Effect of Impeller Extended Shrouds on Centrifugal Compressor Performance as a Function of Specific Speed

Centrifugal compressors for gas compression applications usually employ low-pressure ratio, backward-swept impellers with vaneless diffusers. To increase the compressor flow range and speed, impeller blades are occasionally trimmed, resulting in an extended shroud configuration. The effect of extended front and back impeller shrouds on the performance of centrifugal compressors with vaneless diffusers, and the variation of this effect as a function of specific speed, is thus of concern and is the subject of this paper. An investigation was carried out on two backward-swept shrouded impellers of common blade tip and inducer hub diameters, but different inducer tip diameters (corresponding to low and high specific speeds), with the front and back shrouds extending 20 percent above the blade’s outside diameter.