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Basics of Fluid Mechanics, 2014a

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358 CHAPTER 10. POTENTIAL FLOW<br />

9.0<br />

8.0<br />

7.0<br />

6.0<br />

5.0<br />

4.0<br />

3.0<br />

2.0<br />

1.0<br />

-9.0 -8.0 -7.0 -6.0 -5.0 -4.0 -3.0 -2.0 -1.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0<br />

-1.0<br />

-2.0<br />

-3.0<br />

-4.0<br />

-5.0<br />

-6.0<br />

-7.0<br />

-8.0<br />

-9.0<br />

Fig. -10.12. Stream lines and Potential lines for Doublet. The potential lines are in gold color<br />

to crimson while the stream lines are cyan to green color. Notice the smaller value <strong>of</strong> the<br />

stream function translates the smaller circle. The drawing were made for the constant to be<br />

one (1) and direct value can be obtained by simply multiplying.<br />

Or after some arrangement equation (10.157) becomes<br />

(<br />

ψ = U 0 r sin θ 1+ Q )<br />

0<br />

2 U 0 πr 2<br />

(10.158)<br />

Denoting<br />

Q0<br />

2 U 0 π as −a2 transforms equation (10.158) to<br />

The stream function for ψ =0is<br />

ψ = U 0 r sin θ<br />

0=U 0 r sin θ<br />

(1 − a2<br />

r 2 )<br />

(1 − a2<br />

r 2 )<br />

(10.159)<br />

(10.160)<br />

This value is obtained when θ =0or θ = π and/or r = a. The stream line that is<br />

defined by radius r = a describes a circle with a radius a with a center in the origin.

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