轴向间距对二次水滴运动特性及沉积规律的影响

基于有限体积法、计算流体力学研究了某核电大功率汽轮机次末级的二次水滴侵蚀问题,采用Lagrangian方法求解了水滴的离散输运方程,利用Eulerian方法求解了叶栅内蒸汽的流动,并为叶栅通道内的汽相流动与水滴运动建立了数学模型.在定常条件下,通过轴向间距对二次水滴运动特性及沉积规律的影响研究发现:脱离静叶尾缘的水滴在叶栅通道空间中均呈现出向上端壁倾斜的运动趋势,由此获得了叶栅通道中水滴在各固壁面的沉积率；加大轴向间距可以减小二次水滴对动叶片的撞击速度,增大大颗粒水滴抛落到轴向间距上端壁的沉积率.所以,依据大颗粒水滴的集中沉积区域可以确定动叶表面去湿沟槽的适宜位置,该位置应位于吸力面上半部的前缘至中弦区域之间.

Influence of Axial Clearance on Movement Characteristic and Deposition of Secondary Droplets

Secondary droplet erosion in the penultimate stage of a nuclear power large steam turbine was investigated by CFD on the basis of the finite volume method.The discrete phase transport model of the water droplets was solved using the Lagrangian formulations,and the Eulerian conservation equations were applied to solve the steam flow in blade cascades.The mathematical model of steam flow and droplets movement in the cascade passage was established.The influence of axial clearance on the movement characteristic and deposition of secondary droplets was examined under the steady condition.The results show that the movement of all the water drops from the trailing edges of the stationary blade displays the tendency to slope up to the tip and then the deposition rates of water drops on all the walls in the blade passage can be obtained.The impact velocity of secondary drops on the moving blades decreases and the deposition rate of large droplets dropping onto the top of axial clearance increases if the axial clearance is greater.In addition,the suitable positions of the moisture-removal grooves should be distributed from the leading edge to 50% axial chord of the rotating blades according to the concentrated deposition areas of large droplets.