An overview of the acoustics of boundary layer flows over rough surfaces and surfaces with discontinuities at low Mach number is presented. Roughness noise is dominated by dipole radiation produced by unsteady tangential pressure forces on the uneven surface. Pressure fluctuations may be generated by turbulence of the overriding boundary layer or by the wakes of upstream roughness features, but in either case the sound can be predicted from the wall pressure frequency spectrum and the surface geometry. Small discontinuities, such as steps and gaps, are special cases of isolated two-dimensional roughness. Forward steps are much louder than backward steps because the former generate strong turbulence close to the step. Gap noise is dominated by any exposed forward-step portion of the gap. Rounding can substantially reduce forward step noise, and moderate sweep does not alter the noise-generation mechanism.

中文翻译：

---

流过刚性墙壁的声音

概述了边界层流过粗糙表面和低马赫数不连续表面的声学。粗糙度噪声主要是由不平坦表面上的不稳定切向压力产生的偶极辐射。压力波动可能是由上层边界层的湍流或上游粗糙度特征的尾流产生的，但在任何一种情况下，都可以从壁面压力频谱和表面几何形状预测声音。小的不连续性，例如台阶和间隙，是孤立的二维粗糙度的特例。向前的脚步声比向后的脚步声响亮得多，因为前者会在靠近脚步声的地方产生强烈的湍流。间隙噪声由间隙的任何暴露的前步部分支配。四舍五入可以大大减少前步噪声，