On the Effects of Tip Clearance and Operating Condition on the Flow Structures Within an Axial Turbomachine Rotor Passage

Abstract

Effects of tip clearance size and flowrate on the flow around the tip of an axial turbomachine rotor are studied experimentally. Visualizations and stereo-particle image velocimetry (PIV) measurements in a refractive index-matched facility compare the performance, leakage velocity, and the trajectory, growth rate, and strength of the tip leakage vortex (TLV) for gaps of 0.49% and 2.3% of the blade chord, and two flowrates. Enlarging the tip clearance delays the TLV breakup in the aft part of the rotor passage at high flowrates but causes earlier breakup under pre-stall conditions. It also reduces the entrainment of endwall boundary layer vorticity from the separation point where the leakage and passage flows meet. Reducing the flowrate or tip gap shifts the location of the TLV detachment from the blade suction side (SS) upstream to points where the leakage velocity is 70–80% of the tip speed. Once detached, the growth rates of the total shed circulation are similar for all cases, i.e., varying the gap or flowrate mostly shifts the detachment point. The TLV migration away from the SS decreases with an increasing gap but not with the flowrate. Two mechanisms dominate this migration: initially, the leakage jet pushes the TLV away from the blade at 50% of the leakage velocity. Further downstream, the TLV is driven by its image on the other side of the endwall. Differences in migration rate are caused by the smaller distance between the TLV and its image for the narrow gap, and the increase in initial TLV strength with decreasing flowrate and gap.

Numerical investigation the shape of groove on tip leakage vortex suppression of a NACA0009 hydrofoil

“…Li et al [5] experimentally investigated the effect of tip clearance size and flow rate on the flow rate around the tip of an axial turbomachine rotor and found that the generation position and movement trajectory of the clearance vortex system change depending on the clearance width, which in turn affects the clearance turbulence losses. Through numerical simulation, Wu et al [6] found that the C-shaped groove can effectively reduce the flow rate of tip leakage flow, thereby inhibiting the generation of high-speed leakage flow.…”

Dynamic Analysis of Tip Leakage Phenomena in Axial Flow Pumps Using a Square-Cavity Jet Model

“…Currently, the most advanced research on the Tip Leakage Vortex (TLV) phenomenon is in the field of compressors. In recent years, researchers have analyzed experimental data from axial compressors [24][25][26], employing a cavity model with longitudinal slots to simulate the interaction between the TLF mainstream and jet, as well as the rolling up of TLV [27], simplifying the complex internal flow path of the impeller. Direct numerical simulation (DNS) studies on the leakage model of rotors [28] have shown that simple model flows, when simulated with high precision, can adequately depict the development and evolution of leakage vortices.…”