Commonly, the pipe diffuser and deswirler are aerodynamically decoupled from each other to ensure better mixing of the inhomogeneous pipe flow before entering the deswirler and to prevent upstream effects of the deswirler bend and blading on the pipe diffuser. Close-coupling of these two components, however, can lead to a significantly lower radial extent of the stage, resulting in a decrease of stage weight and engine frontal area. The geometry investigated includes a centrifugal compressor stage with a compact diffusion system, including a pipe diffuser and tandem deswirler whose first blade row is immerged into the pipe diffuser. Stage and component performance of this compact configuration is compared to two different stage configurations with decoupled deswirlers. Performance maps and 1-D pressure build-up data show that the compact stage is able to reach efficiency and pressure build-up of the compared stages which contain the same impeller and same diffuser inlet geometry. The performance of one of the compared stages with significantly higher radial stage extent is even exceeded. However, a loss in surge margin of about 2% has been detected which seems to be the major problem in reducing stage size by close-coupling the deswirl system to the pipe diffuser, since this can have a major effect on the diffuser inlet pressure build-up.

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