小容积流量工况对排汽缸的影响分析

Analysis of the Influence on the Little Volume Flow Condition for Exhaust Hood

汽轮机末级排汽是影响排汽缸运行的关键因素。对汽轮机末级与排汽缸流场进行了数值模拟,得到当末级处于不同容积流量工况时,排汽缸内流动特性及气动性能。结果表明:随着容积流量的减小,排汽缸内流线分布恶化,扩压通道内靠近外导流环区域出现漩涡,其范围及强度随容积流量减小而增加,扩压性能下降;排汽通道流线紊乱度增加,出现复杂涡系,出口截面流动稳定性下降;大尺度漩涡的存在增加了排汽缸能量损失,静压恢复系数下降,总压损失系数增大。

The state of exhaust steam in last-stage has an obvious influence on the exhuat hood. A numerical simulation coupled with the last-stage and the exhaust hood was conducted to get the flow characteristics and aerodynamic performance of the exhaust hood while the last-stage was run in different volume flow condition. According the anslysis,the streamline distribution in the exhaust hood deteriorates under the small volume flow condition. As a result of the vortex appears near the external diversion ring in the diffuser and it enhances along with the reduce of the volume flow,the performance of the exhaust hood decreases; there would be complex vortices in the exhaust passage and bring about the decrease of the flow stability in the outlet section; the existence of the scale vortex increases the energy loss in exhaust hood,meanwhile the pressure recoverycoefficient reduces and total pressure loss coefficient increases.