| The angular velocity sensor based on magnetohydrodynamics(MHD)does not contain any rotating parts,has no mechanical saturation,can respond to high-speed and high-frequency vibration,and is suitable for measuring the micro angular vibration of space structures.The design and optimization of MHD angular velocity sensor structure directly determines the accuracy of the sensor.Theoretical analysis and experimental research are needed for the influencing factors of key noise sources.The wall roughness of the closed annular channel in the MHD angular velocity sensor is directly related to the fluid velocity near the wall,and then affects the fluid state in the channel and the contact resistance of the channel wall.In this dissertation,the roughness theory and fine simulation of the closed annular channel in MHD angular velocity sensor,the wall microstructure design and wall contact resistance under the guidance of roughness theory are studied as follows:1)The working principle of MHD angular velocity sensor and the coupling method of electro-magnetic-flow field are described in detail.A refined simulation method of laminar flow roughness based on user-defined function is introduced.2)In the laminar flow roughness model,the roughness viscosity model(RVM)is most suitable for the closed annular channel.However,due to the large velocity gradient between the inner and outer walls of the closed annular channel,the simulation effect of the traditional RVM model is not accurate enough.The local Reynolds number is proposed to replace the global Reynolds number to solve the roughness-viscosity ratio,and the traditional RVM model is modified.The results predicted by the modified RVM model are consistent with the trend in the literature.3)The modified RVM model is used to study the roughness theory of MHD angular velocity sensor through simulation.It is found that the greater the roughness,the smaller the radial secondary flow,one of the error sources of the sensor.A wall microstructure similar to rough element is designed in the radial direction to suppress the secondary flow,and the simulation analysis is carried out.The results show that when the depth of microstructure is designed to be 20μm,the average periodic inner diameter velocity decreases by 9.8%,which effectively reduces the error caused by radial secondary flow.4)Particle image velocimetry is used to measure the velocity.It is found that the experimental and simulation results under different roughness are basically consistent,and the error of average relative velocity is no more than 2%,indicating that the modified RVM model can simulate the roughness effect related to velocity.The roughness affects the pressure through the flow velocity,and then affects the contact resistance.In order to get the effect of roughness on contact resistance,the relationship between roughness and pressure and the relationship between pressure and contact resistance are simulated and explored experimentally respectively.The results show that the larger the relative roughness is,the larger the variation range of dynamic contact resistance of outer wall is,and the variation range is different with axial position.The variation range of dynamic contact resistance is-0.0226μΩ0.0157μΩ with relative roughness of 0.016,and it is the smallest at normalized axial positions η =0and η =0.94. |
