MEASUREMENTS OF FLOW IN CENTRIFUGAL COMPRESSOR DIFFUSERS USING A LASER VELOCIMETER.

Measurements of the velocity field in centrifugal compressor diffusers using a laser-two-focus velocimeter are presented. The exit flow distribution of high specific speed centrifugal compressor impellers is extremely distorted. The flow in vaneless diffusers is influenced by the distorted impeller exit flow. In vaneless diffuser, the flow distortion in the peripheral direction, such as rotating jet-wake region behind each impeller channel, was decreased smoothly. The flow distortion in the axial direction, however, was intensified and flow separation occurred near the shroud wall. On the other hand, no separation was observed in the diffuser with small height guide vanes on the shroud side wall. It was clearly shown that these guide vanes on the shroud side wall made the distorted flow uniform effectively.