| Film cooling is an important cooling technology applied to gas turbine blades.Research on this technology in the industry has been dedicated to improving film cooling performance.The main ways to improve are the development of highly efficient holes and the development of spoiler structures.Among them,the method of providing a spoiler structure outside the simple cylindrical hole can relatively reduce the difficulty and cost of processing while taking into account the cooling performance.In recent years,researchers have proposed a new type of crescent-shaped block and conducted preliminary experimental studies on it.However,the flow mechanism of the block,the cooling performance and whether the cooling efficiency can be further improved through optimization remain to be explored.Aiming at the above-mentioned problems related to crescent-shaped block,this paper uses numerical simulation to study the flow mechanism of crescent-shaped block to enhance the cooling effect,and uses large eddy simulation to analyze the vortex structure in its flow field.Aiming at the geometric parameters of the crescent-shaped block,taking the maximum average cooling effectiveness as the optimization goal,combined with back propagation neural network and genetic algorithm,the shape optimization of upstream and downstream crescent-shaped blocks was carried out at blowing ratio M=0.5 and 1.5.And further explored the cooling performance of the optimized block when applied to the cascade environment.The result show that the cooling effectiveness after placing the crescent block is significantly higher than that of the cylindrical hole without block.The interaction between the upstream block and the high-temperature mainstream gas produces an anti-kidney vortex pair,and the interaction between the downstream block and the cold air also produces an anti-kidney vortex pair,anti-kidney type vortex pair weakens the adverse effect of kidney vortex pair.By analyzing the distribution of the vortex structure in the flow field obtained by the large eddy simulation,it is found that the horizontal vortex legs of the hairpin vortex in the cylindrical hole model will induce a kidney vortex pair,while the horizontal vortex legs of the new hairpin vortex generated by the crescent-shaped block will induce kidney vortex pair.The optimized block model has a different degree of improvement in the average cooling effectiveness value compared to the reference block.At the blowing ratio is 0.5 and1.5,the downstream optimized block model has a relative increase of 6.2% and 98.3%,while the upstream block model has a relative increase of 127.8% and 16.6%.By comparison,at the blowing ratio M=0.5 and 1.5,the average cooling effectiveness and total pressure loss coefficient of the upstream optimized block are higher than those of the downstream optimized block.when the optimized block is applied in the cascade environment,the cooling effectiveness and total pressure loss coefficient of the upstream optimized block model are also higher than those of the downstream optimized block model. |
