| Continuous wave mud pulse transmission technology is the frontier development direction of data-driven mud pulse transmission technology.To resist complex noise interference and ensure reliable and high-speed transmission,the downhole continuous wave pulser needs to generate a highly similar sinusoidal original pressure waveform.Therefore,the design of the rotary valve structure is particularly important.Considering that the oscillating shear valve has the advantages of less clogging and convenient waveform modulation than the rotary valve,this paper proposed a scheme that the end face structure of the rotary valve and the non-end structure of the rotor are optimized,which was under the premise of motor acceleration-uniform speed-deceleration,to obtain the shape of the rotary valve that can be applied on site.The main work is as follows:The optimal design index of the rotor under non-uniform motion conditions is set.When the end face structure was designed,the correlation coefficient between the theoretical pressure difference and standard sinusoidal signal are used as the evaluation indexes.When the non-end surface structure was designed,the minimum of mean value and amplitude difference of the hydraulic torque received by the rotor were used as evaluation indexes.Under the non-uniform speed condition(acceleration-uniform-deceleration),the rotary valve structure optimization algorithm for the end face structure of the oscillating shear valve was presented.Based on the relationship between the flow area of the valve port and the pressure difference of the fluid,the polar coordinate equation of the flow area of the valve port was established.By analyzing the variation between the flow area and the relative rotation angle of the rotor to the stator,a straight-arc fan shape valve optimization method,which can output pressure sinusoidal wave signal with correlation coefficient up to 0.9997 was obtained.The rationality of the end face structure design is verified.The computational fluid dynamics of the rotary valve are analyzed in depth,and the simulation model with straight-arc-sector end structure is established by Ansys.The UDF is used to realize the variable speed movement of the rotary valve.Therefore,the variation law of the differential pressure and the rotation angle of the valve port is obtained,and the numerical calculation and fluid simulation results are compared and analyzed.The design method of non-end structure of oscillating shear valve has been deeply studied.The research shows that hydraulic torque is the critical factor affecting the optimization of non-end structure.Therefore,the numerical calculation of hydraulic torque is carried out on the basis of momentum moment.The finite element analysis software is used to simulate the stress process of the rotor,the relationship between the hydraulic torque and the rotation angle of the valve body is analyzed.A non-end structure of the rotor,which can make the mean and amplitude difference of the hydraulic torque smaller is obtained.An improved Oscillating shear valve orifice is designed based on a fan-shaped valve port with a stator diameter of 90 mm and a rotor diameter of 80 mm.The structure of the oscillating shear valve is with a circular arc radius of 26.7 mm,a straight line of 1.08 mm,an inclination angle of 15°,a rotor thickness of 5 mm,and a stator-rotor clearance of 1 mm.This valve type can generate a sinusoidal pressure waveform with a correlation coefficient of up to0.999 or more,and at the same time,a smooth hydraulic torque can be obtained to reduce the control difficulty of the motor. |
