Effect of non-axisymmetric endwall contouring and swirling inlet flow on film cooling performance of turbine endwall

Abstract

Non-axisymmetric endwall contouring (NEC) is one of the verified approaches to suppress secondary flows and improve aerodynamic performance. However, the design of NEC brings significant challenges to the design of endwall cooling structures. Herein, a pressure-sensitive paint experimental approach was used to obtain the film cooling effectiveness of the NEC endwall with a purge slot in this study. Three NEC types were adopted: NEC (COS), NEC (SIN), and NEC (−SIN). In addition, lean premixed combustion technology was used to achieve lower levels of NOx emissions. The turbine inlet was characterized by high turbulence and strong swirling. The effects of different swirling angles (±10, ±20, and ±30°) and densities were further explored. Due to the NEC profiling changing the secondary flow near the endwall area, coolant from the purge slot was better attached to the slot exit position, leading to a significant increase in the size of the high-cooling-efficiency region. With the mass flow ratio (MFR) varying from 0.5 to 2%, the film cooling effectiveness of the flat and NEC endwalls had similar variation characteristics. When the MFR = 0.5%, the area-averaged cooling efficiencies of the NEC (COS), NEC (SIN), and NEC (−SIN) endwalls could be improved by 2, 12.5, and 20%, respectively. Positive swirling and smaller negative swirling inflow could improve the film cooling effectiveness inside the channel. The case of SA = +20° had the best improvement, where the film cooling effectiveness of the NEC (COS), NEC (SIN), and NEC (−SIN) endwalls could reach up to 29, 35, 36, and 34%, respectively. The NEC (−SIN) endwall was less sensitive to the effects of the swirling inflow.