CFD ANALYSIS OF FLOW AROUND AEROFOIL FOR DIFFERENT ANGLE OF ATTACKS

Transcription

1 CFD ANALYSIS OF FLOW AROUND AEROFOIL FOR DIFFERENT ANGLE OF ATTACKS

2 PRESENTATION OUTLINE AIM INTRODUCTION LITERATURE SURVEY CFD ANALYSIS OF AEROFOIL RESULTS CONCLUSIONS

3 AIM To understand the aerodynamic flow of air around an airfoil To study the change of angle of attack on the lift and drag forces of an airfoil for a NACA series blade, using CFD (Fluent).

4 WHAT ARE AIRFOIL? Airfoils are 3-D structures used to create aerodynamic forces Mean Chamber Line: Set of points halfway between upper and lower surfaces» Measured perpendicular to mean chamber line itself Leading Edge: Most forward point of mean chamber line Trailing Edge: Most reward point of mean chamber line Chord Line: Straight line connecting the leading and trailing edges Chord, c: Distance along the chord line from leading to trailing edge Chamber: Maximum distance between mean chamber line and chord line» Measured perpendicular to chord line

5 Most of lift is produced in first 20-30% of wing (just downstream of leading edge) Lift due to imbalance of pressure distribution over top and bottom surfaces of airfoil (or wing) If pressure on top is lower than pressure on bottom surface, lift is generated 2. As V p HOW DOES AN AIRFOIL GENERATE LIFT? Incompressible: Bernoulli s Equation Compressible: Euler s Equation 1 2 p V constant 2 dp VdV 3. With lower pressure over upper surface and higher pressure over bottom surface, airfoil feels a net force in upward direction Lift Lift = PA

6 RESOLVING THE AERODYNAMIC FORCE Relative Wind: Direction of V Angle of Attack, a: Angle between relative wind (V ) and chord line Total aerodynamic force, R, can be resolved into two force components Lift, L: Component of aerodynamic force perpendicular to relative wind Drag, D: Component of aerodynamic force parallel to relative wind

7 Lift (for now) SYMMETRIC AIRFOIL Angle of Attack, a A symmetric airfoil generates zero lift at zero a

8 Lift (for now) SAMPLE DATA: CAMBERED AIRFOIL Angle of Attack, a A cambered airfoil generates positive lift at zero a

9 NACA FOUR-DIGIT SERIES First digit specifies maximum camber in percentage of chord Second digit indicates position of maximum camber in tenths of chord Last two digits provide maximum thickness of airfoil in percentage of chord Example: NACA 2415 Airfoil has maximum thickness of 15% of chord (0.15c) Camber of 2% (0.02c) located 40% back from airfoil leading edge (0.4c) NACA 2415

10 NACA 0029 SYMMETRIC AEROFOIL ZERO LIFT AT ZERO ANGLE OF ATTACK WIDELY USED BLADE IN WIND TURBINES AND LOW SPEED AIRCRAFTS LOT OF PREVIOUS STUDY ON THIS MODEL COORDINATES GENERATED IN MS-EXCEL COORDINATES EXPORTED TO AUTO-CAD AND PROFILE DRAWN. NACA Profile generated in solid works

11 Methodology Profile co-ordinates generated in Excel Profile drawn in Auto-Cad Import geometry in Gambit and Meshing Import mesh in Fluent and apply boundary conditions Solve Post Processing & Results Boundary conditions: Air Velocity: 100m/s (at different angle of attack) In-compressible fluid flow analysis (Low Mach) Velocity =100m/s Angle(deg.) Angle(rad.) cosθ sinθ X-velocity Y-velocity

12 MESH GENERATED IN GAMBIT 20c 12.5c 25c

13 MESH GENERATED IN GAMBIT

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19 Flow comparison for 0 & 5 degree of attack

20 Static Pr. Comparison for different angle of attack

21 Velocity Comparison for different angle of attack

22 0 0

23 5 0

24 10 0

25 Pr. Coefficient Comparison for different angle of attack C p p q p C p p q p p p 1 V 2 2

26 Results Angle(deg.) C l C d Conclusions 1.The flow around an aerofoil is plotted and studied. 2.The Lift & drag coefficients of NACA 0029 aerofoil is computed for different angle of attacks. 3.The lift coefficients is a linear function of angle of attack for lower α. 4.The drag coefficient is a non-linear function of α. 5.The results can be further validated through wind tunnel testing