AN EXPERIMENTAL STUDY OF ANNULAR DIFFUSER PERFORMANCE

The work described in this paper is concerned mainly with an experimental
investigation of subsonic turbulent flows through annular diffusers having
divergence angles of 17.5 and 9 degrees for the casing and hub, respectively,
with an area ratio of 2.1. The performance of the tested diffuser was measured
for a variety of throat dimensionless velocity (1) using different strut
geometries. Two kinds of struts with airfoil and cylindrical cross-sections
were installed separately at different locations inside the tested diffuser. The
results indicated that, the magnitude of the dimensionless velocity (h) at the
throat perimeter is dependent upon the strut cross-section and its location. The
performance of the tested diffuser is improved when cylindrical struts with
suitable diameters are set at an appropriate position in the diffuser. Increasing
the blockage due to the presence of struts was found to be substantially
increases the tendency of separation. The total loss coefficient due to non￾uniformity of flow at the diffuser entrance was found to be significantly
greater on the casing than that on the hub. It appeared also that, a better
performance was achieved with the cylindrical struts due to the increase in
turbulent mixing in the wake region.