Numerical Simulation On The Secondary Flow Of Stage In Steam Turbine

With the increase of single unit capacity in Coal-fired power plant, inlet steamparameters and flow of turbine is gradually on the increase, gradually making theratio of steam flow and blade height increase, and corresponding cascade high of unitSteam flow decrease, which has caused considerable the secondary flow loss.Therefore, understanding the reasons of loss and distribution within the stage hasgreat significance for the effective control of the secondary flow losses and improvingthe efficiency of steam turbine stages.Based on finite element finite volume method and fully implicit multigridcoupling algorithm, high-pressure cylinder stages three-dimensional steady-state flowfield of a300MW steam turbine was simulated adopting SST k-ω turbulence modeland using numerical simulation software CFX. First of all, Three-dimensionalsteady-state flow field has been simulated in the300MW steam turbine high-pressurereactionary stage stator cascade. The paper analyzes and calculates the developmentalcharacteristics of the secondary flow in the lower wall of the cascade channels and theaerodynamic characteristic of the cascade and reveals the characteristic of evolutionof vortices in cascade channels. Secondly, the paper makes a three dimensionalsteady-state numerical simulation to a full stage flow field of the300MW steamturbine high pressure cylinder. Finally, the distributed situation of stage internal flowfield had been analyzed and calculated between not considering the diaphragm sealclearance and tip clearance and considering that.The calculation results show that the secondary flow loss of cascade endwall isbound up with shape surface of cascade and the steam condition of upper and lowerside wall. It was found that the strength of secondary flow develops rapidly and twoobvious vortex areas which change the total pressure loss coefficient and exit flowangle along the blade high direction could form near the blade convexity of the upper and lower. Meanwhile, by the analysis and comparison of considering and withoutconsidering the two kinds of flow field characteristic with diaphragm seal clearanceand tip clearance，the leakage vortex formed by the clearance leakage has greatinfluence on the mainstream movement. There is a great difference between withoutconsidering the clearance leakage condition and the upper and lower passage vortexformation region. And the secondary flow loss due to clearance leakage is larger thanwithout considering clearance leakage. Passage vortex in rotor cascade seems to haveweakened due to the roll suck function of leak vortex, along the radial to the cascadecentral, the down passage vortex would gradually become bigger and stronger owingto the influence from upstream clearance leakage of diaphragm gland.