Transonic aerodynamics including strong effects from heat addition

Abstract

Gasdynamic phenomena in transonic flows caused by the phase transition of the fluid components of vapor/carrier gas mixtures and pure vapors have been investigated in theory and experiment. The dominating parameters, the cooling rate of the expansion and the reservoir conditions (vapor pressure) are varied to investigate the coupled process of the nonequilibrium phase transition after homogeneous nucleation and the equilibrium condensation in flows near a Mach number of unity. The numerical code is applied to compute transonic flows of water vapor/carrier gas mixtures in indraft wind tunnels and in atmospheric flight, flows of nitrogen vapor in cryogenic wind tunnels or shock tubes and the equilibrium condensation process in flows over airplane wing sections. The computation of the inviscid flow field is based on an explicit finite volume method that solves the time-dependent 2-D Euler equations linked with the classical nucleation theory and microscopic or macroscopic droplet growth laws. Turbulent boundary layer calculations demonstrate viscous effects and the development of the nonequilibrium phase transition in shear layers. Emphasis is given to supercritical rates of the heat release and shocks inside the nucleation zone and aerodynamical shocks with evaporation of the condensate. The main contribution is achieved from the phase transition in the inviscid flow with rates of heat addition q/cpT01 typically <10%. Nevertheless, transonic flow fields become seriously affected and the pressure drag and lift of airfoils change up to 60%. The sign of these variations changes sensitively with the free-stream Mach number and the angle of attack. Atmospheric flight condensation processes develop near equilibrium and cause a significant increase in the pressure drag. Computations on the basis of given heat source distributions show that homogeneous nucleation initiates heat release to the flow just in the most sensitive region over the airfoils.