预旋进气小尺寸涡轮叶片冷却的流场研究

Numerical Study of Pre-Swirl Flow in Rotating Cascade of a Small Gas Turbine

关键词:  燃气轮机  涡轮叶片  转静盘腔  预旋  流动  数值模拟

Key words:  Gas turbine  Turbine blade  Rotor-stator cavity  Pre-swirl  Flow  Numerical simulation

摘要:

为了了解和掌握一种具有直通式冷气预旋进气系统的小型燃气轮机涡轮转子叶片的流场,在旋转雷诺数Reθ=4.66×10⁶和冷却空气的无量纲质量流量C_w=1750时改变预旋角θ的大小,使其在15°~90°变化,通过数值研究得到了预旋角对涡轮盘腔、连管和涡轮叶片内冷却空气的流动以及叶栅通道中燃气的流动的影响。结果表明:(1)预旋角的变化会改变涡轮盘腔、连管和涡轮叶片冷气进口附近局部区域的流场,但是对涡轮叶片内其它区域和叶栅通道中的流动基本没有影响。(2)随着预旋角的增大,涡轮盘腔内预旋进气冷气射流的轴向穿透深度先增大后减小；当θ<45°时冷却空气沿外围屏流向转盘接收孔,而当θ>45°时冷却空气沿内围屏流向转盘接收孔；气流的周向速度随着预旋角的增大而减小。(3)垂直进气时连管内存在多个回流区和很大的涡流,流动损失较大,而采用预旋进气能够减弱或消除这些流动结构,存在最优预旋角θ_opt,θ_opt≈45°,此时连管的有效流通面积最大。 

Abstract:

A CFD numerical study on the flow field in a rotating cascade of a small gas turbine, which adopted direct-transfer pre-swirl cooling system, was conducted by using ANSYS CFX 12.0 with shear stress transport (SST) turbulence model. A numerical model was obtained according to the actual turbine blade geometry and operating conditions. In the calculations, the pre-swirl angle θ ranges 15°~90° for rotational Reynolds number and non-dimensional mass flow rate of cooling air equals to 4.66×10⁶ and 1750, respectively. The effects of pre-swirl angle on the flow in cavity, connector pipe, inside and outside of the blade were analyzed. The results show that:(1) The flow behavior of cavity, connector pipe and area around the serpentine inlet changes with pre-swirl angle, but the flow in other places is basically invariable when pre-swirl angle changes.(2)The axial depth which can be reached by the pre-swirl air jet in cavity is observed to increase firstly and then decrease as pre-swirl angle increases. The circumferential velocity diminishes with increasing pre-swirl angle.(3)Several recirculation and vortex exist simultaneously in the connector pipe when θ=90°, and these flow structures can be weakened or removed if θ<90°. There is an optimal pre-swirl angle θ_opt≈45°.