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Pressure Distribution, Lift and Drag on an Airfoil

# Pressure Distribution, Lift and Drag on an Airfoil - Mech...

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Mech 392: Mechanics of Fluids II Experiment II Pressure Distribution, Lift and Drag on an Airfoil Objectives The objectives of this experiment are: (i) to examine the effect of angle of attack on the pressure distribution on an airfoil, (ii) to investigate the effect of angle of attack on lift and drag, and (iii) to investigate the effect of slots and flaps. Background The most common application of airfoils is aircraft lifting surfaces (wing, elevator, rudder). Airfoils are also a crucial component of turbomachinery (such as turbines, pumps and fans) and propellers. The usual explanation for lift is that the air velocity over the top of the wing is faster than the mean velocity, whereas that along the lower side is slower than the mean. Bernoulli’s theorem then implies a lower pressure on the top and a higher pressure on the bottom, resulting in a net upward lift. Figure 1: Streamlines and pressure distribution about an airfoil Two important airfoil parameters, lift and drag, are usualy expressed as dimensionless coefficients: C L = L 1 / 2 ρ U 2 A (1) C D = D 1 / 2 ρ U 2 A (2) In airfoil theory, the increased velocity over the top and the decreased velocity on the bottom is explained in terms of a circulation which is induced by the relative motion of the wing with respect to the flowfield. The concept of circulation is very important in the 1

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analysis of various aerodynamic and hydrodynamic problems. The analysis assumes ideal fluid flow and is justified by the fact that for streamlined bodies at high Reynolds numbers, viscous effects are confined to a very thin boundary layer. The analysis yields
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