Model Validation for an Active Magnetic Bearing Based Compressor Surge Control Test Rig

In this paper, we present experimental test data for the validation of a recently introduced mathematical model for centrifugal compression systems with variable impeller axial clearances. Employing the active magnetic bearings (AMBs) of a compressor built for the experimental study of surge, the axial clearance between the impeller and the static shroud is servo controlled, and the measured variations in the compressor output flow are compared with the mathematical model. The steady state and the dynamic responses of the compression system induced by varying the impeller tip clearance are measured and compared with the theoretical predictions, and the states of the compression system in surge condition are collected and analyzed. Parameters in the compression system model, such as the Greitzer parameter $B$ and Helmholtz frequency $ωH$ are experimentally identified. Also, the servo dynamics of the magnetic bearing that controls the axial impeller position is determined experimentally. To further validate the mathematical model and the feasibility of using the impeller tip clearance for controlling surge, we present a design example for an active surge controller based on the derived model, and simulate the response of the compression system. This design exercise also helps us understand the possible challenges that one could face in the design and implementation of a successful surge controller.