Entropy generation in bypass transitional boundary layer flows

Abstract

The primary objective of this study is to evaluate the accuracy of using computational fluid dynamics (CFD) turbulence models to predict entropy generation rates in bypass transitional boundary layers flows under zero and adverse pressure gradients. Entropy generation rates in such flows are evaluated employing the commercial CFD software, ANSYS FLUENT. Various turbulence and transitional models are assessed by comparing their results with the direct numerical simulation (DNS) data and two recent CFD studies. A solution verification study is conducted on three systematically refined meshes. The factor of safety method is used to estimate the numerical error and grid uncertainties. Monotonic convergence is achieved for all simulations. The Reynolds number based on momentum thickness, Reθ, skin-friction coefficient, Cf, approximate entropy generation rates, S‴, dissipation coefficient, Cd, and the intermittency, γ, are calculated for bypass transition simulations. All Reynolds averaged Navier-Stokes (RANS) turbulence and transitional models show improvement over previous CFD results in predicting onset of transition. The transition SST k-ω 4 equation model shows closest agreement with DNS data for all flow conditions in this study due to a much finer grid and more accurate inlet boundary conditions. The other RANS models predict an early onset of transition and higher boundary layer entropy generation rates than the DNS shows.