Cooling Performance of the Endwall Vertical Hole Considering the Interaction between Cooling Jet and Leading-Edge Horseshoe Vortex

Interaction between the coolant and the secondary flow plays an important role in endwall cooling performance. For the leading-edge region, oncoming main flow inside the boundary layer impinges onto the vane leading edge and turns into the horseshoe vortex. Horseshoe vortex entrains coolant off the surface, thus posing severe challenges to the cooling design there. Based on analyses on the leading-edge vortex formation mechanism, a new kind of endwall film cooling design, vertical hole upstream of the saddle point, is proposed to obtain more uniform film coverage over the vane/endwall junction region. Coolant injected from the vertical hole can pass over the horseshoe vortex and impinge around the stagnation line on the vane leading edge. Uniform film coverage can be obtained around the vane leading edge where coolant clings to the endwall surface due to the span-wise pressure gradient of the stagnation region. Numerical simulations are conducted about the cooling performance of two main kinds of both isotropic and anisotropic hole geometries for the endwall and vane surface. Results come that the anisotropic hole shows significant advantages over the isotropic one because it suppresses the symmetrical kidney vortices thus weakening the mixture with high-temperature gas. Blowing ratio ( M ) effect is analyzed and conclusions are drawn that the cooling performance of the endwall around the leading edge is sensitive to M and adiabatic film cooling effectiveness peaks at about M = 2.0. Better cooling performance over the vane corner region can be obtained when M gets even higher while the effective film coverage area shrinks. Apart from that, the phenomenon of phantom cooling on the upper triangular region of the suction surface can be observed when coolant on the endwall is entrained by the vortex formed at the corner of the leading edge.