Numerical Investigation of Entropy Generation Distributions in a Transonic Compressor

Abstract

Highly irreversible flows can arise from the rotor tip region which cause compressor performance degradation. The understanding of the flow irreversibility and the spatial distribution in the rotor passage may provide hints to retrofit rotor geometries as well as design efficiency-friendly casing treatments. This paper presents a numerical investigation on the spatial distributions of entropy generation through a control volume analysis on a transonic compressor. The typical loss sources can be classified as the viscous shear on solid boundaries, the shockwaves at the leading edge and within the passage, the tip leakage vortex and the turbulence mixing in the rotor wake in the tip region, however, it is hard to distinguish their individual contributions because they always interact with each other. To avoid this difficulty, this paper targets at the spatial distribution of entropy generation since it can tell the local losses quantitatively as the results of local flow structures and their interactions. Tip clearance is used as a controlled parameter for the investigation. By varying the tip clearance over the blade chord, the tip leakage flow is energized and thus examined first, followed by the other changes of inflow structures reacting to the tip clearance variation. The changes in entropy generation distributions are then carefully compared. Based on the results, the dominative contributor on entropy generation and its impact on total loss are identified. Finally, new casing designs with stepped tip gaps that may ameliorate the entropy generation of the tip region are discussed and numerically validated.