Investigation On Cooling Performance Of Novel Turbulated Cutback Cooling Structure On The Trailing Edge For Turbine Blade

The trailing edge is one of the most pivotal and difficult parts which need to be cooled effectively on the turbine blade.The structure of pressure-side cutback with cooling slot is widely used in the trailing edge due to its advantage in the overall performances in cooling and aerodynamics.The most distinctive features of the trailing edge are its two surfaces,pressure-side and suction-side,which are affected by hot gas.The ejected cooling film acts as an insulating layer to protect the pressure-side.Therefore,the temperature of pressure-side is usually lower than that of suction-side.The only effective cooling method of the suction-side is heat conduction.In view of the above,most researches in the past focused on improving cooling performance of coolant flow as an insulating layer for cutback surface.However,film cooling effectiveness of the cutback surface approaches the theoretical maximum due to tangential slit film cooling.The cooling effectiveness has little space to improve.Accordingly,based on the heat transfer process analysis on the trailing edge cutback structure,a new idea of increasing the convective heat transfer coefficient on the cutback surface,which breaks the traditional way of only focusing on the film cooling effectiveness,is introduced in the present paper to enhance the cutback film cooling effect for trailing edge.And a novel turbulated cutback structure is proposed for the trailing edge cooling based on this idea,which has turbulated structures on the cutback surface for heat transfer enhancement.In this study,numerical simulations have been performed on the trailing edge cutback structure of the high-pressure turbine blade.The distributions of film cooling effectiveness and heat transfer coefficient on the cutback surface are obtained under blowing ratios of 0.5,1.0 and 1.5 respectively.The film cooling performance of straight rib and V-shaped rib turbulated cutback structure are investigated in detail.The numerical and spatial distribution characteristics of film cooling effectiveness and heat transfer coefficient under various rib structures and different blowing ratios are analyzed and compared.For the straight rib turbulated cutback structure,the effects of the structure parameters,rib height,rib width and rib spacing,as well as blowing ratio on the film cooling performance are studied.With the increasing of blowing ratios,the cooling effectiveness on the cutback surface downstream of the straight rib case increases gradually,while the heat transfer coefficient ratio between the turbulated structures and the smooth structure decreases gradually.The increase of rib height leads to the decrease of the cooling effectiveness on the rib downstream.With the increasing of blowing ratios,the heat transfer intensity of the smaller rib height structures is higher than the larger rib height structures.When the rib height is 1.0mm,there is little effect of the rib width on the cooling effectiveness.With the increase of rib width,the heat transfer intensity on the cutback surface downstream increases generally.The difference of heat transfer intensity between various structures increases with the raise of the blowing ratio.When the rib height is 1.0mm and the rib width is 2.0mm,the rib spacing has little effect both on cooling effectiveness and heat transfer intensity of the cutback surface.For the V-shaped rib turbulated cutback structure,the effects of the structure parameters,V-shaped rib angles,opening orientation,rib height,rib width and rib spacing,as well as blowing ratio on the film cooling performance are studied.With the increase of the blowing ratio,the cooling effectiveness of V-shaped rib turbulated cutback structure increases gradually.The heat transfer coefficient ratio between the V-shaped rib turbulated cutback structures and smooth cutback structure increases first and then decreases regularly.The higher heat transfer areas are mainly behind the ribs,which present as heart-shaped distribution.For the smaller height cases,the V-shaped rib angle has little influence on the cooling effectiveness but has great influence on the heat transfer intensity on the cutback surface.Among all the three angles cases studied in this paper,the heat transfer intensity of the 45° case is the highest.The heat transfer intensity on the cutback surface is strongly affected by the rib opening orientation.The lower heat transfer coefficient areas of ?-shaped rib case are in the included angle and near the centerline.While the higher heat transfer areas are mainly distributed on both spanwise sides,the range is less than that of the V-shaped rib case.The heat transfer coefficients of V-shaped rib case are all higher than that of the ?-shaped rib case with the same rib angle.The increase of rib height leads to the decrease of the cooling effectiveness of the rib downstream obviously.The heat transfer intensity of cutback surface increases with the raise of the rib height significantly.With the increase of the blowing ratio,the change regular of the heat transfer intensity with different rib height cases is not always consistent.When the rib height is 1.0mm,there are almost no effects of the rib width on the cooling effectiveness but some effects on the heat transfer intensity for V-shaped case.With the increase of rib width,the heat transfer intensity between the ribs decreases.The difference of heat transfer intensity between various structures is little under different blowing ratios.This is mainly due to the larger rib spacing of the smaller rib width case,which makes the vortex pair fully developed behind the ribs thus has more intense disturbance to the wall.When the rib height is 1.0mm,the rib width is 2.0mm,the cooling effectiveness of cutback surface downstream increases with the raise of the rib spacing.The difference decreases with the increasing of the blowing ratio.When the rib spacing decreases,the number of V-shaped ribs increases,which leads to the high heat transfer area increasing and the overall heat transfer coefficient increasing on the cutback surface.In the present study,the straight rib turbulated cutback structure is optimized according to its cooling performance.The cooling performance of the rib height decline structure,the interrupted straight rib structure and the coolant ribbed channel structure are studied and compared with the straight rib turbulated cutback structure.The film cooling effectiveness of the rib height decline structure decreases slightly when the blowing ratio is 0.5 and increases relatively high heat transfer intensity in the downstream.Compared to the straight rib turbulated cutback structure,the interrupted turbulated cutback structure has a higher improvement on the cooling effectiveness under the lower blowing ratios.The cooling effectiveness of the interlaced structure is relatively high among the interrupted structures.With the length of the back section increases,the heat transfer coefficient of the higher heat transfer area behind the rib end increases gradually and the range gets larger.Compared by the numerical value,the decreasing trend of Nusselt number ratio of interrupted structures with the increasing of blowing ratio is relatively small.Under the higher blowing ratios,the heat transfer coefficient of the interlaced structure of L=1/2 is significantly higher than that of the straight rib structure.The coolant ribbed channel structure decreases the cooling effectiveness on the cutback surface.With the increase of blowing ratio,the difference of cooling effectiveness between the ribbed channel structure and the traditional straight rib structure decreases gradually.Compared with the traditional straight rib structure,the ribbed channel structure can improve the overall heat transfer intensity and the Nusselt number ratios are all more than 1.3.