Page 111 - 48Fundamentals of Compressible Fluid Mechanics

In this chapter the relationships between the two sides of normal shock are pre-
sented. In this discussion, the flow is assumed to be in a steady state, and the
thickness of the shock to be very small. A discussion on the shock thickness will
1
be presented in a forthcoming section .
A shock can occur at
least in two different mecha-
nisms. The first is when a
flow
large difference (above critical direction
value) between the two sides
of a membrane exists, and the
membrane is burst (see the dis-
cussion about the shock tube). c.v.
Of course, the shock travels
from the high pressure to the Fig. 5.1: A shock wave inside of a tube, but it also can
low pressure side. The sec- viewed as a one dimensional shock wave
ond is when many sound waves
“run into” each other and accumulate (some referred to it as “coalescing”) into a
large difference, which is the shock wave (piston relatively fast moving). In fact, the
sound wave can be viewed as extremely weak shock. In the speed of sound anal-
ysis, it was assumed the medium to be continuous, without any abrupt changes.
This assumption is no longer valid in the case of shock. Here, the relationship for
a perfect gas is constructed.
In Figure (5.1) a control volume for this analysis is shown, and the gas
flows from left to right. The conditions, left and right of the shock, are assumed to

1 Currently under construction.

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