The cooling performance of three-row compound angle holes on the suction surface of a rotating turbine blade

Experiments were carried out to study the effects of compound angle,hole arrangement,and blowing ratio on the film cooling performance of multiple rows of holes on the suction surface of a turbine blade.The turbine worked at rotational speed of 600 rpm corresponding to the rotational Reynolds number of 5.36
105.Three rows of cylindrical holes arranged in line or in stagger were drilled on the rotor blade suction surface at the streamwise location of 12.4%,17.8%,and 23.2%,respectively.Three compound angles,with the same streamwise angle of 45but different lateral deflection angles of 45,0,and45,were studied.The film cooling effectiveness was obtained using pressure sensitive paint(PSP)technique with average blowing ratios varied from 0.5 to 2.0.The results showed that the application of compound angle changes the jet direction in the near-hole region and makes the film spread laterally.Compared with the film cooling without compound angle,using positive and negative compound angle can improve overall average film cooling effectiveness by about 20%and 25%,respectively.The effects of the secondary flow also can be weakened.A stagger film trajectory arrangement can achieve more uniform film coverage with higher overall film cooling effectiveness.The film trajectory arrangement of a positive compound angle injection is determined by the combined effect of hole arrangement and blowing ratio.While,the film trajectory arrangement of a negative compound angle injection is almost the same as the hole arrangement and nearly does not change with the blowing ratio.

Flow-Field Analysis of Anti-Kidney Vortex Film Cooling

Film cooling is an important measure to enable an increase of the inlet temperature of a gas turbine and, thereby, to improve its overall efficiency. The coolant is ejected through spanwise rows of holes in the blades or endwalls to build up a film shielding the material. The holes often are inclined in the downstream direction and give rise to a kidney vortex. This is a counter-rotating vortex pair, with an upward flow direction between the two vortices, which tends to lift off the surface and to locally feed hot air towards the blade outside the pair. Reversing the rotational sense of the vortices reverses these two drawbacks into advantages. In the considered case, an anti-kidney vortex is generated using two subsequent rows of holes both inclined downstream and yawed spanwise with alternating angles. In a previous study, we performed large-eddy simulations (which focused on the fully turbulent boundary layer) of this anti-kidney vortex film-cooling and compared them to a corresponding physical experiment. The present work analyzes the simulated flow field in detail, beginning in the plenum (inside the blade or endwall) through the holes up to the mixture with the hot boundary layer. To identify the vortical structures found in the mean flow and in the instantaneous flow, we mostly use the λ 2 criterion and the line integral convolution (LIC) technique indicating sectional streamlines. The flow regions (coolant plenum, holes, and boundary layer) are studied subsequently and linked to each other. To track the anti-kidney vortex throughout the boundary layer, we propose two criteria which are based on vorticity and on LIC results. This enables us to associate the jet vortices with the cooling effectiveness at the wall, which is the key feature of film cooling.