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Research Of Drag Reduction Performance Of Roll Forming Microgrooves On Flat Sheet Metal

Posted on:2016-11-19Degree:MasterType:Thesis
Country:ChinaCandidate:W WangFull Text:PDF
GTID:2181330467499881Subject:Materials Processing Engineering
Abstract/Summary:PDF Full Text Request
Studies found that microstructured surfaces have many functions, such as opticalproperty, frictional property, lubricity property, wear-resistant property, etc, as a form ofmicrostructured surfaces, microgroove surfaces have great value in automobile,shipbuilding, aerospace and pipeline transportation. Because of the predominant dragreduction properties of microgroove surfaces, drag reduction ability and mechanism ofgrooves in different shapes were investigated in this paper.In the researches for drag reduction property of microgroove surfaces, traditionalmethods are wind tunnel experiment and water tunnel experiment in main, but theexperimental conditions are greatly influenced by various factors, costing much time andmoney. In order to overcome the shortcomings of traditional methods, numericalsimulation was used in this paper to research the drag reduction properties of roll formedmicrogroove surfaces. The flow characteristics and drag reduction effects of grooveswith different shapes were compared and analyzed to provide the basis for designingmore effective grooves. This paper follows:1. To verify the veracity and reliability of numerical simulation, a triangular groovewith α=60o、s=0.5mm、h=0.433mm was calculated under the flow velocity of10m/s. Thefriction coefficient of smooth flat surface was nearly the same as the theoreticalcalculation value, proving the high precision and accuracy of the numerical simulation.2. The effect of microgroove on the flow state near wall was analyzed. Based onthe calculation results of triangular groove with α=60o、s=0.5mm、h=0.433mm underdifferent inflow velocity, the wall shear stress, pressure drag, velocity, turbulenceintensity, turbulence kinetic energy and turbulence dissipation rate on the micro-grooveswere investigated. The shear force of level interval on microgroove surfaces was greater than that on smooth surfaces, while the shear force on microgroove surfaces was lessthan that on the smooth surfaces. As a whole, the total wall shear stress on microgroovesurfaces was less than that on smooth surfaces. The pressure drag on smooth surfaceswas0, while the pressure on windward and leeward side of microgroove surfaces wasdifferent, resulting in pressure drag difference. The velocity gradient in the near wallregion of microgroove surfaces was much less than that of smooth surfaces, so theviscous sub-layer was thicker. The turbulent kinetic energy, turbulence intensity andturbulence dissipation rate on microgroove surfaces were less than those on smoothsurfaces, proving the stable flow characteristics on microgroove surfaces.3. The drag reduction mechanism of microgroove surfaces was explored. Theexistence of microgroove surfaces changed the flow state in the boundary layer. Lowspeed whirlpools formed at the bottom of grooves, increasing the thickness of laminarsub-layer and inhibiting the promotion of turbulence, and transforming the slidingfriction into rolling friction between air and walls, playing a role similar to "rollingbearing", reducing the shear stress. The viscous sub-layer of microgroove surfaces wasthicker than that on smooth surfaces, the stable flow area was relatively lager.Micro-grooves only significant affected the boundary layer of fluid but not on outer layerflow field.4. The drag reduction effect of micrgroove with different shapes was researched.The flow states on the microgroove surfaces with sixteen kinds of shapes were numericalsimulated under the flow velocity of10m/s. Results showed that various shapes ofmicro-grooves had drag reduction effects and obvious vortex forms inside them. Thethickness of viscous sub-layer on the surfaces with different shapes of grooves wasnearly same and greater than that on the smooth surfaces. So the steady flow region onthe microgroove surfaces was relatively larger, and it had more bands under low speed.The shear force on triangle and trapezoidal groove surfaces was larger, and the pressuredrag on square and semicircle grooved surfaces was bigger. As the drag reduction ability should be evaluated with the combination of shear force and pressure drag, themicrogroove surfaces with triangle and trapezoidal grooves had better drag reductioneffects, while the effects of square and semicircle groove surfaces were poor. Theturbulent kinetic energy and turbulent strength near wall on the wavy grooved surfaceswere larger than those on surfaces with other shapes, leading to the worst drag reductioneffect.
Keywords/Search Tags:Roll forming, microgroove surfaces, drag reduction, flow field, numericalsimulation, bionic
PDF Full Text Request
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