Numerical analyses have been carried out for the 3-D flow field inside turbine exhaust diffuser-collector systems. The analyses were performed with a multi-block computational fluid dynamics (CFD) package which solves the Reynolds-averaged Navier-Stokes equations and the turbulence (k and ε) transport equations. Complex flow features, including the 3-D screw-type vortices inside the collector as well as the flow interaction near the diffuser-collector interface are revealed and examined. Their impact on the pressure recovery of the whole exhaust system was investigated through numerical simulations. It has been found that significant performance improvement can be obtained by managing the collector vortex size and strength and reducing the interaction loss. The effects of inlet flow conditions, including the velocity profile (blockage, etc) and the turbulence level on the pressure recovery are studied. The CFD analyses have been utilized to obtain a new design of diffuser-collector system with higher pressure recovery and lower manufacturing cost. Significant performance improvement of this new design over the existing design has been confirmed by the data. Comparison of rig test data and CFD predictions indicates that the 3-D CFD procedure has captured the major flow features and can be used as a valuable design tool.

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