Page 433 - Introduction to Continuum Mechanics

Newtonian Viscous Fluid 417

Fig. 6.17

tank, the fluid must flow in a converging- diverging nozzle as shown in Fig. 6.18. The flow in
the converging part of the nozzle is always subsonic regardless of the receiver pressure
p _(</? A The flow in the diverging passage is subsonic for certain range ofp /p (see curves
R 1 K 1
a and b in Fig. 6.18). There is a value ofp at which the flow at the throat is sonic, the flow
R
corresponding to this case is known as choked flow (curve c). Further reductions of/? cannot
K
affect the condition at the throat and produces no change in flow rate. There is one receiver
pressure/? for which the flow can expand isentropically top (the solid curve e.)
JR. R
If the receiver pressure/?, is between c and e, such as d, the flow following the throat for a
R
short distance will be supersonic. This is then followed by a discontinuity in pressure
(compression shock) and flow becomes subsonic for the remaining distance to the exit. If the
receiver pressure is below that indicated by e in the figure, a series of expansion waves and
oblique shock waves occur outside the nozzle.

t That is, the increase in pressure takes place in a very short distance