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joseph July 12, 2001 00:08

Details of Y+
 
Hi,

Could you please throw some light on Y+, and its effects in a solver. and If you know some sites please do send it across.

thanks for your time.

Regards joseph

John C. Chien July 12, 2001 02:36

Re: Details of Y+
 
(1). Y+ appears in the "turbulent boundary layer theory". (2). You need to study the book "boundary layer theory" by Schlichting. (3). It is also part of the turbulence modeling. Y+ is the dimensionless coordinate suitable for the near wall flow behavior for turbulent flows. (4). In order to obtain good resolution and accurate solution, the first mesh point away from the wall, in terms of Y+, should be in certain range according to the turbulence model used. (whether it is a high Reynolds number model or a low Reynolds number model) (5). You should try to read books on "turbulence modeling" to get more information.

Fabian July 12, 2001 03:49

Re: Details of Y+
 
You have to take great care generating the grid anyway, but especially near the walls, depending on the turbulence model you are using (wall functions/no wall functions). Try: Grotjans, H.; Menter, F.R. " Wall Functions for General Apllication CFD Codes", ECCOMAS 98 Proceedings, John Wiley+Sons, 1998, pp. 1112-1117

Bernard Parent July 12, 2001 09:17

Everything you ever wanted to know about yplus..
 
http://geolab.larc.nasa.gov/APPS/YPlus/

(just joking, but it's still an handy site..)

Peter July 12, 2001 15:44

Re: Details of Y+
 
y+ takes into account perpendicular distance from the wall, and density, shear stress and viscosity on the wall (y=0). y+ is an important parameter when you are analysing a solution. Operating at very high values of y+ makes that the first cell in contact with the wall is very far from it, making not possible to take into account what it is occurring near the wall. One always want to operate y+ values close to one but this is just unrealistic since computing time will be too much. Alternatively, it is possible to use wall functions.

Take care with y+, before analysing any solution, take a look at its value


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