Numerical simulation of film cooling effectiveness in a rotating blade at high blowing ratios

Abstract

The film-cooling performance in a low-speed rotor blade of a 1-1/2 turbine stage has been examined using LES approach. Two rows of film holes were positioned on the rotor blade surface, one on the pressure surface and the other one the suction surface, with axial locations of 24.2% and 22.6% of the chord length, respectively. Each row has three cylindrical film-cooling holes with a diameter (D) of 4 mm and a tangential injection angle of 28o on the pressure side and 36o on the suction side. The Reynolds number, based on the mainstream velocity of the turbine outlet and axial length of the turbine, was fixed at Re=1.92×105, the coolant-to-mainstream density ratio (DR) was about 2.0, and the speed of the rotor blade was taken to be 1800 rpm. Several blowing ratios (BR) in the range of 1.0–5.0 were investigated. The effects of blowing ratio, rotation, and curved surfaces were analysed to investigate the effects of the stator–rotor interaction on the film-cooling characteristics. The commercial CFD code STAR-CCM+ was used to run the simulations using the WALE subgrid-scale model for modelling the turbulence. The solutions were obtained by solving the incompressible, 3D Navier–Stokes equations under the rotating coordinates system with the energy equation, and the pressure–velocity coupling was achieved by using the well-known SIMPLE algorithm. The results show that on the pressure side, the film coverage and film-cooling effectiveness increase with increasing BR. A lower BR results in stronger film deflection. The film injection with higher BR produces better film attachment. The film deflects centripetally due to the effect of rotation. On the suction side, the trend of film coverage and film-cooling effectiveness is parabola as the blowing ratio rising and a centripetal deflection of the film is observed. The deflection of the film path could be amplified by decreasing the BR.