Aerodynamic and thermal influence of casing coolant on turbine blade tip

Using CFD simulation methods, the effects of rotor front sealing cooling air and casing cooling air on the tip clearance flow field of a typical turbine engine were investigated. The results show that by mixing into the low-temperature boundary layer of the outer ring wall, the rotor front sealing cooling air hinders the intrusion of high-temperature gas from the pressure side into the tip clearance, to decrease the surface heat load by approximately 20% along the chordwise direction of the blade tip. The injection of casing cooling air into the low-temperature boundary layer of the outer ring wall causes local boundary layer separation, leading to the mixing of high-temperature mainstream gas into the boundary layer. At specific positions, the casing jet also suppresses the relatively low-temperature gas into the tip clearance, ultimately resulting in the intrusion of high-temperature gas into the tip clearance and increasing the surface heat load of the blade tip. When both cooling airs are applied simultaneously, their effects within the tip clearance interfere with each other, leading to the intrusion of high-temperature gas into part of the tip clearance and increasing the local surface heat load at the blade tip. The addition of cooling air increases the total pressure loss at the outlet, with the relative loss caused by casing cooling air being the highest at 7.03%. The impact of the outer ring cooling air on the flow within the tip clearance is significant, and the influence of the outer ring cooling air should not be neglected when designing the cooling system for turbine rotors.