Effect of Vibrational Nonequilibrium on Isolator Shock Structure

摘要

Analyses of dual-model scramjet engines often rely on the assumption of thermally perfect gas,for which theinternal modes of molecular motion are assumed to be in thermal equilibrium. With an increase in enthalpy and in thepresence of shocks and expansion waves,the equilibrium assumption does not hold within a scramjet inlet-isolatorsection. For the flight Mach numbers considered here,the molecular vibrational modes are affected,leading to notonly a change in the gas properties but a redistribution of the total energy. In this work,a multitemperature model isused to describe thermal nonequilibriuni of flow through a square duct with an inlet Mach number of 1.9. The highlyresolved simulations show that the pseudoshock structure is altered due to nonequilibrium,with the leading edgeof the shock structure moving upstream. Moreover,the length of the pseudoshock is considerably increased. Both ofthese effects are shown to be caused by slow relaxation of the N2 molecules. Furthermore,even at the isolator’s exit,equilibrium is not established,which is manifested as a pressure defect. If and when the fluid reaches thermalequilibrium,inside the downstream combustor,there is a potential for a sudden surge in local pressure that couldendanger scramjet operation.