DRAG AND LIFT IN NONADIABATIC TRANSONIC FLOW

Transonic flows with heat addition over airfoils have been calculated for different angles of attack. The fluid is a mixture of an inert car rier gas and a small amount of a condensible vapor. For the phase chan ge process coupled to the flow, two limiting cases are investigated: n onequilibrium condensation after significant supersaturation and homog eneous nucleation and equilibrium condensation. Numerical calculations based on the Euler equations are linked with either the classical nuc leation theory coupled with microscopic or macroscopic droplet growth laws or an equilibrium process. An improved explicit time-dependent di abatic finite volume method is developed and applied to calculate stat ionary flows. Reservoir conditions of pressure, temperature, and vapor content are varied to simulate internal flows in transonic wind tunne ls, turbomachinery, and atmospheric flight at low altitudes. The press ure drag and the lift may increase or decrease. Homogeneous condensati on in internal flows produces a maximum decrease of the pressure drag of about 60% and a maximum lift decrease of 35%. Nonequilibrium phase transition of the vapor content in atmospheric flight decreases the li ft about 10%, whereas the drag remains nearly constant. With the assum ption of the more realistic equilibrium condensation process in atmosp heric flight, the lift changes inversely; it increases about 30%, but the pressure drag increases more than 200%. Nonequilibrium and equilib rium condensation in transonic flow are quite easy to distinguish by t he position and the extension of the normal shock. The equilibrium pro cess enlarges the supersonic area remarkably, whereas it reduces in si ze when the vapor condenses not in equilibrium, i.e., gasdynamic pheno mena may be used as a tool for the Identification of the nature of the actual phase transition process.