Laminar And Transitional Boundary Layer Entropy Generation Over A Flat Plate Under Favorable And Adverse Pressure Gradients
Minimizing entropy generation is important to improve the efficiency of any system. The objective of this study is to use computational fluid dynamics (CFD) to elucidate the effects of pressure gradients on entropy generation rates in laminar and transitional boundary layers. The commercial CFD software, ANSYS FLUENT, is employed. The favorable and adverse pressure gradients are generated using various curved slip top walls. Bypass transition is simulated using the mean inlet velocity and Reynolds stresses from the direct numerical simulation (DNS) conducted by Nolan and Zaki . Various turbulence and transitional models are employed and the results are compared to the DNS data. The factor of safety method is used to evaluate numerical error and grid uncertainties. Three systematically refmed meshes are used to evaluate grid convergence. Monotonic convergence is achieved for all simulations with small grid uncertainties. The boundary layer correlation fUnction, F(lambda), the shear stress correlation, S(lambda), and the dissipation coefficient, C-d, are calculated for the laminar CFD results. The dissipation coefficient, C-d and the intermittency, gamma, are also calculated for the bypass transition CFD results. The laminar CFD results show better agreement with the correlation developed by McEligot than with the Thwaites correlation for F(lambda) and S(lambda). Overall, the percentage differences between the CFD results and the correlations incfease as the magnitude of the pressure gradient variable, beta, increases. The solvers and turbulence models in the transitional simulations are similar to the study by Ghasemi et al . However, this study uses a much finer grid and improved boundary conditions for the inlet. These changes show an improvement for most turbulence models by comparison with the DNS results, especially for the location of transition.