Experimental Study on Turbine Vane Endwall Film Cooling of Slot and Discrete Film-holes

The improvement of turbine entry temperature (TET) has brought great challenges to the design of the cooling system, especially for turbine vane endwall, which is affected by strong secondary flow in the passage, and the flow has complex 3D characteristics. Under the condition of limited supply of coolant, the endwall near leading and pressure surface of the turbine vane cannot be covered by coolant effectively, and thus a refinement of cooling pattern is essential to avoid cooling failure. In this paper, a slot is set up upstream of the endwall, and four patterns of film-hole arrangements (axially arranged circular holes, contour arranged circular holes, axial arranged fan-shaped holes, and contour-arranged circular holes with compound angles) on the endwall inside the cascade are designed. Pressure sensitive paint (PSP) is used to obtain cooling effectiveness of 2% and 4% mass flow rations (MFRs) under the following three conditions: (a) only slot injection; (b) only discrete film cooling; (c) combination of slot and discrete film cooling. Further, the modified superposition formula of cooling effectiveness of slot and discrete film-holes is proposed. The results show that with the increase of MFR, the influence of the horseshoe vortex and the passage vortex is reduced for slot cooling, and the cooling effectiveness on the endwall is also improved so that the transverse average film cooling effectiveness is still more than 0.2 at the position of 1.2Cax. The contour arrangement patterns can effectively improve the cooling effectiveness on the endwall near pressure surface of the vane, and also improve the transverse film cooling effectiveness along the axial direction to a certain extent. The fan-shaped hole reduces the momentum of coolant as well as inhibits the lifting-off effect of the kidney vortex, and its ability to improve cooling effectiveness is more obvious at higher MFR. The presence of compound angles makes the direction of coolant outflow closer to the direction of the mainstream, which is conducive to improving the coverage length of coolant downstream of the hole, but has little influence on improving the average transverse cooling effectiveness. After the combination of slot and discrete film-holes, most of the coolant flows out through the slot, but the patterns of film-hole arrangements effect film coverage on the endwall significantly. The modified cooling superposition formula takes into account the effect of MFR. Compared with the superposition method of Sellers, the accuracy of the modified comprehensive cooling effectiveness prediction is greatly improved, especially downstream of the endwall.