Swirl and Tip Leakage Flow Interaction With Struts in Axial Diffusers

Abstract

A scale model of a typical gas turbine exhaust diffuser (annular followed by conical) is investigated experimentally and numerically. The turbine exhaust flow is modelled using a radial type swirl generator and a simulated tip leakage flow. Static pressure measurements are carried out on the walls and on the center line of the conical part. Four swirl angles and three strut configurations are investigated. Pressure recovery coefficients are depicted as a function of diffuser length. Velocity and turbulence profiles are measured using ID-LDA in two directions. A CFD analysis of the model is carried out using a commercial Navier-Stokes code and the standard as well as the Chen k-ε turbulence model. Even without struts, inlet swirl higher than 8° is found to adversely influence the pressure recovery of the diffuser. The profiled struts showed not to be able to redirect the flow and for swirl angles higher than 10°, cylindrical struts were found to yield better diffuser performance than profiled struts.