Effective Control of Composite Honeycomb Structures on the Tip Leakage Flow in Turbine Cascade

Abstract

Two innovative composite tip structures that combine a honeycomb with a prismoid or spherical bottom have been proposed to actively control the tip leakage flow in a turbine cascade. The mechanisms of inhibiting leakage flow are mainly analyzed from the aspects of detailed flow field, vortex structures, and turbulent kinetic energy dissipation. The influence of geometric parameters like depth and dihedral angle of the prismoid and depth of spherical bottom are discussed. The results show that both composite structures can enhance the vortices generated in cavities and intensify the mixing between honeycomb jets and upper clearance flow, thus achieving better control effect. For a honeycomb-prismoid tip, a 45° dihedral angle performs best, and the control effect is obviously weakened when the depth is greater than 1.5 times that of the honeycomb. A honeycomb-spherical bottom tip reduces the vortex development resistance, which benefited from the smooth transition of the spherical bottom. Its control effect is parabolic with the depth of spherical bottom, and the optimum depth is one-third of the diameter of its corresponding inscribed ball. Compared with a flat tip, a honeycomb tip, honeycomb-prismoid tip, and honeycomb-spherical bottom tip reduce the tip leakage flow by 11.11%, 13.77%, and 15% as well as the loss by 8.17%, 9.4%, and 1.42%.