AN EXPERIMENTAL INVESTIGATION OF A CENTRIFUGAL-COMPRESSOR WITH HUB VANE DIFFUSERS

The present investigation reports results of experimental studies on a centrifugal compressor equipped with hub vane diffusers. The diffuser vane height (h/b) is varied as follows: 0 (vaneless), 0.2, 0.3, 0.4 a nd 1 (vane). The experiments were carried out on a low specific speed centrifugal compressor with a radial tipped impeller with an inducer a t the inlet. The measurements consist of determining performance chara cteristics, measuring static pressures on the hub and shroud and flow traverses with a precalibrated cobra probe at the diffuser exit over o ne passage at five flow coefficients, viz. phi = 0.23 (near surge), 0. 34 (near peak pressure rise), 0.45, 0.60 and 0.75 (near maximum flow). The peak energy coefficient is maximum for the hub vane diffuser with an h/b ratio of 0.2. The hub vane diffusers have a wider operating ra nge than the vane diffuser. At high flow coefficients, the static pres sure rise is substantially low at the throat region of the vane diffus er as the incidence on to the vane leading edge is very high. The mass averaged static pressure coefficient is high in the low-volume range for the hub vane diffuser of h/b = 0.3, but in the high-volume range i t is high for the vaneless diffuser.