| The noise pollution has been already become the third pollution problem currently in addition to air pollution and water pollution in recent decades; therefore,the technologies of reduced noise have received considerable attention due to environmental deterioration.As mechanical equipment of industrial and agricultural production and people's daily life in a wide application range,the operated noise of fan has become an important composing of industrial noise.The aerodynamic noise run accounted for more than 45%of the fan operation noise. The effective control of aerodynamic noise of fan has received considerable attention in the academic and industrial sectors,however,it is difficulty to reduce the aerodynamic noise of fan by only means of engineering.The living body evolves various complex structure and morphological components in order to adapt well to environment and survival demand.The structure,morphological component and material were optimized and coupled each other that possess of many excellent functions,which become new hotspot control aerodynamic noise of the fan by bionic engineering.The key technology and experimental study of the coupling bionic control of aerodynamic noise of fan was mainly study in this paper.The noise 3D model of coupling bionic fan was designed by CATIA.The characteristics of noise were analyzed by use of COMSOL.Based on the basic methods of bionics engineering,the reduced noise theory of coupling bionic fan was extracted,which include:the typical biological-the surface analysis of long eared-owl coupling noise characteristics,coupling bionic silencer,the theoretical model of sound absorption;the design of coupling bionic reducing noise fan model.The researches deal with biology,aerodynamics,aero acoustics and design optimization of turbine machinery,which were multi-disciplinary cross-integration of knowledge.The coupling muffler features of organisms were the basis of this study.The noise of Long eared-owls in North China was compared with a variety of birds. The features of impact of typical organisms form coupling reduced noise were investigated,which the results shown that the flight noise of long eared-owl is much smaller than those of other birds.The surface reduced noise system of long eared-owl surface include:two wings with the non-smooth tile-like shape and the airfoil of owl wing with the special configuration,which made of coupling characteristics with a typical shape and configuration.The particular porous layer of skin and structure of soft Feather at the abdomen composed the structure and morphology of sound-absorbing.The coupling muffler features with long eared-owl wing morphology and configuration include:the long eared-owl wing feathers were soft bulk of the macro effects;the wing edge outline is continuous arc dentate curve and the wing surface composed of a unique geometric outline of the shape and configuration coupling characteristics.Using of reverse engineering,point cloud datum of basic configuration of long ears owl wing of have been obtained,which determine the high of unit and center line spacing ratio that the optimization value is 0.15-0.2. Based on 3D point cloud datum,the muffler physical models have been acquired by CAD;therefore,the coupling silencer mechanism of long ears owl wing has been analyzed by using of finite element simulation.The absorption functions of abdomen,skin of Long eared-owl and Feather were examined and found that it has broadband absorption,which the largest absorption coefficient is 0.5.The skin and Feather of long eared-owl were examined by microscope and found that it was obvious multi-storey structure with different layers and morphological characteristics,which comprised coupling sound-absorbing system with multi-level structure.Found on the bionic information of owl,the coupling cavity bionic acoustic model is composed of micro-level joint board,micro-thin layer and perforated board.Based on the existing sound-absorbing structure theory,the coupling bionic acoustic absorption coefficient model calculation equation was formed;bionic acoustic coupling calculated structure of the absorption and biological characteristics of the prototype has the same trend.Based on coupling noise modeling of typical characteristics of organisms and traditional mechanical noise of wind turbine design theory,the coupling bionic fan aerodynamic noise control system is divided into coupling bionic muffler system and Coupling bionic absorption system.The coupling bionic muffler system of fan was composed of axial flow fan blade airfoil basic outline of a special configuration,blades non-smooth surface morphology and both physical connectivity through the coupling.However,the coupling bionic absorption system of fan was composed of multi-lingual centrifugal fan cochlear absorption structure,surface-slit with a special form of non-smooth and flexible layers are made.Three coupling factors were connected with physical form,which the structural factor is mainly coupling unit.The experimental results shown that the aerodynamic noise of two coupling bionic fan reduction system is lower than those of the former in anechoic chamber.The effect of coupling bionic models of two fan noise reduced was investigated by COMSOL and PATRAN.The simulation system of coupling bionic muffler can be composed of the flow simulation by RANS methods,the analysis of aerodynamic noise sound by Lighthill equation,the computing domain with the mixed mesh of tetrahedron and hexahedral grid.In order to guarantee the numerical accuracy of the calculations the accuracy,the unique mesh principles were composed of the grid refinement on the flow direction,reasonable boundary layer mesh within the region,the grid of near the wall with wing chord about the scale 1/10~4,the non-smooth front airfoil shape,margin,wingtip suitable encryption and the two models from the same grid parameters.The results shown that the noise of coupling bionic silencer model is lower than that of smooth blades,by as much as 2-5 dB.The decrease of the noise may be induced by the optimization of blades surface flow parameters that delay blades around the flow of surface separation or lower leaf surface turbulent boundary layer pressure fluctuation strength that can reduce between blade interference the airflow and the sound energy generated.The vibration modal method was used to analyze the numerical simulation of coupling bionic absorption system.The grid system was encrypted in porous and micro-seam,which the results shown that the noise was obviously decayed through coupling bionic absorption system that was transformed into heat and distributed out it.The coupling reducing noise mechanism was revealed by the numerical simulation of coupling bionic absorption system:First,the movement of air and the hole of wall friction were arisen from sound wave at Feather,the villi and the dermis layer holes,due to friction and viscosity of the role,which a considerable part of sound energy were transformed into heat,thus making sound attenuation, reflective voice weakened,the role played acoustic;Second,because of small holes in the air in a certain frequency of the sound waves under a resonance,the energy of a muffler noise were absorbed;third,in the air between fiber the wall and small holes,the heat loss arose from heat exchange;the fourth,Long-owl hours,surface and air friction can produce high-frequency sound waves within the dermis layer of air between the porous particles faster the vibration and air-holes in the dermis layer of the wall Accelerate the exchange of heat with its skin absorption capacity, the fifth,Long-owl Feather in the air or acoustic villi under deformation and a micro-vibration,sound or kinetic energy can flow into the feathers that can be deformed,thus reducing the noise generated energy,to achieve the purpose of rectifying noise.The primary objective of numerical simulation of flow control is to investigate relations between organisms form coupled noise characteristics and the actual implementation of projects coupled with bionic noise reduction system.The coupled bionic noise reduction mechanism was revealed by numerical analysis.It is practicable to apply the coupled aerodynamic characteristics for fan noise control, which was confirmed by noise experiment.Typical organisms are a very complex system in the existing conditions,which can not be achieved its full modeling.The concept of coupling bionic fan aerodynamic noise control is a new concept for further in-depth post-graduate objects of applied engineering practice and provides a method. |
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