Investigation On Film Cooling Characteristics Of Slot-Sectional Film Holes Combined With Ribbed Cross-flow Channels

The heavy duty gas turbine is by far the most efficient heat-power conversion equipment,and its R&D and manufacturing level represents the level of a country's heavy industry.The improvement of gas turbine thermal efficiency is mainly achieved by raising the turbine inlet temperature.At present,the turbine inlet temperature of advanced gas turbines has far exceed the temperature limit of the blade materials.High efficiency turbine cooling technology is the key to ensure the reliable operation of gas turbines.Especially for turbine blades,the cooling method of external film cooling combined with internal cross-flow channels are widely used.The influence of perpendicular cross-flow on the film cooling performance must be considered in the design of turbine blade cooling method.Most previous studies of film cooling characteristics in the cross-flow channel based on film holes with a circular cross-section,such as cylindrical holes and fanshaped diffusion holes,and their film cooling characteristics and flow mechanism are relatively clear.Earlier studies found slot-sectional holes in the plenum case have better film cooling effectiveness than fan-shaped diffusion holes,but their film cooling performance in perpendicular cross-flow channels with and without ribs has not been carried out,and so do the flow mechanisms.Therefore,this paper studies the film cooling and flow characteristics of slot-sectional holes in perpendicular cross-flow channels with and without rib turbulators using experimental and numerical methods.The numerical method was used to comparatively study the film cooling characteristics of typical fan-shaped holes and slot-sectional holes in perpendicular cross-flow channels.Two computation models include the large rib segment and small rib segment computation models.Their difference is the number of film holes in one rib segment and the cross-sectional parameters of the cross-flow channel.The crossflow channels all include smooth channel,45 deg and 135 deg ribbed cross-flow channels.The remaining parameters keep the same.The numerical results show that,at medium and high blowing ratios,the film cooling effectiveness of the four slotsectional holes is significantly better than that of the fan-shaped hole,and the film cooling effectiveness of the large cross section rectangular diffusion hole is the highest in three cross-flow channels;In the smooth channel,the discharge coefficients of the four slot-sectional holes are higher than that of the fan-shaped hole.But in the 45 deg and 135 deg ribbed channel,there is little difference on film cooling performance between the fan-shaped hole and slot-sectional holes.The rib orientation has a great influence on the discharge coefficient.The four kinds of slot-sectional holes have the highest discharge coefficient in the 135 deg ribbed channel.In the comparison of rib orientations,the film cooling effectiveness in the 60 deg and 120 deg ribbed channels aer slightly better than the 45 deg and 135 deg ribbed channels,but the improvement are limited.At the same time,the 60 deg and 120 deg rib structures increase the flow loss and reduce the discharger coefficient compared to the 135 deg ribbed channel.In this paper,a perpendicular cross-flow flat experiment was conducted.The PSP measurement technology is used to obtain the film cooling performance of slotsectional holes in the perpendicular cross-flow channel and compare it with the smooth channel.The results show that the vertical cross-flow channel leads to a significant change in the film distribution of the slot-sectional holes compared to the smooth case.In the smooth channel,the effectiveness profiles of each hole is basically the consistent.But in the ribbed channel,the two holes in one rib segment behave obviously inconsistent.The effectiveness of post rib hole is significantly higher than that of the pre rib hole,and a lower blowing ratio is needed for the post rib hole to complete a bipeak effectiveness.However,at any blowing ratios,the difference between in-line and counter cross-flow is small.This demonstrates that when the row of diffusion slot holes is located in the center of the ribbed channel,the influence of the rib orientation can be ignored regarding the laterally averaged effectiveness.In the ribbed cross-flow channels,different hole row positions have a significant effect on the film cooling effectiveness.In the in-line flow(45 deg ribbed cross-flow channel),the “fore ribbed” and “rear ribbed” case showed higher film cooling effectiveness than the cross-flow channel with the “center ribbed” scheme.The “rear ribbed” configuration performed best.In addition,the slot-sectional diffusion holes in the counter flow(135 deg ribbed cross-flow channel)were easy to obtain a higher film cooling effectiveness.But at the same time,the position of the film hole rows has little effect on the film cooling performance.