Numerical Simulation And Optimization Of Aerodynamic Performance For Low Pressure Exhaust Hoods Of An Industrial Steam Turbine

The exhaust hood in condensing steam turbines connecting the last stage and condenser is used to recover leaving kinetic energy of the last stage turbine, while guiding the flow from turbine to condenser. The aerodynamic performance of exhaust hood which has a direct effect on the pressure of turbine outlet and the condition of condenser inlet effects the thermal efficiency of the whole steam turbine. In this dissertation, the object of study is upward or downward exhaust hood and axial exhaust hood designed by Hangzhou Steam Turbine Corporation Numerical simulation is used to analysis the flow field of the exhaust hood while the axial exhaust hood is modified for optimization.For downward exhaust hood, different axial velocity distribution at inlet of the exhaust hood alone, exhaust hood combined low pressure stages under different operating conditions are simulated.Results indicate that there are complex vortices which seem to be the major loss in the exhaust hood. Under different inlet conditions,the structure of vortices is also different. The simulation result of the exhaust hood combined with last one stage is different with the exhaust hood combined with last two stages which is more close to reality. The rotation speed of the rotor has a big effect on the performance of the exhaust hood. The simulation result predicts the trendency of the performance of the exhaust hood.For axial exhaust hood, low pressure stages alone, exhaust hood alone with velocity distribution at inlet, exhaust hood combined low pressure stages are simulated.Also the axial exhaust hood is modified to improve the performance. Results indicate that there are big difference of the performance of the exhaust hood under different simulating conditions. There are strong flow interactions between the last stage and exhaust hood which has a strong impact on the aerodynamic performance of the last stage and exhaust hood. According to the flow field of exhaust hood, there are flow separations in the bearing plate and inwall. By changing the angle of the bearing plate and inwall,static pressure recovery coefficient increases40.68%,total pressure loss coefficient reduces31.43%,also flow condition in exhaust hood outlet is improved. By changing the cross section of the oil pipe, static pressure recovery coefficient increases a little, total pressure loss coefficient reduces2.2%.