The wall-shear stress (WSS) fluctuations in the interaction of an oblique shock wave with a flat-plate turbulent boundary layer are investigated by means of direct numerical simulation (DNS) at Mach 2.25. The numerical results agree very well with previous experiments and DNS data in terms of turbulence statistics, wall pressure, and skin friction. The fluctuating WSS characteristics, including probability density function (PDF), frequency spectrum, space–time correlation, and convection velocity, are analysed systematically. It is found that the positively skewed PDF shape of the streamwise WSS fluctuations is significantly changed due to the presence of a separation bubble, while the PDF shape of the spanwise component is slightly affected, exhibiting a symmetric behaviour across the interaction. The weighted power-spectrum density map indicates that the low-frequency unsteadiness associated with the separated shock - exhibits little influence on the spectrum for either component, and no enhancement of the low-frequency energy is observed. A significant reduction in the spatial extent of the two-point correlation is observed, causing spanwise elongated coherence for the streamwise WSS fluctuations in the separation region. Moreover, the elliptic behaviour of the space–time correlations is essentially preserved throughout the interaction, and this is accompanied by a sudden reduction of the convection velocity in the separation bubble.

通过直接数值模拟 (DNS) 以 2.25 马赫的速度研究了斜激波与平板湍流边界层相互作用中的壁剪应力 (WSS) 波动。在湍流统计、壁压力和皮肤摩擦方面，数值结果与之前的实验和 DNS 数据非常吻合。系统地分析了波动的 WSS 特性，包括概率密度函数 (PDF)、频谱、时空相关性和对流速度。发现由于分离气泡的存在，流向 WSS 波动的正偏斜 PDF 形状发生了显着变化，而展向分量的 PDF 形状受到轻微影响，在相互作用中表现出对称行为。加权功率谱密度图表明与分离冲击相关的低频不稳定性 - 对任一分量的频谱影响很小，并且没有观察到低频能量的增强。观察到两点相关的空间范围显着减少，导致分离区域中流向 WSS 波动的展向拉长相干性。此外，在整个相互作用过程中，时空相关性的椭圆行为基本上保持不变，这伴随着分离气泡中对流速度的突然降低。观察到两点相关的空间范围显着减少，导致分离区域中流向 WSS 波动的展向拉长相干性。此外，在整个相互作用过程中，时空相关性的椭圆行为基本上保持不变，这伴随着分离气泡中对流速度的突然降低。观察到两点相关的空间范围显着减少，导致分离区域中流向 WSS 波动的展向拉长相干性。此外，在整个相互作用过程中，时空相关性的椭圆行为基本上保持不变，这伴随着分离气泡中对流速度的突然降低。