Unformatted text preview: CWR 4202 Lecture Packet 4 Relating Shear Stress to Mean Velocity = Eddie Velocity Recall: Using equations from pg. 1 of Lecture Packet Nikuradse's Experiments (supplemental reading assignment 1) relating friction factor to flow conditions (laminar or turbulent), pipe roughness and pipe diameter. ks/D Note: typographic error in text book (supp. Reading 1) listed as D/2ks Friction Factor (f ) = Nikuradse made a major contribution to the theory of pipe flow by objectively differentiating between smooth and rough turbulence in pipes. He carried out a painstaking series of experiments to determine both the friction factor and the velocity distributions at various Reynolds' Numbers. In these experiments, pipes were artificially roughened by sticking uniform sand grains on to smooth pipes. He defined the relative roughness (ks/D) as the ratio of the sand grain size to the pipe diameter. By using pipes of different diameter and sand grains of different size, he produced a set of experimental results of (or f) and Re for a range of relative pipe roughness. Moody's Diagram (Supplemental reading assignment 1) The first attempt to make engineering flow calculations more practical was made by Moody . He produced a plot relating friction factor ( or f) to Re based upon an empirical relationship for commercial pipes, as shown in the Figure below. This figure is now known as the Moody diagram. Friction Factor (f ) = All of the Power Forumla equations (posted on course website and summarized in reading assignment 1) represent flow that fall somewhere on this chart. As engineers we just have to decide which equation is appropriate to our current conditions. Portions of this material were adapted from: Andrew Chadwick, John Morfett and Martin Borthwick. Hydraulics in Civil and Environmental Engineering, Fourth Edition. 2004. Spon Press. NY, NY. ...
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- Fall '08
- Fluid Dynamics, Moody chart, friction factor, Nikuradse