On a method for direct numerical simulation of shear layer/compression wave interaction for aeroacoustic investigations (original) (raw)
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22nd AIAA/CEAS Aeroacoustics Conference, 2016
This study presents the shock-cell noise results obtained with a large eddy aeroacoustic simulation from a dual stream jet. The primary stream is cold and subsonic with an exit Mach number of Mp = 0.89 and a Reynolds number of Rep = 0.57 × 10 6. The secondary stream is cold supersonic and under-expanded with a perfectly expanded Mach number of Ms = 1.20 and Res = 1.66 × 10 6. The computations are performed with the structured multiblock solver elsA. The aerodynamics and aeroacoustics of the flow are studied and analyzed in detail showing good agreement with experimental fits for the lengthscale and shear layer development. An acoustic-hydrodynamic filtering is used in order to compute the characteristic wavelengths of each component and estimate the shock-cell noise frequency. Moreover, the broadband shock-cell noise is captured in the near and far fields.
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1996
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Direct numerical simulation of noise generated by low speed flows requires strong numerical constraints related to the different scales in space and time for the dynamics of the flow and the propagation of sound waves. At low Mach numbers, the aeroacoustic hybrid approaches initiated by Hardin and Pope [An acoustic/viscous splitting technique for computational aeroacoustics, Theoret. Comput. Fluid Dyn. 6 (1994) 323-340] based on separate calculations for the flow and for the acoustic radiation, are therefore attractive. In this paper, we show that such methods can be used for the general case of non-constant density or temperature. The starting point is an asymptotic expansion of the full Navier-Stokes equations that gives a set of equations that retain the presence of density and temperature inhomogeneities, allowing access to the dynamic quantities without the stability constraints related to acoustic waves. Then starting from the solutions of flow fluctuating quantities, we propose several possible developments of the equations to obtain the acoustic field. They Preprint submitted to Computers & Fluids lead to different sets of equations and source terms depending on the level of simplifying assumptions: the perturbed low Mach number approximation (PLMNA) or the linearized Euler equations (LEE) linearized with respect to the mean flow. An isothermal and a nonisothermal spatially evolving mixing layer are taken as test problems. The solutions of the proposed hybrid methods show a satisfactory behavior compared with the reference solution given by a compressible DNS.
1996
In this paper we consider the scattering of sound by two-and three-dimensional bodies with arbitrary geometries. Particular emphasis is placed on the methodology for the implementation of solid wall boundary conditions for high-order, high-bandwidth numerical schemes. The Impedance Mismatch Method (IMM) is introduced to treat solid wall boundaries. In this method the solid wall is simulated using a wall region in which the characteristic impedance is set to a different value from that in the fluid region. This method has many advantages over traditional solid wall boundary treatments, including simplicity of coding, speed of computation and the ability to treat curved boundaries. This method has been used to solve a number of acoustic scattering problems to demonstrate its effectiveness. These problems include acoustic reflections from an infinite plate, acoustic scattering from a two-dimensional finite plate and a cylinder, and acoustic scattering by a sphere and a cylindrical shell.
Numerical analysis of acoustic loads generated by supersonic jets
2017
A hybrid computational fluid dynamics (CFD) and computational aeroacoustics (CAA) method is used to compute the flow and the acoustic field of supersonic jets at a Mach number of 3.6. The flow simulations are performed by highly resolved large-eddy simulations (LES) from which sound source terms are extracted to compute the acoustic field by solving the acoustic perturbations equations (APE). The acoustic loads are determined on the structural components to obtain the correct dynamic behavior of non-rigid surfaces at atmospheric flight conditions using fluid-structure interaction (FSI) methods.
Numerical investigation of the interaction of acoustic disturbances with a shock wave
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Shock dynamics and mechanism of sound generation
2006
The interaction between an oblique shock wave and a pair of parallel vortices is simulated systematically through solving the two-dimensional, unsteady compressible Navier-Stokes equations using a fifth order weighted essentially nonoscillatory finite difference scheme. The main purpose of this study is to characterize the flow structure and the mechanism of sound generation in the interaction between an oblique shock wave and a pair of vortices. We study two typical shock waves of Mach number Ms=1.2 and Ms=1.05, which correspond to two typical shock structures of Mach reflection and regular reflection, respectively, in the problem of shock-vortex interaction. The effects of the strength of the vortices and the geometry parameters are investigated. In addition, we have also considered both cases of passing and colliding vortex pairs. The interaction is classified into four types for the passing case and seven types for the colliding case according to different patterns of the shock ...
Journal of Computational Physics, 2000
Computational aeroacoustics equations are developed using a Janzen-Rayleigh expansion of the compressible flow equations. Separate expansions are applied to an inner region characterized to lowest order by an incompressible flow field and an outer region characterized by propagating acoustic waves. Several perturbation equation sets are developed in the inner and outer regions by truncating the expanded equations using different orders in the perturbation variable, ε, where ε 2 is proportional to the square of the Mach number characterizing the flow. Composite equation sets are constructed by matching the equations governing the inner and outer regions. The highest-order perturbation continuity and momentum equations include an infinite series in ε 2 and are shown to be identical to the equations used in the expansion about incompressible flow approach. As such, the perturbation analysis is used to interpret the physical meaning of the perturbation variables and to highlight the assumptions inherent in this approach. Differences between numerical solutions obtained with the composite equation sets are evaluated for two unsteady flow problems. The lowestorder perturbation equation set is shown to yield adequate acoustic predictions for low Mach number flows. This equation set is considerably simpler to implement into a numerical solver and reduces the required CPU time relative to the highest-order equation set.
ON THE INTERACTION OF A SOUND PULSE WITH THE SHEAR LAYER OF AN AXISYMMETRIC JET
The behavior of a sound pulse from a simulated source in a jet is investigated both experimentally and numerically. Both approaches show that in the low and medium frequencies the far field acoustic power exhibits a marked amplification as the flow velocity increases. Experimentally this changes to an attenuation at the higher frequencies which cannot be computed by the numerical model. This amplification is traced to shear noise terms which trigger the instability waves that are inherent within the flow.