Velocity Profile as an Initial Condition

ylm054 · December 7, 2009, 00:50

When carrying out a transient simulation, is it possible to input a .csv velocity profile as an initial condition for the entire domain?

ylm054 · December 7, 2009, 01:07

that is to say - I have a 2D velocity profile in the XY plane. This profile represents the flow within a circular pipe (drawn from a circle in the XY plane and extruded along the z axis).

The velocity profile is constant in the Z direction. (i.e. if taking a cross-sectional XY plane slice for any value of Z, the profile should be the same).

cfdman · December 7, 2009, 03:45

Hello ylm054,

I think you can do this with using Initial Tab under Domain Window. You have to use an expression which symbolize velocity profile. Then use this expression in Initial Tab under Domain Setting Window.
Be careful you can't use any component of velocity as a variable in other component of velocity.
For example; x_vel=(2*12.5+y/1[m])*1[m/s] expression defines x_vel as a function of "y". If you write "x_vel" to initial contidions/velocity/x component, CFX will give an error. So you can't use a component of velocity as a variable in any other component of velocity.

Good Luck

ghorrocks · December 7, 2009, 05:33

You can use your 2D data to generate an initial condition. Use the 3D interpolation function. If you can describe your points as a CEL expression or some 1D interpolation that is better but if they don't work use a 3D function.

ylm054 · December 7, 2009, 20:48

CFDman: "You have to use an expression which symbolize velocity profile. Then use this expression in Initial Tab under Domain Setting Window."

Is it possible to enter the profile without using an expression? Since CFX doesn't support bessel functions, I dont really think this is an option.

ghorrocks: You can use your 2D data to generate an initial condition. Use the 3D interpolation function. If you can describe your points as a CEL expression or some 1D interpolation that is better but if they don't work use a 3D function.

Once I have a 3D function how do I actually set it to be the initial condition over the entire domain? I get a bad value error when I type the function into the intialisation>cartesian velocity>w velocity box.

December 7, 2009, 00:50	Velocity Profile as an Initial Condition	#1
ylm054 New Member Join Date: Dec 2009 Posts: 10 Rep Power: 17	When carrying out a transient simulation, is it possible to input a .csv velocity profile as an initial condition for the entire domain?

December 7, 2009, 01:07	clarification	#2
ylm054 New Member Join Date: Dec 2009 Posts: 10 Rep Power: 17	that is to say - I have a 2D velocity profile in the XY plane. This profile represents the flow within a circular pipe (drawn from a circle in the XY plane and extruded along the z axis). The velocity profile is constant in the Z direction. (i.e. if taking a cross-sectional XY plane slice for any value of Z, the profile should be the same).

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December 7, 2009, 03:45		#3
cfdman New Member Arda Ersan Join Date: Aug 2009 Posts: 13 Rep Power: 17	Hello ylm054, I think you can do this with using Initial Tab under Domain Window. You have to use an expression which symbolize velocity profile. Then use this expression in Initial Tab under Domain Setting Window. Be careful you can't use any component of velocity as a variable in other component of velocity. For example; x_vel=(212.5+y/1[m])1[m/s] expression defines x_vel as a function of "y". If you write "x_vel" to initial contidions/velocity/x component, CFX will give an error. So you can't use a component of velocity as a variable in any other component of velocity. Good Luck

December 7, 2009, 05:33		#4
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,870 Rep Power: 144	You can use your 2D data to generate an initial condition. Use the 3D interpolation function. If you can describe your points as a CEL expression or some 1D interpolation that is better but if they don't work use a 3D function.

December 7, 2009, 20:48		#5
ylm054 New Member Join Date: Dec 2009 Posts: 10 Rep Power: 17	CFDman: "You have to use an expression which symbolize velocity profile. Then use this expression in Initial Tab under Domain Setting Window." Is it possible to enter the profile without using an expression? Since CFX doesn't support bessel functions, I dont really think this is an option. ghorrocks: You can use your 2D data to generate an initial condition. Use the 3D interpolation function. If you can describe your points as a CEL expression or some 1D interpolation that is better but if they don't work use a 3D function. Once I have a 3D function how do I actually set it to be the initial condition over the entire domain? I get a bad value error when I type the function into the intialisation>cartesian velocity>w velocity box.