SA和SST湍流模型对高超声速边界层强制转捩的适应性

凸起物是高超声速流动中常用的一种人工转捩装置。采用高阶精度算法模拟了高超声速进气道压缩面上的强制转捩流动,转捩装置为一排高度为1mm的钻石型凸起物和斜坡型凸起物。考察了Spalart-Allmaras(SA)模型和剪切应力输运(SST)湍流模型对该问题的适应性。在考察过程中通过丰富的算例分析了网格规模、可压缩修正和空间离散格式等对计算结果的影响。在层流区,计算能与试验取得非常一致的结果。但在湍流区,计算得到的热流通常高出试验数据。经分析发现其原因是强制转捩的湍流边界层与自然转捩的湍流边界层在涡结构上存在较大差别,使得湍流模型的效果较差。针对高超强制转捩湍流涡结构丰富的特点,对SST湍流模型进行了修改。计算结果表明,该修改方法对提高热流精度具有一定效果。

SA and SST turbulence models for hypersonic forced boundary layer transition

Protuberances are widely used for the trip laminar-turbulent transition of boundary layers. A row of 1 mm height diamond and slop protuberances are installed on the compression surface of a hypersonic inlet model. High-order schemes are applied to simulating the forced-transition flows. The Spalart-Allmaras (SA) and shear stress transport (SST) turbulence models are investigated for this kind of flow. Quite a number of numerical tests are taken to examine to what extent grid sizes, compressibility corrections and spatial discrete schemes influence the numerical accuracy. It turns out that the computed results are well consistent with experimental results in the laminar region, while the computed heating transfer rates are much larger than experimental data in the turbulent region. The inconsistency is suspected to be caused by the vortex structure of forced transitional flows which are quite different from natural transitional flows. The abundant vortices in forced transitional boundary layers may degrade the effectiveness of turbulence models. According to the characteristics of vortex structures, a modification to the SST model is suggested for hypersonic turbulent boundary layers caused by forced transition. Numerical tests indicate that the modification can enhance the accuracy of computed heating transfer rates.