Study And Analyse Airfoil Section Using CFD - IJERT

Published by :http://www.ijert.orgInternational Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 6 Issue 09, September - 2017Study and Analyse Airfoil Section using CFDRajat Veer*, Kiran Shinde*,Vipul Gaikwad*, Pritam Sonawane*,*Student,Department of Mechanical Engineering,RMD Sinhgad School of Engineering,Pune.Abstract— In this report coefficient of drag and coefficient oflift is obtained with the help of CFD, it is also obtained by anexperiment which is conducted on wind tunnel. Though both ofthe methods give approximate result for the same test section, anexperimental process has greater cost and quite laborious thanthat of CFD. Analysis of airfoil over two-dimensional subsonicflow at a various angle of attacks and operating at Reynolds’snumber is obtained. The result shown by CFD has closely agreedwith experiment result, thus CFD is a mature tool to predict theperformance of test section at any angle of attack.Yogesh Sonawane##Assistant Professor,Department of Mechanical Engineering,RMD Sinhgad School of Engineering,Pune.GEOMETRYIn aerodynamics, Airfoil design is a major facet. Differentflight regimes show different results. There are basicdissimilarities between symmetric and asymmetric aerofoillike at zero degree angle of attack, Asymmetric airfoils cangenerate lift, while a frequent inverted flights suits symmetricairfoil as in the case of an aerobatic airplane. Thus withoutboundary layer separation, we can use various angles.Subsonic airfoils have a round leading edge around which it isnaturally insensitive to angle of attack [2].Keywords— Flow separation, angle of attack, CFD, coefficient oflift and coefficient of drag, pressure coefficient etc.INTRODUCTIONIt is fact of common experience that a body in motionthrough a fluid experiences a resultant force mainly aresistance to a motion. A class of body exists, for which thecomponent of resultant force normal to the direction of motionis many times greater than the component resisting the motion[1]. An airfoil is a streamlined body found in airplanes,propellers, turbines and many other applications. When anairfoil body passing through any fluid it produces anaerodynamic force which is due to pressure distribution overthe body surface and shear stress distribution over the bodysurface. This aerodynamic force can be resolved into twocomponents known as lift and drag. The force which acts inperpendicular to the direction of motion is called as lift force,and the force which is parallel to the direction of motion iscalled as drag force. Lift is generated by aerofoil primarilydepends upon surface area and angle of attack. The drag forcemainly depends upon the body surface and fluid which isflows over it. This lift and drag force are obtained with thehelp of wind tunnel. A wind tunnel is a machine which used inaerodynamic research to study the effects of air moving onsolid objects. A wind tunnel consists of a tubular passage withthe object under test mounted in the middle. Air is thenmoving past the object by a powerful fan system or othermeans. The test object often called a wind tunnel model, isinstrumented with suitable sensors to measure aerodynamicforces, pressure distribution, or other aerodynamics-relatedcharacteristics. The advance in computational fluid dynamicsmodeling on a high speed digital computer has reduced thedemand for wind tunnel testing. However, CFD results are stillnot completely reliable and wind tunnels are used to verifyCFD predictions.IJERTV6IS090028Fig 1. Airfoil GeometryThe point at front of the airfoil that has maximum curvature isknown as a Leading edge. The trailing edge is defined as thepoint of minimum curvature at the rear of the airfoil. Thestraight line joining the leading edge and trailing edge ofairfoil section is chord line. Chamber line is the locus ofpoint’s midway between the upper and lower surface of anairfoil. The Angle of attack is measured by taking a differencebetween free stream velocity and chord line. It is the ratio of aspan of an aerofoil to the chord length of an aerofoil is calledas the Aspect ratio.COMPUTATIONAL FLUID DYNAMICS (CFD)Computational Fluid Dynamics is a branch of fluidmechanics that analyze problems involving fluid flow by usingnumerical analysis and data structure. The interaction of liquidand gases with a surface defined by boundary condition aresolved with the help of computers, which performs itscalculations. CFD is commonly accepted as referring to theboard topic encompassing the numerical solution, bycomputational methods, of the governing equations whichdescribe fluid flow, the set of Navier-stokes equation,continuity and any additional conservation equation like energyor species concentration. CFD is considered as a bridgebetween the pure experiment and pure theory. Computationalfluid dynamics predict the performance of a system beforewww.ijert.org(This work is licensed under a Creative Commons Attribution 4.0 International License.)47

