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Basics of Fluid Mechanics, 2014a

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444 CHAPTER 11. COMPRESSIBLE FLOW ONE DIMENSIONAL<br />

Using the pressure ratio in equation (11.192) and substituting it into equation (11.196)<br />

yields<br />

⎛<br />

P 1+ k − 1<br />

0 ⎜<br />

∗ = ⎝<br />

2<br />

P 0 k +1<br />

2<br />

M 2<br />

⎞<br />

⎟<br />

⎠<br />

k<br />

k−1<br />

And further rearranging equation (11.197) provides<br />

1<br />

1+ k − 1<br />

2<br />

M<br />

√ k +1<br />

2<br />

M 2<br />

(11.197)<br />

Stagnation Pressure Ratio<br />

⎛<br />

P 0<br />

∗ = 1 1+ k − 1<br />

⎜<br />

⎝<br />

2<br />

P 0 M k +1<br />

2<br />

M 2<br />

⎞<br />

⎟<br />

⎠<br />

k+1<br />

2(k−1)<br />

(11.198)<br />

The integration <strong>of</strong> equation (11.186) yields<br />

s − s ∗<br />

C p<br />

√ √√√√√√√ ⎛<br />

⎞<br />

=lnM 2 ⎜<br />

k +1<br />

⎝<br />

(<br />

2 M 2 1+ k − 1 ) ⎟<br />

⎠<br />

M<br />

2<br />

2<br />

k+1<br />

k<br />

(11.199)<br />

The results <strong>of</strong> these equations are plotted in Figure 11.20<br />

The Fanno flow is in many cases shockless and therefore a relationship between<br />

two points should be derived. In most times, the “star” values are imaginary values<br />

that represent the value at choking. The real ratio can be obtained by two star ratios<br />

as an example<br />

T 2<br />

T 1<br />

=<br />

T<br />

T ∗ ∣ ∣∣∣M2<br />

∣<br />

T ∣∣∣M1<br />

(11.200)<br />

T ∗<br />

A special interest is the equation for the dimensionless friction as following<br />

Hence,<br />

∫ L2<br />

L 1<br />

∫<br />

4 fL<br />

Lmax<br />

D<br />

dx = L 1<br />

∫<br />

4 fL<br />

Lmax<br />

D<br />

dx − L 2<br />

fld Working Equation<br />

( ) ( )<br />

4 fLmax 4 fLmax<br />

=<br />

D<br />

D<br />

2<br />

1<br />

− 4 fL<br />

D<br />

4 fL<br />

dx (11.201)<br />

D<br />

(11.202)

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