中文摘要：

通过应用商用软件ANSYS-CFX数值求解Reynolds-Averaged Navier-Stokes（RANS）方程和k-ε两方程湍流模型的方法对不同流量下的汽轮机末级流场进行了详细的非定常研究分析。本次数值计算的计算域包括末级静叶域、动叶域和弧形扩压段,同时采用叶片约化法减少了计算成本。动叶的围带和拉金（PSC）均考虑在计算域之内以获得更为真实的流场结果。结果表明：末级总总等熵效率和长叶片表面静压呈现明显的周期性波动;随着流量的减小,总总等熵效率和叶片载荷均明显降低,扩压段中出现分离涡,并逐渐扩展到动叶栅通道中;分离涡的频率较低,并对长叶片所受到的气流激振产生影响。

英文摘要：

Detailed unsteady numerical investigations on last stage flow field of steam turbine with different mass flow are conducted using the three-dimensional Reynolds-Averaged Navier-Stokes（RANS） solution and κ-ε turbulent model based oncommercial CFD software ANSYS-CFX.The computational domains in this numerical analysis include last stage stator domain,rotor domain and curved diffusor.Blade reduction method is applied to reduce the computational cost.Shroud and PSC in rotor domain are both considered in this numerical analysis to obtain more actual prediction results.The result shows that：total-total isentropic efficiency of last stage and static pressure on long blade surface present obvious periodic fluctuation;with the decrease of mass flow,total-total isentropic efficiency and blade loading reduce obviously,separation vortex appears in the diffusor and extends to the rotor passages;the frequency of separation vortex is low and affects the flow excitation of long blade.