[Paraview] Oilflow - Surface flow

[Richard GRENON]

Hi Lorenzo.

The Stream Tracer works very well to follow a 3D streamline in a  
volume, but I always got bad results to follow streamlines on a curved 
surface. When you start from a point on a surface to follow a 
streamline, the next point is found with a small step in the direction 
of the tangent vector, but this new point is not on the surface if the 
surface is curved. So the new point should be projected onto the surface 
before proceeding to the next step. It seems that  the Streal Tracer 
algorithm does not project correctly the new point at each step, so you 
get only small pieces of streamlines, depending on the curvature of the 
surface. The more the surface is curved, the more the Stream Tracer has 
difficulties to remain on the surface when following the stream line. 
The Stream Tracer gives good results on a surface only if the surface is 
plane.

For me, the LIC plugin was a marvelous workaround for surface 
streamlines, and for two reasons. First, it gives quickly pretty 
pictures. Second, it gives at a glance the whole surface flow pattern, 
so you can easily identify complex separated flow regions without having 
to guess seed points as you would do with the the Stream Tracer. Now I 
am always using the Stream Tracer for 3D streamlines in a volume and the 
LIC plugin for surface flow patterns.

I don't understand why you say that LIC is "heavy" in Paraview ? Once 
you have a surface vector in your data, you have only to change the 
Representation from Surface to SurfaceLIC and the rendering is 
immediate, and I think faster than computing streamlines. The only 
drawback of LIC is that it depends on your graphic card, and it may not 
work depending on the version of your driver.

Richard.


Lorenzo a écrit :
> Hi all;
> I managed to calculate the wall shear stress in openFoam using the command
>  wallShearStress -latestTime
> and using the results (vector) as in input for the LIC!
>
> That's great!
>
> Now I'd have another question related to this topic:
> as I see the LIC is pretty heavy in paraview even though mine is a small geometry. I'm wondering, once I've loaded the wall shear stress, I could use the stream tracer on it to get more or less what I want. The only problem I'm having is that the line that generates the streamlines needs to be exactly on the surface of my body. Is there any way to attach the line to the surface?
>
> Thank you again!
>
>   
-- 
 Richard GRENON
 ONERA
 Departement d'Aerodynamique Appliquee - DAAP/ACI
 8 rue des Vertugadins
 92190 MEUDON - FRANCE
 phone : +33 1 46 73 42 17
 fax   : +33 1 46 73 41 46
 mailto:Richard.Grenon at onera.fr
 http://www.onera.fr