气膜冷却温度场预测的标通量模型评估研究

Evaluation of Scalar Flux Models on the Thermal Prediction of the Film Cooling Jet Flow

气膜冷却是燃机高温透平叶片的关键冷却技术,准确高效地预测气膜冷却的温度场对于冷却设计具有重要意义。本文针对圆孔射流密度比(DR)为1、速度比(V R)为0.46的工况,基于大涡模拟(LES)的流场数据,单独求解采用不同标通量模型的时均标量输运方程,对比分析了各个模型的预测效果及其参数影响。评估的标通量模型包括梯度扩散模型(GDH)、广义梯度扩散模型(GGDH)和高阶广义梯度扩散模型(HOGGDH)。结果显示,GDH对射流核心的流向扩散预测较弱,对于温度场的分离再附特征也不能准确捕捉。GGDH和HOGGDH模型能够较好地预测下游扩散,对分离再附现象也有较好的反映。本文进一步指出,GGDH和HOGGDH模型引入雷诺应力从而隐含了垂直于标量梯度的输运模式,使其对温度场的预测更为准确。

Film cooling is one of the central cooling technologies in gas turbine. Meanwhile, it is of vital importance to predict the thermal field of film cooling efficiently. In this paper, the time-averaged scalar transport equation was solved using the flow field data from a previous large eddy simulation(LES). The studied case is a cylindrical hole film cooling with DR=1 and V R=0.46.Three different scalar flux models were investigated separately, including the gradient diffusion model(GDH), generalized gradient diffusion model(GGDH) and high-order generalized gradient diffusion model(HOGGDH). The parametric influence of each model was studied and the predicted thermal field for each model was then compared. It was found that the GDH under-predicts the thermal diffusion, and can’t capture the separation and reattachment in the thermal field. However, GGDH and HOGGDH predicts an enhanced diffusion and captures the phenomenon well. It was pointed out that the GGDH and HOGGDH model use the Reynolds stress as the diffusive coefficient, which implicitly incorporate a turbulent scalar transport mode that is perpendicular to the mean scalar gradient, so that the thermal field is predicted more accurately.