LES of rotating film-cooling performance in a 1-1/2 turbine stage

Nabeel Al-Zurfi ^a,b,*, Adel Nasser ^b

a. Mechanical Engineering Department, Faculty of Engineering, University of Kufa, Najaf, Iraq
         b. School of Mechanical, Aerospace and Civil Engineering, The University of Manchester, Manchester, M13 9PL, UK

Abstract: The large eddy simulation method was employed to investigate the film-cooling performance in a low-speed rotor blade of a 1-1/2 turbine stage. The rotor blade height and axial chord length were 99 mm and 124.3 mm, respectively. Two rows of film holes were placed on the rotor blade surface, one each on the pressure and suction surfaces. Each row had three cylindrical film holes with a diameter of 4 mm and a tangential injection angle of 28 on the pressure side and 36 on the suction side. The Reynolds number was fixed at Re=1.92×105 and the coolant-to-mainstream density ratio (DR) was about 2.0. Simulations were carried out for three different rotating speeds of 1800, 2100, and 2400 rpm with the blowing ratio (BR) varying from 0.3 to 3.0. The commercial CFD code STAR-CCM+ was used to run the simulations using the WALE subgrid-scale model for modelling the turbulence. The results show that on the pressure side, the film coverage and film-cooling effectiveness decrease with increasing rotation number (Ro) and increase with increasing blowing ratio (BR). A higher Ro and lower BR result in a stronger film deflection. The film injection with higher BR produces better film attachment. The film deflects centrifugally where the deflection becomes greater with increasing Ro. On the suction side, the film coverage and film-cooling effectiveness increase with increasing either Ro or BR and a centripetal deflection of the film is observed. The deflection of the film path could be amplified by either increasing the Ro at a constant BR or decreasing the BR at a constant Ro. Increasing the rotation weakens the film deflection towards the hub on the suction surface. Overall, it was found that both rotation number and blowing ratio play significant roles in determining the film-cooling effectiveness distributions of the rotor blade surface.

Keywords:  Rotor blade; Large eddy simulation; Film-cooling effectiveness; Turbulence; Rotation; Subgrid-scale