[cedric_duprat]

Hi Eugene,
thank you for your reply,
1- I think (and I think you also will agree) that the effect of pressure gradient is fonction of the geometry, isn't it ?. Mine is a diffuser so I "hope" that the effect won't be negligible ...

2- I agree that the wall model is dependent of y+.
value of y+ give us the area where the first node is (viscous layer, buffer lawer, ...)

3- I also use a Newton-Raphson in my own code without any limiter (10 loops in OF), I didn't try it yet but, I hope getting value for utau (converged one). then I'll check the value of y+ just to know if I used the good law or not.

I'm interrested in Peller, Brun, Manhart (DLES VI) point of vue in wall layer. but, I don't think they used Pmean ...
You had problems with the value of pressure gradients using instantaneous p, can you tell me more about what you did ?


Cedric

[eugene]

Not much to tell, I built a pressure sensitised wall function for the SA DES model, applied it to a side mirror geometry and the results were more or less the same as without it. No actual "problems".

[marhamat]

Hi everyone
By using oodles for turbulent flat plate simulation in 3D(that in it back&front are symmetryplane)i see pressure gradient in my solution.
How i can justify that?

Best regards
Marhamat

[marhamat]

Hi everyone

I add that i used symmetryplane as a upperwall boundry condition.
any idea?

Regards
Marhamat

[cedric_duprat]

Hi Marhamat

I'm not sure to get your graph but, as I understand, your pressure decrease right ?
Does your geometry 200 lenght or do you use cyclic BC to get these results ?
what about your BC inlet and outlet ?

just questions but ....It's just to get better your problem
Cedric

[marhamat]

Hi Cedric

The geometry is same as the last geometry that i point it out (on Saturday, May 05, 2007 - 01:55 am )in this page but in 3D and with these conditions:
Inlet for inlet BC & outlet for outlet Bc.
inlet velocity is uniform = 10 m/s.& nu=1.0e-6
$Dimentions=(1200,20,10)mm. mesh refined.
And i used initial perturbed condition .
As you see pressure decrease in x direction

Thanks alot
Marhamat

[cedric_duprat]

you fixed the velocity at the inlet, what about the pressure value at your outlet BC ? is it, for exemple 0 ?
did you change something at "line division" 40 (see your Graph)?
that's all I was thinking about up to now ...

Cedric

[marhamat]

Yes,the outlet pressure is zero
In this case i used two blockes that in block one the bottom wall is symmetryplane(200mm).and the plate set after it.

Marhamat

[cedric_duprat]

so, ...
I don't get what is the problem, you fixed the pressure at 0 at the outlet so, if your pressure is higher than 0 before (that's your case), the pressure will decrease to get your hand fixed value at the outlet. What do you think of that ?

Cedric

[marhamat]

That's right.

But i want to know in which condition(with which changes)i can get result for turbulent flat plate with zero pressure gradient.

Best regards
Marhamat

[cedric_duprat]

yes, ...sure
so :
1- with your last run (picture) you know the inlet pressure, so why don't you put the same at the outlet ?
2- other solution, why don't you change the outlet BC from fixed value of pressure to zerogradient.

and then, try to check often the pressure in your run so you won't have to wait too long ...
I'm not sure it will help ....

Cedric

[eugene]

Your pressure gradient for a constrained flow (I assume your top bondary is symmetry?) has to be equal to the wall shear stress. That is basic conservation of momentum.

If you want to keep the pressure more or less uniform you will have to change the top boundary to reflect this. Specifically you will have to set the top boundary to some kind of free-stream condition that fixes the pressure at the same value as the outlet and allows fluid to leave the domain.

This can probably (i make no promises!) be achieved by using a totalPressure boundary for both the top and outlet and applying a pressureInletOutletVelocity boundary to U over the same extent. This might cause problems at the junction of the inlet and the top wall though.

[marhamat]

Hi Eugene

I used atomospher condition in top&outlet boundries.but it seems the solution isn't good for turbulent plate.
Do you think i must increase the altitude of my geometry(in this case h/L=0.02 & L=1m)

Thanks alot
Marhamat

[eugene]

Well first off, your "free-stream" boundary is inside the boundary layer! I suggest you place your top boundary 10-20 times further away from the bottom wall.

[cedric_duprat]

hi all,

I'm (again) trying to integrate a near wall scaling with adverse pressure gradient in OF after a few month break on this topic.

1- a "comment-question" on law of the wall in OF, the law add a viscosity at the wall (which is added at the first cells, I guess), is there a discontinuity of the viscosity between the first cell and the second one ? (this question can be also asked for most of the OF' LES models)

2- I need to calculate the pressure gradient in my geometry (axisymetric one).
my question is can I do something like that; the pressure pradient vector is avaiable at the cell center by:

volVectorField gradp = fvc::grad(p);

I transpose it in Cylindric coordinate system

fvPatchVectorField& gradpCCSin = gradp.boundaryField()[PatchID];

CCSin[PatchID] = ccs.toLocal(cartFaceCentres[PatchID]);
CCSin[PatchID][1] = CCSin[PatchID][1] + neg(CCSin[PatchID][1])*360;

and then, I would like to get the tangent component. but the vector::Y is the orthoradial one isn't it ? :
scalar dpds = ccs.toLocal(gradpCCSin).component(vector::Y);

still following, the end is coming soon :

so if I use snGrad(p) (the wall normal direction ?)* ccs.toLocal(gradpCCSin).component(vector::Y),
will it be the tangential component of grad(p) ?

I'm not sur to get what I want and, I'm not sure to take the easiest way ...
Can someone give me his point of view on that method?

Thank you,
Cedric

[susanjackson24]

hi all
i am a new user of Open FOAM,i want to use oodles solver in openfoam,and i have a basic question about it.
1-i know that the filter width have various definition such as (dxdydz)^(1/3) and ... i want to know which one of these definition used in openfoam.
2-what does the meaning of Lesdelta and its option such as van dreist and parndtl and cube root vol?
Best regards
susan

[hadi]

Hey susan,

delta is the filter width, cubeRootVol is the filter width that you have mentioned in your message.
VanDriest is a damping function used to make the contribution of the sgs model goes to 0 near the wall boundary.
Take a look at .C files to see how it is calculated.


Hope it helps!
Hadi

[ehsanyasari]

Hi Eugene and all
Thanks Eugene.
Our thease is about filtration in LES.
We study LESfilters codes (LESfilter,NewFilter,Simple,Laplace,anistropic) but we have following problem about them:
1-Algorithm and Formulation of filtration that used in these codes.
2-According to the discription part of laplacefilter.H and anisotropicfilter.H :

Description
Kernel as filter as Test filter with ratio 2
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~~~~~~~~~~~~~~~~~~~
Box filter: g = delta2/24 -> g = delta2/6
Spherical box filter: g = delta2/64 -> g = delta2/16
Gaussian filter: g = delta2/24 -> g = delta2/6

what is "g" parameter and where is the effect of "g" in these codes.
3-What is "widthcoeff_" that used in these codes?

We REALLY need the answer of these question.thanks for your help.

[eugene]

Sorry, I did not code and never use the filters so cannot answer your question off-hand.

[armin_h]

Hello all

would you please any one let me know how can i push flow into the pipe in openfoam?
I have created the geometry of the pipe and also the mesh.
I need to see the velocity profile which comes from the moving flow into the pipe.
I am new user of openfoam and i dont know how can i put the amounts for the u velocity and see the motion of the fluid inside the pipe.

I would appreciate any comments.

sorry if it is not an advance question.

Cheers
Armin