Page 193 - 48Fundamentals of Compressible Fluid Mechanics

9.7. WORKING CONDITIONS 155

constant pressure
lines

1’’

2’’
1’
1 2’
2

Fanno lines

Fig. 9.7: The development properties in of converging nozzle

is constant because it is a function of the
nuzzle design only. The exit Mach number, N decreases (remember this flow is
b
nozzle. The entrance Mach number, N
. At end of the range
, N H I . In the range of 9 the flow is all supersonic. b
on the supersonic branch) and starts (WYX(Z [
) as N H N
HQ
In the next range 8 9 The flow is double choked and make the adjust-
ment for the flow rate at different choking points by changing the shock location.
8
The mass flow rate continue to be constant. The entrance Mach continues to be
8
constant and exit Mach number is constant.
The total maximum available for supersonic flow9 9 , W`XaZ [
, is only
theoretical length in which the supersonic flow can occur if nozzle will be provided

with a larger Mach number (a change the nozzle area ratio which also reduces the

mass flow rate.). In the range9 : , is more practical point.
In semi supersonic flow9 : (in which no supersonic is available in the

"
tube but only the nozzle) the flow is still double chocked and the mass flow rate

is constant. Notice that exit Mach number, N is still one. However, the entrance

.
It worth noticing that in the : the mass flow rate nozzle entrance
b
, reduces with the increase of WYXaZ [
Mach number, N
velocity, and the exit velocity remains constant! 13
the end is really the pressure limitation or the
8
break of the model and the isothermal model is more appropriate to describe the

In the last range :
13 On personal note, this situation is rather strange to explain. On one hand, the resistance increases
and on the other hand, the exit Mach number remains constant and equal to one. Is anyone have
explanation for this strange behavior suitable for non–engineers or engineers without background in
fluid mechanics.