Abstract: A second-order-closure turbulence model method is used to calculate the influence of turbulence and roughness on boundary layer transition, and an experimental test is provided. The calculating results of influence of turbulence and roughness on boundary layer transition position are consistent with the experimental data of the present paper and of others. The turbulent energy distribution in the process of transition from laminar to turbulent flow has been calculated, its change shows that the laminar breakdown should occur at y/δ = 0.5, which agree with the Van Driest's result,i. e. the initial laminar breakdown should occur at y/δ=0.57 obtained by the vorticity Reynold's number approach.

Key words: turbulence effacts, roughness effacts, boundary layer transiton, boundary layer stability