# Initial velocity field in StarCCM+

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 December 18, 2008, 16:54 Initial velocity field in StarCCM+ #1 Subhadeep Guest   Posts: n/a I want to initialize a 3D velocity field to my problem u(x) = f(y) = a cubic velocity profile u(y) = 0.0 u(z) = 0.0 I understand the scalar field function but not quite sure how to implement this vector field to my problem. f(y) will look like : a*pow(\$\$Position[1],3) + b*pow(\$\$Position[1],2) + c*\$\$Position[1] All the vector field function examples are kind of problem specific and I am unable to figure out how I will achieve what I am trying. So if anyone could point me in the right direction then that will be great.

 December 18, 2008, 17:17 Re: Initial velocity field in StarCCM+ #2 a Guest   Posts: n/a The field function you are looking for is \$\$Centroid not \$\$Position. Just paste the code you have written into a new field function definition, and set the initial velocity in the x direction to use that field funciont.

 December 18, 2008, 17:22 Re: Initial velocity field in StarCCM+ #3 Subhadeep Guest   Posts: n/a not quite following what you are trying to say here. Why should I use centroid first of all? Secondly, should this be a scalar or vector field function? if scalar and u(x) only how will I make sure u(y) and u(z) = 0, respectively?

 December 21, 2008, 04:40 Re: Initial velocity field in StarCCM+ #4 steve Guest   Posts: n/a Hi Make your FF (field function) of type vector not scalar. Give it the definition [0,0,\$YourFieldFunction] You can use position, it is the vertex position and is known to STAR-CCM+ before you hit initialise. The value of centroid is calculated during initialisation. With position there can be potentially problems with tolerances particularly if you try a FF containing for example a sqrt operation if a vertex position falls below zero , hence I like to use centroid. Regards Steve

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