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Old   April 15, 2008, 22:19
Default Sinusoidal boundary condition
  #1
Rohan
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Hi everybody,

I have created a domain in CFX11 to resemble a drop (5mm in diameter) on a surface. At the flat boundary (bottom) of the drop i have imposed a no-slip boundary condition where U and W have been defined as a sinusoidal velocity condition. This is to represent the droplet being actuated by surface acoustic waves being generated by the substrate upoon which it sits.

U= A*Sin(wt-kx) and W=A*Cos(wt-kx)

My suspision is that the waves are not moving along the surface with time (as they are supposed to). How do i verify this in post. When I create a key frame animation to show streamlines as they evolve from 10-100 seconds, the contour plots of the veocity on the boundary remain stationary. I also want to know if the way I have defined the boudary condition allows CFX to vary it with time.

Thanks in advance.

Rohan
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Old   April 16, 2008, 12:25
Default Re: Sinusoidal boundary condition
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cfd-student
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Yes there is a way to do that in CFX. I need to impose a similar time varying boundary condition which is pressure varying with time. I have even posted a message on forum but still havent received any reply for it. If you find out how to do that please let me know. Thanks
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Old   April 16, 2008, 15:18
Default Re: Sinusoidal boundary condition
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CycLone
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Insert the expression "A + B*sin(omega*(t-t offset))" as you boundary condition instead of a single value.

Where "A" is a constant value of pressure or velocity, or whatever the boundary condition defines (use appropriate units), and "B" is the magnitude of the fluctuating component. "omega" is the frequency in radians per second and "t" is just the CFX variable for time and "t offset" is the phase offset, if necessary.

...or create your own expression.

-CycLone
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Old   April 18, 2008, 05:48
Default Re: Sinusoidal boundary condition
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cfd-student
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What I am trying to do is build a simple pipe and then whistle through it to analyse if CFX will give me standing wave in the pipe. I just want to do very simple acoustic simulation at the out set.

For that I think I will have to make my simulation compressible and have pressure inlet at the inlet boundary. So instead of giving a value for pressure I would insert the equation that cycLone gave us? Is that how its suppose to work?
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