An introduction to standard velocity wall functions that are modified for surface roughness. This treatment is adopted by all mainstream CFD codes (OpenFOAM, Fluent, CFX, Star). The following topics are covered:

1) 4:40 How is the log-law velocity profile for smooth surfaces modified to account for roughness?

2) 7:51 What are the roughness height (Ks) and the roughness constant (Cs)?

3) 19:30 How do CFD codes account for roughness?

#cfd #wallfunctions #roughness

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Some useful references:
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1) ANSYS FLUENT User Manual
7.3.14 Wall Boundary Conditions

http://www.afs.enea.it/project/neptun...

2) T. Cebeci and P. Bradshaw
Momentum Transfer in Boundary Layers
Hemisphere Publishing Corporation, New York 1977.

https://www.amazon.co.uk/Momentum-Tra...

3) J. Nikuradse
Law of Flow in Rough Pipes
Technical Memorandum 1292, National Advisory Committee for Aeronautics, 1950.

https://ntrs.nasa.gov/archive/nasa/ca...

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Disclaimer
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The methods, algorithms, equations, formulae, diagrams and explanations in this talk are for educational and demonstrative purposes only. They should never be used to analyse, design, accredit or validate real scientific / engineering / mathematical structures and flow systems. For such applications, appropriate trained, qualified and accredited (SQEP) engineers / scientists should be consulted along with the appropriate documentation, procedures and engineering standards. Furthermore, the information contained within this talk has not been verified, peer reviewed or checked in any way and is likely to contain several errors. It is therefore not appropriate to use this talk itself (or any of the algorithms, equations, formulae, diagrams and explanations contained within this talk) as an academic or technical reference. The reader should consult the original references and follow the verification and validation processes adopted by your company / institution when carrying out engineering calculations and analyses. Fluid Mechanics 101 and Dr. Aidan Wimshurst are not accountable or liable in any form for the use or misuse of the information contained in this talk beyond the specific educational and demonstrative purposes for which it was intended.