论文标题
湍流并在声学衬里上增加了阻力
Turbulence and added drag over acoustic liners
论文作者
论文摘要
我们提出了孔隙分辨的方向数值模拟（DNS）的湍流在穿孔板上放牧的湍流，这与飞机发动机上发现的声学衬里非常相似。我们的DNS探索了一个较大的参数空间，包括孔隙率，厚度和粘性板直径的影响，在摩擦雷诺数$re_τ= 500 $ - $ 2000 $上，这使我们能够开发出强大的理论，用于估算由声学衬里诱导的拖动。我们发现，声学衬里可以被视为具有壁正态渗透性的多孔表面，并且表征其附加阻力的相关长度尺度是壁正常式Forchheimer系数的倒数。与其他类型的多孔表面不同，带有毛孔内的达尔西亚速度的多孔表面不同，声学衬里的孔内部的流动是完全湍流的，壁正常速度波动的幅度与近壁周期中的峰值相当。我们为声学衬里提供了明确的证据，这是一个完全粗糙的机制，也通过压力阻力的相关性增加证实。一旦达到了完全粗糙的渐近线，规范的声学衬里就会提供与沙粒粗糙度相当的添加阻力，粘性高度与板尺寸的粘液尺寸的Forchheimer渗透率相匹配。
We present pore-resolved direction numerical simulations (DNS) of turbulent flows grazing over perforated plates, that closely resemble the acoustic liners found on aircraft engines. Our DNS explore a large parameter space including the effects of porosity, thickness, and viscous-scaled diameter of the perforated plates, at friction Reynolds numbers $Re_τ= 500$-$2000$, which allows us to develop a robust theory for estimating the added drag induced by acoustic liners. We find that acoustic liners can be regarded as porous surfaces with a wall-normal permeability and that the relevant length scale characterizing their added drag is the inverse of the wall-normal Forchheimer coefficient. Unlike other types of porous surfaces featuring Darcian velocities inside the pores, the flow inside the orifices of acoustic liners is fully turbulent, with a magnitude of the wall-normal velocity fluctuations comparable to the peak in the near wall cycle. We provide clear evidence a fully rough regime for acoustic liners, also confirmed by the increasing relevance of pressure drag. Once the fully rough asymptote is reached, canonical acoustic liners provide an added drag comparable to sand-grain roughness with viscous-scaled height matching the inverse of the viscous-scaled Forchheimer permeability of the plate.
