Effect of injection angle on film cooling characteristics and loss mechanism of contracted double-jet hole in a flat plate

With the inlet temperature of gas turbine continuously increases, film cooling is commonly used to protect the blades. However, the kidney vortex generated by the mixing between mainstream and film injection is negative to the film attachment, which deteriorates the film cooling characteristics. To solve the problem, a kind of contracted double-jet hole is introduced to form an anti-kidney vortex to balance the adverse effect of the kidney vortex. By studying the flow mechanism of the contracted double jet hole in a flat plate model under different geometric parameters, the foundation for the application of contracted double jet hole on blades is established. Different injection angles including the inclination angle and compound angle were considered to improve the film cooling effectiveness and aerodynamic loss in a flat plate. The Reynolds Average Navier-Stokes (RANS) method of the SST k - omega turbulence model is chosen to solve the above arrangement. The results show that a merging process happens before the anti-kidney vortex is formed and three vortices remain, causing an asymmetric distribution of film coolant. Changes of injection angle affect the flow field mainly through Vortex 3. As for different inclination angles at different blowing ratios, a best inclination angle at 30 degrees when blowing ratio equals to 1.5. The laterally averaged cooling effectiveness reaches 0.36. After changing the compound angle, the cooling effectiveness can be improved. Film Cooling Uniformity Coefficient (CUC) is introduced to evaluate whether the distribution of coolant is symmetric. Other than the factors mentioned above, rate of entropy creation per unit volume is affected by the distance between the two legs of the anti-kidney vortex. Analysis of the entropy increase per unit in combination with a Q-criterion analysis reveals the interaction mechanism of coolant and mainstream. The region of entropy increase caused by viscous work per unit volume over 500 W/(m 3 & sdot; K) reveals the entropy increase cause by mainstream and coolant is mainly because of the velocity difference between mainstream and coolant and the rate of the entropy increase caused by temperature per unit volume indicates that the mainstream will be enrolled into the anti-kidney vortex pair. The analysis of the entropy increase per unit also reveals the loss mechanism of Vortex 3 on anti-kidney vortex pair.