Analysis Of Airfoil Flow Pattern Using CFD - IJERT

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Special Issue - 2018International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Confcall - 2018 Conference ProceedingsAnalysis of Airfoil Flow Pattern using CFDV. Gayathri Kanimozhi,Department of Aeronautical Engineering,Parisutham Institute of Technologyand Science, Thanjavur, Tamil Nadu, India.Abstract— In this paper, Flow pattern of airfoil over twodimensional subsonic flow at a various angle of attacksoperating at Reynolds’s number is obtained. Analysis on theairfoil profile is carried out to find the values of CD and CLat different values of angle of attack.The result shown byCFD has closely agreed with experiment result, thus CFD isa mature tool to predict the performance of test section atany angle of attack.basic dissimilarities between symmetric and asymmetricaerofoil like at zero degree angle of attack, Asymmetricairfoils can generate lift, while a frequent inverted flightssuits symmetric airfoil as in the case of an aerobaticairplane. Thus without boundary layer separation, we canuse various angles. Subsonic airfoils have a round leadingedge around which it is naturally insensitive to angle ofattack [2].Keywords— Flow separation, angle of attack, CFD, coefficientof lift and coefficient of drag, pressure coefficient etc.I.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 whichthe component of resultant force normal to the directionof motion is many times greater than the componentresisting the motionFig 1. Airfoil Geometry[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 distributionover the body surface and shear stress distribution overthe body surface. This aerodynamic force can be resolvedinto two components known as lift and drag. The forcewhich acts in perpendicular to the direction of motion iscalled as lift force, and the force which is parallel to thedirection of motion is called as drag force. Lift isgenerated by aerofoil primarily depends upon surface areaand angle of attack. The drag force mainly depends uponthe body surface and fluid which is flows over it. This liftand drag force are obtained with the help of wind tunnel.A wind tunnel is a machine which used in aerodynamicresearch to study the effects of air moving on solidobjects. 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,is instrumented with suitable sensors to measureaerodynamic forces, pressure distribution, or otheraerodynamics-related characteristics. The advance incomputational fluid dynamics modeling on a high speeddigital computer has reduced the demand for wind tunneltesting. However, CFD results are still not completelyreliable and wind tunnels are used to verify CFDpredictions.II. GEOMETRYIn aerodynamics, Airfoil design is a major facet.Different flight regimes show different results. There areVolume 6, Issue 14The point at front of the airfoil that has maximumcurvature is known as a Leading edge. The trailing edge isdefined as the point of minimum curvature at the rear ofthe airfoil. The straight line joining the leading edge andtrailing edge of airfoil section is chord line. Chamber lineis the locus of point’s midway between the upper andlower surface of an airfoil. The Angle of attack ismeasured by taking a difference between free streamvelocity and chord line. It is the ratio of a span of anaerofoil to the chord length of an aerofoil is called as theAspect ratio.III. COMPUTATIONAL FLUID DYNAMICS (CFD)Computational Fluid Dynamics is a branch of fluidmechanics that analyze problems involving fluid flow byusing numerical analysis and data structure. Theinteraction of liquid and gases with a surface defined byboundary condition are solved with the help of computers,which performs its calculations. CFD is commonlyaccepted as referring to the board topic encompassing thenumerical solution, by computational methods, of thegoverning equations which describe fluid flow, the set ofNavier-stokes equation, continuity and any additionalconservation equation like energy or speciesconcentration. CFD is considered as a bridge between thepure experiment and pure theory. Computational fluiddynamics predict the performance of a system beforePublished by, www.ijert.org1

