基于伴随方法的方腔噪声主动控制研究

Adjoint-based active control of open cavity noise

基于伴随方法的梯度求解具有与设计变量数目无关的特点,适合多参数、高维度的优化控制。本文基于伴随方法对非定常二维可压缩方腔流致噪声开展了初步的主动控制研究,其长深比L/D=2,基于深度的雷诺数(Re)为3000。同时,为了实现长时域的流动控制,引入预测控制技术提高伴随过程的稳定性,成功实现对长时域流动噪声的主动控制。方腔上方的剪切层由于Kelvin-Helmholtz不稳定性快速增长,卷起的旋涡会撞击到后拐角从而产生强的噪声辐射。在开展方腔噪声控制之前,首先开展了流场对后拐角附近激励的敏感性分析,结果表明后拐角压力振荡对方腔前缘边界层附近区域非常敏感。因此,在方腔前缘边界层附近区域基于伴随方法施加了二维时空变化的体积力,并成功降低了噪声辐射。结果表明当前的主动控制改变了近场声源区压力振荡分布,在全辐射方向上抑制了噪声,总声压级最大降幅约2dB。

The gradient solution based on adjoint method is independent of the number of design variables,which is suitable for multiple parameters,high-dimensional optimizations.An adjoint-based preliminary active control of flow-induced noise is carried out on an unsteady compressible cavity flow.In order to realize the long-time flow control,we introduce the predictive control technology in order to improve the stability of the adjoint process,which successfully achieves the long-time active control of flow-induced noise.Present paper is devoted to studying two-dimensional compressible cavity flow,the length/depth ratio is 2 and the depthbased Reynolds number is 3000.The shear layer above the cavity undergoes rapid growth due to Kelvin-Helmholtz instability,the rolled-up vortices will impinge on the rear edge of the cavity and produce intensive noise radiation.Before applying noise control,the sensitivity analysis is firstly performed for the whole flow field to the excitation near the rear edge,the results indicate that the pressure oscillations near the rear edge are sensitive to the flow in the boundary layer region close to the leading edge,which is suitable for applying control excitations.Therefore,the two-dimensional spatiotemporal forcing based on the adjoint method in the shear layer region close to the leading edge is employed,which decreases the noise radiation successfully.The results show that the active control changes the distribution of near-field pressure oscillations in the region of noise sources,and the noise radiation is suppressed at all directions with a maximum reduction of overall sound pressure levels about 2 dB.