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asherah February 19, 2010 18:45

A girl fail to plot velocity profile when mesh changes + Wall function
Hi everyone I am new here, its great to find out that people discuss theirs difficulty here. I have been stuck with those problems for two weeks, and never get it sorted out! The deadline is coming soon….

Dimension is like this, it's a 0.05 m x0.05 m square duct, corresponding to x, and y axis , the duct is 0.5 meters long along z axis.

This is my First Problem: currently I am working on simulation fluid in square duct, I have already set up one model, for Prism layer thickness 0.0006 and layer for 10, one for turbulent and one for Laminar. Both fully developed.

However when I change the number of Prism layer in turbulent flow, clear mesh, create mesh again, clear solution, ran solution again. After an hour, after applied the volumetric mesh, the plot of velocity (the scalar part is a line probe rest in the centre) is totally blank! I have been change the x-axis position from 0 1 0 to 1 0 0, or 0 0 1, neither of them gives me plot. (the correct one should be 0 1 0, because I am only interested the velocity varies along y axis.)

Before I made the change and ran the simulation, the velocity profiles works fine.

Is anyone know what’s happening here? This happens to my laminar simulation as well, when I made change the Number of Prism layer. At the beginning I thought the program probably stops working because my mesh might be too fine, so I changed the thickness to 0.006, and the velocity plot is still blank (I can get velocity from scene), continuity line already convergent, so it can’t be not converging….

The second problem is that I made a function names u+ by using field function. The function has been defines as $$Velocity[2]/$Ustar. Ustar has been defines. I chose the bottom plate as the scalar part, because u star is a square root of (wall shear stress/ density). I plot U+ against wall Y+ yes, that is wall function. Again, as I have stated in problem one: when I made any changes, it failed to plot. However when it works, it gives a line going down. I don't know why…the shape meant to be going up? another problem here is that Y+ didnot go beyond 1.8 ....

Please please if you know anything, please let me know. This project meant to be 4 people’s projects, my groupmates drops out, so I have to finish it on my own. I am highly appreciated with your time bear with me.
Many thanks


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