| Power industry is the pillar industry for the national production, providing strong support for the sustained and rapid economic and social development. The phenomenon that the thermal power and the nuclear power is the central part of the power generation will persist. As the key measurement to convert the thermal energy to the mechanical energy in the thermal power plants and the nuclear power plants, steam turbine has significant influence on the normal and efficient operation of the power plants. To improve the steam turbine efficiency will not only bring great economic benefits, but also be able to reduce the emissions. Because the low pressure stage is the main part to limit the power capacity and the efficiency, it has great significance to make research on the two-phase steam turbine flow in the low pressure steam turbine.To develop a fast and reliable calculation method for the wet steam flow property, the Euler equations suitable for the S2 stream surface in the arbitrary orthogonal curvilinear system were derived in detail firstly, while the expressions and solving method of all the items in the equations were also given. The central flowpath S2 stream surface calculation method was then developed with the adoption of the non-conservative variables, the implicit time marching method, the upwind approximate factorization format, the 3rd order TVD difference scheme and the Riemann solver, etc. The numerical precision of the S2 stream surface calculation method was validated by the application to calculating the flow parameters of a flowpath with pump and the Mason Laval nozzle. Because the inviscid Euler equations were used as the governing equations, a loss model to simulate the secondary flow losses caused by the fluid viscosity, which was in term of the quadratic function, was also proposed. The quadratic function and the exponential function with the geometric and the aerodynamic parameters were adopted to describe the vortex core loss and the boundary layer loss respectively. The S2 stream surface calculation method with the loss model was then applied to predicting the performance of a linear cascade and a 1.5-stage low pressure turbine respectively. Compared with the experimental and the full three dimensional calculation results, the S2 stream surface calculation method with the proposed secondary flow loss model was able to predict the total performance and the aerodynamic parameters distribution with credible accuracy while the calculation resource consumption reduced significantly.Three calculation models for the thermal properties of vapor and steam, which were suitable for the S2 stream surface calculation method, were developed. They were the“Ideal Steam” model which calculated the thermal properties by using the formulations of ideal gas and the varied variables, the “IF97 Table” model which calculated the thermal properties by making several blocking and inerratic thermal tables with the IAPWS-IF 97 industrial formulation, the “Young Function” model which calculated the thermal properties by the simple function for the vapor and steam proposed by Young J B. A part of the Mollier diagram was also made by the three different models to examine the calculation precision of the vapor and steam at different states. It was seen that the results of the “IF97Table” model and the “Young Function” model were almost the same with each other, but the result of the “Ideal Gas” model was little worse, especially in the zones away from the evaluated h-s curve and in the wet steam region. A calculation method for the equilibrium wet steam was then developed by using the three different models, and it was applied to predicting the performance of a 1-stage low pressure steam turbine with super-heated vapor and a 1.5-stage low pressure steam turbine with wet steam respectively, and the results were used to be compared with the three dimensional ones. It was found that the results of the three models for the turbine with super-heated vapor were almost the same with each other, and the “Ideal Gas” model cost the shortest time to finish the calculation. But the calculation error of the “Ideal Gas” model for the wet steam turbine was noticeable, while those of the two other models were close to the full three dimensional results, supplying a credible calculation method for the equilibrium wet steam flow property.On basis of the above work, a calculation method considering about the two-phase wet steam flow with spontaneous condensation was developed with the Eulerian/Eulerian multi-phase model. The classic nucleation theory and the governing equations for the wetness and the droplet number were applied to describe the generation and growth of the liquid phase. The 2nd order NND difference scheme and the FVS type Van Leer format were used to solve the governing equations of the liquid phase. The “Young Function” model was chosen to calculate the thermal properties of the vapor and liquid. In the application to the Laval nozzles with the non-equilibrium wet steam flow, a better agreement with the experimental results were obtained by adding a correction function f to the nucleation rate formulation to introduce the nucleation position moving forward and the nucleation intensity increasing. The S2 stream surface calculation method was then applied to the performance prediction of a 3-stage low pressure steam turbine by using the single phase,the equilibrium wet steam and the non-equilibrium wet steam with a moisture loss model respectively. It was found that the through flow ability was strengthened and the aerodynamic efficiency was reduced while the wet steam was taken into account. Compared with the results with the equilibrium wet steam flow, the subcooling in the non-equilibrium wet steam flow lead the wetness emerged later, while the aerodynamic parameters in the supersaturation zones became lower and the difference of the parameters in the wet steam zones changed to be smaller. At the same time, limited by the exit pressure, the blade load of the last rotor tended to be larger. Besides, the moisture losses in the turbine stage with wet steam should not be neglected, among which the super-saturation loss, the condensation loss and the braking loss were obvious particularly, providing some suggestions for the steam turbine design.Finally, the effects of the added correction function to the nucleation rate formulation and its calculation precision were further validated by the application to the Moses-Stein Laval nozzle and the White cascade using the full three dimensional program. A profiling method for the non-axisymmetric end wall in term of the sine function was developed. It was applied to re-profile the end wall of the White cascade to study its influence on the aerodynamic performance and the nucleation property of steam turbine. It was seen that the frontal placed crest had little influence on the performance. If the non-axisymmetric end wall warping located nearby the trailing edge, the aerodynamic loss increased significantly with a sharp flow separation on the corner of the suction side. While the crest was in the middle of the axial chord, a well improvement of the aerodynamic performance was achieved. Besides, the steam condensation nearby the end wall was restrained significantly while the non-axisymmetric end wall warping was in the middle axial chord or closing the trailing edge, supplying a well foundation to improve the aerodynamic performance and control the steam condensation in the steam turbine. |
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