Research On Characteristic Of Curtis Stage Of Steam Turbine

Naval steam turbine has the practical operating characteristic with multiple work conditions and variable speeds, whose two rows governing stages have paramount role on turbo-set with economical efficiency, safety and matching performance of every nozzle. The two rows governing stage of conventional naval steam turbine is Curtis stage, whose pressure distribution way maybe unreasonable in the matter of aerodynamic performance. The second stator acts as only the turning blade and the most pressure drop is in the nozzle, which leads the stage efficient of the governing stage lower. For the common cruising condition of the naval steam turbine, the power of governing stage is about 70 percent of the set'delivered power, so the stage efficient of the governing stage has a huge influence on the economical efficiency of naval steam turbine. In this dissertation, the semi-Curtis stage is used. In order to enhance the utilization efficiency of the airflow velocity, the pressure drop is divided into two rows of stator blades with the same magnitude. Based the above design concept, the corresponding structure form is established to meet the requirements of aerodynamic characteristics in this dissertaton.In the present paper, the 3D flow field numerical simulation of these velocity stages are carried out by using the business software CFX. It points out that Curtis stage, the first nozzle stator hardly undertake all the stage enthalpy drop, the first rotor blade is nearly the pure impulse type, the aerodynamic load is very high. A larger reaction is adopted for the turning blade in order to keep the second rotor blades have enough power outputs while not being in the blowing state. For all that, the flow loss of the stage is still higher.The whole stage numerical simulation is carried out for the new type turbine stage designed by using the semi-Curtis structure form. The results point out that the pressure drop of the governing stage is divided into two rows of stator cascades to reduce the aerodynamic load of the first stator compared to Curtis stage, which can reduce the flow loss by high load. The second stator cascades become to be reaction type of vane from impulse type one and the flow passage has strong convergence, which enhance the work capacity of the flow in the second rotor blade, as well as the aerodynamic performance of this rotor blade, so the flow efficiency of governing stage is improved.By computing the new type Curtis stage with two set of nozzles, which point out that owing to the after blade row undertake higher pressure drop, the pressure of the first stator nozzle outlet is far higher than the back pressure of the governing stage, which cause larger influence on the pressure distribution of the non-nozzle region. The pressure drop of the second stator undertaking is rather lager, and the flow parameter in the second stator cascade flow passage can be well-distributed by strong convergence of the second stator, at the same time, the chord length of the second stator is obvious lager than the first rotor's, which can weaken the unsteady fluctuation of aerodynamic parameter at the inlet of the first rotor.The unsteady numerical simulation is performed on the two stage at the inlet, and the CLOCK effect of two stator rows is computed. It is pointed out that different CLOCK locations correspond to different wake transport features. In one period, the unsteady fluctuations of the pressure on two stator blade surfaces are very small, while the pressure fluctuation amplitude of the rotor blade is far larger than that of the stator vane. The difference is mainly resulted from the unsteady effect.