requires the flow to have finite speed of sound, but this can place severe time-step restrictions on most solvers. Advances in entropy-stable CFD methods for ideal gases have provable non-linear stability, and such methods appear to be extensible to weakly compressible fluids if a closed-form expression for thermodynamic entropy is available. Classical state equations like Tumlirz-Tait cannot accurately predict both speed of sound and entropy, while the IAPWS 95 formulation is unwieldy for some applications. In this work, a state equation has been developed to calculate specific volume of water at modest conditions. The method defines specific volume as a function of speed of sound and entropy, then correlates experimental data to find equations for these quantities as functions of pressure and temperature, allowing intermediate quantities to be extracted directly. Comparing the results of this equation on its domain of 5 °C to 30 °C to NIST data yields at most a 0.24% deviation in specific volume. |
Sunday, November 18, 2018 8:52AM - 9:05AM |
A05.00005: Hydroacoustics of an open-water ship propeller Vincenzo Armenio, Marta Cianferra, Andrea Petronio We use the advective Ffowcs Williams and Hawkings equation to evaluate hydroacoustics of a ship propeller in open sea. The hydrodynamic field is computed using Large Eddy simulation for incompressible flow field; the acoustic field is reconstructed by solving the quadrupole terms through direct calculation of the volume integrals. For the hydrodynamics, we use the dynamic Lagrangian model for the closure of the SGS stresses and a wall-layer model. We consider a propeller well studied in literature for a single value of the advance ratio J=1.068 (https://www.sva-potsdam.de/en/potsdam-propeller-test-case-pptc). A grid of about 6 millions cells is used to reproduce accurately both the stresses over the propeller and the wake, the latter responsible of quadrupole noise. The equations are solved in a fixed-to-the-body frame of reference. Different noise generation mechanisms are investigated separately. Thickness and loading terms related to the propeller shape and velocity, provide significant pressure disturbance in the near field. The quadrupole contribution is investigated in relation to the presence of vorticity persisting in the wake. |
Sunday, November 18, 2018 9:05AM - 9:18AM |
A05.00006: Investigation of Propeller Noise Using LES and an Acoustic Analogy Jacob Keller, Praveen Kumar, Krishnan Mahesh The flow field of a five-bladed marine propeller operating at design condition is used to calculate far-field sound. The flow field is obtained using large eddy simulation (LES) and far-field sound is computed using the Ffowcs-Williams and Hawkings acoustic analogy. The physics of sound generation is examined by analyzing both the near-propeller flow field and far-field sound. While the blades generate strongly tonal noise, the overall acoustic signature of the propeller is broadband. The propeller is found to be acoustically compact at frequencies up to 100 times the rotation rate. The majority of sound is generated by localized unsteadiness at the blade tip, due to shedding of the tip vortex. Two other notable sound generation mechanisms are: convection of boundary layer turbulence past the blade trailing edge and interaction of the blade root wakes with the propeller-hub surface. Acoustic energy is found to be distributed among higher frequencies as local Reynolds number increases radially along the blades. |
Sunday, November 18, 2018 9:18AM - 9:31AM |
A05.00007: Computation of wall pressure fluctuations in compressible turbulent channel flows Yi Liu, Kan Wang, Meng Wang An accurate description of the spatiotemporal characteristics of the fluctuating surface pressure in wall-bounded flows is important for predictions of structural vibration and acoustic radiation. In this study direct numerical simulations are performed using high-order non-dissipative schemes to investigate the unsteady wall pressure in compressible channel flows at Mach numbers of 0.4 and 1.5 and friction Reynolds numbers of up to 510. The simulations are shown to capture both convective and acoustic contributions to the wavenumber-frequency spectra of wall-pressure fluctuations. At fixed frequencies acoustic peaks are identified at streamwise acoustic wavenumbers. These peaks are much lower than the convective peaks and decrease with decreasing Mach number. At Mach 0.4, the acoustic peaks are several orders of magnitude weaker than the convection peaks, indicating very small acoustic contributions, which is in contrast to predictions from semi-empirical models. The effect of a small surface hump on the wall pressure statistics will also be discussed. |
Sunday, November 18, 2018 9:31AM - 9:44AM |
A05.00008: Statistics fo Dynamic Pressure Measurements in a Rectangular Cavity Ryan F Schmit, Cody Butzer, Ian Maatz Historically, record length and processing methods have limited the physics that can be extracted from a dynamic pressure measurement in a rectangular cavity. Limited record length, window size, overlap, and averaging have produced resulting spectra with sharp tonal peaks and relatively smooth broadband noise. This has led to a simplified understanding of the cavity, even though CFD and numerous non-intrusive experimental methods have shown different spectral features. A recent experiment captured 8 seconds at Mach 0.7 and 15 seconds at Mach 1.5 of dynamic pressure measurement at 100 kHz sample rate in a rectangular cavity with a Length to Depth ratio of 5.6. The Reynolds number for both Mach numbers were 2e^6/ft. Using statistical analysis we will show how the tonal peaks vary in both the frequency and amplitude when the window size is varied. Using histograms we will show that the historical average may not be the statistical average. |
Sunday, November 18, 2018 9:44AM - 9:57AM |
A05.00009: Kolmogorov’s spectral energy cascade in nonlinear acoustic and thermoacoustic wave turbulence Prateek Gupta, Guido Lodato, Carlo Scalo Gupta, Lodato, and Scalo (J. Fluid Mech. (2017), vol. 831, pp. 358-393) have demonstrated the existence of an equilibrium spectral energy cascade in shock waves formed as a result of continued thermoacoustic amplification consistent with Kolmogorov’s theory for high-Reynolds-number hydrodynamic turbulence. Recently, Gupta and Scalo (21^{st} International Symposium on Nonlinear Acoustics, 2018) have developed a rigorous theory of spectral energy cascade in an ensemble of nonlinear acoustic waves, which fully develop into randomly distributed shock waves resulting in acoustic wave turbulence. The dynamics are shown very similar to the homogeneous isotropic turbulence in a box. In this work, we elucidate the energy dynamics utilizing the mathematically exact energy corollary for second order nonlinear acoustics thus identifying the second-order energy norm for acoustics. For randomly initialized nonlinear waves, the mean energy in the domain decays with a -2/3 law in time due to coalescence of shock waves. In the spectral space, the energy corollary yields analytical expressions of energy, energy flux, and energy dissipation in spectral space. Analogous to the Kolmogorov's theory, we derive dimensionless scaling laws for energy spectra of acoustic wave turbulence. |
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