Problem with split option
 

Hi

I am having problem with splittind certain volumes. Here is the problem:

There is a cylindrical reactor of dia 340mm and height 500 mm. In this a solid cubical substrate has to be kept whichis in form of combination of 100 parallel sheets, each of size 200X200X0.3 mm, kept at intervals of 0.2 mm between any two sheets(like a book in a jar). Now I want to split volume of reactor with that of each sheet because sheet is solid cube while reactor is fluid. But gambit is giving me the error for splitting more than one sheet and is crashing. Kindly help. I have to basically remove sheet volume from reactor and also keep the sheet inside. I tried with subtract with retain option that also is not working fine.

Plz Help
Akshayy Garg

Are your sheets full inside your reactor? (when you compare 200x200x0.3 with 133x500, I understand that sheets are also ouside from the reactors. Then you will have problem with the substract)
Maybe I didn't understand

Hi Thanks for reply. Sorry. I entered a wrong diameter. Its 340mm. I have corrected it. Akshayy Garg (IIT Delhi)

Try to substract first just one sheet from your volume
And post the error

Hi
This is my first question here.Iam simulating the flow over solids(squares).For this, I created a domain(big rectangle) with solids squares inside.I have subtracted the square faces from the big rectangular face.I see the big surface getting distorted after I subtract one particular square face.I have easily subtracted all other faces. How to slove this?:confused:

a zoom of interested area may help to understand

Thank you Max for the response.
Please look in to the zoomed in view of the previous image
thank you

this is just a bug on display (especially with shaded mode turned on)
Turne shaded mode off, and again on.
Should be ok
To be sure, just mesh the surface and you will see

Thank you for the reply.
You are right.I have easily meshed .
thank you

hi
Iam simulating the flow over solids(squares).For this, I created a domain(big rectangle) with solids squares inside.I gave velocity inlet boundary condition at the entrance and pressure outlet at the exit.I have meshed it and transferred to fluent.I have applied periodic boundary conditions at the inlet making the outlet shadow. I have run the case for different grids with convergence criterion of 10-6.As I refine the grid the the curve goes flatter.Why is this happening? Which value is to be taken for further analysis?please find attached a pic of the grid independent study result.

please details more: display your model with BC, and also give more detail on your curves: what are you studying with grid independancy?

Grid independent study
 

Thanks for the response.
Please find the following files attached
1.Model with boundary conditions with out mesh
2.Model after mesh generation


a.After mesh generation ,mesh is transferred to FLUENT.
b.Periodic boundary conditions are applied at inlet making the outlet shadow.Convergence criterion is kept at 10-6.
c.After convergence,a vertical rake exactly at the center of the model is created .Velocity magnitude along the rake is exported to excel sheet.
Then the mesh is refined and send to FLUENT and steps (b) and (c) are repeated.I have done this with many(6) times.The velocity magnitude curves go flatter with refinement. If I change my convergence criterion to 10-7,all curves coincide how coarser or how finer I change my grid.
What convergence should I take? Which curve value should I take for my study?
I am confused.Why is this happening?:confused:
Thank you

-periodicity BC should be already defined in Gambit. It requires a linked mesh
Do you created it?

-on the doc file with the mesh, is the square at the center a solid body?

-If you create a rake exactly at the middle of your model, then it should cross also the solid bodies. And it means your rake should have discontinuities (at solid bodies)

Display the velocity distribution around solid.

Thanks for the reply.
I did not apply linking the edges in GAMBIT.I have given the periodic boundary conditions in FLUENT.Is there any thing wrong if I follow this way?Now
I have given liking the edges and I have to see if there will be a change.

Hi Max,
I have applied the edge link and applied the periodic conditions.I have run he case in fluent keeping the convergence criterion as 10-6.I want to compare the velocity profile.Now I have changed the grid and made so finer and very coarser .The velocity profile exactly overlaps on the reference what ever be the grid size.how to solve this?

