基于雷诺平均Navier-Stokes方程的表面传热系数计算

采用有限体积法数值求解控制二维绕流的雷诺平均Navier-Stokes(RANS)方程组,计算了光滑和粗糙NACA0012翼型以及圆柱表面的局部表面传热系数.分析了近壁面网格间距、湍流模式和表面粗糙度模型对数值计算结果的影响.结果表明:切应力输运(SST)湍流模型能够区分层流和湍流边界层的对流传热特性,并能预测转捩的发生;采用Spalart-Allmaras(S-A)扩展模型能够计算粗糙壁面的对流传热系数,但采用忽略转捩函数的S-A模型不能有效计算层流边界层的传热系数.当近壁面网格间距接近10-5量级的黏性子层时,在光滑和粗糙壁面都能得到准确的传热系数分布.结合合适的近壁面网格间距,湍流模式和表面粗糙度模型可以得到与实验数据十分接近的表面传热系数曲线.通过与求解不可压缩RANS方程得到的结果比较后发现,不可压缩RANS方程主要忽略了压缩和黏性耗散效应,这种效应可以通过绝热升温项的形式并入总体热分析.

Calculation of surface heat transfer coefficient based on Reynolds-averaged Navier-Stokes equations

Reynolds-averaged Navier-Stokes (RANS) equations governing two-dimensional external flow were numerically solved using finite volume method. Local surface heat transfer coefficients on surface of smooth and rough NACA0012 airfoil and cylinder were calculated. The effects of near wall mesh spacing, turbulent and surface roughness model on the numerical calculation results were discussed. The features of convective heat transfer in laminar and turbulent boundary layers can be distinguished by shear stress transport(SST)turbulent model, moreover, the transition can be predicted using SST turbulent model. The reasonable heat transfer coefficients on rough walls are calculated using Spalart-Allmaras (S-A) extended model, but the convection heat transfer coefficients in laminar boundary layer can not be calculated effectively by S-A turbulent model neglecting transition function. The near wall mesh spacing should approach order of 10^-5 in viscous sub-layer for obtaining accurate heat transfer coefficients on both smooth and rough walls. The curves of surface heat transfer coefficients are close to experimental results if appropriate near wall mesh spacing, turbulent and surface roughness models are used. The effect of compressibility and viscous dissipation is neglected by incompressible RANS equations, but can be incorporated into overall thermal analysis in the form of adiabatic heating term.