Chapt06

The slope of the logarithm law remains the same 1 but

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: ratio /d. For any given /d, the friction factor becomes constant (fully rough) at high Reynolds numbers. These points of change are certain values of u*/ : u* 5 5: 70: u* u* hydraulically smooth walls, no effect of roughness on friction transitional roughness, moderate Reynolds-number effect 70: fully rough flow, sublayer totally broken up and friction independent of Reynolds number For fully rough flow, 70, the log-law downshift B in Fig. 6.12a is | v v B | e-Text Main Menu | 1 ln Textbook Table of Contents 3.5 | Study Guide (6.61) 348 Chapter 6 Viscous Flow in Ducts and the logarithm law modified for roughness becomes 1 u ln y B B 1 ln y 8.5 (6.62) The viscosity vanishes, and hence fully rough flow is independent of the Reynolds number. If we integrate Eq. (6.62) to obtain the average velocity in the pipe, we obtain V u* 1 f 1/2 or 2.44 ln 2.0 log d /d 3.7 3.2 fully rough flow (6.63) There is no Reynolds-number effect; hence the head loss varies exactly as the square of the velocity in this case. Some numerical values of friction factor may be listed: /d f 0.00001 0.0001 0.001 0.01 0.05 0.00806 0.0120 0.0196 0.0379 0.0716 The fricti...
View Full Document

This note was uploaded on 10/27/2009 for the course MAE 101a taught by Professor Sakar during the Spring '08 term at UCSD.

Ask a homework question - tutors are online