Experimental Measurement of Endwall Aerothermal Performance With Various Slashface Configurations in a Transient Test Facility

Abstract

Abstract. To accommodate installation flexibility, metal thermal expansion, and component vibration, a clearance, referred to as a slashface gap, always presents between adjacent blade endwalls. Sufficient coolant is fed into this gap to prevent high-temperature gas ingestion, thereby avoiding the overheating risks of blade root and wheel component. Nevertheless, the phenomenon of gas ingestion into the slashface upstream and leakage egestion away from slashface downstream is common due to endwall axial static pressure gradients. This may result in significant differences in metal thermal expansion during the actual operation of gas turbines, thereby developing downsized gaps. Aiming to present insights into leakage flow physics and associated endwall aerothermal performance with nonuniform slashface, various narrower upstream slashface geometries were designed, and endwall heat transfer coefficient (h) and film cooling effectiveness (η) were measured in a novel transient test facility. In addition, to further help understand near-endwall flow behavior and flow patterns at the slashface interface, the supportive numerical predictions were also performed at the same flow conditions. Results demonstrated that there are four typical flow behavior parts from slashface leading edge (LE) to trailing edge (TE), identified as gas ingestion region, gas egestion region, interaction region and leakage egestion region. The narrower upstream slashface can limit the axial distance of fully gas-dominated region to 0.45 Cx and 0.31 Cx, yet will induce greater radial ingestion depth at slashface leading edge. With decreasing upstream slashface width, endwall low-heat-transfer region scale significantly enlarges, and the peak in heat transfer coefficient decreases by approximately 11.5% and 21.4%. Simultaneously, leakage from the narrower upstream slashface also improves endwall film cooling performance, particularly in the triangular region, and film cooling effectiveness increases by approximately 35.3% at MFRslashface = 0.5% and 29.7% at MFRslashface = 0.75%. Higher leakage flowrate is beneficial for limiting the axial distance of fully gas-dominated region, by providing higher-momentum leakage to overcome endwall static pressure barrier. Nevertheless, it is proved powerless against greater radial ingestion introduced by the narrower upstream slashface, and leads to partial leakage being dissipated ineffectively. This suggests that the response to prevent gas ingestion cannot simply rely on increasing pure flowrate, and also necessitate additional strategies during the actual operation of gas turbines. Otherwise, the blade root and wheel component are exposed to significant overheating risks.