Investigation on heat transfer characteristics of ultra-large grooved deep blade tip under the influence of multi-factor coupled

This study investigates the impact of various geometric parameters on the heat transfer characteristics of a turbine rotor blade's tip shoulder surface, using temperature-sensitive paint (TSP) technology. The parameters include four types of outer ring cooling air, six groove depths, and five clearance sizes. Combined with numerical simulation, the influence mechanism was explored to guide the optimal design of improving the heat transfer and flow behavior of turbine blade tip. It is found that the circumferential outer ring cooling air alone reduces the heat load of blade tip in the range of 0 similar to 50 % of blade chord length, and the combination of circumferential and axial outer ring cooling air reduces the heat load in the range of 50 %-100 % of blade chord length. Compared to the flat tip structure without outer ring cooling air and a clearance height of 1.5 % of the blade height, the average Nusselt number (Nu) on the blade tip shoulder surface decreases by 26.8 % with circumferential outer ring cooling air and by 28 % with combined circumferential and axial outer ring cooling air. The investigation emphasizes the advantages of utilizing ultra-large grooves over conventional-scale grooves and flat tip structures. Ultra-large grooves induce substantial recirculation vortices within the grooves, which help mitigate leakage flow velocity at the blade tip, thereby reducing erosive effects and heat load. Compared to conventional-scale grooves and flat tip structures, ultra-large grooves can achieve maximum reductions of 37.3 % and 33.8 %, respectively. Furthermore, ultra-large grooves exhibit minimal changes in dimensionless velocity within the clearance, thereby reducing the impact of variations in clearance height on thermal loads at the suction side of blade tip and tip clearance. Notably, the maximum standard deviation of the suction side tip Nu for ultra-large grooves is reduced by approximately 79.93 % compared to conventional-scale grooves, effectively minimizing fluctuations along the chord direction.