基于分离涡模拟的平板气膜涡系结构与流动损失数值研究

Detached Eddy Simulation of Vortex Structure and Flow Loss of Flat Film Cooling

关键词:  燃气轮机  气膜冷却  冷气掺混  迎风涡  气动损失  雷诺应力  分离涡模拟

Key words:  Gas turbine  Film cooling  Cooling air mixing  Upright vortex  Aerodynamic loss  Reynolds stress  Detached-eddy simulation

摘要:

气膜冷却在保护高温部件的同时，主流与冷气干涉会形成复杂的涡系结构并造成掺混损失，研究二者之间的作用机理对指导气冷涡轮优化设计具有重要意义。本文采用DES（Detached-Eddy Simulation）方法对平板圆柱气膜孔的流场进行非定常数值模拟，分析了涡系演变规律以及掺混损失。结果表明：随着吹风比的提高，冷气射流与主流的流动掺混过程表现为两种不同的模式，低吹风比时下游冷气主要受顺时针方向的迎风涡控制，高吹风比时逆时针方向的迎风涡和顺时针方向的背风涡同时控制下游冷气运动；频谱分析显示，流场扰动存在着明显的倍频关系，基频信号由脱落涡产生，频率大小与吹风比呈线性关系；损失分析表明，流场损失主要由冷气与主流的温差换热导致，占总熵损失的90%以上。

Abstract:

The interaction between mainstream and cooling air will form a complex vortex structure and cause mixing losses，while the film cooling protects the high temperature parts. It is extremely important to study the interaction mechanism between loss and vortex structure for optimizing air-cooled turbine structure. The DES（Detached Eddy Simulation） method was used to compute the unsteady film-cooling flow field of flat plate cylinder hole， then the evolution law of the vortex system and the mixing loss were analyzed. As results， there are two different motion modes in the film flow field dominated by the windward vortex with the increase of the blowing ratio. The downstream cooling air at low blowing ratio is mainly controlled by the clockwise windward vortex，and at high blowing ratio， the anti-clockwise windward vortex and the clockwise leeward vortex simultaneously control the movement of the downstream cooling air. Spectral analysis shows that there is a clear multiple relationship among the flow field disturbance frequencies. The fundamental frequency signal is generated by the shedding vortex， and the frequency is linearly related to the blowing ratio. Loss analysis shows that the flow field loss， which accounts for more than 90% of the entropy loss， is mainly caused by the heat transfer between the cooling air and the mainstream.