The film cooling performance of chevron holes with different inclination angles and exit lateral diffusion angles has been studied experimentally and numerically. The inclination angles include 35° and 55°. The exit lateral diffusion angles include 20° and 25°. The film cooling effectiveness, heat transfer coefficient and discharge coefficient were measured on a flat plate model by transient liquid crystal measurement technique under four blowing ratios. The results show that the large inclination angle reduces the film cooling effectiveness. The influence of diffusion angle has two aspects: the large diffusion angle leads to mainstream ingestion and decreases film cooling effectiveness at M=1.0 and 1.5; however, the large diffusion angle increases the film cooling effectiveness at high blowing ratio of 2.0, because the larger hole exit area decreases the normal momentum component of the film jet. The large inclination angle decreases the heat transfer coefficient in the right downstream region at M=0.5 and 1.0. The large diffusion angle enhances the heat transfer in the right downstream of the holes in M=0.5~1.5 conditions. The chevron hole with large inclination angle generally has the highest discharge coefficient.

Investigation of the Influence of Inclination Angle and Diffusion Angle on the Film Cooling Performance of Chevron Shaped Hole

Enhanced film cooling performance of a row of cylindrical holes embedded in the saw tooth slot

Numerical evaluation of film cooling performance of transverse trenched holes with shaped lips

Experiments have been performed to investigate the effect of mainstream turbulence on the three-dimensional distribution of the full coverage film cooling effectiveness for two enlarged actual twisted vanes with cylindrical or shaped holes. The film cooling effectiveness was measured by transient liquid crystal technique at mainstream turbulence intensities of 2%, 9% and 15%. The mass flow rate ratios range from 5.5% to 12.5%. There are 3, 8 and 7 rows of film holes on the suction side, leading edge and pressure side, respectively. Results show that for the cylindrical hole vane the high mainstream turbulence intensity decreases the film cooling effectiveness in the top region and down region of pressure side in the low mass flow rate ratio of 5.5%, while the effect is opposite in the high mass flow rate ratio of 12.5%. The film cooling effectiveness in the middle region of pressure side decreases obviously with the increase of the turbulence at the low mass flow rate ratio of 5.5%, while the influence of increasing turbulence weakens gradually with the increase of mass flow rate ratio. Moreover, the high mainstream turbulence improves the film cooling effectiveness in the further downstream of the holes on suction side at the high mass flow rate ratio of 12.5%. For the shaped hole vane, the increase of mainstream turbulence decreases the film cooling effectiveness at all mass flow rate ratios. This study reveals the influence rule of the mainstream turbulence on the film cooling effectiveness in the different regions of the three-dimensional vane surface. The results would guide the designs of engineering heat transfer with application in gas turbine blade/vane cooling.

Experimental Investigation on the Effect of Mainstream Turbulence on Full Coverage Film Cooling Effectiveness for a Turbine Guide Vane

In the present study, the trenched configurations, including traditional trench (TT), fillet trench (FT) and varying-radius trench (VRT), are numerically investigated at different conditions in terms of downstream cooling effectiveness and flow fields. Different trench width and fillet radii are discussed at different blowing ratios and density ratios. Results show that the downstream lips mainly change the downstream pressure distributions and then change the lateral coolant distribution. The downstream fillet can reduce the penetration of coolant and improve laterally averaged effectiveness in the configurations with the narrow trench at modest blowing ratios. The enhancement of cooling effectiveness near the centerline plane is the positive effect of downstream fillet. This enhancement becomes more obvious with the increase of fillet radius, except for high blowing ratio. The fillet lip, compared with TT cases, also leads to a decline of coolant lateral spread for configurations with the wide trench and large radius, and more decline in the lateral direction deteriorates downstream overall cooling performance. Besides, the increase of density ratio contributes to a higher cooling effectiveness for fillet trench configurations. VRT cases guarantee the streamwise extension and lateral spread of coolant, therefore improving downstream cooling effectiveness further at blowing ratio M=1.0 and 1.5.

Effect of Different Trench Lips on Downstream Film Cooling Effectiveness and Flow Fields

Film cooling performance about a row of dual-fanned holes with injection angles of 30°, 60 ° and 90° were experimentally investigated at blowing ratios of 1.0 and 2.0. Dual-fanned hole is a novel shaped hole which has both inlet expansion and outlet expansion. A transient thermochromic liquid crystal technique was used to reveal the local values of film cooling effectiveness and heat transfer coefficient. The results show that injection angles have strong influence on the two dimensional distributions of film cooling effectiveness and heat transfer coefficient. For the small injection angle of 30 degree and small blowing ratio of 1.0, there is only a narrow spanwise region covered with film. The increase of injection angle and blowing ratio both leads to the enhanced spanwise film diffusion, but reduced local cooling ability far away from the hole. Injection angles have comprehensive influence on the averaged film cooling effectiveness for various x/d locations. As injection angles are 30 and 60 degree, two bands of high heat transfer coefficients are found in mixing region of the gas and coolant. As injection angle increases to 90 degree, the mixing leads to the enhanced heat transfer region near the film hole. The averaged heat transfer coefficient increases with the increase of injection angle.

Film cooling performance of a row of dual-fanned holes at various injection angles

The invention discloses a double-layer wall outer circle structure of a gas turbine, and belongs to a gas turbine structure. The double-layer wall outer circle structure of the gas turbine comprises an annular impact wall and blades. The impact wall comprises an outer wall body and an inner wall body. A plurality of impact holes are uniformly formed in the outer wall body. Lateral wall bodies are arranged at the two ends of the outer wall body. Supporting edges are arranged under the lateral wall bodies, and the inner wall body is located on the supporting edges. A plurality of air film holes are uniformly formed in the inner wall body. The inner wall body is connected with the outer wall body through a connecting mechanism. Under the condition that the gaps between blade tips and the outer circle inner wall body keep unchanged, the relative movement speed of the blade tips and the inner wall body is lowered through rotation of the inner wall body, and the pneumatic loss caused by relative movement is lowered by 5-10%. Due to rotation of the inner wall body, the speed of leaking fuel gas in the blade tip gaps and near the inner wall body is lowered, and the density-flow ratio between cold air sprayed by the air film holes and the leaking fuel gas in the gaps is improved, which means that the needed cold air amount is reduced in order to reach a certain cooling effect.

Haofeng Wang

Papers

Film cooling performance of a row of dual-fanned holes at various injection angles

Double-layer wall outer circle structure of gas turbine