High spatiotemporal resolution wall shear stress measurement and multi-scale energy characterization in turbulent boundary layers

Obtaining accurate wall shear stress (WSS) measurements with high spatiotemporal resolution remains a significant challenge in turbulent boundary layers (TBLs) research. We present the adjustable spatio-temporal resolution cross correlation (ASTRCC) algorithm. This method combines temporal ensemble averaging with elongated interrogation windows (IWs). It resolves the competing demands between spatial and temporal resolution in PIV-based approaches. When validated against direct numerical simulation (DNS) data at friction Reynolds number Reτ=360, the ASTRCC algorithm demonstrates a 34% reduction in mean absolute error and a 36% reduction in root mean square error compared to the traditional single-row cross correlation (SRCC) method. Our experimental implementation in TBLs at Reτ=519 achieves high spatiotemporal resolution (Δx+≈8.5, Δt+≈0.6), facilitating detailed characterization of instantaneous WSS dynamics. Multi-scale decomposition analysis reveals three distinct structural contributions to WSS fluctuations. Large-scale structures (λ+≈103–104) account for 46% of total energy. Medium-scale structures (λ+≈102–103) contribute 37%. Small-scale structures (λ+≈101) represent 17%. Our quadrant analysis establishes that sweep events exhibit strong correlations with high-WSS regions, while ejection events predominate in low-WSS areas, with WSS disturbances convecting at 0.53U∞ (where U∞ is the free-stream velocity). These results provide quantitative evidence for the multi-scale nature of WSS generation and establish the pronounced influence of large-scale structures on near-wall WSS dynamics, thereby offering experimental foundations for enhanced turbulence modeling and flow control strategies.