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Basics of Fluid Mechanics, 2014a

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352 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. -10.11. Stream and Potential line for a source and sink. It can be noticed that stream<br />

line (in blue to green) and the potential line are in orange to crimson. This figure is relative<br />

distances <strong>of</strong> x/r 0 and y/r 0 . The parameter that change is 2 π φ/Q 0 and 2 πψ/Q 0 . Notice<br />

that for give larger <strong>of</strong> φ the circles are smaller.<br />

Notice that the stream function has the same dimensions as the source/sink flow rate.<br />

The stream lines can be obtained by utilizing similar procedure. The double<br />

stream function is made from the combination <strong>of</strong> the source and sink because stream<br />

functions can be added up. Hence,<br />

ψ = ψ 1 + ψ 2 = Q 0<br />

2 π (θ 1 − θ 2 ) (10.131)<br />

The angle θ 1 and θ 2 shown in Figure 10.11 related other geometrical parameters as<br />

θ 1 = tan −1<br />

y<br />

x − r 0<br />

(10.132)<br />

6 coth 2 (x) − 1 = cosh2 (x)<br />

sinh 2 (x) − 1 = cosh2 (x) − sinh 2 (x)<br />

sinh 2 (x)<br />

cosh 2 (x) − sinh 2 (x) =1the identity is proved.<br />

and since by the definitions

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