First question is: is your periodicity ok
in Fluent you can display your results with periodicity.
It can help you to know if your periodicity is well defined.
check in Graphics Periodicity Panel -> https://www.sharcnet.ca/Software/Flu...436.htm#273992

Concept of periodic conditions
 

Hi,
For the same problem mentioned above (flow over the solid particles),I have applied periodic conditions by specifying mass flow rate.Does this mean that I have applied fully developed flow conditions in this small domain?
If I have applied fully developed conditions,the value of velocity along the length must not change.(du/dx=0).
But in this case ,the velocity variation exists in the small domain but it is cyclic in the big domain.With periodic conditions Am I imposing no variation of velocity in the considered small domain?
Thanking You
Vijayalakshmi

on your post #12 (second picture), you seem to mesh the solid square.
Why?
On your first picture, you displayed your BC. Can you also display the periodic BC

Concept of periodic conditions
 

Thanks for the response.
Please find attached the picture 4.1 which shows the full domain of the flow.The second picture(4.2) shows the region selected for simulation.Initially I meshed the squares region also.Now I have changed it and meshed only fluid region only.
There will be a pressure drop in the flow.I want to specify mass flow rate at the inlet.
My question is if I apply periodic conditions in fig 4.2,am I imposing fully developed conditions?If so, there will not be any variation in the velocity along the length in fig 4.2(du/dy=0).But what I wanted was the variation in velocity along the small domain,which repeats in the big domain.where am I going wrong?
Please clarify.

Concept of periodic conditions
 

I think I did not attach the specified.Please look in to these pics.Attachment 28122

did you see this tutorial: https://www.sharcnet.ca/Software/Flu.../tg/node23.htm

I think you have to set your periodic BC with mass flow rate (as you already did), but I am not agree as you writing that du/dy= 0.
If you impose the massflow, then in the middle (0.5*l1) of your domain you have the critical section and your fluid will accelerate for maintaining same massflow.
Do you already have some results? can you display the velocity distribution?

Concept of periodic conditions
 

Hi
Thanks for the response.
1.I have gone through the tutorial you suggested before starting my work.
2.I have done the tutorial for the developed flow through pipes.
for both of the above cases,same periodic conditions with pressure drop will be given.
In the second case,there is no change in the velocity profile (du/dy=0) after simulation.
In the first case,du/dy should not be the same.But we follow the same procedure of giving periodic conditions as that was done for case2.
How are this happening?

display velocity and pressure distribution

Concept of periodic conditions
 

Hi
Thanks for the reply.Please find attached the contours of X velocity,and pressure. mass flow rate is 0.0003575kg/s

if you set the max velocity very low in the scale , do you see any velocity between all your squares?

Concept of periodic conditions
 

Hi MAx,
How can we use same periodic conditions to
1.flow with a pressure drop,which is geometrically periodic in nature,and is not fully developed(like the model in fig 4.2 which I use for simulation).
and also to
2.Flow with a pressure drop,and fully developed flow(like fully developed flow through circular pipe)
Iam getting confused.

I don't know.
I am not experienced with periodic flow.
Did you check if you get velocity distribution between your solid squares ?

Max, I also have one more doubt.. I am studying the heat transfer rate within an isothermal medium which is not moving(still) and it s at temp T1. The medium is confined within two large black isothermal walls of temp T2.
If we have to specify a wall as isothermAL, we can just give the value of the temperature in boundary conditions>>edit>>thermal >>thermal conditions>>temperature....

Am i right??

And if we want to specify a medium (fluid /solid) as isothermal, how to give a specified temperature for that? Because in boundary conditions panel, for solid or fluid, we can only edit the name and nothing else.. plssssssssssss tell me how to specify a still medium as isothermal... ?? Do we have to specify it in reference values section ?? or do we have to give it under cell zone conditions>>edit>>Fixed values>>Temperature ???

I tried it with fixed value once an as i am wrking in radiation heat transfer problems, i dont think I am right...

plsssssssssssss give me ur suggestions, max... I badly need it..

I suggest you to open a new thread in the fluent subforum
You will have more chance to have answer of your thermal question

pressure drop in periodic flow
 

Hi Max,
I have simulated flow over solids through a channel.I have applied periodic boundary conditions at the inlet and exit of the pipe. Can I use the pressure drop indicated in periodic boundary conditions menu after the convergence of the case as pressure drop /L for my further work?
Can you please clarify.