Instabilities of Compressible Flows with Internal Heat Addition

Abstract

Flows of heterogeneous media and multiphase flows such as mixtures of pure vapors, vapor/carrier gas mixtures, gas flows with solid particles and droplets prevail in many engineering problems in fluid mechanics and industry. Phase transition of rapidly expanding vapor or vapor/carrier gas mixtures is usually not observed at thermodynamic equilibrium. Because heat is added to the flow by condensation of a component of the fluid itself, flow and heat addition cannot be separated. Moreover, when dealing with water vapor, flow and condensation process are coupled in the most sensitive transonic flow regime. Due to the kinetics of nucleation and droplet growth the heat addition starts near Mach number one at maximum mass flux density where any small disturbance leads to global changes of the flow pattern. Internal heat addition after nonequilibrium phase transition immediately causes thermal choking (Delale, Schnerr and Zierep [1]) with steady or unsteady moving shock waves and instabilities like high frequency pressure oscillations. Self-excitation develops because of the instantaneous interaction of the shock with the phase transition process. Control and handling of these steady and unsteady two-phase flows require a well founded understanding of gasdynamics, of nonequilibrium condensation kinetics and their interaction in the most sensitive transonic flow regime.