Published by :http://www.ijert.orgInternational Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 6 Issue 09, September - 2017installing it in real life. CFD predict which design changes aremost crucial to enhance the performance. Moreover, there areseveral unique advantages of CFD over experimental-basedfluid system design. CFD provides more detail and comprehensive information. Ability to study system under zero hazardous conditions atand beyond their normal performance limits. Power consumption of CFD is low as compared to a windtunnel.CFD Analysis of temperature, velocity, and chemicalconcentration distribution can help an engineer to understandthe problem correctly and provide ideas for getting the bestresolution.ANGLE OF ATTACKWhen you stretch your arm out through window of carwhich moves at high speed, you can feel that your arm pullback while colliding with oncoming air and when you holdyour hand outside of window in parallel to the direction ofroad and just inclined it in certain angle, you feel like yourhand push upward it is because of oncoming air strikes at yourhand. Angle Of Attack is the angle between the reference lineof a body and relative wind or oncoming air [3]. On an airfoilsuch as one on a wind turbine, it is the angle between thechord line and relative wind vector. The relation between anangle of attack, the coefficient of lift and coefficient of drag isas follows:Fig 2. Variation of Angle of attack vs Coefficient of LiftA typical graph of coefficient of lift against the angle of attackof the airfoil section is studied. One of the first things noticedis the fact that at an angle of attack of 0 , there is a positivecoefficient of lift, and, hence, positive lift. One must move to anegative angle of attack to obtain zero lift coefficients. It willbe remembered that this angle is called the angle of zero lift. Asymmetric airfoil was shown to have an angle of zero lift equalto 0 as might be expected. From the diagram we can see thatas an angle of attack increased coefficient of lift associatedwith it is also increases up to a certain maximum point knownas a stall angle. Above this angle, however, the lift coefficientreaches a peak and then declines. The angle at which the liftcoefficient (or lift) reaches a maximum is called the stallangle. Beyond the stall angle, one may state that the airfoil isstalled and a remarkable change in the flow pattern hasoccurred.Originally the value of drag coefficient is zero at zerodegree angle of attack. But then as we increase an angle ofattack drag coefficient will also increase before and after stallcondition occurs. Minimum drag coefficient occurs at a smallpositive angle of attack corresponding to a positive liftcoefficient and builds only gradually at the lower angles. Nearto the stall angle, C D increase rapidly because the greateramount of turbulent and separated flow occurred.FLOW SAPERATIONAll solid objects travelling through fluid experience viscousforces occur in the layer of fluid close to the solid surfacewhich acquires a boundary layer of fluid around them.Boundary layers can be in the form of laminar or turbulent. Bycalculating the Reynolds number of the local flow conditionswe can make a decision that the flow is laminar or turbulent.When the boundary layer travels far enough against an adversepressure gradient and at the same time the speed of theboundary layer relative to the object falls almost to zero thenFlow separation occurs. In aerodynamics, flow separation canoften result in increased drag. For this reason, much effort andresearch have gone into the design of aerodynamic andhydrodynamic surfaces which delay flow separation and keepthe local flow attached for as long as possible.OPERATING PARAMETERSAnalysis on the airfoil profile is carried out to find the valuesof CD and CL at different values of angle of attack .Here we aregoing to analyse the Airfoil of Chord Length 160 mm usingCFD. For that we take some initial assumptions or boundaryconditions for our problem which are as follows.a)Span of airfoil 0.3 mb) Density of air 1.208 kg/m3c)Length of airfoil 0.16 md) Velocity of wind 30.48 m/se)Fluid Air as idealf)Operation Pressure 13 barFig 3. Variation in Angle of attack vs Coefficient of DragIJERTV6IS090028www.ijert.org(This work is licensed under a Creative Commons Attribution 4.0 International License.)48

Published by :http://www.ijert.orgInternational Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Vol. 6 Issue 09, September - 2017MESH GENERATIONToday there is numerous analysis software which is gettingused for geometry-integrated mesh generation and postprocessing purpose. ANSYS ICEM CFD has desired effectthat it keeps close relationship with geometry during meshgeneration and post-processing. From geometry to meshgeneration in an analysis, it provides refined geometryacquisition, mesh generation, post-processing and meshoptimization tools. The mesh generation properties in ICEMCFD offers from, a capability to parametrically create gridsfrom geometry in multi-block structured, unstructuredhexahedral, tetrahedral, hybrid grids consisting of hexahedral,tetrahedral, pyramidal and prismatic cells; and Cartesian gridformats combined with boundary conditions.Fig 6. Contour of static pressure at 14 Degree AOAAbove figure shows pressure distribution on the upper andlower surface of airfoil for 14º angle of attack. The value of liftcoefficient is maximum at this angle of attack. Hence it iscalled as angle of attack. Value of lift coefficient is 0.2095.Maximum lift is due to maximum pressure difference on theupper and lower surface of the airfoil.Fig 4 . Mesh generationI.RESULTWe have plotted the pressure contours as well as velocitycontours for chord length of 0.16 m and changing the values ofangle of attack. Following are the cases at the stall angle andfew degrees before and after it.a) Pressure ContoursNext Figure shows pressure distribution on the upper andlower surface of airfoil for 10º angle of attack. There ispositive pressure on the upper surface and negative pressureon the lower surface. Value of lift coefficient is 0.17769.Fig 7. Contours of pressure at 16 Degree AOAAbove figure shows pressure distribution on the upper andlower surface of airfoil for 16º angle of attack. There ispositive pressure on the upper surface and negative pressureon the lower surface. Value of lift coefficient is 0.08087.It isobserved that lift generated decreases after the stall angle.Fig 5. Contour of static pressure at 10 Degree AOAIJERTV6IS090028www.ijert.org(This work is licensed under a Creative Commons Attribution 4.0 International License.)49