Effect of Thermal Nonequilibrium on Captured Mass Flow Rate of Scramjet Inlets

The numerical simulation of a scramjet is often based on the thermal equilibrium model, but the flow inside the inlet and isolator is likely to be in thermal nonequilibrium due to shock-based compression. The objective of this study is to investigate the effect of thermal nonequilibrium on the mass flow rate captured by the scramjet inlet. Numerical simulations based on the thermochemical nonequilibrium model (thermal nonequilibrium) and the chemical nonequilibrium model (thermal equilibrium) were adopted to study the mass flow rate of the HyShot II scramjet with the incoming flow Mach numbers Ma_∞ ranging from 6.0 to 8.0. The results show that the maximum difference of the mass flow rate between thermal nonequilibrium and equilibrium reaches 10.7% at Ma_∞ 8 with T_∞ 300 K. The primary cause of the mass flow rate difference is the oblique shock wave angle difference between nonequilibrium and equilibrium. The relative magnitudes of oblique shock wave angles and flow parameter ratios across the wave under equilibrium and nonequilibrium are theoretically discussed in an intuitive way. A simplified model for the HyShot II is established to predict the mass flow rate difference between thermal nonequilibrium and equilibrium. The result shows that the expression of captured mass flow rate has a significant amplification effect on the slight difference of wave angles between thermal nonequilibrium and equilibrium, which means that the effect of thermal nonequilibrium cannot be ignored for scramjet in some cases.