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Unformatted text preview: (a) low-speed,
laminar flow; (b) high-speed, turbulent flow; (c) spark photograph of
condition (b). (From Ref. 4.) 6.2 Internal versus External
Viscous Flows Both laminar and turbulent flow may be either internal, i.e., “bounded” by walls, or
external and unbounded. This chapter treats internal flows, and Chap. 7 studies external flows.
An internal flow is constrained by the bounding walls, and the viscous effects will
grow and meet and permeate the entire flow. Figure 6.6 shows an internal flow in a
long duct. There is an entrance region where a nearly inviscid upstream flow converges
and enters the tube. Viscous boundary layers grow downstream, retarding the axial flow
u(r, x) at the wall and thereby accelerating the center-core flow to maintain the incompressible continuity requirement
Q u dA const (6.3) At a finite distance from the entrance, the boundary layers merge and the inviscid
core disappears. The tube flow is then entirely viscous, and the axial velocity adjusts
slightly further until at x Le it no longer changes with x and is said to be fully developed, u u(r) only. Downstream of x Le the velocity profile...
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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