吹风比对平板气膜冷却效率影响的数值模拟

 为了揭示吹风比M对气膜冷却效果的影响规律,在M=0.5,1.0,1.5,2.0工况下对平板气膜冷却圆柱孔模型和扩散孔模型进行了流动和传热的数值模拟对比研究。计算时基于控制容积法对三维定常不可压缩N-S方程进行离散,采用SIMPLEC算法,湍流模型选取可实现k-ε着模型,壁面函数采用增强壁面函数,分析比较了壁面温度分布、速度矢量和气膜冷却效率。结果表明,随吹风比增大,射流容易脱离壁面。在孔口附近区域,对圆孔而言吹风比对冷却效率的影响不明显,而对扩散孔冷却效率随吹风比增加而提高。在射流向下游发展过程中,就扩散孔而言较大的吹风比使得射流沿流向的覆盖区域增大;就圆孔而言较大的吹风比射流出现了回流,近下游位置处的冷却效率提高而远下游处的冷却效率降低。由此可见,针对不同的孔型,冷却效率随吹风比的变化规律不尽相同,圆孔的冷却效率不随吹风比单调变化,扩散孔的冷却效率随吹风比的增加而提高。

Numerical Simulation of Film Cooling Efficiency at Different Blow Ratios

Numerical simulations were carried out to verify the influence of blow ratios on the film cooling effectiveness. With the blow ratio M taking values of 0.5, 1.0, 1.5, 2.0, numerical simulations were carried out on the fluid flows and heat transfers in a cylindrical hole and a fan-shaped hole. By using the realizable k-ε turbulence model with an enhanced wall function, based on the bulk flow control, the three-dimensional steady incompressible N-S equations and the method of SIMPLEC, the mean flow velocity at the exit of the hole and the temperature of the cooled wall were calculated to analyze the film cooling effectiveness. Different blowing ratios were compared on the influence of the film cooling effectiveness. The results indicate that when the blow ratio increases, the jet tends to lift off the wall. Within the scope of this study, in the near field of the hole, for the cylindrical hole, the blow ratio has no obvious effect on the film cooling effectiveness, however, for the fan-shaped hole, the film cooling effectiveness increases with the blow ratio. As the jet goes downstream of the flow direction, for the fan-shaped hole, the jet coverage area increases while for the cylindrical hole, a back-flow is found and the film cooling effectiveness is enhanced around the near downstream field but decreased in the far downstream field. Thus the cooling effectiveness does not change monotonously with the blowing ratio for the cylindrical hole, but for the fan-shaped hole, the film cooling effectiveness increases with the blow ratio.