Numerical simulation of roughness-induced boundary layer transition

For the purpose of simulating roughness induced transition, new boundary conditions of turbulent dissipation rate ω and eddy viscosity μ_t for rough surface were added to Langtry's γ-Re_θ transition model, furthermore, the empirical correlation equation of transition momentum thickness Reynolds number Re_θ was rewritten by introducing a new parameter, equivalent sand roughness height k_s, making it appropriate for simulating roughness-induced transition. Numerical simulation was made referring to the wind tunnel data of several rough flat plate experiments and a variable-pressure-gradient plate experiment, and the results were satisfactorily compared with the experiment data. Main conclusions are as follows: Surface roughness enhances the heat transfer, increases the skin friction coefficient and shifts the transition position upstream compared with smooth cases; roughness degree of 0.15mm could shift the transition position upstream for about 40%; influence of surface roughness on natural transition is significant, while the influence on separation induced transition is inconspicuous.