Incomplete velocity profile import

MissCFD · January 25, 2015, 17:16

Hello,

In CFX, I would like if I import a velocity profil which is incomplete near wall as initial conditions, is the software will complete automatically with linear and log laws ?

Thank you for your help

awesim · January 26, 2015, 06:33

Hello MissCFD,

when defining the velocity profile as a user function you can check boxes to extend the minimum and maximum values. As far as I know it will just take the last value for every subsequent location until reaching the next bound (probably a wall). So make sure the values closest to the walls are no outliers.

Hope that helps,
Simon

MissCFD · February 22, 2015, 19:55

Thank your for your answer Simon.

I have an another question in the same way. If i import a velocity profile as a user function, is the cells size of my mesh must be less or greater than distance between two points of my velocity profile ? I tend to say that it's "less".

Thank you for your help again.

Quote:

Originally Posted by awesim

Hello MissCFD,

when defining the velocity profile as a user function you can check boxes to extend the minimum and maximum values. As far as I know it will just take the last value for every subsequent location until reaching the next bound (probably a wall). So make sure the values closest to the walls are no outliers.

Hope that helps,
Simon

awesim · February 23, 2015, 04:24

In terms of stability for your simulation it shouldn't really matter how many sampling points you choose for your profile or what distance there is between your nodes, respectively. But it will affect the precision of your inlet boundary flow since the actual values at the nodes of your grid will be interpolated from the given profile. So most accurate would be to have a profile which points are already located on the nodes of your inlet boundary. But in most cases that's not really necessary.

Thomas MADELEINE · February 23, 2015, 11:32

From what I understood of importing BC :
with basic options, when you import a profile CFX create a function (RxRxR -> R) so at each point in space it has a value for your variable (velocity).
Since you have only some point (from your mesh), CFX interpolate it to a continuous function (with a basic linear mode between two points). After that when you use the function for your BC it just match the point of your current mesh with the function.

I think you can use some option for the function to use a logarithmic law to interpolate the function.

January 25, 2015, 17:16	Incomplete velocity profile import	#1
MissCFD Senior Member Join Date: Aug 2014 Posts: 160 Rep Power: 11	Hello, In CFX, I would like if I import a velocity profil which is incomplete near wall as initial conditions, is the software will complete automatically with linear and log laws ? Thank you for your help

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January 26, 2015, 06:33		#2
awesim New Member Join Date: Oct 2014 Posts: 14 Rep Power: 11	Hello MissCFD, when defining the velocity profile as a user function you can check boxes to extend the minimum and maximum values. As far as I know it will just take the last value for every subsequent location until reaching the next bound (probably a wall). So make sure the values closest to the walls are no outliers. Hope that helps, Simon

February 23, 2015, 04:24		#4
awesim New Member Join Date: Oct 2014 Posts: 14 Rep Power: 11	In terms of stability for your simulation it shouldn't really matter how many sampling points you choose for your profile or what distance there is between your nodes, respectively. But it will affect the precision of your inlet boundary flow since the actual values at the nodes of your grid will be interpolated from the given profile. So most accurate would be to have a profile which points are already located on the nodes of your inlet boundary. But in most cases that's not really necessary.

February 23, 2015, 11:32		#5
Thomas MADELEINE Senior Member Thomas MADELEINE Join Date: Oct 2014 Posts: 126 Rep Power: 11	From what I understood of importing BC : with basic options, when you import a profile CFX create a function (RxRxR -> R) so at each point in space it has a value for your variable (velocity). Since you have only some point (from your mesh), CFX interpolate it to a continuous function (with a basic linear mode between two points). After that when you use the function for your BC it just match the point of your current mesh with the function. I think you can use some option for the function to use a logarithmic law to interpolate the function.