Optimization And Simulation Analysis Of Downhole Generator Turbine And Its Support Structure

The downhole generator is a kind of instruments which utilize mud flow energy to generate power circularly,and it is widely used in MWD / LWD system.The turbine of the downhole generator is rotated by the impact of the mud during work,it's normal working condition decides to its supporting bearings directly.At present,the turbine support bearings of mainstream products are contacted with mud directly.However,it's poor lubrication conditions and easy to wear limits the operation life of the downhole generator.Aiming at the above problems,the investigation based on the existing downhole generator structure,researched and optimized a new type of turbine support structure to extend the life of support bearing,optimized the parameters of the guide wheel and turbine blades.The main research contents are as follows:(1)Investigate of the current situation of domestic and foreign downhole generator technology,which the trends are high power,long life,compact structure.And put improving the operation life of turbine support bearing as the core research idea;(2)A structure of cantilever supported turbine was proposed according to the principle of downhole generator and its main structure.The turbine rotation was supported by a central shaft,and moves the support bearing into a closed lubrication chamber to improve its working environment;And used rolling bearing instead of sliding bearing.Adopted the combined sealing method of mechanical seal and rotating movable seal ring and add the balance piston mechanism to reduce the sealing pressure under the downhole working conditions;(3)Based on the theory of fluid movement in the guide vane and turbine channel and the actual use of mud output volume,adopted the blade form of equal thickness and equal pitch,and modified the parameters of guide vane of 7 blades,4 mm blade thickness and 23° helix angle.Research the combination of turbine blade profile parameters in each displacement range on this basis;(4)Selected the appropriate numerical solution according to the CFD analysis theory and the flow characteristics of downhole mud.Simulated the flow field of different turbine blade parameters using Fluent software;Optimize the turbine blade parameters of each displacement range based on the axial force and torque of the blade,and determined the forces of the guide vane and turbine under the condition of upper limit displacement;(5)By using finite element analysis researched the static and dynamic characteristics of turbine support structure.And verified the rationality of the structure and material selection;The maximum equivalent stress is 345.18 MPa when the maximum mud displacement is 55L/s;Obtained the first six modes after modal analysis and research the resonance problem by harmonic analysis;Also obtained the transient response of the central shaft during the turbine start-up process after the transient dynamic analysis of the central shaft,the maximum equivalent stress is 658.8MPa which is far less than the yield limit.Through the above work,mastered the design and modeling method of each part of the downhole generator,optimized the hydraulic guide wheel and turbine blade parameters;and carry out three-dimensional flow field dynamics analysis and finite element analysis to verify its rationality.The research results provide guidance for the research of downhole generator.