基于Navier-Stokes／Kirchhoff方程的悬停旋翼跨声速气动声学计算

研究了Kirchhoff积分面是否有盖有底,以及是否计及旋翼网格上的流场值,这两个因素对噪声预测结果的影响.发展了一种基于重叠网格的计算悬停旋翼远场噪声的数值方法.数值计算过程分为流场模拟和声场模拟两部分.悬停旋翼流场的数值模拟是在两个相互重叠的网格上进行的:在高质量的旋翼网格上求解Navier-Stokes方程,用于模拟旋翼附近的粘性流动和近场尾涡的捕捉;在远离粘性区域处布置符合悬停流场物理特征的圆柱形背景网格,控制方程为Euler方程,用于远场尾涡的捕捉.计算得到的流场信息插值到用于声场计算的Kirchhoff积分面上.观测点处的噪声可以认为是由这个完全包含桨叶的Kirchhoff积分面上的面元(声源)发声得到.远场声波的传播由Kirchhoff积分公式描述.计算结果表明:采用有盖有底的Kirchhoff积分面并且同时计及旋翼网格流场值时,计算得到的HSI噪声与实验值吻合最好.

Transonic hovering rotor aero-acoustic predictions using Navier-Stokes/Kirchhoff method

An numerical method based on chimera techniques was developed to compute the far-field acoustic signature of a helicopter rotor in hover. The numerical simulation was carried out in two parts of flowfeild simulation and acoustic prediction. The aerodynamic field was evaluated by solving equations on a system of overset grids--a NS solver based upon an efficient rotor mesh to simulate the viscous flow and vortex wakes near the rotor blades,a Euler solver based upon a cylindrical back mesh which was conformed with the nature topology of rotor hovering problem and was far from the viscous area to capture far-field wake. Computed flowfield information was interpolated onto a Kirchhoff integration surface. The far-field noise can be computed by integrating pressure data of cells of the Kirchhoff surface that completely encloses the rotor blades. The sound propagation to the far field was computed with Kirchhoff formalism. This paper focused on studying the influence of choosing Kirchhoff surface including top and bottom or not and considering the flow solution of rotor mesh or not on the result of noise prediction. As a demonstration of the overall prediction scheme,only using the integration surface with top and bottom and considering simultaneously the flow solution of rotor mesh,the computed result of far-field noise for high-speed impulsive case showed the best agreement with experimental data.