Compressible turbulent boundary layers with heat addition by homogeneous condensation

Homogeneous condensation in transonic viscous flow is computed using a combination of analytical and numerical methods. The procedure is based on the perturbance method for the shock/boundary-layer interaction of Bohning and Zierep for adiabatic flow. In this paper, the model was extended for applications to boundarylayer flows with internal nonequilibrium heat addition. For the simulation of the homogeneous condensation process we use the classical nucleation theory of Volmer and the molecular Hertz-Knudsen droplet growth law. One momentum equation of the Navier-Stokes equations is solved by a time-stepping procedure combined with a mixing length turbulence model. Objective in view is the analysis of the macroscopic phenomena of nonequilibrium heat addition from homogeneous condensation of water vapor in transonic flows with high velocity and temperature gradients normal to the main flow direction. In detail, the cooling rate, the nucleation rate, the droplet radius, and the condensate mass fraction in the boundary layer are discussed. Approaching the wall surface and in comparison to the inviscid diabatic flow just outside of the boundary layer the nucleation process and the deposition of droplets, i.e. the condensate fraction contours, are shifted downstream, continuously or stepwise, depending on the pressure gradients at the boundary-layer edge. From the comparison of the integral boundary layer variables we conclude that the friction coefficients change only moderately, whereas the displacement and momentum thickness are found to be more sensitive to the homogeneous condensation onset.