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Indexed by:会议论文

Date of Publication:2021-01-26

Abstract:Numerical investigation was conducted on three-dimensional steady flows in the last three stages of a 100MW industrial steam turbine, by using the commercial CFD software CFX. An equilibrium condensation model was adopted to describe wet steam two-phase flows. The internal flows in blade passages and the structure of leakage flows in blade tip clearances were analyzed in detail under design and off-design operation conditions. The aerodynamic performances of the last three stages under different operation conditions were also compared. To explore the influence of the axial clearance on the aerodynamic performance, the axial relative position was altered between the second and the third stages and the flow characteristics in the blade passages were analyzed under the design condition. The turbine performance parameters varying with the relative axial clearance alteration were obtained. The axial clearance alteration changes the flow development at the outlet of the second stage rotor and then the flow state at the third stage inlet. Too small an axial clearance leads to flow instabilities at the second stage outlet, disturbing the inlet flow of the next stage. Conversely, too large an axial clearance will lengthen the axial size and may cause shaft system vibrations. This paper provides a theoretical basis for choosing the axial clearance between stages of a 100MW industrial steam turbine. Results also show that flow separations occur around the last stage blade due to the negative attack angle under low flow rate conditions. The flow separations in upstream stage passages cause the extension of the separation zones in the next stage flow passages, and the tip clearance leakage flow was correspondingly affected. The diagram of the corresponding relationships between the flow rate and the turbine aerodynamic performance was acquired, the reasons of the flow loss caused by low flow rate conditions were analyzed in detail. ? 2015 The Japan Society of Mechanical Engineers.