Lecture # 3

27
Lecture # 3 Airfoil Aerodynamics

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Lecture # 3. Airfoil Aerodynamics. Aerodynamic Coefficients. C l = (Lift force/unit span)/(q c) C d = (Drag force/unit span)/(q c) C m = (Pitching moment/unit span)/(q c 2 ) where q is the dynamic pressure, q = 0.5 r V 2 , and c is the airfoil chord. Some Questions. - PowerPoint PPT Presentation

Transcript of Lecture # 3

Page 1: Lecture # 3

Lecture # 3

Airfoil Aerodynamics

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Aerodynamic Coefficients

• Cl = (Lift force/unit span)/(q c)

• Cd = (Drag force/unit span)/(q c)

• Cm = (Pitching moment/unit span)/(q c2)

where

q is the dynamic pressure, q = 0.5 V2, and c is the airfoil chord

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Some Questions

• What is an airfoil?

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Some Questions

• What is an airfoil?

• What aerodynamic characteristics are we interested in knowing?

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Some Questions

• What is an airfoil?

• What aerodynamic characteristics are we interested in knowing?

• What are the geometric parameters that describe an airfoil?

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Some Questions

• What is an airfoil?

• What aerodynamic characteristics are we interested in knowing?

• What are the geometric parameters that describe an airfoil?

• What are the factors that influence the aerodynamic characteristics?

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Airfoil Geometry

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Geometric Construction of an Airfoil

From NASA Sp-367 by Taly

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Airfoil Camber line Variations

From NASA Sp-367 by Taly

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Lift Coefficient versus angle of attack

From Introduction to Flight by Anderson

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Drag Bucket

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Influence of Airfoil Geometry on airfoil aerodynamics

• What are some of the geometric factors that influence the aerodynamic performance of an airfoil?– Thickness to chord ratio, t/c

• Location of max t/c

– Nose radius– Camber

• Maximum camber• Location of max camber

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Aerofoil Thickness

• What is the influence of thickness?

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Aerofoil Thickness

• What is the influence of thickness?

• Influence of t/c on lift coefficient– Clmax increases with increasing t/c up to t/c in

the order of 13-15% at t/c > 15% begins to Clmax decrease.

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Aerofoil Thickness

• What is the influence of thickness?• Influence of t/c on lift coefficient

– Clmax increases with increasing t/c up to t/c in the order of 13-15% at t/c > 15% begins to Clmax decrease.

• Influence of t/c on drag coefficient– Cdmin increases with increasing t/c

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Leading edge nose radius

• What is the major effect of the leading edge radius on airfoil performance?

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Leading edge nose radius

• What is the major effect of the leading edge radius on airfoil performance? – Effects airfoil stall characteristics

• Small leading edge radius has a sharp stall break

• Large leading edge radius has a gentle stall break

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Camber

• What is the influence of camber on the aerodynamic characteristics?

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Camber

• What is the influence of camber on the aerodynamic characteristics?

• Increasing camber increases zero lift angle of attack.

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Camber

• What is the influence of camber on the aerodynamic characteristics?

• Increasing camber increases zero lift angle of attack.

• Camber can be used to get a low drag coefficient at the designed lift coefficient.

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Camber

• What is the influence of camber on the aerodynamic characteristics?

• Increasing camber increases zero lift angle of attack.

• Camber can be used to get a low drag coefficient at the designed lift coefficient.

• The maximum lift coefficient of moderately cambered airfoil sections increase with increasing camber.

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Camber• What is the influence of camber on the

aerodynamic characteristics?• Increasing camber increases zero lift angle of attack.• Camber can be used to get a low drag coefficient at

the designed lift coefficient.• The maximum lift coefficient of moderately

cambered airfoil sections increase with increasing camber.

• Camber can effect the stall behavior.– For airfoil sections that have the maximum camber far

forward the stall is very abrupt

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What other factors besides geometry influence the aerodynamic characteristics?

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What other factors besides geometry influence the aerodynamic characteristics?

• Aerodynamic coefficients are a function of – Geometry– Angle of attack– Reynolds number– Mach Number

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Maximum Lift Coefficient

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Minimum Drag Coefficient