Bionic Design And Numerical Simulation Of The Birds Airfoil Of Axial Flow Blade For Air-Conditioner

With the rapid development of the technology and living standards,there is a growing requirement for electrical appliances such as air conditioners to regulate indoor air quality.Reducing the noise of the air conditioning outdoor units has become an essential research topic,while satisfying the required aerodynamic performance.We systematically studied the noise and aerodynamic performance of axial flow fans in air conditioning outdoor units using a combined approach of theoretical analysis,numerical calculation,and experimental research,which is intended to regulate the mutual impact between the noise and aerodynamic performance of air conditioning outdoor units.In this thesis,based on the cross-section of seagulls’wing profile and the bionic wavy leading edge,we performed a bionic design on the fan impeller of a household air conditioning outdoor unit and established a bionic wavy leading-edge impeller,a seagull airfoil impeller,and a coupled bionic impeller.The effect of these bionic impellers on the aerodynamic performance of air conditioning outdoor units was analyzed by numerical simulations and we compared them with the original impeller.The results showed that under rated conditions,the total pressure efficiency of the bionic wavy leading-edge impeller,the seagull airfoil impeller,and the coupled bionic impeller（I-2,I-3,and I-4）respectively increased by 0.62%,1.81%,and 2.82%compared to the original impeller（I-1）.In addition,we also studied the surface static pressure,the characteristic section static pressure,the axial airflow velocity,and the surface vortex distribution of these four impellers.The results showed that the pressure gradient on the surface of I-4 is more uniform than that of other impellers,and the difference between the suction and pressure side of I-4 is also smaller than that of other impellers.Bionic structures can improve the static pressure distribution of impellers,but the coupled bionic structure can further reduce the surface eddy currents and backflow,and suppress turbulent noise.The maximum axial airflow velocity of I-4 is 12.2 m s^-1,which can ensure the outlet flow of air conditioning outdoor units,and the coupled bionic structure can reduce the separation bubbles on the blade surface,causing the main airflow more stable.We applied the steady-state convergence results as the initial flow field for unsteady calculations in this thesis.With the sliding mesh and large eddy simulation（LES）methods,we analyzed the impeller surface broadband noise,the sound pressure directivity,and the sound pressure level spectrum.The results indicated that there is a high-value broadband noise close to the leading edge and blade tip.The overall broadband noise of I-3 is 3.59d B lower than that of I-1,while I-4 is lower than I-3 at the blade tip and leading-edge positions.With the coupled bionic optimization,the sound pressure level directivity distribution changes from"8"for I-1 to"0"for I-4,and the overall sound pressure level of I-4 reaches 7.9 d B,which is lower than that of I-1.The sound pressure levels of I-2,I-3,and I-4 are lower than that of I-1 in the low to mid-frequency range,while the broadband noise and discrete noise of I-4 in the low to mid-frequency range are lower,especially near 1000 Hz.In this thesis,we acquired the best impeller I-4,which underwent fluid-structure interaction analysis in five operating conditions to verify its safety.The results indicated that the maximum stress for I-4 is 40.718 MPa,leading to the minimum safety factor of3.49,which is greater than the allowable safety factor of 2,indicating that the strength is sufficient.Additionally,the maximum deformation of the blade is 27.537 mm,which accounts for only 2.73%of the blade height,indicating the negligible deformation.Modal analyses of I-4 and I-1 in free,centrifugal force,and aeroelasticity states were also compared in this thesis.The results showed the similar vibration modes in all three states,and I-4 has a lower vibration frequency than I-1,which can reduce the fatigue and damage and has the higher stability..Furthermore,the maximum deformation of I-4 is smaller and more uniform than that of I-1.Overall,we obtained the optimal coupled bionic structure and verified its safety by studying the aerodynamic performance,flow field and noise of four kinds of air conditioning outdoor axial flow fans.The findings of this study have theoretical significance for the development of high-performance and low-noise axial flow fans in the future.