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sloshing simulation k epsilon turbulence modeling

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Old   December 22, 2016, 01:10
Unhappy sloshing simulation k epsilon turbulence modeling
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naveen kumar s
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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
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Old   December 22, 2016, 05:27
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Glenn Horrocks
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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.
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Old   December 22, 2016, 05:55
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naveen kumar s
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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,.
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Old   December 22, 2016, 06:06
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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.
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Old   December 26, 2016, 02:33
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naveen kumar s
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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,
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Old   December 26, 2016, 04:54
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Quoting post #2:

Quote:
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.
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Old   December 27, 2016, 03:56
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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,
Attached Images
File Type: jpg yy.JPG (70.0 KB, 9 views)
File Type: jpg solvery+.JPG (93.9 KB, 7 views)
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Old   December 27, 2016, 06:36
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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+.
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