Demonstration of an integral method for estimating wall shear stress in complex high-speed flows

TL;DR

This paper introduces a simple integral method to estimate wall shear stress in complex high-speed turbulent flows, demonstrating accuracy within 5% error across various challenging conditions.

Contribution

It presents a novel integral formulation based on the Favre-averaged momentum equation that is applicable to complex flow scenarios including rough surfaces and pressure gradients.

Findings

Predicted shear stress error was no more than 5%.

Method works with over 40% missing near-wall data.

Applicable to flows with curvature, roughness, and pressure gradients.

Abstract

Turbulent flows over blunt bodies with distributed roughness present a class of problems relevant to hypersonic atmospheric entry systems. However, accurate predictions of shear stress on such bodies remains elusive. This work presents a simple integral formulation to infer wall shear stress based on the Favre-averaged streamwise momentum equation, integrated once in the wall-normal direction. The proposed integral formulation eliminates streamwise dependence, relying only on data and gradients extracted in the wall normal direction. Eight demonstration cases were selected to show the contributions of the various terms of the integral equation, the associated error in the estimate, and outline practical considerations when estimating the wall shear stress for complex flow conditions. In all cases, the error in the predicted shear stress compared to a more traditional approach was no more than 5%, with many cases having much lower error. Notably, the method was found to be viable even for surfaces in the transitionally rough and fully rough regimes by appropriate selection of a virtual origin, as well as flows over curved surfaces or with pressure gradients. Finally, the method produces acceptable estimates of shear stress even in the extreme condition when over 40% of the near-wall boundary layer data is absent. In brief, the present integral method is general and applicable to flows with curvature, surface roughness, and pressure gradients.