A detailed study of the swirling flow in a rectangular volute of a centrifugal compressor is presented. The 3D flow field has been measured by means of a five hole probe at six different cross sections for three different operating points of the compressor.

For high mass flow, the large radial velocity component at the diffuser exit creates a strong swirling flow with a forced vortex type of velocity distribution. The centrifugal force resulting from this motion is balanced by the increase of static pressure from the swirl center to the volute wall. Due to the effect of circumferential curvature a zone of high through flow velocity occurs next to the volute inner wall.

Less swirl is generated for optimum mass flow resulting in smaller pressure gradients over the cross section. Low energy fluid accumulates near the inner wall of the cross section.

For low mass flow, a large region of separated flow is observed and more uniform static pressure has been measured over the cross section.

The effect of the tongue on the flow structure in the first and last cross section is also discussed.

This study is the follow-up of previous studies described in ASME paper 89-GT-183 and 90-GT-49. The results obtained verify the previous studies and provide a better understanding of the flow structure inside internal volutes of rectangular cross section.

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