汽轮机再热后级内颗粒冲蚀特性

Solid Particle Erosion in the Reheat Stage of the Steam Turbine

汽轮机再热后级内叶片受到固体颗粒冲蚀,严重影响着汽轮机的安全经济运行。以某超临界汽轮机再热后第1+1/2级(第一级与相邻级的喷嘴)扭叶片为研究对象,通过拉格朗日法模拟不同粒径颗粒三维运动轨迹,并采用Finnie冲蚀模型,研究不同动静轴向间隙及不同负荷下颗粒对叶片的冲蚀特性。结果表明,由于动叶高速旋转,颗粒撞击到动叶时会获得与主流方向相反的速度,进而又反弹回静叶。较大粒径颗粒在动静叶片轴向间隙内"反复反弹"是造成再热后级内冲蚀的主要原因。适当增大动静轴向间隙可以有效地减少反弹回静叶的颗粒数量。当动静轴向间隙为5 mm时,反弹回静叶的颗粒为10%,轴向间隙增大为8 mm时,没有颗粒反弹回静叶。当机组负荷降低时,固体颗粒撞击叶片后的反弹角增大、反弹回静叶的数量增多,颗粒在动叶和下级静叶轴向间隙内反弹后,只有极少颗粒能够流出下级静叶。

Solid particle erosion in the reheat stage seriously affects the safe and economic operation of the steam turbine. Taking twisted blades in the 1＋1/2 reheat stage（the first stage and the adjacent nozzle） of one supercritical steam turbine as the study object, the three-dimensional motion trajectory of particles with different particle diameters is calculated based on Lagrange method, and the erosion characteristics on the blades caused by the solid particles under the conditions of different axial clearances between the rotor blade and the stator blade and different loads are researched by using Finnie erosion model. The results show that due to the high-speed rotation of the rotor blade, if the particles impact the rotor blade, they will obtain the speed of the mainstream in the opposite direction, and then rebound to the stator blade. The erosion performance in the reheat stage is mainly caused by the ‘repeatedly rebound’ of the particles with larger size in the axial clearance between the rotor blade and the stator blade. Increasing the axial clearance between the rotor blade and the stator blade properly can effectively reduce the number of the particles rebounded to the stator blade. When the axial clearance is 5 mm between the rotor blade and the stator blade, there are 10% particles rebounding to the stator blade, when the axial clearance is 8 mm, no particles rebound to the stator blade. As decreasing the load of the turbine unit, the rebound angle of solid particles is increased after impacting the blades as well as the number of the particles rebounded to the stator blade, and only a few particles can flow out the stator blade after the particles’ rebound in the axial clearance between the rotor blade and the next stator blade.