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Int. J. Mech. Eng. & Rob. Res. 2012 Chandrakant Sagat et al., 2012

EXPERIMENTAL AND CFD ANALYSISOF AIRFOIL AT LOW REYNOLDS NUMBER

Chandrakant Sagat1*, Pravin Mane1 and B S Gawali1

The determination of lift and drag of airfoil from wind tunnel measurements is discussed forincompressible flow. Calculated the upper and lower surface pressure and velocity of an airfoilis essential for calculating the forces on it. The Effects of model support are neglected. Nosimplifying assumptions on the flow along the test section walls are made. The purpose of loadmeasurements on the model is to make available the forces and moments so that they may becorrected for tunnel boundary and utilized in predicting the performance of the full-scale vehicleor other device at different angle of attack from 0o to 20o and at maximum velocity 15 m/s. Airfoilanalysis of the airfoil at low Reynolds no. and comparing experimental results and cfd results.

Keywords: Airfoil, Angle of attack, CFD, Low reynolds no., Wind tunnel

INTRODUCTIONLift and Drag are considered aerodynamicforces because they exist due to the movementof the aircraft through the air. The weight pullsdown on the plane opposing the lift created byair flowing over the wing. Thrust is generatedby the propeller and opposes drag caused byair resistance to the frontal area of the airplane.During takeoff, thrust must overcome drag andlift must overcome the weight before theairplane can become airborne. In level flight atconstant speed, thrust exactly equals drag andlift exactly equals the weight or gravity force.

ISSN 2278 – 0149 www.ijmerr.comVol. 1, No. 3, October 2012

© 2012 IJMERR. All Rights Reserved

Int. J. Mech. Eng. & Rob. Res. 2012

1 Department of Mechanical Engineering, Walchand College of Engineering, Sangli 415146.

Research Paper

*Corresponding Author: Chandrakant Sagat, sagat_chandu@rediffmail.com)

The purpose of load measurements on themodel is to make available the forces and

moments so that they may be corrected fortunnel boundary and utilized in predicting theperformance of the full-scale vehicle or otherdevice. Today, every time a new model of anairplane, automobile or railroad vehicle isintroduced, the structure is designed to be

lighter to attain faster running speed and lessfuel consumption. It is possible to design alighter and more efficient product by selectinglighter materials and making them thinner foruse. But the safety of the product is

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Int. J. Mech. Eng. & Rob. Res. 2012 Chandrakant Sagat et al., 2012

compromised unless the required strength ismaintained. By the same token, if only thestrength is taken into consideration, the weightof the product increases and the Economicfeasibility is impaired. We are using pressuredistribution method and by using strain gaugeis developed Setup for the measurement ofthe lift and drag forces for an airfoil (Jewel,1999).

Computational Fluid Dynamics (CFD) isone of the branch of fluid mechanics that usesnumerical methods and algorithm to solveand analyze problems that involve fluid flowand heat transfer. CFD is an art of replacingthe integrals or partial derivatives in theequations governing the fluid flow withdiscretized algebraic form, which in turn aresolved to obtain numbers for the flow field incontrast to a closed form analytical solution(Anderson, 1995). Using CFD the complexflow behavior can be clearly visualized, whichwill be helpful to redesign and improve theefficiency of the equipment. Advances in CFDand its wide applications are proving for itsstability. Hence CFD technique can beapplied for analysis lift force and drag forceover the testing model.

Figure 1: Cantilever BeamLoad at Free End

EXPERIMENTAL SETUPSet Up by Using Strain Gauges

The experimental setup is done by using straingauges on the cantilever beam (Figures 1 and2) (Khurmi, 1999).

Deflection of Beam l is equal to

3

wll

EI...(1)

Moment of the inertia for rectangle

3

12

bdl ...(2)

Pressure Coefficient (Gordon, 1987).

At any point in the flow where the localpressure coefficient C

p is defined as

212

atmp

p pC

U ...(3)

Figure 2: Photographof the Cantilever Beam With Setup

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Int. J. Mech. Eng. & Rob. Res. 2012 Chandrakant Sagat et al., 2012

Setup by Pressure DistributionMethod

The Total or Stagnation Upstream Pressure PT

as Measured by an impact probe (e.g., a Pitottube) is the sum of the static and dynamicpressure at that point i.e.,

Figure 3: Geometric and DynamicParameters of Airfoils

21

2TP P U ...(4)

Thus, CP may also be written in terms of the

differential pressures

PT

P PC

P P ...(5)

The presence of the airfoil in the test sectionwill affect the test section velocity, e.g., at a150 angle of attack the local velocity over theairfoil will increase to about 1.02 times theupstream. The lift force is customarilyexpressed as a dimensionless lift coefficientper unit span length.

Coefficient of Lift Force

2

2L

LC

U bc ...(7)

2

sin

12

i

L

s p p dsC

U c ...(8)

Coefficient of Drag force

21

2D DF C A ...(8)

Wind Tunnel Testing of an Airfoil

A rectangular wing airfoil model having chordlength 252 mm, span 227 mm and aspect ratio0.9 used for measurement of pressuredistribution over upper and lower surface. Thepressure tapings were made along thechamber line with successive percentage ofchord length (Schneemann et al., 2010).Smallholes were drilled with 1/64" drill in a directionperpendicular to the surface and up to camberline of airfoil. From bottom surface drills of 1/16" were drilled to match with the above holes.The pressure tapings and tap numbers onaerofoil are as shown in Figure 4.

