I want to use standard sandpapers of different grit sizes to impart flow resistance to a surface. I am wondering how to convert the roughness of sandpaper to an equivalent sand-grain roughness. Is there any established correlation between grit size and equivalent sand-grain roughness?
Dear Dr Dr Armin: Please take a look at the following useful links:
https://www.usna.edu/NAOE/_files/documents/Faculty/schultz/Flack,%20Schultz%20-%20Hydraulic%20Roughness%20Scales,%202010.pdf
https://ligrani.com/surface-roughness/
Regards--
You have two ways:
1- Set up a flume, cover it by that sand paper, measure velocity profile with ADCP and then find the boundary layer and where it hits the surface, you can back calculate roughness height (Also you may do it with a wind tunnel and smoke which will be cheaper and easier to set up).
2- The original moody diagram is based on the flow regime when it passes over a uniform sand particles which is glued over a surface (this is exactly "sand paper" per se!) It was the work of Johann Nikuradse. Read his 1933 paper and correlated the roughness of the sand paper to his sand sheets.
Apparently the first approach is more reliable.
Hope it helps,
Kaveh
This might be useful:
https://www.sciencedirect.com/topics/engineering/equivalent-sand-grain-roughness
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