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Basics of Fluid Mechanics, 2014a

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

M 2 is a continuous monotonic function that decreases with 4 fL<br />

D<br />

. The entrance Mach<br />

M 1 is a non continuous function with a jump at the point when shock occurs at the<br />

entrance “moves” into the nozzle.<br />

1<br />

Fanno Flow<br />

M 1<br />

as a function <strong>of</strong> M 2<br />

Entrace Mach number<br />

0.9<br />

0.8<br />

0.7<br />

0.6<br />

0.5<br />

0.4<br />

0.3<br />

⎯⎯<br />

4fL<br />

D = 0.1<br />

= 1.0<br />

= 10.0<br />

= 100.0<br />

0.2<br />

0.1<br />

0<br />

0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1<br />

Exit Mach number<br />

Tue Oct 19 09:56:15 2004<br />

Fig. -11.26. M 1 as a function M 2 for various 4fL<br />

D .<br />

Figure 11.26 exhibits the M 1 as a function <strong>of</strong> M 2 . The Figure was calculated by<br />

utilizing the data from Figure (11.20) by obtaining the 4 fL<br />

D<br />

∣ for M 2 and subtracting<br />

max<br />

the given 4 fL<br />

D and finding the corresponding M 1.<br />

The Figure (11.27) exhibits the entrance Mach number as a function <strong>of</strong> the M 2 .<br />

Obviously there can be two extreme possibilities for the subsonic exit branch. Subsonic<br />

velocity occurs for supersonic entrance velocity, one, when the shock wave occurs at<br />

the tube exit and two, at the tube entrance. In Figure (11.27) only for 4 fL<br />

D<br />

=0.1 and<br />

4 fL<br />

4 fL<br />

D<br />

=0.4 two extremes are shown. For<br />

D<br />

=0.2 shown with only shock at the<br />

exit only. Obviously, and as can be observed, the larger 4 fL<br />

D<br />

creates larger differences<br />

between exit Mach number for the different shock locations. The larger 4 fL<br />

D larger M 1

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