Experimental Investigation of the Flow in Diffusers Behind an Axial Flow Compressor

The flow fields of four diffusers situated at the rear of a one-stage axial flow compressor was experimentally investigated. Through modification of the compressor operating point a wide range of variations of the side wall boundary layers and the radial velocity distribution outside of the boundary layers at diffuser inlet could be achieved. The three dimensional flow field at both diffuser inlet and outlet is analysed. Changes of inlet blockage and radial velocity distribution and their resulting effects on pressure recovery are thoroughly presented. Compared with the results of measurements at diffusers, typically with ducted flow inlet conditions, higher values of pressure recovery are observed. Established design rules, based on investigations of diffusers with carefully developed inlet flow, are checked regarding their applicability for diffusers in turbomachine environment.