Numerical Investigations on the Aerodynamic Performance of Last Stage Bucket with Part-Span Connector

Long last stage bucket often utilizes part-span connector (PSC) to address various structural issues, however pay little attention to its impact on the aerodynamic performance. In this paper, the aerodynamic performance assessment of last three stages in low pressure steam turbine with PSC on last stage bucket is numerically conducted through solving the three-dimensional Reynolds-Averaged Navier-Stokes (RANS) and k-epsilon turbulent model based on CFD software ANSYS-CFX. Structured hexahedral grid with reasonable quality is generated for all three stages including last stage bucket with PSC. Three types of grids are used to conduct the grid number independence test. Two kinds of PSCs with different span locations are utilized in last stage bucket. Detailed flow field analysis and comparison of last three stages at designed and off-designed operational conditions without and with two different PSCs are presented. The results show that the two different part-span connectors reduce total-total isentropic efficiency by 0.11% and 0.22%. The mass flow and torque are pushed to upper and bottom as the presence of PSC. The cross flow vortex caused by pressure gradient between pressure and suction side leads to aerodynamic loss.