变物性与热辐射对发汗冷却过程的影响规律研究

Influence of Variable Thermophysical Properties and Thermal Radiation on Convection Heat Transfer in Transpiration Cooling

采用两层k-ε湍流模型对高温条件下有发汗冷却时的矩形槽道内湍流流动和换热进行了数值模拟。计算结果表明:随着冷却气体流量的增加,在发汗冷却壁面附近主流气体的温度梯度大大减小,壁面温度、局部对流换热系数都迅速下降;变物性条件下同时考虑热辐射时数值计算得到的平均St相对值(St/St0)随修正注入率F/St0的变化比已知的常物性条件下的值小;随着高温气体温度的上升,变物性和热辐射对与高温流体接触的表面温度有较大影响,热辐射对壁面温度的影响比变物性更大,而对流换热系数所受的影响不大;当主流为高温气体(如:2500K)、而壁面温度较低时(如:800K)热辐射的影响不大,发汗冷却效果仍然很明显。

The two-layer k-ε model was used to calculate the turbulent flow and heat transfer characteristics in a rectangular channel with transpiration cooling.The calculated results showed that increasing cooling flow rate greatly reduced the wall temperature,the local convection heat transfer coefficient and the temperature gradient in the main flow near the transpiration cooling wall.The changes of the ratio of St/St_0 for various values of the modified blowing ratio F/St_0 for variable thermophysical properties with consideration of thermal radiation were less than the changes for constant properties.Increases of the main flow temperature increased the effect of the variable properties and thermal radiation.The influence of thermal radiation on the wall temperature was stronger than the influence of variable thermophysical properties.The influence of the variable properties and thermal radiation on the convection heat transfer coefficient was small.When the main flow temperature was high (e.g.2500 K) and the wall temperature was low (e.g.800 K),the effect of the thermal radiation was not strong and the transpiration cooling effect was still obvious.