Airfoil Nomenclature

AIRFOIL NOMENCLATURE

•Mean camber line :

locus of points halfway between upper surface and

lower surface •Chord line: •Chord:

line joining leading edge & trailing edge

distance between leading edge & trailing edge

distance between upper & lower surface measured perpendicular to chord •Thickness: •Camber:

maximum distance between mean camber line and chord

 At • At leading edge circular shape with radius 0.02c

AIRFOIL DESIGN:

4 SERIES AIRFOIL: INPUT PARAMETERS: 1.chord(c), 2.max.camber, 3.position of maximum camber on chord

MEAN LINE:

Forward of maximum ordinate After maximum ordinate Where m=maximum ordinate of mean line expressed as fraction of chord P=chordwise position of maximum camber THICKNESS DISTRIBUTION:

5 SERIES AIRFOIL MEAN LINE:

THICKNESS DISTRIBUTION:

4 digit series airfoil: 1 st digit : max camber in 100 th of chord 2 nd digit : location of max camber along the chord from leading edge in 10 th of chord  Last two digits: max thickness in 100 th of chord 

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5 digit series airfoil: 1 st digit when multiplied by 3/2 gives design lift coefficient* in 10 th of camber  Next two digit divided by 2 gives location of max camber along the chord from leading edge in 10 th of chord  Last two digits:max thickness in 100 th of chord 

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6 series laminar flow series airfoil: 1 st digit : signifies series 2 nd digit : location of minimum pressure in 10 th of chord from leading edge 3 rd digit: design lift coefficient in tenth  Last two digits:max thickness in 100 th of chord 

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* Design lift coefficient is the theoretical lift coefficient for the airfoil when the angle of attavk is such that the slope of the mean camber line at the leading edge is

LIFT GENERATION Lift can be achieved in two ways: 1.Cambered profile 2.Angle of attack

video

LIFT GENERATION

if a streamline is curved, there must be a pressure gradient across the streamline, with the pressure increasing in the direction away from the centre of curvature.

VARIATION OF LIFT WITH ANGLE OF ATTACK

Slope a0 is not influenced by Re ; However,Cl max is dependent upon Re. Cl max is governed by viscous effects and Re is a similarity parameter that

VARIATION OF LIFT WITH CAMBER

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Steady, two-dimensional inviscid, momentum equations in (x; y) coordinates is,

Let r is the direction normal to the local streamwise direction and s is the local streamwise direction. In this coordinate system, the inviscid momentum equations are

From eq.(3)

This is Bernoulli’s equation Now from Eq.(4) For Upper surface,

For lower surface,

EFFECT OF THICKNESS: 

Increasing the thickness on a cambered airfoil will tend to decrease the radius of curvature of the upper surface, and increase the radius of curvature of the lower surface. On upper surface,

on the lower surface

Addition of thickness to a cambered airfoil tends to lower both the upper and lower surface pressure and the lift is an integral of the upper and lower surface pressure dierence, the resulting lift will be relatively unaffcted by thickness.

LIMITING FACTORS: Adverse pressure gradient responsible for flow separation

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