小容积流量下汽轮机末级叶片流场特性分析

Numerical Analysis on Flow Field of Steam Turbine Last Stage at Small Volumetric Flow

借助商用计算流体动力学软件CFX,选择入口质量流量不变,改变出口背压的方式,对不同容积流量下某大型汽轮机低压缸末级进行了全三维黏性定常流动的数值研究,全面分析了低压缸末级的流动特性。结果表明:在背压10k Pa(相对容积流量k=0.52)下,末级动叶10%叶高截面受逆压梯度的作用,在吸力面近尾缘区域开始发生流动分离,并随着流量的进一步减小,逐渐发展形成回流涡。背压升高到15k Pa(k=0.36)时,负攻角首先导致末级动叶50%叶高截面前缘区域发生流动分离,随着流量的进一步减小,流动分离产生的涡逐渐增大;90%叶高处由于扭转角度较大,负攻角的作用一直不大,但是压力升高到25k Pa(k=0.23)时,开始受到静叶扩压和动叶离心力产生的叶顶涡的影响,流场比较混乱。从15k Pa(k=0.36)开始,由于静叶扩压和动叶离心力影响,动静叶叶顶出现漩涡,后随压力升高逐渐增大,同时由于动叶旋转离心力造成的径向压力梯度,叶根尾缘区域也出现漩涡,并随压力升高向流道前部发展。

Using the commercial computational flow dynamics software CFX, the 3d steady viscous flow field of the last stage blade with different volume flow has been studied. This paper analysis the flow field of the last stage blade in detail. The result show that a separation caused by the adverse pressure gradient occurs at the 10% blade distance plane near the trailing edge of the last stage rotor when the back pressure rises tol0kPa（ 52% of the design mass flow rate）. And then a separation caused by the negative attack angle occurs at 50% blade distance plane near the leading edge of last stage rotor when the back pressure rises to 15kPa（36% of the design mass flow ）. A negative attack angle occurs at 90% blade distance plane near the leading edge when the back pressure rise to15kPa（52% of the design mass flow rate）, but the influence of the negative attack angle is small. The flow field s at 90% blade distance plane becomes complicated when back pressure rise to 25kPa.