Robust transition sensor for wall-modeled large-eddy simulation detecting turbulent breakdown in transitional boundary layers

The aerodynamics and thermodynamics of fluid machinery in many engineering applications are highly sensitive to the location of boundary layer transition. While the wall-modeled large-eddy simulation (WMLES) has served as a powerful tool for high-fidelity turbulent flow simulations at realistic high Reynolds numbers, conventional WMLES cannot capture the transition because the wall models generally assume fully developed turbulence. Prior studies have introduced transition sensors to activate the wall model based on turbulent kinetic energy (TKE), aiming to account for transition effects in WMLES. The TKE-based sensors, however, have been validated under limited conditions and may fail, for example, if the transition location is affected by wall temperature. The present study develops a robust transition sensor for WMLES capable of predicting the transition locations for a broad range of transitional flows, including cases with wall heating or cooling. The proposed sensor is based on Reynolds shear stress and designed to detect the onset of transition associated with turbulent breakdown, which causes a rapid increase in skin friction. Numerical tests for the subharmonic transition of high-subsonic boundary layers demonstrate the superiority of the proposed sensor over the existing sensors in predicting the characteristic skin friction distributions for different wall temperatures.