Numerical Investigation Of The Leakage Flow In Highly-loaded Turbine Cascade With Honeycomb Tip

With the development demande of morden aro-engine turbine characterized by high thrust-weight ratio and low specific fuel consumption, it is a development trend to increase aerodynamic load and reduce turbine series in the design of high-performance turbine. As the turbine is developed towards highly-loaded direction, tip leakage flow and the caused loss have more and more significant influence on the turbine performance. Thus, the further research on the leakage flow and its abatenebt strategies has significant meaning in improving the aerodynamic property of the gas turbine.Honeycomb seal having the abradable property is extensively used in seal the radial tip clearance in turbomachinery because of its excellent seal behavior. In this paper, a novel strategy of using honeycomb seal which is applied on the rotor tip to inhibit the tip leakage flow has been proposed, and the physics models of highly-loaded turbine cascades with and without tip honeycomb seal have been established. The influence mechanism of tip honeycomb seal on the leakage flow and the generation mechanism of leakage loss has been studed compared with the general flat cascade by numerial calculation method. The influence of various relative gap heights and different incidence angles on tip leakage flow is also been investigated. The discussions of the effect of the honeycomb tip on decreasing leakage flow and improving the efficiency provide the according for control methods of tip leakage flow.Through the comparative investigation between honeycomb tip and flat tip turbine cascades, the results indicate that the honeycomb tip has positive effect on inhibiting the tip leakage flow. The fluid in the tip gap flows into the honeycomb chambers to form vortex, which causes the energy dissipation. In addition, the jet flows caused by the recoil of the flow in the honeycomb chambers increase the leakage flow resistance and reduce flow speed, which has the same process of “pneumatic fence”. In contrast to the conventional flat turbine cascade, the honeycomb tip cascade with the same gap height of 1% blade span has a leakage massflow decrease about 10%, and a circumferential velocity decrease nearly 20%. The tip leakage vortex is undermined in honeycomb tip cascade due to the decrease of the leakage flow and the circumferential velocity of the clearance flow. As a result, the loss caused by the mixing process among the leakage flow, passge mainstream and the wake is reduced to a smaller extent nearly 4% compared to the flat tip cascade. What is more, the study of the influence of various relative gap heights and different incidence angles on tip leakage flow show that the honeycomb tip can supperss the tip leakage flow effectively in all conditions investigated. With the increase of the gap height, the leakage flow is increased linearly. Considering the property of abradable seal in honeycomb tip cascadethe, a smaller height of tip can be got, resulting in a better sealing effect. Different incidence angles bring the change of the tip leakage flow field structure and the complex vortex structures.