A Parametric Study on the Fluid Dynamics and Performance Characteristic of Micronozzle Flows

Abstract

The present study investigates the fluid dynamics and performance characteristics in micro nozzle flows with changes in various geometric parameters using Navier-Stokes simulation based on slip wall boundary conditions. The various geometric parameters considered for the study are 1) area ratio with fixed throat dimension and 2) the semi-divergence angle variation with no change in area ratio. The simulation results show that the flow choking for micro nozzle happens not at the geometric throat; rather pushed downstream to the divergent channel of the nozzle. This is due to the thick boundary layer growth which reduces the effective flow area and shifts the minimum allowable flow area downstream to the throat. The distance to which the choking point shifts downstream to the throat reduces with Maxwell's slip wall conditions compared to the conventional no-slip wall condition. The downstream movement of the choking point from the throat reduces with an increase in area ratio and with increase in divergence angle with fixed area ratio. This is due the fact that the increase in area ratio and divergence angle increases the nozzle height at any particular section in the divergent portion of the nozzle. As a result of this, the boundary layer profile also moves upward and the restriction of potential core by the thick boundary layer reduces which in turn leads to an increase in the effective minimum flow area downstream to the throat.