The effect of high temperature induced variation of specific heat on the hypersonic turbulent boundary layer and its computation

For hypersonic vehicles,as the temperature in its boundary layer usually exceeds 600 K,for which the molecular vibrational degree of freedom is excited,the perfect gas model is no longer valid.In this paper,the effect of high temperature induced variation of specific heat on the hypersonic turbulent boundary layer of flat plates is investigated by direct numerical simulations with the perfect gas model,i.e.with constant specific heat,as well as with a variable specific heat gas model.The comparison of the results from the two gas models has found that the effect of the variation of specific heat on the velocity of the turbulent boundary layers is relatively small,while its effect on temperature,such as the mean temperature,the temperature fluctuations,is appreciable.It is also found that the mean specific heat is quite close to the specific heat calculated by using the mean temperature,indicating that it is possible to do turbulence modeling.The modeling is done under the variable specific heat gas model with the mean temperature as the variable.The feasibility of such consideration is verified by applying the SST model for variable specific heat turbulence computation.