3-DIMENSIONAL FLOW MEASUREMENTS IN CONICAL AND STRAIGHT WALL CENTRIFUGAL-COMPRESSOR VANELESS DIFFUSERS

In the current work three-dimensional pow measurements in two types of centrifugal compressor vaneless diffuser were obtained using hot wire anemometry. The first diffuser was conical, designed to give a consta nt flow area, while the second straight wall diffuser had a constant a xial width. Measurements of mean velocity, pow angle and velocity fluc tuation level were obtained on eight cross-sectional planes in each di ffuser. The jet-wake pow pattern and the impeller blade wakes are clea rly visible at the inlet of both diffusers. Mixing out of the blade wa ke proceeds more rapidly in the straight diffuser. The hub boundary la yer also develops more rapidly in this diffuser because of the adverse pressure gradient. Velocity fluctuation level measurements highlight the mixing regions within the diffusers. Recommendations are also made for the design of vaned diffusers. A larger vaneless space would be r equired with a straight wall diffuser and significant twisting of the vane would be required for both diffuser geometries if significant inc idence losses are to be avoided.