Analysis of Unsteadinesses in a Vaned Diffuser of Centrifugal Machinery.

Abstract

The aim of this article is to present experimental results obtained on a fan composed of a radial impeller matched with a vaned diffuser. There is no volute downstream to the diffuser. Consequently the diffuser outlet is at free air. The particularity of this machinery is that the diffuser design flow rate corresponds to 80% of the impeller one. Investigations have been made for five different flow rates. Global performances of the machine are evaluated thanks to pressure measurements and averaged velocities obtain with a three holes probe, at nine angular positions at diffuser inlet and outlet just as five radial positions in a middle section of a blade-to-blade passage. In order to better characterize separations observed in previous experimental and numerical studies unsteady pressure measurement campaigns have been carried out. The transducers are located at five positions on the pressure face and four positions on the suction face on diffuser vanes in a blade-to-blade plane. For each position, three transducers are located at three different heights, from hub to shroud. Unsteadinesses revealed by these measurements just as theirs effects on the diffuser performance are analysed.