Numerical Simulation of Active Control on Tip Leakage Flow in Axial Turbine

In an effort to reduce the blade tip clearance leakage in turbine designs, this article aims to numerically investigate the effects of active jet-flow injected from the blade tip platform upon the blade tip clearance flow. A CFD code integrated with dense-correction-based 3D Reynolds-averaged Navier-Stokes equations together with the well-proven Reynolds stress model (RSM) is adopted. The variation of specific heat is taken into consideration. The effects of jet-flow on the tip clearance flow are simulated at two tip clearance heights, each with five differently located injection holes and three jet-flow mass rates. In this way, the article elucidates the mechanism of active injection control, analyzes the topological tip clearance flow structure, and, finally, calculates the turbine efficiency considering the effects of the jet-flow. The results show that the mass rate of the third jet-flow turn to be the optimum in maximizing the turbine efficiency. The jet-flows through combined holes could increase the efficiency by 0.35% with loose tip clearance, and by 0.3% with tight tip clearance. The number of saddle points is equal to that of nodes near the injection hole, which satisfies the singularity point distribution law.