| With the continuous improvement of the gas turbine performance,the inlet temperature and pressure drop ratio of the turbine rotor blades are getting higher and higher.The cooling design of the turbine rotor blade has drawn more and more attentions due to the harsh working environment.The increase of the the turbine inlet temperature and pressure drop ratio results in the higher heat loading and stronger secondary flows such as the tip leakage flow,the horseshoe vortex,and the passage vortex,which further increase the difficulty of cooling the blade suction/pressure surface,the blade tip and the blade platform of the high-pressure turbine.The cooling configurations of the turbine blade including the suction/pressure surface,tip and platform zones need to be improved or redesigned to enhance the cooling effectiveness.The increase of the film cooling effectiveness is an effective way to increase the overall cooling effectiveness of the turbine rotor blade.The effect of vertical cross-flow on the film cooling effectiveness of the diffusion slot hole was experimentally investigated on a flat plate model.Meanwhile,the film cooling effectiveness of different slot-based diffusion hole were compared,aiming at proposing a novel slot-based diffusion hole to improve the film cooling effectiveness under the effect of vertical cross-flow.When the vertical cross-flow exists,an asymmetrical anti-kidney vortex structure appears downstream of the film hole,and the cooling effectiveness of the film hole is lower than that fed by plenum.When the blowing ratio is greater than or equal to 1.5,the reduction of the area-averaged film cooling effectiveness exceeds 22%.At the medium blowing ratio,the film cooling effectiveness of the diffusion slot hole with lateral inclination angle is higher than that of the normal diffusion slot hole.This is due to the formation of a pair of vortexes with the same strength and the same rotation direction at the downstream of the lateral inclined diffusion slot hole,which increases the attachment capability of coolant injection.The film cooling effectiveness of the diffusion slot hole and fan-shaped hole on the rotor blade surface was also compared experimentally.In addition,the effects of the stream-wise location of film hole and the density ratio of the coolant to the mainstream on the film cooling effectiveness of the pressure surface were also studied.The film cooling effectiveness of diffusion slot hole is significantly higher than that of the fan-shaped hole on the pressure surface.When the film holes are close to the leading edge,the diffusion slot hole has the most obvious improvement in film cooling effectiveness,and the area-averaged film cooling effectiveness can be increased by 0.2.The farther the film holes are away from the leading edge,the higher the film cooling effectiveness is.Compared with the fan-shaped hole,the film cooling effectiveness of the diffusion slot hole is less sensitive to the film hole stream-wise location,resulting from the better attachment capability of the coolant discharged from the diffusion slot hole.However,the attachment capability of the coolant discharged from the diffusion slot hole is weaker than that of the fan-shaped hole on the suction surface,which leads to the cooling effectiveness of the fan-shaped hole is higher than that of the diffusion slot hole.The effects of the film hole position,the blade tip clearance,the blowing ratio,and the incidence angle on the film cooling effectiveness of the suction surface squealer tip were studied experimentally and numerically.Experimental investigation shows that compared with the arrangement with the film holes along the camber line or near the suction surface,the blade tip has a higher cooling effectiveness when the film holes are arranged near the pressure surface.The position of the "reattachment line" on the blade tip varies with the change of the blowing ratio and tip clearance.The coolant discharged from the film holes near the pressure surface flows to the pressure surface at the low blowing ratio.When the blowing ratio is increased to BR=2.0,the coolant injection has a good blocking effect on the blade tip leakage flow,and the "separation bubble" is limited in the region between the pressure surface and the film holes,leading to the coolant flows to the suction surface directly.The "reattachment line" constantly migrate to the suction surface with the increase of the blade tip clearance,resulting in the increase of the amount of the coolant flowing to the pressure surface.Based on the experimental results,a method for arranging the film holes to obtain full coverage film cooling on the suction surface squealer tip is proposed and verified by experiments.Numerical calculation results show that compared with the negative incidence angle,the positive incidence angle can greatly improve the film cooling effectiveness of the film hole along the camber line and near the suction surface.The effects of the axial slot structures,the shapes and arrangements of the film holes on the blade platform film cooling effectiveness were studied experimentally,and the flow field was analyzed by numerical calculation.The experimental investigation indicates that the film coverage of the axial slot is an approximately triangular region composed of the "downstream boundary of the axial slot exit","passage vortex boundary" and "suction side leg of the horseshoe vortex ".Compared with the convergent slot,the axial slot with +55° guide fences has a more obvious effect on improving the film cooling effectiveness of the blade platform.The acceleration effect of the convergent slot breaks through the restriction of stagnation zone of the blade leading edge to the coolant discharged from the axial slot,and the film has the widest circumferential coverage immediately downstream the axial slot exit.The diffusion slot hole has a higher film cooling effectiveness than the traditional fan-shaped hole on the blade platform.When the blowing ratio is BR=2.5,the relative increase of the areaaverage film cooling effectiveness of the diffusion slot hole exceeds 40% in comparison with the fan-shaped hole.The "flat-long" feature of the diffusion slot hole makes its cooling effectiveness is more sensitive to the film hole layout than that of the fan-shaped hole.When the orientation angle of the film hole near the pressure surface leading edge is deviated to the pressure surface,the cooling effectiveness in the pressure surface corner region can be significantly increased.Based on the experimental results,a method for arranging the film holes according to the blade profile and blade platform geometric parameters to improve the cooling effectiveness on the blade platform is proposed.The coolant discharged from the axial slot causes the "saddle point" and "separation line" move forward,resulting in the coolant trajectory ejected from the film holes near the separation line to deflect to the suction surface. |
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