Numerial Investigation Of Curtis Stage Retrofit In Steam Turbine

In the present paper,the aerodynamic characteristics of a naval steam turbine curtis stage which designed according to the traditional design concept were numerical simulated by using the business software CFX.In the traditional design concept of curtis stage,the first column of the nozzle plays the main role to drop the enthalpy of stage,and the height of subsequent blade can rapidly increase,this is very good to reduce the endwall loss in subsequent blades.In addition,what’s more is that the conventional curtis stage is designed by pure impulse with small ratio and undertakes about 70% of the whole set’s enthalpy drop,so that to meet the design requirements of light weight,compact structure.However,there are three nozzle groups in fully circumference,each group has low partial air inflow rate,in order to achieve the purpose of regulating power in the factors of the top location of curtis stage nozzles,the high parameters of steam and the short blade.The shor tblades with high load can increase local inlet loss,the flow efficiency of first column nozzle is very low.The reaction o f the first column rotor,the second column stator(also known as the wizard leaf)and the second column rotor is very low.In the relative and absolute coordinate system,the boundary layer of blade surface is almost not flow under the conditions of press ure drop,and the transition and separation may occur,then the profile loss is very large.The flow conditions in the bad influence,which lead to the loss of traditional curtis stage is very high,and then reduce the relative internal efficiency of naval steam turbine,especially in the cruising condition.Traditional curtis stage using the nozzles to adjust,the local air inflow rate of the three nozzles which distribute in the first column blade of turbine is different,and the thickness between nozzle group is certain.Due to the existence of local air intake and partition,the first column nozzle exit flow field structure distortion along the circumferential direction,leads to the subsequent flow field is unsteady flow.Especially for any rotor in the process of its rotation week,not only through the mainstream area and wake area of three groups nozzle blade,but also through three areas without air flow of nozzle area partition,The rotor rotating enter or leave a nozzle group after 2 or 3 moving blade pitchs,then aerodynamic load of blade could reach the normal work load condition,which forms the unsteady flow phenomenon in the internal of curtis stage.