In this book flow through diffuser for different casing angles has been analyzed.A diffuser is a device for converting the kinetic energy of an incoming fluid into 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 inlet swirl and casing wall angle on flow characteristics.The annular diffuser considered in the present case has both the hub and casings are diverging with equal angles and hub angle keeping constant as 5°.