Extending the applicability of RANS turbulence closures to the simulation of transitional flow around hydrofoils at low Reynolds number

Abstract

Growing interest in marine autonomous systems such as underwater gliders and autonomous underwater vehicles (AUVs) has led to the increase of research on hydrofoil performance at low Reynolds numbers, bringing forward the issue of simulating laminar to turbulent transition using computational fluid dynamics (CFD). Most conventional turbulence closures in practical Reynolds-averaged Navier-Stokes (RANS) simulations are incapable of predicting transition with excessive turbulence generation near the leading edge, deriving from their eddy viscosity assumption. Having the potential of inherently predicting transition by solving the near wall flow accurately, three Low-Re RANS closures with anisotropy consideration are selected and evaluated for their ability to capture both separation-induced transition and natural transition. The empirical γ−Reθ transition model is also assessed in this work. Comparison with published experiments shows the capability of the four turbulence closures to capture separation-induced transition accurately. Predicting natural transition remains more challenging: two Low-Re closures exhibit the potential to capture natural transition only at medium grid finesse levels, whereas the γ−Reθ model evidences challenges in reproducing the correct flow physics. The lag elliptic blending model provides the most accurate solution owing to its consistent grid convergence, high accuracy for predicting the hydrodynamic coefficients, and ability to reproduce the correct transition physics.