AE 2020 INTRODUCTION
A bit of history
Fluid mechanics is a very old field. Over three centuries ago, Sir Isaac Newton
devoted an entire book in his work known as
Principia Mathematica
to fluid mechanics
(1687). Newton believed that fluid dynamics could be modeled by viewing fluid
molecules as rigid particles that obey the classical particle equations of motion. He
developed a model for the lift coefficient generated by the airfoils. This model assumed
that when the fluid particles hit a solid surface, they lose all their momentum in a
direction normal to the surface, and thereafter slide down the sides of the body. This
model stated that
a
2
sin
2
=
l
C
In 1777, D'Alembert (a French scientist) did a series of experiments on ships in
canals, and proved that the above equation is wrong.
In 1781, Euler (a Swiss Engineer)
used theoretical reasoning to show that lift coefficient should be proportional to sin
α
,
and not to sin
2
α
.
Later on we will see that
lift behaves like
a
p
sin
2
=
l
C
From such humble beginnings and false steps, the field of fluid mechanics grew.
Many researchers such as Lilienthal (1890s) and Langley (1906) worked on the
development of airfoils, gliders and wings. Other researchers and engineers (Rankine
1820-1872, Froude, de Laval, Pelton) worked on turbomachinery, pumps, wind mills and
so on, which relied on aerodynamic principles.

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