Design of Curved Annular Diffusers

Abstract

Influence of curvature distribution and area-ratio (AR) distribution on the pressure fields within the curved annular diffuser are discussed. General guidelines for end-wall contouring to control the pressure gradients on the diffuser walls are evolved and further demonstrated through computational fluid dynamics (CFD) simulations. Also, detailed guidelines for controlling the adverse pressure gradients (APG) on duct walls are presented. A geometry generation methodology (GGM) which enables both design and evaluation of curved annular diffusers based on the guidelines evolved is presented. The approach presented deals with the sensitivity of the duct performance parameters to duct wall modifications. In that sense, the work per se is not a description of an automated optimization process, but rather about the physical principles that can guide such an optimization. An aggressive diffuser design space is identified with ducts of maximum slope of 50 deg and maximum divergence angle between the outer and inner walls of 10 deg for length to inlet height ratio ranging from 1.25 to 2.5. Part of the identified design space for which the flow separation can be eliminated based on the guidelines evolved is demarcated. The need for flow control, possibly passive, is established for more aggressive designs.