Unformatted text preview: is impossible physically. For E Emin two solutions are possible: (1) large depth with V Vc, called subcritical, and (2) small depth with V Vc, called supercritical. In subcritical flow, disturbances can propagate upstream because wave speed C0 V. In supercritical flow,
waves are swept downstream: Upstream is a zone of silence, and a small obstruction
in the flow will create a wedge-shaped wave exactly analogous to the Mach waves in
Constant q Horizontal
hf y=E EGL
E v v Subcritical
yc Fig. 10.8 Specific-energy considerations: (a) illustration sketch;
(b) depth versus E from Eq.
(10.29), showing minimum specific
energy occurring at critical depth. | V2
2g Critical y Supercritical
0 (b) (a) | e-Text Main Menu E E min | Textbook Table of Contents | Study Guide 10.4 Specific Energy; Critical Depth 673 Fig. 9.18c.2 The angle of these waves must be
1 sin c0
V 1 sin (gy)1/2
V (10.34) The wave angle and the depth can thus be used as a simple measurement of supercritical-flow velocity.
Note from Fig. 10.8b that small changes in E...
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This note was uploaded on 10/27/2009 for the course MAE 101a taught by Professor Sakar during the Spring '08 term at UCSD.
- Spring '08