[navi]

hello anybody help me in this,

I am simulating sloshing phenomena in rectangular tank in cfx, I wanted to find y+, I done some study but all the study are there for flow past an object, but in my case fluid inside tank,
how can I find y+,
how can I know this y+ value is in a good range,
how this y+ works

[ghorrocks]

It makes no difference if it is flow past an object or sloshing in a tank, y+ is calculated the same way. y+ is just calculated at wall boundaries using the local flow conditions and the distance to the first node off the wall.

But keep in mind y+ and boundary layer modelling in general is not always applicable. I would think water sloshing in a tank is likely to be an example where it is not very important. But you are wise to check it regardless and understand what it means.

[navi]

Okay thanks.
How can i calculate, as for flow condition here it's sloshing, bottom half there will ne liquid and top half there will be air, and after excitation there will ne movement of liquid to top wall also,. How can i calculate., i seen one equation using kinetic energy , how can i give kinetic energy value,. on sloshing problem,.

[ghorrocks]

Here is a good link: Can someone explain the Y plus value

And any decent CFD textbook should go into this in some detail. It is a fundamental concept in CFD.

It is also a variable in the CFX output file by default, so you should be able to see it without calculating anything. It will be in the additional variable list, accessible by pressing the puzzlingly labelled "..." button.

[navi]

yeah i got.. thank you,
but yplus has minimum and maximum, what this minimum value, means variable yplus is a dimensionless number it should have one value, what will be the suitable range for k-epsilon model for sloshing, means i got yplus value 135. y+ < 200 is good mesh will suit on k-E model,

[ghorrocks]

Quoting post #2:

I would think water sloshing in a tank is likely to be an example where it is not very important. But you are wise to check it regardless and understand what it means.

So do a sensitivity analysis and work it out for your case.

[navi]

yeah i studied and understand this is not much important in my simulation




but i need to justify so many things in this to my boss,
like he is asking me to refine mesh size by assuming y+ value of k-epsilon between 30 to 200,

then i have seen equation in ansys manual and CFD forum also got equations
CFD forum equation is[ y+ = (((density^2 * Cmu^(1/2) * K)^(1/2))/viscosity) * (distance from wall) ] equation 1

and ansys manual equation i have attached,

with this equation how can I calculate mesh size, by giving y+ value,

[ghorrocks]

For a transient flow you will get a time history of y+. So you need to somehow get a representative y+, maybe average or maximum value. Then you work out the necessary mesh size for that y+.

[ParsaMohammadi]

The same problem after 6 years
I simulate a similar case in Fluent
Do you remember how you solved this problem?

[SJTUMEzzq]

Originally Posted by navi

hello anybody help me in this,

I am simulating sloshing phenomena in rectangular tank in cfx, I wanted to find y+, I done some study but all the study are there for flow past an object, but in my case fluid inside tank,
how can I find y+,
how can I know this y+ value is in a good range,
how this y+ works

I am a beginner of FLOW 3D. I have a technical question. How did you apply the harmonic excitation in FLOW 3D. I want to simulate the sloshing behavior of cryogenic propellent in a tank. But I don't know how to apply an excitation. I would be very grateful if you tell me.

[ghorrocks]

The same problem after 6 years

Didn't I answer it 8 years ago?

How did you apply the harmonic excitation in FLOW 3D

No idea. Try the Flow 3D forum. This is the CFX forum. I know exactly how to do it in CFX but that will not help you much.

But in general: a simplified method is to move the gravity vector. Be aware that this only an approximation of the true motion. To be completely accurate you need to do a moving mesh simulation where the tank undergoes the motion you prescribe.