INSTABILITIES AND BIFURCATION OF NONEQUILIBRIUM 2-PHASE FLOWS

New instabilites of unsteady transonic flows with non-equilibrium phas e transition are presented including unsymmetric flow patterns with mo ving oblique shock systems in supersonic nozzles with perfectly symmet ric shapes. The phenomena were first detected when performing experime nts in our supersonic wind tunnel with atmospheric supply and could be perfectly reproduced by numerical simulations based on the Euler equa tions, i.e. neglecting the viscosity of the fluid. The formation of th e liquid phase is modelled using the classical nucleation theory for t he steady state together with the Hertz-Knudsen droplet growth law and yields qualitatively and quantitatively excellent agreement with expe riments in the unsteady flow regime with high-frequency oscillations i ncluding the unstable transient change of the structure from symmetric to unsymmetric flow. For engineering applications the sudden increase or decrease of the frequency by a factor 2 or more and of the pressur e amplitude at the bifurcation limits is of immediate practical intere st, e.g. for flutter excitation of turbomachinery blading.