超微涡轮动叶栅叶顶间隙对流场影响的数值模拟

Numerical Simulation of the Influence of the Blade Tip Clearance on the Flow Field of an Ultra-micro Turbine Rotating Cascade

通过数值求解基于雷诺时均的三维定常粘性N-S方程,结合RNGk-ε湍流模型和非平衡壁面函数,对一种超微型向心涡轮动叶栅内的流动情况进行了数值模拟。揭示了具有极低展弦比动叶栅叶顶间隙对流场参数分布和气动损失的影响,为超微涡轮的设计和改进提供了理论依据。模拟结果表明,叶顶间隙的大小对通道内马赫数分布有重要影响,其中顶部间隙射流所引发的泄漏涡与主流的掺混是主流马赫数降低的重要原因;叶顶间隙的存在使得总压损失系数均匀化,即近壁区和主流区的总压损失都较高;动叶栅在叶展方向上的载荷分布均匀,弦向载荷主要由接近尾缘的弧段承担;模拟中还解析出三维的尾迹涡,这主要是动叶栅尾缘过厚所导致,应进行叶型改进。

Through a numerical solution of the Reynolds number time-averaged 3-D steady viscous N-S equation and in conjunction with a RNG k-ε turbulent flow model and a non-equilibrium wall surface function, numerically simulated was the flow state in the rotating cascade of an ultra-micro radial turbine. As a result, the influence of the rotating cascade blade tip clearance with an extremely low aspect ratio on the parameter distribution and aerodynamic losses of the flow field was revealed, providing a theoretical basis for the design and improvement of ultra-micro turbines. The simulation results show that the magnitude of the blade tip clearance exercises a major influence on the distribution of Mach number inside the flow passages. Among others, the mixing and dilution of the leakage vortex with main streams caused by the jet flow from the blade tip clearance constitutes the major cause for a decrease in Mach number of the main stream. The existence of the blade tip clearance makes the total pressure loss coefficients homogeneous, i.e. the total pressure losses in both the wall-neighboring region and main stream zone are relatively high. The load on the rotating cascade along the blade span direction assumes a uniform distribution, and the load in the chord direction is mainly undertaken by the arc segment close to the trailing edge. During the simulation, a three-dimensional wake vortex was identified through an analysis. This is mainly caused by an excessively thick trailing edge of the rotating cascade, making it necessary to improve the blade profile.