|
[Sponsors] |
April 8, 2008, 11:29 |
Equivalent Sand Grain Roughness
|
#1 |
Guest
Posts: n/a
|
Hi,
I am trying to figure out how to calcualte the required sand grain roughness to use on a surface. I have a real roughness height of 0.0005m and would like to know how to enter this into CFX. I found the equations K+=yR(Rho/Mu)u* ...etc... but dont really see how they help me! I have calculated values for y+, ut, u+, u*, tauW, y* but dont know where my roughness height of 0.0005 comes into this? Cna anyone shed some light or talk me through it, Cheers |
|
April 8, 2008, 15:16 |
Re: Equivalent Sand Grain Roughness
|
#2 |
Guest
Posts: n/a
|
I had a case that needs the roughness too. After spending a little time, I just assumed the roughness published in most books for material is the equivalent sand grain roughness required in CFX. Is this right?
|
|
April 8, 2008, 17:06 |
Re: Equivalent Sand Grain Roughness
|
#3 |
Guest
Posts: n/a
|
Im not to sure to be honest, I have an actual roughness height and need this converting to sand grain roughness, which is different.
|
|
April 8, 2008, 23:59 |
Re: Equivalent Sand Grain Roughness
|
#4 |
Guest
Posts: n/a
|
Try reading Boundary Layer Theory by Schlichting. It is described in detail there.
http://www.amazon.com/Boundary-Layer.../dp/3540662707 |
|
April 9, 2008, 06:24 |
Re: Equivalent Sand Grain Roughness
|
#5 |
Guest
Posts: n/a
|
Thanks for the reference but that book has been taken out of all the library's in Bristol, must be all us keen students!
|
|
April 12, 2010, 09:55 |
|
#6 | |
Member
prout
Join Date: May 2009
Posts: 32
Rep Power: 17 |
Quote:
See "Extensions of the Spalart–Allmaras turbulence model to account for wall roughness"B. Aupoix and P. R. Spalart, doi:10.1016/S0142-727X(03)00043-2 And "Turbulent flow in smooth and rough pipes", J.J Allen, M.A Shockling, G.J Kunkel and A.J Smits, doi: 10.1098/rsta.2006.1939 |
||
July 31, 2014, 09:08 |
|
#7 |
New Member
federico
Join Date: Jan 2013
Posts: 13
Rep Power: 13 |
here is an article with conversion factor and also it has good references
http://ijmem.avestia.com/2012/PDF/008.pdf |
|
January 16, 2024, 03:56 |
|
#8 |
New Member
prashant godse
Join Date: Jul 2023
Posts: 10
Rep Power: 3 |
i have used 30 micron sand grain size for rotor 67 so how much it equivalent to in microns rms.
|
|
January 16, 2024, 19:57 |
|
#9 |
Super Moderator
Glenn Horrocks
Join Date: Mar 2009
Location: Sydney, Australia
Posts: 17,862
Rep Power: 144 |
Have you read the description of wall roughness definition in the CFX documentation? This is discussed there. See Solver Modelling Guide, section 4.2.4.
__________________
Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum. |
|
January 18, 2024, 09:47 |
|
#10 |
Senior Member
Erik
Join Date: Feb 2011
Location: Earth (Land portion)
Posts: 1,188
Rep Power: 23 |
Look at Fedefrance's post right above yours, that reference is about as good as it gets. Keep in mind there is no exact "equivalent", just an approximate relationship.
|
|
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
nutRoughWallFunction and Surface Roughness Documented | AlanR | OpenFOAM Programming & Development | 64 | January 6, 2024 08:13 |
equivalent sand roughness height | LSC | CFX | 3 | December 23, 2012 13:50 |
equivalent sand grain roughness | attax | CFX | 0 | September 8, 2005 10:44 |
NACA standart roughness | DAK565656 | Main CFD Forum | 2 | August 24, 2005 01:47 |
Roughness adaptation in CFX 4.4 | Bart | CFX | 1 | May 2, 2003 09:32 |