Special Issue - 2018International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Confcall - 2018 Conference Proceedingsinstalling it in real life. CFD predict which design changesare most crucial to enhance the performance. Moreover,there are several unique advantages of CFD overexperimental-based fluid system design. CFD provides more detail and comprehensiveinformation. Ability to study system under zero hazardous conditionsat and beyond their normal performance limits. Power consumption of CFD is low as compared to awind tunnel.CFD Analysis of temperature, velocity, and chemicalconcentration distribution can help an engineer tounderstand the problem correctly and provide ideas forgetting the best resolution.IV. ANGLE OF ATTACKWhen you stretch your arm out through window of carwhich moves at high speed, you can feel that your armpull back while colliding with oncoming air and whenyou hold your hand outside of window in parallel to thedirection of road and just inclined it in certain angle, youfeel like your hand push upward it is because of oncomingair strikes at your hand. Angle Of Attack is the anglebetween the reference line of a body and relative wind oroncoming air [3]. On an airfoil such as one on a windturbine, it is the angle between the chord line and relativewind vector. The relation between an angle of attack, thecoefficient of lift and coefficient of drag is as follows:Fig 2. Variation of Angle of attack vs Coefficient of LiftA typical graph of coefficient of lift against the angle ofattack of the airfoil section is studied. One of the firstthings noticed is the fact that at an angle of attack of 0 ,there is a positive coefficient of lift, and, hence, positivelift. One must move to a negative angle of attack to obtainzero lift coefficients. It will be remembered that this angleis called the angle of zero lift. A symmetric airfoil wasshown to have an angle of zero lift equal to 0 as might beexpected. From the diagram we can see that as an angle ofattack increased coefficient of lift associated with it isalso increases up to a certain maximum point known as astall angle. Above this angle, however, the lift coefficientreaches a peak and then declines. The angle at which thelift coefficient (or lift) reaches a maximum is called thestall angle. Beyond the stall angle, one may state that theairfoil is stalled and a remarkable change in the flowpattern has occurred.Originally the value of drag coefficient is zero at zerodegree angle of attack. But then as we increase an angleof attack drag coefficient will also increase before andafter stall condition occurs. Minimum drag coefficientoccurs at a small positive angle of attack corresponding toa positive lift coefficient and builds only gradually at thelower angles. Near to the stall angle, C D increase rapidlybecause the greater amount of turbulent and separatedflow occurred.V. FLOW SAPERATIONAll solid objects travelling through fluid experienceviscous forces occur in the layer of fluid close to the solidsurface which acquires a boundary layer of fluid aroundthem. Boundary layers can be in the form of laminar orturbulent. By calculating the Reynolds number of thelocal flow conditions we can make a decision that theflow is laminar or turbulent. When the boundary layertravels far enough against an adverse pressure gradientand at the same time the speed of the boundary layerrelative to the object falls almost to zero then Flowseparation occurs. In aerodynamics, flow separation canoften result in increased drag. For this reason, much effortand research have gone into the design of aerodynamicand hydrodynamic surfaces which delay flow separationand keep the local flow attached for as long as possible.VI. OPERATING PARAMETERSAnalysis on the airfoil profile is carried out to find thevalues of CD and CL at different values of angle of attack.Here we are going to analyse the Airfoil of Chord Length160 mm using CFD. For that we take some initialassumptions or boundary conditions for our problemwhich 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 DragVolume 6, Issue 14Published by, www.ijert.org2

Special Issue - 2018International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Confcall - 2018 Conference ProceedingsMESH GENERATIONToday there is numerous analysis software which isgetting used for geometry-integrated mesh generation andpost-processing purpose. ANSYS ICEM CFD has desiredeffect that it keeps close relationship with geometryduring mesh generation and post-processing. Fromgeometry to mesh generation in an analysis, it providesrefined geometry acquisition, mesh generation, postprocessing and mesh optimization tools. The meshgeneration properties in ICEM CFD offers from, acapability to parametrically create grids from geometry rahedral, hybrid grids consisting of hexahedral,tetrahedral, pyramidal and prismatic cells; and Cartesiangrid formats combined with boundary conditions.Fig 6. Contour of static pressure at 14 Degree AOAAbove figure shows pressure distribution on the upperand lower surface of airfoil for 14º angle of attack. Thevalue of lift coefficient is maximum at this angle ofattack. Hence it is called as angle of attack. Value of liftcoefficient is 0.2095. Maximum lift is due to maximumpressure difference on the upper and lower surface of theairfoil.Fig 4 . Mesh generationRESULTSWe have plotted the pressure contours as well as velocitycontours for chord length of 0.16 m and changing thevalues of angle of attack. Following are the cases at thestall angle and few 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 negativepressure on the lower surface. Value of lift coefficient is0.17769.Fig 7. Contours of pressure at 16 Degree AOAAbove figure shows pressure distribution on the upperand lower surface of airfoil for 16º angle of attack. Thereis positive pressure on the upper surface and negativepressure on the lower surface. Value of lift coefficient is0.08087.It is observed that lift generated decreases afterthe stall angle.Fig 5. Contour of static pressure at 10 Degree AOAVolume 6, Issue 14Published by, www.ijert.org3

