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Old   April 27, 2008, 18:40
Default Wall Roughness
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LKF
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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.
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Old   April 27, 2008, 19:20
Default Re: Wall Roughness
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LKF
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Sorry, typo on the Rz values. I'm only looking at values up to about 3E6 micro-inch. Not 1E9!
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Old   April 28, 2008, 07:26
Default Re: Wall Roughness
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John Parry
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3E6 micro-inch is 3 inches. Can you elaborate on the application? How thick is the boundary layer?

John Parry, Research Manager, Flomerics Ltd.
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Old   April 28, 2008, 08:06
Default Re: Wall Roughness
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LKF
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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,
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Old   April 28, 2008, 10:49
Default Re: Wall Roughness
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LKF
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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.
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Old   May 8, 2008, 10:22
Default Re: Wall Roughness
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Kelly Cordell-Morris
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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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