Experimental analysis of wall shear rates in Taylor–Couette–Poiseuille flow across laminar, transitional, and turbulent regimes

This paper presents a detailed experimental investigation of the near-wall transport dynamics in Taylor-Couette-Poiseuille flows using measurements of the large-scale variations of local wall-shear-rate components. A three-segment electrodiffusion probe was used to conduct multiple experiments across a wide range of Taylor numbers (300 < Ta <2520) and Reynolds numbers (2 < Re <32) to capture laminar, transitional, and turbulent flow conditions. Both azimuthal and axial wall shear rate component measurements were made in order to directly correlate the effects of flow structures on the transport of momentum in the near-wall region. The results show that the average azimuthal wall shear rate is primarily influenced by the Taylor number, while its variation with the Reynolds number remains within the experimental uncertainty. On the other hand, the large-scale shear rate dynamics are strongly influenced by the flow structures. More specifically, vortical flows have almost identical average wall shear rates as helical flows but distinctly different temporal characteristics and fluctuation magnitude. The differences in large-scale wall shear dynamics between the two flow structures arise from distinct mechanisms of momentum transfer; vortices induce high shear rates through rapid radial inflow and outflow, whereas helices generate low shear rates via a much more uniform shear distribution due to their oblique configuration. These findings suggest that the average wall shear stress alone is insufficient to determine the transport processes occurring in the wall region. Localized measurements are required in order to establish the relationship between flow structure and transport dynamics within the measurement bandwidth. These findings provide new insight into shear-induced transport in rotating flows and establish experimental benchmarks for the development and validation of transport models.