Effect of back pressure and divergent section contours on aerodynamic mixture separation using convergent–divergent micronozzles

A numerical investigation of the aerodynamic separation associated with converging–diverging two-dimensional planar micronozzles is reported. The impact of divergent section shapes such as linear, bell, and trumpet, the effect of different back pressure conditions, and the associated flow and separation features are studied. Simulations used the direct simulation Monte Carlo method and are validated with the available experimental data. The lateral separation effect is found to be influenced by the nozzle divergent section shape. The separation performance of micronozzles of different throat sizes indicates the dependence of the exit Kn on separation performance. The bell shape of the divergent section produced higher flow alignment, a thicker subsonic layer, more reduction in exit velocity, and lower separation performance than linear and trumpet shapes. The divergent section with a trumpet shape is preferred for higher species separation performance. The back pressure conditions at the exit of the nozzle are found to play a significant role in the curvature of streamlines and flow characteristics, which may play a vital role in mixture separation performance.