ANALYSIS OF FLOW SEPARATION IN ANNULAR DIFFUSER

Abstract

A diffuser is a equipment which is used for converting the kinetic energy of received fluid into pressure. When fluid passes through the diffuser there is incessant retardation of the fluid flow due to which kinetic energy changes into pressure energy. This process is called diffusion. Diffuser is a important element in flow machinery . The present work involves the CFD analysis of flow separation in annular diffuser. The annular diffuser considered in the present case has both the hub and casings are diverging with unequal angles and hub half angle keeping constant as 5°. The geometries of all the diffusers are calculated for constant area ratio 2 and 3 and equivalent cone angle of 200. Swirl angle of 00, 7.50, 12.50, 17.50 & 250 are introduced at the inlet. The characteristic quantities such as static pressure distribution at hub and casing walls, velocity profiles at various sections and flow patterns have been presented for studying the flow separation. Results are analyzed and it reveals that at lower swirl angle the separation is near to the casing whereas at higher swirl the point of separation shifts towards hub side. Introduction of swirl is found to substantially increase the rate of rise of static pressure at casing wall. The difference in static pressure between hub and casing wall increases with increase in swirl angle. The point of flow separation tends to shift away from the casing wall and can be completely vanished with high degree of inlet swirl however it may appear at the hub.