EFFECT OF CASING ROTATION ON THE PERFORMANCE OF DIFFUSER

Abstract

A diffuser is a device for converting the kinetic energy of an incoming fluid into pressure efficiently. The task of a diffuser is to decelerate the flow and to regain total pressure. As the flow proceeds through the diffuser there is continuous retardation of the flow resulting in conversion of kinetic energy into pressure energy. Such a process is termed as diffusion. Diffuser forms an important part in flow machinery and structures. The present study involves the CFD analysis of effect of casing rotation on annular diffuser performance using Fluent.. CFD analysis is conducted without swirl in an annular diffuser with the inlet velocity profile obtained experimentally. The variation in parameters i.e. Axial Velocity, Radial velocity, Swirl Velocity and Pressure Co-efficient, in the flow through annular diffuser studied along the various sections of the diffuser and also at various casing rotation speeds for a diffuser of constant length and Area Ratio. The velocity and pressure variations are calculated for different casing rotations. The various values of casing RPM studied are 200, 400, 600, 800, 1000, 1200, 1400, 1600, 1800, 2000, 2200, 2400, 2600, 2800, 3000 and 3200 rpm. In order to predict the performance characteristics of an annular diffuser, the Geometric parameters of annular diffuser are calculated for constant area ratio and length. The data is obtained with respect to a inlet velocity of 60 m/s. It is assumed that the flow is exhausted to atmosphere, so pressure at exit of diffuser is assumed to be atmospheric. The results are depicted in the form of variation of pressure coefficient along the diffuser length at different casing rotation. and velocity (axial velocity, radial velocity, swirl velocity) variation from hub to casing (along the diffuser height). These graphs are at no swirl condition and also variation of pressure coefficient with respect to casing rotation at no swirl condition. The pressure recovery coefficient at hub and casing side has been worked out.