A numerical study of anti-vortex film-cooling holes designs in a 1-1/2 turbine stage using LES

Nabeel Al-Zurfi ^a,b,*, Ali Turan ^c, Adel Nasser ^c, Ahmed Alhusseny ^a,b

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

Abstract: The primary focus of the present study is to investigate the impact of anti-vortex holes design on the film-cooling performance in a film-cooled rotor blade model using the large eddy simulation method (LES). One row of the film holes was positioned on the pressure surface of the rotor blade. This row had three cylindrical holes (the main hole in the present study) with a diameter (D) of 4 mm and a tangential injection angle of 28 deg. Each main hole supplemented with the addition of two symmetrical side holes (anti-vortex holes), which branch out from the same main hole. Three positions for the anti-vortex side holes were considered; namely: upstream to the outlet of the main hole; in line with the main hole; and downstream of the main hole. The Reynolds number was fixed at Re=1.92×105 and the speed of the rotor blade was taken to be 1800 rpm. The blowing ratio varied from 1.0 to 5.0 and the density ratio of coolant to mainstream was 2.0. Compared to the base hole, the film cooling performance of the all anti-vortex cases showed obvious improvement at all blowing ratios. The middle stream side holes and downstream side holes each demonstrated good film cooling performance at all blowing ratios, while the upstream side holes perform well only at a lower blowing ratio. The presence of side holes can restrain the CRVP (counter rotating vortex pairs) intensity of the main hole and reduce the coolant lift-off, improving the film coverage and film cooling effectiveness. The downstream side holes can perform better in reducing the CRVP intensity.

Keywords:  Rotor blade; Large eddy simulation; Film-cooling effectiveness; Turbulence; Rotation; Anti-vortex hole