fluid_mechanics

636 Chapter 11 ■ Compressible Flow
Oblique shock wave
Compression Mach waves
Compression
Mach waves
V 2 < V 1
V 1
Flow decelera-
F I G U R E 11.31
tion across Mach waves.
F I G U R E 11.32
wave.
Oblique shock
Detached
curved shock
Attached
oblique shock
(a)
(b)
F I G U R E 11.33 Supersonic flow over a wedge: (a) Smaller wedge angle results in
attached oblique shock. (b) Large wedge angle results in detached curved shock.
V11.8 Twodimensional
compressible
flow
direction and even sharp corners are actually rounded. Mach waves or compression waves can coalesce
to form an oblique shock wave as shown in Fig. 11.32.
The above discussion of compression waves can be usefully extended to supersonic flow impinging
on an object. For example, for supersonic flow incident on a wedge-shaped leading edge
1see Fig. 11.332, an attached oblique shock can form as suggested in Fig. 11.33a. For the same incident
Mach number but with a larger wedge angle, a detached curved shock as sketched in Fig.
11.33b can result. A detached, curved shock ahead of a blunt object 1a sphere2 is shown in the photograph
at the beginning of this chapter. In Example 11.19, we considered flow along a stagnation
pathline across a detached curved shock to be identical to flow across a normal shock wave.
From this brief look at two-dimensional supersonic flow, one can easily conclude that the
extension of these concepts to flows over immersed objects and within ducts can be exciting,
especially if three-dimensional effects are considered. Reference 6 provides much more on this subject
than could be included here.
11.8 Chapter Summary and Study Guide
In this chapter, consideration is given to the flow of gas involving substantial changes in fluid
density caused mainly by high speeds. While the flow of liquids may most often be considered
of constant density or incompressible over a wide range of speeds, the flow of gases and vapors