| With the development of economy,the demand for output power and cycle efficiency of gas turbine is increasing.Therefore,exploring more efficient blade cooling technology to achieve higher inlet initial temperature of gas turbine has become a hot research topic.Film cooling is one of the most commonly used cooling methods;and the air/mist film cooling can greatly improve the cooling effectiveness without changing the structure,and has a very broad prospect.In this paper,a novel cooling structure,ramp-trench hole with an upstream ramp and a serrated trench,is proposed for the first time.Based on the plate and blade end-wall model,combined with the new cooling method of air/mist film cooling,the numerical simulation was carried out with Fluent.The main findings are as follows:1.In the flat plate simulation,the larger the blowing ratio,the more obvious the advantage of the ramp-trench hole compared with the other three basic structures.When the blowing ratio is 0.5,the maximum increase of the efficiency of ramp-trench hole(α=25°)relative to serrated trench hole is 16.6%;when the blowing ratio is 1.0,it is 18.3%;and when the blowing ratio is 1.5,it is 43.8%.The height of the vortex caused by the ramp-trench hole(α=25°)was significantly lower than that of the serrated trench hole.And due to the obvious enhancement of lateral spreading,the cooling fluid carried by the vortex pair will be greater than the high temperature mainstream.The result is that although it will cause a slight rise in the cooling core,it will also bring the upper half of the coolant to the wall.This characteristic determines that the ramp-trench hole can make full use of the latent heat of vaporization of droplets to improve the film cooling effectiveness.2.There is no linear relationship between the film cooling effectiveness and the ramp angle.The ramp angle needs to be within a certain range to improve cooling performance.Among the six ramp angles studied,α=30° has the best cooling performance.The average enhancement rate of contrast α=0° was 32.0%.When the ramp angle increases,the negative impact of the cooling jet core rise and the efficiency improvement caused by the lateral spreading enhancement always exist at the same time.Under the same droplet diameter,the higher the mist mass fraction,the higher the film cooling effectiveness.The cooling effect is best when the mist mass fraction and diameter are 10%and 10μm,respectively.The average efficiency increase was 125.6%compared with the basic situation without droplets.3.In the end-wall model,the overall change rule of air and composite cooling medium with droplets is similar.From 0° to 45°,the efficiency decreases first,then increases and then decreases with the increase of ramp angle.However,the variation of the two working fluids will be different.The variation trend of efficiency with flow direction is also different under different ramp angles.After the addition of droplets,the film cooling effectiveness and efficiency enhancement of α=40° were significantly better than that of α=0°,and the efficiency increased by 4%.Within a certain ramp angle,the ramp-trench hole can still play a certain role in promoting the latent heat advantage of droplet vaporization.However,with the increase of ramp angle,a channel vortex will be formed near the suction side and its intensity will increase gradually;the channel vortex causes the film to bulge and gradually detach from the wall,resulting in reduced cooling effectiveness.The above conclusion proves that the ramp-trench hole has a great advantage in improving the cooling effect,and has a guiding significance for the design of the end wall cooling structure in the future. |
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