Betriebsverhalten und Aerodynamik einer kompakten Radialverdichterstufe mit Pipe-Diffusor

This thesis represents an experimental investigation of a compact aero engine centrifugal compressor stage with pipe-diffuser and tandem deswirler in which the vanes of the first deswirl row are immerged into the diffuser channel. This geometrical arrangement eliminates a vaneless space between diffuser and deswirler, which is present in current conventional centrifugal compressor stages and can result into much lower outer stage diameters. In addition to the nominal centered alignment of the first deswirl row vanes within the diffuser channel, a variation of the circumferential positioning of the deswirler towards diffuser suction and pressure side was conducted. Furthermore, a bleed extraction between impeller and diffuser was varied. For a comparison of the compact compressor stage to conventional stage designs, additionally three compressor stages with vaneless space between diffuser and deswirler were experimentally investigated, whereas each stage contained a different deswirl system. Impeller and diffuser inlet geometry of all four stages were the same.The study demonstrates that the compact centrifugal compressor stage reaches similar performance values in terms of pressure build-up and efficiency as the stages with decoupled deswirlers. In comparison to a conventional stage with simple one row prismatic deswirl vanes, the compact stage even shows a significant increase in performance. However, the compact stage looses surge margin compared to all three reference stages. Also, a shift of the characteristics of the different stage components was detected. The impeller of the compact stage shows a slightly higher pressure build-up and slightly lower work input. Furthermore, the diffuser inlet shows a significant increase in pressure build-up which is linked to the loss in surge margin. Within the diffuser channel the pressure build-up is lower due to the lower dynamic head at the channel inlet. This results from the increased diffusion at the diffuser inlet. The three-dimensionally designed deswirlers of the compact stage and of two reference stages are showing equal characteristics, whereas the pressure build-up of the deswirler of the last reference stage with prismatic vanes is significantly decreased and the total pressure loss increased.With a total-to-static stage balancing, a variation of the circumferential positioning of the deswirler to the diffuser of the compact compressor stage shows very small changes in pressure build-up and efficiency. However, the surge margin increases from suction to pressure sided positioning of the deswirler relative to the diffuser. With a total-to-total balancing of the stage, the pressure sided positioning of the deswirler relative to the diffuser shows the smallest losses but also the highest Mach-numbers at the stage exit