Research On The Characteristic Of The Multistage Axial Hydraulic Turbine Of The Boost Turbopump

For high pressure hydrogen/oxygen staged combustion rocket engine,boost turbopump technology can effectively improve the anti-cavitations performance of propellant pump and reduce the weight of rocket propellant tanks.The oxygen boost turbopump is usually driven by an axial hydraulic turbine,which is rarely consulted in public literatures,and the internal flow structure and flow loss mechanism are not clear.In terms of this problem,the main work of this paper is as follows:(1)On the basis of AMDC loss model,a one-dimensional design method of multi-stage axial hydraulic turbine is established.Based on the modular design concept,a program for one-dimensional design of the hydraulic turbine is wrote based on Python.And the influence of relevant parameters on the design results is studied.(2)Based on the multi-stage axial hydraulic turbine of SSME,the numerical simulation of the flow field of the hydraulic turbine without gap and with gap are carried out.The detailed flow structures inside the hydraulic turbine are obtained.The vortex structure of the horseshoe vortex,the channel vortex and the leakage vortex are captured.The development process and entropy increase distribution in the cascade channel are analyzed.The flow law in hydraulic turbine is similar to that of small aspect ratio gas turbine.(3)The influence of tip clearance on hydraulic turbine performance and flow structure are numerically studied.The increase of tip clearance will lead to a significant decrease in turbine performance.When the gap ratio increases by 1%,the mass flow will increase by an average of 0.95% and the efficiency will decrease by an average of 2.1%.The increase of tip clearance leads to more proportion of fluid passing through the tip clearance,and the leakage of blade tip clearance through static blade is greater than that of rotor blade tip clearance.In the tip clearance area,there is a separation bubble structure along the edge of the pressure surface.The relative movement of the end wall to the blade will enhance the channel vortex near the end wall and obstruct the leakage flow,and may have a recirculation zone on the blade tip surface.In the rotor cascade,the leakage flow will form a leakage vortex near the suction surface.And then,the leakage vortex will mixed with passage vortices and the main flow,resulting in a great loss.The larger the gap is,the larger the intensity and scale of the leakage vortex will be,which also means the greater flow loss.However,in the stator cascade,there is no obvious leakage vortex.The main reason maybe the influence of upstream flow,and the leakage flow of stator tip clearance is sucked by the upstream flow.(4)Numerical calculation of hydraulic turbine under variable conditions is carried out.The change of the stage-velocity ratio directly changes the attack angle of the blade.The change of the attack angle has a significant effect on the flow of the first half of the tip clearance.The back gap flow is mainly driven by the pressure difference force between two sides and is less affected by the attack angle.Finally,the difference between water and liquid oxygen as the working fluid was compared.It was found that the efficiency values of the two at the same stage speed ratio have a small difference,and the efficiency value calculated by water can be corrected by Reynolds number to obtain the liquid oxygen working condition,and the correction formula was given.