Radiation and outflow boundary conditions for direct computation of acoustic and flow disturbances in a nonuniform mean flow
TL;DR: In this article, a set of radiation and outflow boundary conditions for problems with nonuniform mean flows are developed, which are usually many orders of magnitude smaller than that of the mean flow.
Abstract: It is well known that Euler equations support small amplitude acoustic, vorticity and entropy waves. To perform high quality direct numerical simulations of flow generated noise problems, acoustic radiation boundary conditions are required along inflow boundaries. Along boundaries where the mean flow leaves the computation domain, outflow boundary conditions are needed to allow the acoustic, vorticity and entropy disturbances to exit the computation domain without significant reflection. A set of radiation and outflow boundary conditions for problems with nonuniform mean flows are developed in this work. Flow generated acoustic disturbances are usually many orders of magnitude smaller than that of the mean flow. To capture weak acoustic waves by direct computation (without first separating out the mean flow), the intensity of numerical noise generated by the numerical algorithm and the radiation and outflow boundary conditions (and the computer) must be extremely low. It is demonstrated by a test problem ...
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TL;DR: Explicit numerical methods for spatial derivation, filtering, and time integration are proposed in this article with the aim of computing flow and noise with high accuracy and fidelity, and they are constructed in the same way by minimizing the dispersion and the dissipation errors in the wavenumber space up to kΔx = π/2 corresponding to four points per wavelength.
883 citations
Cites methods from "Radiation and outflow boundary cond..."
...In this case, the equations governing the acoustic far-field [29,30] are solved in three rows of points using standard 5-point stencil schemes for the y-derivatives....
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TL;DR: In this paper, a review of computational methods for computational aero-acoustics applications is presented, and some of the computational methods to be reviewed are quite different from traditional CFD methods.
Abstract: Computational fluid dynamics (CFD) has made tremendous progress especially in aerodynamics and aircraft design over the past 20 years. An obvious question to ask is "why not use CFD methods to solve aeroacoustics problems?" Most aerodynamics problems are time independent, whereas aeroacoustics problems are, by definition, time dependent. The nature, characteristics, and objectives of aeroacoustics problems are also quite different from the commonly encountered CFD problems. There are computational issues that are unique to aeroacoustics. For these reasons computational aeroacoustics requires somewhat independent thinking and development. The objectives of this paper are twofold. First, issues pertinent to aeroacoustics that may or may not be relevant to computational aerodynamics are discussed. The second objective is to review computational methods developed recently that are designed especially for computational aeroacoustics applications. Some of the computational methods to be reviewed are quite different from traditional CFD methods. They should be of interest to the CFD and fluid dynamics communities.
529 citations
TL;DR: A hierarchy of computational approaches that range from semi-empirical schemes that estimate the noise sources using mean-flow and turbulence statistics, to high-fidelity unsteady flow simulations that resolve the sound generation process by direct application of the fundamental conservation principles is discussed in this paper.
520 citations
Cites background from "Radiation and outflow boundary cond..."
...Tam and Dong [206] allow for a nonuniform mean flow on the boundary by replacing the linear perturbations in the BC with departures from the base flow....
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TL;DR: In this paper, a simple new zonal boundary condition has been proposed based upon the addition of dissipative and convective terms to the compressible Navier Stokes equations, which is based upon a simple addition of convective and dissipative terms.
Abstract: A simple new zonal boundary condition has been proposed. It is based upon the addition of dissipative and convective terms to the compressible Navier Stokes equations
374 citations
TL;DR: In this article, the authors investigated the noise radiated by a subsonic circular jet with a Mach number of 0.9 and a Reynolds number of 65000 computed by a compressible Large Eddy Simulation (LES) and demonstrated the feasibility of using LES to predict accurately both the flow field and sound radiation on a domain including the acoustic field.
Abstract: This study investigates the noise radiated by a subsonic circular jet with a Mach number of 0.9 and a Reynolds number of 65000 computed by a compressible Large Eddy Simulation (LES). First, it demonstrates the feasibility of using LES to predict accurately both the flow field and the sound radiation on a domain including the acoustic field. Mean flow parameters, turbulence intensities, velocity spectra and integral length scales are in very good agreement with experimental data. The noise generated by the jet, provided directly by the simulation, is also consistent with measurements in terms of sound pressure spectra, levels and directivity. The apparent location of the sound sources is at the end of the potential core in accordance with some experimental observations at similar Reynolds numbers and Mach numbers. Second, the noise generation mechanisms are discussed in an attempt to connect the flow field with the acoustic field. This study shows that for the simulated moderate Reynolds number jet, the predominant sound radiation in the downstream direction is associated with the breakdown of the shear layers in the central jet zone.
365 citations