STUDY OF DIFFUSERS WITH MOVING WALL

Abstract

A diffuser is a device for converting the kinetic energy of an incoming fluid into pressure efficiently. 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 hub velocity on annular diffuser performance using Fluent and also the prediction of effect of swirl on the flow separation. Swirling flows are very common in technical applications, especially in hydraulic machinery, and require sophisticated modeling. The variation in parameters i.e. Axial 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 hub rotation speeds for a diffuser of constant length and Area Ratio. The velocity and pressure variations are calculated for different hub rotations. The various values of hub RPM studied are 200, 800, 1600, and 3200. The results are present in the form of velocity and pressure coefficient diagrams along with the pressure coefficient and velocity contours. The pressure recovery coefficient at hub and casing side has also been worked out. For casing wall angle there is no separation observed at the casing wall for no swirl condition. With further increase in angle there is a separation observed at the hub wall. A high amount of swirl is required to suppress the separation on the hub wall for hub wall angle of .