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Kutta Condition
Thought Experiment
1
Suppose we model the flow around an airfoil using a potential flow approach.
We know the following:
LV
ρ
∞
′ =
Γ
u
φ
=∇
K
0
D
′ =
0
ω
=
K
0
un
=
KK
i
Bernoulli applies
Question
:
How many potential flow solutions are possible?
Answer
:
Infinitely many!
For example:
Both of these flows have circulation which are not all equal
12
LL
′′
Γ≠Γ⇒ ≠
1
Anderson, Sec. 4.5
V
8
p
L'
Flow #1
Flow #2
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View Full DocumentKutta Condition
16.100
2002
2
Another difference can be observed at the trailing edge:
As a result of this and the physical evidence, Kutta hypothesized:
In a physical flow (i.e. having viscous effects), the flow will smoothly leave a
sharp trailing edge. 
Kutta Condition
⇒
Flow #1 is physically correct!
Let’s look at Flow #1 a little more closely:
Finite angle T.E.
)
0
(
>
te
α
Flow leaves t.e. smoothly.
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 Fall '03
 willcox
 Dynamics, Aerodynamics

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