# Wall Roughness

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 April 27, 2008, 18:40 Wall Roughness #1 LKF Guest   Posts: n/a Sponsored Links Has anybody had luck (or attempted) to simulate very rough walls in FLOWORKS? I'm currently trying to validate textbook calculations for Rz values in the order of 1E6 - 1E9 micro-inch and I am not getting results that correlate whatsoever. Thanks for the insight/opinions.

 April 27, 2008, 19:20 Re: Wall Roughness #2 LKF Guest   Posts: n/a Sorry, typo on the Rz values. I'm only looking at values up to about 3E6 micro-inch. Not 1E9!

 April 28, 2008, 07:26 Re: Wall Roughness #3 John Parry Guest   Posts: n/a 3E6 micro-inch is 3 inches. Can you elaborate on the application? How thick is the boundary layer? John Parry, Research Manager, Flomerics Ltd.

 April 28, 2008, 08:06 Re: Wall Roughness #4 LKF Guest   Posts: n/a Hello, thanks for the reply. Yes, 3E6 is 3 inches. Is this within the limits of the calculation scheme used by FLOWORKS to calculate wall shear stress and the resultant pressure drop along a flow domain? The application I'm trying to model is loosely based on ambient airflow through mine shafts with shotcrete finished walls or just blasted/bored. It's large scale models (15 to 30 foot diameters) - I would anticipate bl thickness in the order of 6 inches to perhaps 18 inches. What scheme does FW use for bl approximation? Additionally, where can I review the residual values after the calculations have finished iterating? The word 'residual' doesn't even show up in the FW help files when I search for it. Thanks for the assistance,

 April 28, 2008, 10:49 Re: Wall Roughness #5 LKF Guest   Posts: n/a I've continued to look into wall roughness effects. Not only are my results not lining up hand calcs, pressure drop along a 800 ft section (with fully developed flow) is not even varying for different Rz values.

 May 8, 2008, 10:22 Re: Wall Roughness #6 Kelly Cordell-Morris Guest   Posts: n/a Do you have access to the validation examples in Floworks? In EFD Lab one of the validation examples is flow over smooth and rough plates. I have just quickly changed the parameters of one of these models and obtained a pressure drop profile. What parameters are you using to check for convergence? The drag coefficent would perhaps be one to use? Cd = F / ((0.5*rho*V^2)*A)) F=drag force, A=surface area, rho=fluid density, V=fluid velocity

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