The slip effect of micro-droplets in Rankine vortex

Abstract

The method of moments with interphase slip is simplified to numerically study the interaction between nanoscale droplets and gas flow in a Rankine vortex. In the method, the flow of gas phase and the moments of the droplets size distribution are calculated respectively and the transfers of momentum and heat between the gas and the droplets which are expressed by the moments are introduced into the governing equations as the source terms. In this way, the velocity slip between the gas phase and the droplet phase is captured by the present method. Then, the method is used to simulate the flow of Rankine vortex where the water droplets with constant radius are injected into the vortex core. The results show that the vortex is disturbed and the droplets move outward due to the effect of the velocity slip between the phases. The larger the droplet radius, the stronger the velocity slip effect. When the radius of the injected droplets is small, the vortex keeps stable and the droplets aggregate as a ring outside the core of the vortex. When the droplets radii are large enough, the vortex is not stable any more due to the strong slip effect and negative vorticity is induced in the core of the vortex. The droplets form a swing arm and spiral out of the vortex. At last, the effects of the growth of droplets on the vortex evolution and interphase slip are also investigated. The grown droplets spiral out and the position of maximum mean radius also moves outward with time. In the vortex core, condensation stops after a short time because no more vapor is supplied. With the growing process, more momentum is transferred from the gas phase to the droplets and the slip velocity between droplets and gas vanishes more quickly.