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

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/S_t0for various values of the modified blowing ratioSt/S_t0for 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.