trying to understand the boundary condition "oscillatingFixedValue"
 

Hi foamer,

I would like to setup oscillatingFixedValue with the equation

u = 2.7 + 16(sìn2pit/16)

I saw the guide at

https://openfoamwiki.net/index.php/M...tingFixedValue

if I understand exactly, the inlet velocity will:
inlet
{
type oscillatingFixedValue;
value uniform 0; // Initialization value
refValue uniform (1 0 0); // Reference value for oscillation
offset (1.7 0 0); // Oscillation mean value offset
amplitude constant 16; // Amplitude of oscillation
frequency constant 0.0625; // frequency
}
Following the equation, I set offset 1.7 will it plus 1 to 2.7?
https://openfoamwiki.net/images/math...6b9cb308f3.png

Thank you
Thanh

I ran inlet BCs above no problem with Tjunction tutorial. I only confuse about the "refValue" and "offset":

1. The offset should be filled 2.7 or 1.7?
2. If I want to reverse in x-direction, can I only add minus in refValue and offset? Will it exactly become: refValue uniform (-1 0 0); offset (-1.7 0 0)?

Does anyone can help me explain my question?

Greetings Thanh,

I don't understand what's the doubt you're having? I've checked the source code and the expression on the wiki seems to be correct:

Therefore, it's a basic mathematical expression. If "refV" is set to 1.0, then you're left with this:

The rest is simple math, namely for having a final offset of 2.7 (with refV =1), you need the "offset" parameter to be 1.7.

And when in doubt, don't be afraid to simulate with OpenFOAM and test things yourself. If you create a simple test case, you can easily test if this works as intended or not. Specifically, if you want to be able to prove that it works as intended, you should in fact do that simple test case first!

Best regards,
Bruno

Hi Bruno,

Your explaination is very clearly at refVal. I have simulated with Tjuntion tutorial with inlet Bcs above. I only confuse that offset should be 2.7 or 1.7.

Thank you so much.

I add more answer the oscillating. If the equation don't have offset:
So the result will wrong if equation was set follow equation describe above with refV=1, Amp =16, offset =0. Because the equation return



Therefore, I think the amplitude always equal to 1. In other hand, refV =16 and offset =-16 as the equation become:


That's it.

Use groovyBC for the BC, it is easier

Hello everyone,

I am not sure if this is the right place to asked, but maybe one of you might help me. In my case I have an airfoil in a channel. Now my task is to implement a condition for an oscillating stream. I thought I might use oscillatingFixedValue for it.

I tried for my inlet condition under 0/U:

type oscillatingFixedValue;
refValue (1.56 0 0); //my verlocity
amplitude 0.05;
offset 0;
frequency 0.8;
value uniform (0 0 0)

When I have a look in to the vectorplot I can't see any movement of the vectors, so I think it doesn't work.
Have anyone a hint for me how I can fix my problem?

I would be very gratefule!

Thank you and best regards,
Stephie

Quick answer: Sorry, but you're being too vague in order to give an accurate answer. The best I can say is that you should compare with the plot of the oscillation you're requesting: Plot[0. + 1.56 (1. + 0.05 Sin[2*pi*0.8* t]), {t, 0, 10}]
And/or that perhaps you're not familiar enough yet with the time controls in ParaView?

Beyond this, I suggest:

• Take a step back and use a simple tutorial case from OpenFOAM and test this boundary condition.
• That next time, please follow more closely these instructions: http://www.cfd-online.com/Forums/ope...-get-help.html ;)

I say this because you did not specify what settings you have in "controlDict" and if you're solving in transient or steady state.