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

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 361 on the suction side.The Reynolds number was fixed at Re=1.92×10^(5)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 filmcooling 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.

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

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 Z 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.