It is well established that the flow between the impeller tip and the diffuser throat is very influential on the performance and flow range of a centrifugal compressor stage. Detailed measurements of a parametric selection of pipe diffusers have been carried out within this region using a combination of conventional pneumatic and high speed pressure transducers.

Four pipe diffuser designs were examined. The first and datum consisted of 31 pipes, representing a design with minimal meridional step (or sidewall expansion) between impeller tip and diffuser throat. The step size was increased to 1.3 for the second design resulting in a 22 pipe diffuser. A further increase of sidewall expansion ratio to 1.7 with 13 pipes was completed following favourable results from the 22 pipe tests. The final diffuser was of hybrid design consisting of an oval rather than circular throat cross-section. This departure allowed for a 13 pipe diffuser without sidewall expansion.

Flow range and performance comparisons are made in addition to detailed measurements which clearly show that strong planar pulsations dominate the distorted diffuser throat flow. Larger pressure pulsations are quantified for the designs with low numbers of pipes.

This content is only available via PDF.