Effects of Swirl Distortion on a Centrifugal Compressor at Off-Design Operating Conditions

Estimating the performance effects of different installations of various compression system rotors is of paramount importance. This effort utilizes the Single Stage Centrifugal Compressor (SSCC) at Purdue University with a modular radial-to-axial inlet to generate offset inlet swirl pairs with minimal total pressure distortion. This is a centrifugal compressor with an impeller designed for inlet prewhirl. The effects of operating at high incidence while ingesting swirl distortions are analyzed. At the design speed, the effects on stage total pressure ratio and mass flow rate were comparable with expected performance effects of swirl, with an increase in both parameters caused by counterswirl. At low speed and higher incidence, the opposite trend was true. Coswirl configurations were superior at high and low speeds for efficiency due to the reduced incidence. Stage total temperature rise had a linear dependence on area-averaged incidence. The axial velocity distribution at the aerodynamic interface plane is analyzed along with the circumferential swirl and total pressure profiles. Total pressure distortion had little to no effect on incidence. A method of reconstructing the circumferential average incidence at the inlet of the compressor using rotational frequency, radius, blade metal angle, and circumferentially averaged axial velocity and swirl angle is presented.