Abstract
AbstractAccording to the design requirements of high-temperature combustion chamber, an advanced shaped hole structure was designed for film cooling. Numerical method was applied in this study to investigate the flow and heat transfer characteristics of shaped holes and compared with those of cylindrical holes. The influence of the forward expansion angle of shaped holes on the flow and heat transfer was studied. The results show that compared to cylindrical holes, the diffused structure of shaped holes decreases the momentum of jet flow, improves the adhesion characteristics of the cooling air film, increases the diffusion of the coolant air outflow and improves the cooling efficiency between adjacent columns of holes in the lateral direction. When the forward expansion angle increases, the expansion section induced the flow vortex, which reduces the radial velocity of coolant flow and enhances the diffusion of cooling air film both in streamwise and spanwise directions. However, as the forward expansion angle increases further, the scale of vortex inside the shaped hole grows. Too large vortex inside the shaped hole increases the coolant eject angle, which weakens the film covering effect. Additionally, the shaped hole results in an increase in lateral spreading and enhances the cooling effect between adjacent columns of the film hole. The enhancement of the film cooling characteristics is due to the change in the shape of the film hole, resulting in the enhancement of the flow vortex, which induces complicated secondary flow.
Highlights
With an increase in performance of modern aeroengine, the inlet temperature of modern gas turbine engines has reached 2,000°C [1]
Yuen et al [10,11] carried out experimental study on film cooling with cylindrical, compound angle and fan-shaped holes, and the results indicate that compound angle holes gave the higher values of effectiveness when compared with the non-compound case at blowing ratio (BR) > 1, but at BR < 0.67, the conclusion was on the contrary
The results show that the film cooling effectiveness distribution of all models at low BRs is similar, and when the blowing is relatively high, the jet from cylindrical hole detaches from the penetrate wall so that the cooling performance is poorer, and the fan-shaped hole maintains great cooling performance
Summary
With an increase in performance of modern aeroengine, the inlet temperature of modern gas turbine engines has reached 2,000°C [1]. Bohn and Moritz [20] conducted a series of numerical simulations for a plat plate with seven rows of cylindrical and shaped holes and reported that a lower inclined angle gave higher cooling effectiveness and forward and lateral expansion angles reduced the exit radial velocity of cooling gas, which led to an improvement in film coverage. Kanani et al [21] studied film cooling effectiveness on a flat plate with cylindrical and laterally diffused holes with a streamwise angle of 30° and a spanwise angle of 0° They found that a better lateral coverage and a higher cooling effectiveness value were obtained by laterally diffused hole since the laterally diffused structure decreased the momentum of coolant jet flow at the exit of the hole. Particular attention was paid to explore the effect of forward expansion angle on flow field and film cooling performance of shaped hole in which the lateral expansion angle was fixed
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