Stall Margin Improvement in a Transonic Compressor With a Casing Treatment: Flow Mechanism

Abstract A compressor casing treatment with circumferential casing grooves (CCGs) is studied in detail. The primary objective of the current paper is to unearth the main driving fluid mechanism that changes the stall margin in a transonic compressor with CCGs. Large eddy simulation (LES) is applied to calculate the transonic compressor flow fields with and without CCGs. The present investigation shows that CCGs reduce the mass flow through the tip gap by about 16% near the stall condition. Calculated flow fields show that most of this reduction of tip leakage flow occurs near the CCGs. Reinjected flow from the CCGs pushes the tip leakage flow radially inward below the casing and changes how the tip leakage flow collides with the incoming main passage flow. However, a detailed examination of the calculated flow in the tip region shows that the reinjected flow does not contribute to the reduction of the overall blockage generation. The primary driver for reducing blockage generation with CCGs is the reduction of overall mass flowrate through the tip gap. In the present investigation, measurements show a very small decrease in efficiency with CCGs at the design flow condition, although the difference in efficiency is within the measurement uncertainty. Results from the LES simulation at the design condition with CCGs show that the tip leakage vortex (TLV) is pulled toward the blade suction side and double leakage flow is eliminated. The result is that the simulated efficiencies with and without CCGs are almost the same.