Research For The Electromechanical Matching Performance Of Counter-rotating Fan Based On Electromagnetic-fluid-structure Coupling Analysis

Counter-rotating fan is a kind of axial flow fan with a special structure.Its front and rear impellers are installed directly on the shaft ends of two motors.The two impellers are working impellers as well as the guide impellers for each other.They spin in the opposite directions to form its counter-rotating structure.Due to this mechanical structure,counter-rotating fan has the advantages of small fan size,high pressure coefficient and good performance of reversing airflow.It has been widely used in mine ventilation,tunnel ventilation,boiler air blowing and other air providing cases.In practical applications,however,the counter-rotating fan has such problems as the difficulty in matching the two motors and severe electromechanical resonance of the whole system under certain air supply conditions.Therefore,doing further research into the working mechanism of the counter-rotating fan,identifying the key factors that influence its properties,predicting and controlling its operating performance effectively are the important precondition for ensuring the stable operation with high precision of counter-rotating fan.In order to reveal the coupling performance and interaction effects between electromagnetic field and fluid field,the electromagnetic-fluid coupling model of the counter-rotating fan,with the electrical machine and the wind machine regarded as a whole,was built based on the finite element theories of electromagnetic field and fluid field.Meanwhile,the information interaction mechanism,as well as the state variable residual and the transient time step were introduced.By using the step regression solution technique,the motor electromagnetic-field numerical computation under non-inertial load and the fan fluid-field numerical computation under varying impeller speed were performed,and then,the entire process of coupling simulation analysis in heterogeneous software were completed,which established the foundation for the research work of this paper.Combined with the experimental measurement,the numerical simulations were carried out to analyze the performance of counter-rotating fan.The characteristic curves were obtained from the performance parameters.The system efficiency that takes the electric power as input was brought into the efficiency evaluation.To improve the system efficiency value in the initial and intermediate tunneling stages,the three-layer balanced winding,which has relatively high winding factors for twopoles and three balanced branches for each phase,was constructed on the basis of twin-pole-pairs slot number phase diagram.In addition,the design procedures of its pole-changing motor were explained in detail.The speeds of the front and rear motors were adjusted appropriately to achieve suitable fan performances for different tunneling stage.The theoretical basis for the speed control and energy saving of a high-performed counter-rotating axial flow fan can be set up.The counter-rotating fan is an electromechanical device in which the electromagnetic force and the aerodynamic force coordinate together.To make a thoroughly investigation on the electromechanical resonance and electromechanical resonance in the operational process,the analytic calculation and numerical simulation methods of electromagnetic and aerodynamic force are presented respectively.The interference coefficient of the isolated airfoils was taken into account when calculating the aerodynamic force of the cascade analytically.However,through simulation method based on Bernoulli equation,the aerodynamic force on per unit area of each blade can be calculated directly and accurately.For the electromagnetic force,the analytic calculation method based on the Maxwell equations was used to calculate the amplitudes of the fundamental and harmonic force waves in radial directions,while the time-varying curves of the force waves in radial and tangential directions can be obtained directly through numerical simulation based on the Maxwell stress calculation method equivalent to the virtual displacement method and the appropriated integration path selection.And then,the time-varying curves of the electromagnetic and aerodynamic torque were obtained by the simulation method superior to the analytic method.The time-domain curves of motor electromagnetic torque and fan aerodynamic torque were obtained,then Fourier-transformed and analyzed for the harmonic components.Meanwhile,the resonance effect induced by the same-frequency components between the harmonic electromagnetic and aerodynamic torques was investigated.The impellers with different blade numbers were built with the aid of a3 D laser scanner,and then the torque resonance conditions under four blade number combination schemes was analyzed to explore the relation between vibration and resonance.Moreover,the torque resonance under four slot number combination schemes was explored so as to determine the optimal matching type of two-stage impellers and motors.By using RNG k-? turbulence model,the mechanical resonance arise from the electromagnetic force and aerodynamic force with same frequency was studied and main parameters characterized the turbulence flow were obtained.The relationship between the turbulence intensity and system efficiency was presented.With the turbulence energy and the dissipation rating,the distribution acoustic power on the fan surface were calculated.In the research of electromagnetic noise,the concentrated force in time domain,as well as its real and imaginary parts were obtained.The harmonic response analysis for stator core and motor case with different rotor slot number were respectively performed in ANSYS Mechanical,meanwhile,the numerical calculation of sound pressure level were accomplished in ANSYS Acoustic.