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help: wave making resistance on submerged sphere |
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June 9, 2012, 08:25 |
help: wave making resistance on submerged sphere
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#1 |
Member
Amin
Join Date: Mar 2012
Posts: 60
Rep Power: 14 |
Hello all
I'm trying to simulate a 3D free surface flow around a sphere. because its first time that i work on free surface, please help me about that problem! these are my questions: 1. what's the domain(height,weight,width as a function of sphere diameter) in this case 2. Boundary conditions of domain 3. turbulence properties 4. in which reynolds number we have to use turbulent and which one we have to use laminar? 5. solver should be interFoam? 6. some paper and articles about this problem to validate the result like Cd, wave making resistance and some other data. i'm in force, please help me as soon as you can my friends. thanks for your attentions and sorry for my bad English. |
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June 9, 2012, 08:26 |
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#2 |
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Amin
Join Date: Mar 2012
Posts: 60
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is there any body here that worked on this case before my friends?
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June 13, 2012, 08:41 |
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#3 |
Member
Amin
Join Date: Mar 2012
Posts: 60
Rep Power: 14 |
friends please help me
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June 13, 2012, 09:45 |
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#4 |
Senior Member
Nima Samkhaniani
Join Date: Sep 2009
Location: Tehran, Iran
Posts: 1,266
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your question is vague, however let me give you some estimation, it may be incorrect
1) i think the domain atleast should be 2 or 3 times of sphere radius in each direction 2) How is your flow? do you have inlet, outlet? or the sphere is in quiescent liquid (it dpeneds on your simulation) 3,4) i suggest you to find papers in this field, then you will find which turbulence model you should use or when it is turbulence! 5) yes, interFoam is a good choice, it has a color function VOF 6) we are not going to research instead of you friend |
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June 14, 2012, 09:45 |
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#5 |
Senior Member
Albrecht vBoetticher
Join Date: Aug 2010
Location: Zürich, Swizerland
Posts: 237
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Hi Amin,
interFoam is a good choice, I'd confirm. One advice: take good care of the turbulence model, if you want to avoid a lot of discussions and not being a turbulence expert, include as much physics to that as possible. My suggestion is using LES, because then you account for the influence of the sphere geometry on the turbulence (Wendling I.: Dynamische Large-Eddy Simulationen turbulenter Strömungen in komplexen Geometrien" PhD Tech University Darmstadt 2007 and Ferziger J. H. "Direct and Large Eddy Simulations of Turbulence" in Numerical Methods in Fluid Mechanics Bd 16) but check that most parts of the grid should be of hexaedral cells for good accuracy. Use LES together with the Dynamic Mixed Subgrid Scale Model (DMM) for example as developed by the LTT Rostock. You need the DMM model to account for the influence of the free surface on the turbulence, where the so called backscatter-effect plays a key role (Salvetti et al. "Large-eddy simulation of free-surface decaying turbulence with dynamic subgrid-scale models" In: Phys. Fluids 9(8) 1997) Look for the LTT Rostoch OpenFOAM extensions, together with their simple grid filter that performs the clipping of negative turbulence viscosities based on Taylor series approximations. (Kornev et al. "A simple clipping procedure for the dynamic mixed model based on Taylor series approximation" In: Communications in Numerical Methods in Engineering 22 2006) This setup will make a good shift from laminar to transient to full turbulence and it will take care of your geometry and surface, otherwise you will have to explain very well why your turbulence setup (RANS etc.) fits to your case. If you use an inlet and you don't use a predefined velocity profile but feed in the fluid as a block with same velocity over height, give the inlet some area without wall friction, otherwise you conflict with typical boundary conditions like noSlip (in the U file) at the slope, followed by some area with wall friction so that the turbulent velocity profile can develop before hitting the sphere. And another thing: If you have an outlet, use zeroGradient as the boundary condition here in your p_rgh file, if you use fixed value 0 as sometimes recommended your fluid gets reflected at the outlet, funnily only if the outlet is situated in the positive coordinate system quadrant. No explanations for this behavior so far but good to know. |
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June 14, 2012, 12:32 |
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#6 |
Member
Amin
Join Date: Mar 2012
Posts: 60
Rep Power: 14 |
thanks Dear nimasam
i using a cubic domain with inlet outlet and side walls i searched alot but couldn't find any paper that says in free surface problem around a sphere, which reynolds number is critical number. so i asked question 4 thank you again for your reply and help |
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June 14, 2012, 12:37 |
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#7 |
Member
Amin
Join Date: Mar 2012
Posts: 60
Rep Power: 14 |
Thanks Dear vonboett
i will read articles that you mentioned and do your advised and reply the results. thanks again for your help |
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June 23, 2012, 13:07 |
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#8 |
Member
Amin
Join Date: Mar 2012
Posts: 60
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Friends. i need an article that present the value of drag or Cd for different value of submergence depth(cylinder or sphere) and reynolds number.
this cylinder or sphere moving the free surface. please help if you know or have these articles. thanks |
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July 25, 2012, 14:50 |
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#9 |
Senior Member
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you can refer to the White Fluids Mechanics. in this notebook you will find your answers.
I think it was chapter 07: flow past immersed bodies. |
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July 28, 2012, 16:54 |
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#10 |
Member
Amin
Join Date: Mar 2012
Posts: 60
Rep Power: 14 |
Hi Mostafa
I read it before but i couldn't see any thing. |
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July 29, 2012, 03:10 |
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#11 | |
Senior Member
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Quote:
the Reynolds number: http://adsabs.harvard.edu/abs/1955JPSJ...10..694K the Drag Coefficient: http://www.grc.nasa.gov/WWW/k-12/airplane/shaped.html |
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