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Unformatted text preview: Effect of Rough Walls It was not known until experiments in 1800 by Coulomb  that surface roughness has
an effect on friction resistance. It turns out that the effect is negligible for laminar pipe
flow, and all the laminar formulas derived in this section are valid for rough walls also.
But turbulent flow is strongly affected by roughness. In Fig. 6.9 the linear viscous sublayer only extends out to y
5. Thus, compared with the diameter, the sublayer thickness ys is only
Red f 1/2 umax Parabolic
curve V (a) V
umax | v v Fig. 6.11 Comparison of laminar
and turbulent pipe-flow velocity
profiles for the same volume flow:
(a) laminar flow; (b) turbulent flow. (b) | e-Text Main Menu | Textbook Table of Contents | Study Guide 6.4 Flow in a Circular Pipe 347 0.10
∋ = 0.0333
d 0.06 0.0163
0.04 0.00833 f 0.00397 ∆B
Sm 0.00198 64
Red 0.00099 0.02 oth h ug Ro Eq. (6.55a) Eq. (6.54) ≈1n ∋ + log 0.01 yu*
v 10 3 10 4 10 5 10 6 Red (a) (b) Fig. 6.12 Effect of wall roughness
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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