Figure 4: Aerofoil and Pressure Tapings

Tygon tubes are inserted in these tap holesfor measurement of gauge pressure byconnecting with multi-tube manometer.

Table 1: Aerofoil Surface Coordinates

Tap X/C Surface Y/C (%)

Number (%) Upper Lower

Leading Edge 0.0 8.00 7.0

Point 1 and 7 4.0 10.80 4.0

Point 2 and 8 8.0 12.00 3.0

Point 3 and 9 24.0 14.80 0.9

Point 4 and 10 49.2 14.60 1.0

Point 5 and 11 68.8 11.20 2.3

Point 6 and 12 82.0 10.10 3.9

Trailing Edge 100.0 7.20 7.1

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Int. J. Mech. Eng. & Rob. Res. 2012 Chandrakant Sagat et al., 2012

EXPERIMENTAL ANALYSIS

Results for the Coefficientof Pressure

• Coefficient of pressure at velocity 15 m/s

at various Angle Of Attack 0 to 20 Degree.

• Results for velocity ratio V/Vinfinity for

velocity at 15 m/s.

Figure 5: Coefficient of Pressureat Velocity 15 m/s at Various Angle

of Attack 0 to 20 Degree

Figure 6: Coefficient of Pressureon Upper Surface at Velocity 15 m/s

at Various Angle of Attack 0 to 20 Degree

Figure 7: Coefficient of Pressureon Lower Surface at Velocity 15 m/s

at Various Angle of Attack 0 to 20 Degree

Figure 8: Velocity Ratio vs. X/CLocation of an Airfoil

Figure 9: Shows the Velocity Ratioat Upper Surface of an Airfoil

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Int. J. Mech. Eng. & Rob. Res. 2012 Chandrakant Sagat et al., 2012

Figure 10: Shows the Velocity Ratioat Lower Surface of an Airfoil

Figure 11: Shows the Coeff. of Lift, Coeff.of Drag and Coeffi. of Momentvs. X/C Location of an Airfoil

RESULTS OF CFD ANALYSIS(VIJAY KORE, 2011)

Figure 13: Shows that PressureDistribution Over the Airfoil at Velocity

12 M/S Angle of Attack 10 DegreeContours of Dynamic Pressure (Pascal)

Figure 12: Shows that PressureDistribution Over the Airfoil at Velocity

12 m/s Angle of Attack 10 DegreeContours of Static Pressure (Pascal)

Figure 14: Shows that PressureDistribution Over the Airfoil at Velocity

12 M/S Angle of Attack 10 DegreeContours of Total Pressure (Pascal)

Figure 15: Shows that VelocityDistribution Over the Airfoil at Velocity

12 M/S Angle of Attack 10 DegreeContours of Velocity Magnitude (M/S)

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Int. J. Mech. Eng. & Rob. Res. 2012 Chandrakant Sagat et al., 2012

Figure 16: Shows that Contoursof Pressure Coefficient Over the Airfoil

at Velocity 12 M/S Angleof Attack 10 Degree

Figure 17: Shows the Velocity VectorDiagram at Velocity 12 M/S at Angle

of Attack 10 Degree

CONCLUSIONThe coefficient of pressure is analyzed in theupper and lower surface of the airfoil for theangle of attack varies from 0° to 10°. Theresults showed that the upper surface haslower negative coefficient of pressure at higherangle of attack and lower surface has lowernegative coefficient of pressure at lower angleof attack.

The results demonstrate the pressuredistribution over the airfoil. The pressure on thelower surface of the airfoil is greater than that ofthe incoming flow stream and as a result of thatit effectively pushes the airfoil upward, normalto the incoming flow stream. On the other hand,the components of the pressure distributionparallel to the incoming flow stream tend to slowthe velocity of the incoming flow relative to theairfoil, as do the viscous stresses.

The Coefficient of lift and coefficient of dragof an airfoil is depends upon the pressuredistribution and velocity distribution of anairfoil.

REFERENCES1. Anderson John D (1995), Computational

Fluid Dynamics, Basics with Applications,McGraw Hill Publications, ISBN 0-07-113210-4.

2. FLUENT 6.3.26 (2006), Tutorial Guide.

3. Gordon C Oates University of WashingtonSeattle, Aerothermo dynamics of GasTurbine and Rocket Propulsion, ThirdEdition Book, Washington.

4. Jewel B Barlow, William H Rae and Jr.Alan Pope (1999), Low Speed WindTunnel Testing, Book Wiley India Pvt. Ltd.

5. Jorge Schneemann, Pascal Knebel,Patrick Milan and Joachim Peinke(2010), Lift Measurements in UnsteadyFlow Conditions.EWEC - European windEnergy Conference, Warsaw.

6. Khurmi R S (1999), Strength of Material,Book.

7. Vijay Kore (2011), “Performance Analysisand Simulation of an Axial Fan”, M.Tech.Thesis 2011.

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Int. J. Mech. Eng. & Rob. Res. 2012 Chandrakant Sagat et al., 2012

C Chord

b Span

u Velocity

Cd

Coefficient of Drag

Cl

Coefficient of Lift

CP

Coefficient of Pressure

L Lift

D Drag

Re Reynolds Number

u Free Stream Velocity

Angle of Attack

Density

APPENDIX

Abbreviations and Acronyms