粗糙壁面诱导的流动转捩数值模拟方法

为预测粗糙壁面诱导的流动转捩，对Langtry提出的γ-Re_θ转捩模型增加粗糙壁面的比耗散率和涡黏性的边界条件，并对模型中的经验关联函数——转捩动量厚度雷诺数进行修正，引入等效沙粒表面粗糙度作为变量，使模型具有一定的预测粗糙壁面诱导的流动转捩的能力.对粗糙平板自然转捩算例和变压力梯度平板绕流算例进行数值模拟，计算结果与风洞实验数据符合的较好.主要结论如下:表面粗糙度一般会增加边界层内的传热系数和阻力系数，同时使层流到湍流的转捩位置提前；自然转捩的转捩位置受表面粗糙度影响较大，与光滑壁面相比，平板算例中0.15mm的表面粗糙度使转捩位置提前40%；分离诱导转捩的转捩位置受表面粗糙度影响较弱，随着表面粗糙度逐渐增加，转捩位置和分离泡位置略有后移，且分离泡强度逐渐减弱，分离泡之后的阻力系数增加. 

Numerical simulation method of roughness induced transition

For the purpose of simulating roughness induced transition, the boundary conditions of turbulent dissipation rate and eddy viscosity for rough surface were added to Langtry's γ-Re_θ transition model; furthermore, equivalent sand surface roughness height was introduced to rewrite the correlation equations of the transition momentum thickness Reynolds number, making it appropriate for roughness-induced transition. Numerical simulation was made by referring to the wind tunnel data of several rough flat plate experiments and variable-pressure-gradient plate experiment, in which the results were satisfactory. Main conclusions are made as follows:surface roughness will enhance the heat transfer, increase the skin friction coefficient and shift the transition position upstream in general compared with smooth cases; effects for natural transition is significant, as surface roughness of 0.15 mm could shift the transition position upstream about 40%; while affect for separating induced transition is weaker; with the increase of surface roughness, transition position and separating bubble position are shifted backwards a little, the strength of separating bubble becomes weaker while the friction coefficient increases.