| Chinese shale gas reserves rank first in the world.To solve the energy problem,the country has recently vigorously promoted the extraction of shale gas.As the core equipment for shale gas extraction,the electric drive fracturing system has shown the development trend of replacing the traditional diesel-driven fracturing system because of its advantages such as high individual power,low noise and strong continuous operation capability.The electric drive fracturing system is mostly vehicle-mounted,so its drive motor is usually designed with a high electromagnetic load and high power density,resulting in serious heat generation and high temperature rise,which seriously affects the operational reliability and requires accurate prediction of motor-wide temperature rise distribution and effective suppression.However,due to the large size and complex structure of the motor,it is difficult to accurately simulate the motor full-domain fluid flow behavior and predict the temperature rise distribution by traditional methods,and a multi-physics field coupling analysis is required.Therefore,this paper focuses on the multi-physics field coupling analysis and temperature rise suppression of the fracturing pump drive motor.Firstly,the electromagnetic field analysis model and the full-domain fluid field-temperature field analysis model were established according to the dimensional parameters and cooling structure of the fracturing pump drive motor,respectively.And the physical model is simplified according to the fluid flow characteristics and heat transfer.On this basis,the interactions,effects,and constraints among the electromagnetic field,fluid field,and temperature field are analyzed.The bi-directional coupling analysis is split into "forward" and "reverse" to fully consider the influence of temperature on the loss characteristics of the motor,internal fluid flow,and convective heat transfer.The data mapping method is used to map the data between the heterogeneous grid nodes of different analysis models.A multi-field,bi-directional coupling analysis method for the fracture pump drive motor is developed.On this basis,the multi-field bidirectional coupling solution of the prototype was carried out to obtain the full-domain flow-thermal and loss characteristics of the motor as well as the internal fluid flow characteristics,flow distribution,and temperature rise distribution of each structure.The differences between unidirectional and bidirectional coupling are also compared and analyzed.The results show that the two-way coupling analysis method has a significant effect on the thermal conductivity,viscosity,and motor loss distribution of the cooling fluid.The increase in thermal conductivity directly increases the convective heat transfer intensity.An increase in viscosity leads to a decrease in fluid flow rate,an increase in viscous heat,and fluid pressure drop.The increase in total losses changes the heat source distribution.The motor temperature rise becomes higher due to the combination of the above effects.Finally,a test prototype was developed and a platform test was built to obtain the loss and temperature rise of the prototype at rated operating conditions.The comparative analysis of the data shows that the relative errors of loss and temperature rise between the two-way coupling analysis and the test value are 3% and 4.4%,which are 3% and 0.6% lower than those between the one-way coupling analysis and the test value and are closer to the test value.It verifies the rationality of the established multi-field coupling analysis model and the effectiveness of the proposed bi-directional coupling analysis method.Based on the field synergy theory,the stator cooling reinforcement structure,the air deflector,is designed based on the spatial fluid flow characteristics and stator winding temperature rise distribution at the air outlet side of the motor.The mechanism of the air deflector in the stator cooling strengthening is analyzed.The cooling strengthening capability is verified by using multi-field bi-directional coupling analysis.The average flow rate of cooling air near the end winding was increased from 7.0m/s to27.5m/s,and the maximum and average temperature rise of the stator winding decreased by 5.2K and 2.6K,or 4.5% and 2.2%,respectively.The effects of the position parameters and size parameters of the air deflector on the flow-thermal characteristics of the motor were further investigated.Based on the full factorial test method,the optimal combination of air guide parameters is determined,which can reduce the maximum stator winding temperature rise by 9.0K,with a reduction of 7.7%.And on this basis,the cooling enhancement effect of an air deflector is studied in depth,and the principle of application of an air deflector in motor stator cooling enhancement with universal applicability is formed.Based on fluid dynamics theory,the effect of the rotor guide vane on the fluid flow behavior and temperature rise distribution characteristics of the motor was investigated using the multi-field bidirectional coupling analysis method.It is found that the rotor guide vanes can change the flow distribution of cooling air and suppress vortex generation,and the flow rates in the axial ventilation channel between the stator core and the housing and air gap increase by 0.21kg/min and 0.52kg/min,respectively,with an increase of 0.2% and 8.6%.The cooling air flow rate on the inner and outer surfaces of the stator core is increased,which in turn increases the convective heat transfer intensity and enhances the heat dissipation capacity in the stator region.On this basis,the effects of the number of the rotor guide vane and geometrical structure parameters on the flow-thermal characteristics of the motor are obtained.The influence law of the rotor guide vane in motor cooling enhancement and the method of extension application are revealed by the response surface method.The dissertation also analyzed the mechanism of the role of axial ventilation holes in the cooling enhancement of electric motors and determined the factors affecting their cooling enhancement capability,including the size,number,and location of axial ventilation holes.The Taguchi method is applied to study the influence law and degree of influence of each influencing factor on the magnetic-fluid-thermal characteristics of the motor,and the optimal grade value of each factor is given,which can reduce the maximum temperature rise of the motor stator winding by 8.2K,a reduction of 7.1%.The degree and law of influence of each factor are integrated,and the principle of improvement of axial ventilation holes in motor cooling enhancement is proposed.The research results of this dissertation can provide a reference for temperature rise prediction and cooling enhancement of the fracturing pump drive motor.The proposed multi-field bi-directional coupling research method,and cooling enhancement structure,and application principles can be used in other motor cooling enhancement. |
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