Study On Optimization Of Regulating Stage Variable Working Condition And External Bypass Characteristics Of A Marine Steam Turbine

The design and improvement of marine steam turbine are generally based on satisfying the applicable conditions of ships and the existing processing technology,and the adaptive structural improvement and optimization are carried out on the basis of the original turbine according to the expected target.Firstly,the thermal analysis is carried out on a target steam turbine,and the structural adjustment design of four schemes(throttle adjustment,nozzle adjustment I and II,and adjustment with bypass nozzle)is carried out.Through one-dimensional calculation and comparative analysis of the thermal characteristics of the improved steam turbine under various working conditions of ships,a scheme of bypass adjustment of graded steam operation under rated load and no bypass conventional operation under partial load is proposed.According to the results of one-dimensional calculation,the three-dimensional numerical simulation of the flow field in the regulating stage is carried out.The results show that the static cascade in the local inlet regulating stage bears a large aerodynamic load.The shock wave generated after the oblique expansion of the steam flow interferes with the boundary layer on the back arc of the local arc section to separate the flow.The axial clearance between the static cascade and the static cascade is small,and the steam flow in the week direction space is insufficient,resulting in uneven distribution of the outlet steam flow in the week direction.After entering the rotor blade,the steam flow forms a local shock wave at the leading edge.After the wave,flow separation occurs in the local back arc region,resulting in large flow loss in the stage.Under the condition of two valves opening,the lower the partial load,the lower the stage efficiency.After clarifying the characteristics and distribution of the original regulating stage with large aerodynamic load and large flow loss,this paper,on the premise of keeping the blade structure unchanged as far as possible,makes modification calculation and analysis on the static blades by the traditional way of controlling secondary flow(static blade inclination,end wall warping Fermentation starter,endwall fence).The results show that the blade inclination and the installation of Wing fence on the meridian end wall reduce the energy loss of the blade to a certain extent,while the warping of the Fermentation starter on the meridian end wall has little effect and even deteriorates the flow effect in the flow passage.Then,the influence of the swept composite modification on the aerodynamic performance of the regulating stage is further studied.The research shows that the swept stator has certain gain under working conditions 1,2 and 4,and the gain in working condition 4 is higher than that in other working conditions,while the in-stage efficiency decreases under working condition 3.After the leading edge of the back arc of the rotor blade is sharpened,the supersonic Mach number of the wave front is not large under working conditions 1,2 and 4.The intensity of the shock wave at the leading edge of the rotor blade after sharpening is weakened,the acceleration effect of the steam flow after sharpening is not obvious,the separation in the upper region of the back arc is intensified,and the stage efficiency is reduced to a certain extent.However,under working condition 3,the shock wave intensity is weakened,the flow separation degree is slightly increased,but the stage efficiency is slightly increased.Finally,according to the operation characteristics of the bypass regulating stage under high operating conditions of the steam turbine,the matching research between the pressure loss of the bypass valve and the flow rate of the whole machine is carried out in the way of whole machine segmentation for the high pressure steam turbine,and the flow field characteristics of the matching points are analyzed.The adaptive swept modification of the static blades of the pressure stage is continued,and the matching of the pressure loss flow rate of the modified valve and the characteristics of the whole machine are further analyzed.The results show that under the design of radial straight blades,the valve pressure loss at the matching point is 12.93%,the valve flow ratio coefficient is 0.5,and the machine efficiency is 78.1644%.The swept back of stationary blades reduced the ratio coefficient to 0.41768,the valve pressure loss to 10.1%,the turbine output slightly increased,and the turbine efficiency increased by 0.3433%.