Instantaneous Tip Clearance Measurement of a Centrifugal Compressor Impeller Using Capacitive Sensors

Abstract

For centrifugal compressors with high stage pressure ratio, an unshrouded impeller is generally used. The impeller performance deteriorations are caused by the pressure loss due to the vortex of tip leakage flow and its mixing with impeller's main flow. On the other hand, the amount of tip clearance is varied by the change of the compressor operating conditions. Therefore, in order to ensure the compressor performance, we need to know precisely how much tip clearance exists at the actual centrifugal compressor operating condition.

From these back grounds, authors developed a tip clearance measurement method with capacitive gap sensors. Tip clearance measurements were conducted for several rotational speeds and flow rates to reveal the effect of the compressor operating conditions on the impeller tip clearance. Finally, the transient tip clearance measurement during the surge was also conducted to evaluate the unsteady rotor behavior within the surge cycle.