# creating velocity inlet profile on star ccm+

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 May 26, 2009, 13:06 creating velocity inlet profile on star ccm+ #1 New Member   Lorenzo Join Date: May 2009 Posts: 2 Rep Power: 0 hallo , i'm an italian student and i've some problems with star ccm+. i need to create a velocity log law profile but i don't know how to compile a field function. i 've tried to create some function component and to assemble these on vector one with no results. i add my attempts: i've tried to introduce the z variable with \$\$Position[2] u(z) component definition: ((0.164696691/0.4)*log((\$\$Position[2]+5.32267E-05)/5.32267E-05*0.866)-3.084 v(z) component definition: -(0.164696691/0.4)*log((\$\$Position[2]+5.32267E-05)/5.32267E-05)*0.5 help me please thanks a lot

 May 27, 2009, 03:37 #2 Senior Member   Join Date: Mar 2009 Posts: 203 Rep Power: 10 In my ccm the z variable is "Position_2" and to use them I make \$Position_2 /edith says: Often the field function is only shown when you had "used" them in a scene, don't know why but I only have the "Position"-Vector, when I used the scalar displayer Position -> Laboratory -> Z, I have the field function Position[Z]. I hope it helps you. Last edited by Maddin; May 27, 2009 at 03:40. Reason: new idea

 May 27, 2009, 05:14 #3 New Member   PA Join Date: Mar 2009 Posts: 23 Rep Power: 9 I actually did something similar with a power-law profile based on a desired flow rate where I used several field functions to calculate Re, exponents etc. If you are using a cylindrical boundary (e.g. a pipe) you might find it easier to define a local cylindrical coordinate system (placed in the center of the inlet) and then use \$\$Centroid(name_of_your_cylindrical_coordinate_sys tem)[0] \$\$Centroid(name_of_your_cylindrical_coordinate_sys tem)[1] \$\$Centroid(name_of_your_cylindrical_coordinate_sys tem)[2] to calculate the velocity based on the distance from the center of this CS. Consult the manuel regarding the details of the x, y, z of the cylindrical coordinate system. Hope this helps a bit...

 June 8, 2009, 09:55 thanks very much at all #4 New Member   Lorenzo Join Date: May 2009 Posts: 2 Rep Power: 0 thanks very much at all!! i've solved my problem i don't understand why, but starccm+ don't love number squared...and on my first expression i've digited ^2 and not the simple number result. well! if you need to simulated a velocity profile for an atmospheric boundary layer, the best way is to write the log law in component like what i've do and to create a field function velocity where put the component expression.like this [((0.164696691/0.4)*log((\$\$Position[2]+5.32267E-05)/5.32267E-05)*0.866)+3.084 , -(0.164696691/0.4)*log((\$\$Position[2]+5.32267E-05)/5.32267E-05)*0.5 ,0] thanks again good luck at all

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