The Effect of Hub Leakage Flow on Two High Speed Axial Flow Compressor Rotors

The effect of hub leakage flow on the performance of two high speed transonic rotors is investigated through numerical simulations and experiments. The leakage flow emanates from a small gap between the stationary and rotating parts of the hub flow path upstream of the rotor. Results of both the experiments and CFD simulations show that the introduction of a small leakage flow (0–25% of the main passage flow) can reduce the total pressure rise produced by the rotor across the entire span and generate a significant deficit in the total pressure profile near the hub. Numerical simulations done with a sinusoidal distribution of the leakage flow across the rotor pitch show that this deficit is present even when there is zero net leakage. Particle tracer studies of CFD simulations show that this deficit is due to the flow blockage produced by the radial migration of the low momentum leakage fluid. The performance degradation trends predicted by the simulations are qualitatively confirmed in the experimental investigation.