Research On Aerodynamic Design Method And Flow Control Of Helium Turbine

The closed Brayton power plant,using helium as the working fluid,has the advantages of no external working fluid,high power density,long working hours and no pollution,which provides an effective method to solve the power problem of propulsion device.As one of the key components of the helium closed Brayton cycle power system,the performance of the helium turbine will directly affect the reliability of the entire power plant.However,due to the special physical and chemical properties of the working fluid,the helium turbine has the characteristics of many stages,high load coefficient,low aspect ratio and large turning angle,which leads to the high proportion of boundary layer loss and endwall flow loss.Therefore,the efficiency of the helium turbine is generally low.It is of far-reaching significance to study the boundary layer flow characteristics of the helium turbine cascade and the endwall loss mechanism and control for improving the aerodynamic performance of the helium turbine.Firstly,the aerodynamic design of a helium turbine,which belongs to a pre-cooled engine,is studied in this paper.The effects of flow coefficient,load coefficient and reaction degree on the aerodynamic performance of the turbine are studied.The efficiency is high while ensuring the load power consumption.The research results show that the best design scheme is when a two-stage design is adopted,the flow coefficient is 0.5,the load coefficient is 1.8,and the reaction degree is 0.2.This helium turbine has the characteristics of low aspect ratio,large turning angle,small flow coefficient and high load coefficient.Because of the high boundary layer loss and endwall loss,the efficiency of helium turbine is only 85.57%.Secondly,in order to solve the problem of high loss of helium boundary layer,taking the first-stage rotor blade mid-diameter section as the research object,the effects of inlet turbulence,attack angle and Reynolds number on the surface boundary layer flow of the blade is studied separately.By comparing the transition point position,the size of the separation bubble,the thickness of the boundary layer,the load coefficient,the total pressure loss coefficient and other parameters,it is found that the negative angle of attack,high turbulence,high Reynolds number can reduce or even eliminate the boundary layer separation downstream of the suction surface.In a wide range of negative angle of attack can maintain a low total pressure loss,and the efficiency is highest at-5° angle of attack.In order to explore the best load distribution form of the helium turbine rotor blade,the front loading,uniform loading and after loading blade were studied under different conditions,and it was found that the uniform loading blade was the best choose under low Reynolds number condition.In the design and high Reynolds number condition,the aerodynamic loss of the front loaded cascade is the smallest,and the load coefficient is high,and the work ability is stronger.Finally,aiming at the problem of large endwall loss,the first stage of helium turbine is selected as the research object.Through comparative analysis of the difference between the internal flow and aerodynamic performance of the first-stage rotor blades with straight blades,forward bowed,backward bowed,and reverse J-shaped designs,the results show that the reverse J type is the best design scheme when the bending height is 50% and the bending angle is 20°.It is not only improving the mainstream flow and the stage efficiency by 0.1%,but also increasing the output power of the stage.Through the research on the performance of J-type design under variable working conditions,it is found that the efficiency of reverse J-type design is higher than that of the original design at different working conditions,and it has good performance under variable working conditions.especially at the low working conditions of 15 kg/s mass flow,the efficiency is increased by 2.3% compared with the original design.