Influence of non-uniformities on evaluation of cooling effectiveness of turbine blades

As compared with the cooling flow in the stator, the flowfield of the cooling injected flow in the rotor is more complicated due to the situation and operation condition of the rotor blades. Several factors may effect the cooling flowfield such as the rotation of the blades, the unsteady interaction between the rotor and stator, the stator wake and cooling flow injected from the trailing edge of the stator, the secondary flow in the path flow of the upstream stator and the shock wave in the stator. Numerous studies have focused on the influence of the unsteady wake of the upstream stator and the effect of secondary flow on an isolated stator or rotor is considered in most investigations. In order to investigate the influence of the upstream passage vortex and wake on the cooling effectiveness of the turbine blade separately, the film cooling of moving turbine blades, with preceding delta wing or cylindrical rod, is studied under different blowing ratio by three-dimensional numerical simulation, and the influence of the passage vortex strength and position on the film cooling effectiveness is compared with that of the upstream wake. Results show the passage vortex has large influence on the flowfield and cooling effectiveness of the turbine blade, and its influence range is from the hub to the shroud and depends on the size of passage vortex. The cooling effectiveness on turbine blades, especially near the hub of the pressure surface, decreases with increasing passage vortex strength. The distribution of the cooling effectiveness on the pressure surface is dominated by the passage vortex strength and the cooling effectiveness on the suction surface is sensitive to the blowing ratio. The influence of the passage vortex on the cooling effectiveness is much larger than that of the upstream stator wake. The influence of the upstream wake on the cooling effectiveness changes along the main stream direction, while that of the passage vortex displays along the span wise direction.