Modeling of self-excited oscillation of non-equilibrium condensation in transonic moist air flow

Abstract

Atmospheric air is a popular working fluid in gas power plants and turbomachinery which always contains water vapor. The vapor condensation occurs in transonic flow when the temperature drops below dew point during the accelerating expansion and affects the performance of equipment and safety. The unsteady condensation model based on nucleation and droplet growth model, and the Shear Stress Transport (SST) viscous turbulence model for moist air condensing in transonic flows was proposed. The prediction accuracy of steady and unsteady condensing flows was validated by experimental data and theory. The unsteady frequency and fluctuation intensity of pressures for symmetric and asymmetric condensing oscillation modes were discussed. A new formula (f0 = 1.992Φ01.539ws0.3853) of dimensional frequency related with inlet relative humidity and saturated vapor mass fraction was obtained. Then, periodic mass flux, pressure loss and droplet mass generation rate distributions at different carrier gas pressure were analyzed. The pressure loss coefficient represents the energy loss. As the carrier gas pressure increases, the mass flow rate increases, but the energy of condensation-induced shock decreases. Combined with the analysis of the distribution of liquid mass fraction, it is also found that Mach number and pressure fluctuation are induced by condensation wave due to heat release. Finally, the velocity phase diagrams and heat addition of per unit volume at different oscillation modes were assessed. It reveals the maximum heat addition amounts of per unit volume for three symmetric modes are 1.28 × 103, 1.48 × 103 and 1.54 × 103 MW m−3 along the increase of humidity.