Study On The Flow Field Of Impulse Mechanism Of Mud Pulser

The thesis has been done on the basis of the research project of high rate mud pulse telemetry system,has calculated and analyzed the flow field of of Impulse Mechanism of Mud Pulser,with UG and CFD as a software platform,and compared with experimental validation,to guide the structural design,reduce design time and improve efficiency.In this paper,it analyzes the flow field on mud pulse generater with the computational fluid dynamics method.The main work and research are as follows:1)Analyzed the working mechanism of the mud pulse generator and factors of pulse signal attenuation and methods to improve pulse strength,The rotor's hydraulic torque is a very important performance factor for Operating Characteristics of mud pulse generator;Initially,we designed the stator and rotor structures and used UG software to create their three-dimensional models.2) Assuming the flow mode of mud pulse generater to create a three-dimensional flow model and to do flow field numerical computation;Analyzed the characteristics of a variety of turbulence models,velocity-pressure coupling algorithms and discrete manners;Selected the most suitable model and algorithms for this research by comprehensive analysis and evaluation;Finally;3) The paper studied the flow field characteristics of the mud pulse generator by numerical calculation,and the flow field analysis and calculations were studied separately from these factors of the rotor blade shape,rotor blade thickness,the number of rotor blades,rotorthe speed of the rotor, the gap between the stator and rotor;4)Compared with the experiments. tal results,the numerical calculation results were verified with the feasibility of the resulThis paper made a comprehensive analysis for the characteristics of the rotor flow field and its causes, the following conclusions:Shape of the rotor opening have a greater impact on the performance of the pressure pulse generator,Sector valve port and rectangular port valves have a dramatic impact on the fluid motion of the pressure pulse generator and by changing the blade edge,make it tend to smoothly change.The changes of the leaf shape can effectively reduce the force of the rotor withstood,such as the rotor with the triangular valve port and,studies show that the withstanded force of the rotor the rotor with the triangular valve port is better,compared with the rotors of sector valve port and rectangular port valves;In the condition of the constant mud flow and the constant gap between the stator and rotor,the changes in the thickness of the rotor blades had little effect on pressure pulse strength and pressure pulse waveform,However, the hydraulic torque of the rotor withstood makes a great change,along with thickening the rotor blades,hydraulic torque of the rotor blades of gradually increases;In the same condition of the mud flow and the gap between the stator and rotor, increasing in the number of the rotor blades leads to the increase of the flow area the axial clearance caused by, resulting in weakening of the pressure pulse signal and the hydraulic torque of the corresponding rotor is also reduced accordingly.Under the circumstances of the different number of leaves, in order to obtain the same amplitude of the pressure pulse signal,we turn it that the gap between the four-blade stator and rotor is decreased,and the torque is still smaller than the torqueof the three-blade rotor. So it can reduce the rotor torque by increasing the number of rotor blades and has improved control performance of the motor.The change of the speed of the rotor has no significant impact on pressure waveform,but with the speed of the rotor increasing; phase of the torque lags. To change the gap between the stator and rotor produces a very large impact on hydraulic torque of the rotor and the pressure pulse. As the gap increases,pressure amplitude decreases,the hydraulic torque of the rotor suffered reduces obviously.Through the above analysis,we obtained some basic principles of structural design of the rotor:the change of rotor valve port openings tend to change shape smooth,the pressure wave of triangular valve port is more smooth than sectorial valve port and rectangular valve port,and was closer to the sine wave;Under the premise of ensuring the strength, to minimize the thickness of leaves;Reasonable choice of the gap between the stator and rotor. In the above-mentioned principle, we selected a more appropriate rotor structure to study the relationship between the mud flow and the gap,and obtained the corresponding curve. In the gap between the 0-2mm, we get the higher magnitude of the pressure, but the changes of pressure waveform is a bit confusing,especially as flow increases,the waveform changes more confusably.In the gap for the 2-8mm, pressure amplitude changes relatively large.When the gap is greater than 10mm, the pressure amplitude changes slowly.Through research and analysis we identify the curves of the pressure pulse intensity and flow and clearance,which has some engineering significances for selecting the mud flow and the gap mud pulse generator required of in different depth of drilling.