Special Issue - 2018International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Confcall - 2018 Conference Proceedingsb) Velocity ContoursAnd by conducting experiment on wind tunnel weobtained values of coefficient of lift and drag andcompare it with values obtained from CFD to show thathow precise CFD is. We obtain values of coefficient ofLift and Drag by using CFD and the values are as follows:Angle Of .12532160.875540.04377Fig 8. Contour of velocity magnitude at 10º AOAAbove figure shows the magnitude of velocity contourover an airfoils for 10º angle of attack. It is seen that flowseparation takes place close to trailing edge. Hence liftgenerated is more compared to 16º angle of attack.Here we obtain values of coefficient of Lift and Dragexperimentally and are as follows:Fig 9.Contour of velocity magnitude at 14º AOAAbove figure shows the magnitude of velocity contourover an airfoil for 14º angle of attack. It is seen that flowis streamlined op to the trailing surface. Flow separationis very less. Hence, maximum lift is generated.Angle ofattack(α)Area ofAirfoil(A m .89240.016425.89160.048610.84910.016424.84-0. 0939 0.01642CL/ CD-5.72Finally after comparing both of the above charts we cansay that CFD is mature tool to predict the performance ofairfoil section. CFD showed precise results which alsoobtain from experimentally.Fig 10. Contour of velocity magnitude at 16º AOAAbove figure shows the magnitude of velocity contourover an airfoil for 16º angle of attack. It is seen that flowseparation takes place away from the trailing edge. Hencelift generated is less compared to 16º angle of attack.Volume 6, Issue 14Published by, www.ijert.org4

Special Issue - 2018Angle OfAttack-202581013141516International Journal of Engineering Research & Technology (IJERT)ISSN: 2278-0181Confcall - 2018 Conference ProceedingsCL by 520.800130.908900.920260.87554CL by experimental-0. 093900.1750.25320.40.53530.67840.81220.89240.8491% EFERENCES[1][2][3][4][5]CONCLUSION:The objective of the work was to understand the flowpattern over an airfoil and study the stalling effect usingCFD. From the present study, it is seen that CFDcontributes to the significant understanding of flowpattern over an airfoil. The following are the importantconclusions drawn from the studies carried out in thepresent work.[6]Karna S. Patel, Saumil B. Patel, Utsav B. Patel, Prof. Ankit P.Ahuja, “CFD Analysis of an Aerofoil”, International Journal ofEngineering Research, March 2014, ISSN:2319-6890, VolumeNo.3, Issue No.3, PP 154-158.Ashish Kadve, Dr. Prashant Sharma, and Abhishek Patel.“Review onCFD Analysis on aerodynamic dsigh optimization of windturbine rotor blade”, International Journal of Innovation andEmerging Research inEngineering, February 2016, Volume 3, Issue 5, PP 178-183.P. B. Makwana, J. J. Makadiya, “CFD Analysis of Airfoil atHigh Angles of Attack”, International Journal of EngineeringResearch and Technology, April 2014, ISSN 2278-0181Volume 3, Issue 4, PP 430-437.Anderson R F, the Aerodynamic Characteristics of SixCommonly Used Airfoils over a Large Range of Angle ofAttack, National Advisory Committee for Aeronautics, 1931.1) For airfoil with chord length 160 mm, the coefficientof lift increases from -0.47815 for 0 to 1.2026 for 15 angles of attack and again decreases to 0.8754 for 16 .2) The values of CD and CL obtained from CFD are closeto those obtained from wind tunnel test. The smallvariation is due to the leakage losses in the wind tunnel.3) The maximum value of lift coefficient is obtained atthe stall angle. The value of maximum lift goes onincreasing with increasing the cord length.4) After the stall angle, the flow separation occurs awayfrom the trailing edge which reduces the lift generated.Volume 6, Issue 14Published by, www.ijert.org5

CFD provides more detail and comprehensive information. Ability to study system under zero hazardous conditions at . and beyond their normal performance limits. Power consumption of CFD is low as compared to a wind . tunnel. CFD Analysis of temperature, velocity, and chemical . concentration distribution can help an engineer to

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