基于转捩模型及声比拟方法的高精度圆柱分离涡/涡致噪声模拟

基于七阶加权紧致非线性格式(WCNS-E8T7),结合延迟分离涡模拟(DDES)和Ffowcs WilliamsHawkings声比拟方法,对亚临界雷诺数下单圆柱、圆柱-翼型的分离涡/涡致噪声问题进行了数值模拟.针对亚临界雷诺数下圆柱尾迹中的转捩问题,发展了基于γ-Reθ模型高精度转捩-延迟分离涡模拟(Tran-DDES)方法,并与传统基于全湍流剪切应力输运(SST)模型的高精度DDES方法进行了对比.单圆柱模拟结果表明:传统SST-DDES方法会造成平均流场的回流区增大,压差阻力偏小等问题;而添加转捩模型的Tran-DDES方法与实验符合得很好.圆柱尾迹中添加翼型后,翼型对圆柱附近流场产生影响,使SST-DDES方法造成的圆柱后回流区偏大的问题减弱,并与Tran-DDES模拟结果差异变小.但在脉动量预测以及脉动产生的噪声预测方面, Tran-DDES方法仍与实验符合得更好.     

Diffraction of acoustic waves on the leading edge of a flat plate in a supersonic flow

A scheme is proposed for calculating the intensity of the acoustic wave field generated by diffraction of a beam of acoustic waves on a sharp leading edge of a flat plate in a supersonic flow. This wave field is shown to be a functional of the mass-flow amplitude distribution in the acoustic field at the level of the plate surface upstream of the latter. This distribution can be found on the basis of measurements. The discontinuity of the normal-to-plate component of the velocity perturbation on the plate edge plays an important role in determining mass-flow fluctuations along the plate. At large distances from the leading edge of the plate, where the diffraction wave on the boundary-layer edge degenerates into longitudinal acoustic waves, the amplitude of mass-flow fluctuations decreases with increasing distance from the leading edge and depends on wave orientation.Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 2, pp. 64–70, March–April, 2005.     

Downstream subsonic jet noise: link with vortical structures intruding into the jet coreRayonnement acoustique aval des jets subsoniques : lien avec l'intrusion de structures tourbillonnaires dans le cône potentiel

A subsonic circular jet with a Mach number of 0.9 and a Reynolds number of 65 000 is computed by a compressible Large Eddy Simulation (LES) to determine both the flow field and the sound field in the same calculation. The noise radiated by the jet, provided by LES, is in good agreement with experimental data of the literature in terms of sound pressure spectra, levels and directivity, showing the feasibility of this direct noise calculation. The dominant sound generation mechanism is also investigated, by presenting a correlation between its radiation, observed for an angle of 30° from the downstream direction, and the intrusion of vortical structures into the jet core. To cite this article: C. Bogey, C. Bailly, C. R. Mecanique 330 (2002) 527–533.     

Computational aeroacoustics applications based on a discontinuous Galerkin method

caa simulation requires the calculation of the propagation of acoustic waves with low numerical dissipation and dispersion error, and to take into account complex geometries. To give, at the same time, an answer to both challenges, a Discontinuous Galerkin Method is developed for Computational AeroAcoustics. Euler's linearized equations are solved with the Discontinuous Galerkin Method using flux splitting technics. Boundary conditions are established for rigid wall, non-reflective boundary and imposed values. A first validation, for induct propagation is realized. Then, applications illustrate: the Chu and Kovasznay's decomposition of perturbation inside uniform flow in term of independent acoustic and rotational modes, Kelvin–Helmholtz instability and acoustic diffraction by an air wing. To cite this article: Ph. Delorme et al., C. R. Mecanique 333 (2005).     

Development of numerical techniques for near‐field aeroacoustic computations

This work is concerned with the development of a numerical scheme capable of producing accurate simulations of sound propagation in the presence of a mean flow field. The method is based on the concept of variable decomposition, which leads to two separate sets of equations. These equations are the linearised Euler equations and the Reynolds‐averaged Navier–Stokes equations. This paper concentrates on the development of numerical schemes for the linearised Euler equations that leads to a computational aeroacoustics (CAA) code. The resulting CAA code is a non‐diffusive, time‐ and space‐staggered finite volume code for the acoustic perturbation, and it is validated against analytic results for pure 1D sound propagation and 2D benchmark problems involving sound scattering from a cylindrical obstacle. Predictions are also given for the case of prescribed source sound propagation in a laminar boundary layer as an illustration of the effects of mean convection. Copyright © 1999 John Wiley & Sons, Ltd.     

关于气动声学数值计算的方法与进展

气动声学数值计算是近年才出现的研究领域.本文介绍了气动声学数值计算的方法和有关的问题、边界条件的处理以及计算非线性声波的数值方法和进展.讨论了计算气动声学(CAA)的特性及其与计算流体力学(CFD)的差异,指出气动声学数值方法的关键是建立能保持色散关系的差分方程和正确处理无反射边界条件.对于非线性声波传播的问题,为了得到正确的解,应注意提高差分格式对短波的分辨能力,同时发展能抑制“伪”振荡(短波)而对长波基本不起作用的数值方法.     

Computation of aeolian tone from a circular cylinder using source models

The generation of aeolian tones from a two-dimensional circular cylinder situated in a uniform cross-flow is investigated. The major emphasis here is placed on identifying the important noise generation mechanisms. Acoustic-viscous splitting techniques are utilized to compute modelled acoustic source terms and their corresponding acoustic fields. The incompressible Reynolds averaged Navier-Stokes equation is used to compute the near-field viscous flow solution, from which modelled acoustic source terms are extracted based on an approximation to the Lighthill’s stress tensor. Acoustic fields are then computed with an acoustic solver to solve the linearized Euler equations forced by the modelled source terms. Computations of the acoustic field based on the approximated Lighthill’s stress tensor are shown to be in good agreement with those computed from the surface dipole sources obtained using Curle’s solution to the acoustic analogy. It is shown in this paper that the stress tensor source term in the streamwise direction makes a comparable, but slightly larger contribution to the overall radiated field, compared with that due to the stress tensor in the direction normal to the mean flow. In addition, it is shown that shear sources, which arise due to the interaction between the fluctuating velocity and the background steady mean velocity, make the greatest contribution to the acoustic field, while the self-noise sources, which represents the interaction between the fluctuating velocities, is shown to be comparably negligible.