# Dimensionless wall distance

 Register Blogs Members List Search Today's Posts Mark Forums Read

 March 2, 2014, 20:32 Dimensionless wall distance #1 New Member   Join Date: Nov 2011 Posts: 7 Rep Power: 5 Hi there! I would like to ask about the dimensionless wall distance. In many papers are three-dimensional domains described using ,,. I am not sure how to compute it for other axis (, ). Wall can be computed as . Where is the friction velocity at the nearest wall, y is the distance to the nearest wall and is the local kinematic viscosity of the fluid. ** Where is the wall shear stress and is the fluid density at the wall. *** Where is the dynamic viscosity, u is the flow velocity parallel to the wall and y is the distance to the wall. Is it computed for let's say as follows? but are without change? I am not sure about the wall shear stress component (gradient of u) Thank you for any hints or recommendations.

 March 3, 2014, 04:26 #2 Member   Join Date: Jun 2012 Posts: 40 Rep Power: 5 As far as I know the dimensionless wall distance is measured orthogonal to the wall which is usually called yplus and sometimes zplus. Never heard of xplus but it might just be dependent on how you set you coordinate system.

 March 3, 2014, 08:41 #3 New Member   Join Date: Nov 2011 Posts: 7 Rep Power: 5 Thank you. I thought as you do, but you can find , widely used in domain descriptions. For example as shown here: in LES of three-dimensional wing (http://www.iccfd.org/iccfd7/assets/p...3604_paper.pdf). It is possible to find it in other papers too. I am not sure if and are "normalized" with respect to the wall . I could not find any source with explanation. Probably, there is a trivial answer (that's why..). Any idea guys? Thank you.

 March 13, 2014, 05:33 #4 Senior Member   Rami Ben-Zvi Join Date: Mar 2009 Posts: 147 Rep Power: 8 Hi Messik, I guess there are two issues in your post requiring consideration: 1. The "u" should actually be interpreted as the velocity parallel to the wall, not the x-velocity component. 2. The "y" in wall shear stress needs be interpreted as the normal-to the wall coordinate rather than the y-coordinate. Then the and the follow naturally by merely changing components. I hope this helps, Rami

 March 15, 2014, 07:55 #5 Member   Join Date: Jun 2011 Posts: 51 Rep Power: 6 Hi messik, In 3D flows u may have the other commonents of shear stress, which IMHO makes sense to have the dimless in all three components. Although the boudary layer develops mainly normal to the wall, the resolution of the mesh in all the other two components is also important for the accuracy of your results. If you consider that u are resolving the laminar sub-layer (y+=1) it may be also important that your mesh in the other components fits within (x+/z~30). I think that u use the half of the mesh size and the velocity gradients in the right directions u can find those dimless. Regards,

 Thread Tools Display Modes Linear Mode

 Posting Rules You may not post new threads You may not post replies You may not post attachments You may not edit your posts BB code is On Smilies are On [IMG] code is On HTML code is OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post rks171 Main CFD Forum 7 June 16, 2012 15:39 minger Main CFD Forum 0 July 6, 2011 07:45 Worth FLUENT 2 June 13, 2009 03:04 Luke FLUENT 0 March 15, 2006 12:42 Chris FLUENT 0 June 22, 2004 06:10

All times are GMT -4. The time now is 05:55.