[1988]

hi everyone
I have a question about axial velocity in fluent specially in 3D curved pipes.
It is an elbow which the velocity inlet is in X direction and I have got contour in X direction and it shows velocity correctly but in the same section I have got an axial velocity and it shows wrong contour and quantities I can't understand axial velocity and I don't know is it trustful or not?

[A CFD free user]

Hi,
It seems that you didn't define the axial direction correctly in your geometry modeler. I think, you should redefine the coordinate.

[CFD-fellow]

For axisymmetric problems, in which the rotation axis must be the x axis, the x direction is the axial direction and the y direction is the radial direction. (If you model axisymmetric swirl, the swirl direction is the tangential direction.)

Axial velocity means the velocity in x direction in axisymmetric problems. So when your solver is not axisymmetric, axial velocity is meaningless (but sometimes has meaning!).
Get your z-velocity contour. Is it the same as your axial velocity contour?

[1988]

thanks for support the velocity contour in z direction gives me just zero and I think at inlet I don't have any vector in z direction,

[delfel]

Originally Posted by 1988

hi everyone
I have a question about axial velocity in fluent specially in 3D curved pipes.
It is an elbow which the velocity inlet is in X direction and I have got contour in X direction and it shows velocity correctly but in the same section I have got an axial velocity and it shows wrong contour and quantities I can't understand axial velocity and I don't know is it trustful or not?

If I follow correctly, your simulation is 3D, correct? I don't have Fluent in front of me, but I believe you define the axis that sets the axial, radial and tangential directions for the contour plots under the cell zone conditions panel. Does that help?

[1988]

thanks for your support that's right but I don't know how to do that moreover the geometry was made by some pictures and I don't know all of angels and dimensions (it is 3d pipe that bends are not in the same plane) so finding axial velocity in each part by calculating the angels is some how needs great deal of effort.

[Ranjith Kumar J]

Originally Posted by CFD-fellow

For axisymmetric problems, in which the rotation axis must be the x axis, the x direction is the axial direction and the y direction is the radial direction. (If you model axisymmetric swirl, the swirl direction is the tangential direction.)

Axial velocity means the velocity in x direction in axisymmetric problems. So when your solver is not axisymmetric, axial velocity is meaningless (but sometimes has meaning!).
Get your z-velocity contour. Is it the same as your axial velocity contour?

Yes you are right even Im dealing with a diffuser duct of rectangular crosssection which is axis-symmetric and also has inlet flow velocity at 30m/s from x axis direction.Therfore i thought of x axis as the axial direction.when i plotted contours i got z velocity contour matching with axial velocity contour and not the xvelocity contour.

Which i later figured out that when you change x from 0 to 1 and change z from1 to 0 in cellzoneconditions tab would solve that problem!!!!!

But now the problem is to find Crossflow velocity(perpendicular to axial velocity).Now i dont know whether crossflow velocity is the same as radial velocity or tangential velocity or neither of them.Please explain what the respective velocities mean actually?

I also need to plot diiferent vector plots of crossflow velociitres at different sections?

PLEASE HELP!!!!!!!!!!

[Ranjith Kumar J]

CAN SOMEONE PLEASE HELP ME???????????

DESPERATELY NEED AN ANSWER....

[saifmasood]

Originally Posted by CFD-fellow

For axisymmetric problems, in which the rotation axis must be the x axis, the x direction is the axial direction and the y direction is the radial direction. (If you model axisymmetric swirl, the swirl direction is the tangential direction.)

Axial velocity means the velocity in x direction in axisymmetric problems. So when your solver is not axisymmetric, axial velocity is meaningless (but sometimes has meaning!).
Get your z-velocity contour. Is it the same as your axial velocity contour?

I have done simulation on shuttlecock. But when i plot contours of radial velocity and tangential velocity , the contiurs are not appropriate. Can you please let me the problem associated with contour.
fluentp1-1-02000.jpg

t.jpg

[Ahmed_Sk]

Originally Posted by CFD-fellow

For axisymmetric problems, in which the rotation axis must be the x axis, the x direction is the axial direction and the y direction is the radial direction. (If you model axisymmetric swirl, the swirl direction is the tangential direction.)

Axial velocity means the velocity in x direction in axisymmetric problems. So when your solver is not axisymmetric, axial velocity is meaningless (but sometimes has meaning!).
Get your z-velocity contour. Is it the same as your axial velocity contour?

Hi,
You said that for axis symmetric problems, the rotation axis must be x-axis. Why is that? In my case, I am doing a simulation in Fluent with an axis symmetric rotating model with the axis of rotation in the y-direction. So, does that mean when I will go to plot velocity vectors (u, v, w) in Post processing, radial, axial and tangential velocity coressponds to u, v, and w respectively? For example, u=radial, v=axial and w=tangential. Or u and v become interchange?

[CFD-fellow]

Hi,
The reason is that in documentation it has mentioned that axis boundary must be in x direction and also must not be in negative Y values. So you cant even start a simulation with axis boundary in Y direction. You should rotate your mesh by 90 degrees and do your simulation.

[Ahmed_Sk]

Originally Posted by CFD-fellow

Hi,
The reason is that in documentation it has mentioned that axis boundary must be in x direction and also must not be in negative Y values. So you cant even start a simulation with axis boundary in Y direction. You should rotate your mesh by 90 degrees and do your simulation.

Could you share the link of that documentation which you gave reference of? I am looking to resolve my confusion about velocity vectors gradients I obtained for my model. It shows different directions which I expected initially.

[LuckyTran]

Originally Posted by Ahmed_Sk

Could you share the link of that documentation which you gave reference of? I am looking to resolve my confusion about velocity vectors gradients I obtained for my model. It shows different directions which I expected initially.

You're talking about apples and oranges.

The axis boundary condition must be on the y=0 line. It's in the Fluent manual.

The axial velocity is the velocity vector in a different basis. You can have the "axis" of this coordinate system be in any direction.

You need not use an axis boundary condition when you want to reference your velocity as axial/radial/tangential system. You also need not use axial/radial/tangential system when you are using an axis boundary condition. You can use an axis boundary condition and stick to cartesian coordinates.