Learning Forum

[Dato]

As shown at title, I know the color represent the magnitude of the chosen parameter.  But what does the size of vector mean?

Any of your answers will help me a lot.

 

[Federico]

Hello, 

the size is only for visualization purposes. You can modify the size of the displayed vectors to one that best suits you.

[Dato]

Hello Federico,

Thank you for your reply. I know that. My calculation has converged. But my velocity vectors graphic displayed somewhere seems strange. You can see below.

It's one of  cross section along flow direction. As you can see it, the size of velocity near the gap is much more larger than main stream region. I am confused by this graphic.

Does it really only for visualization? Are there any physical or mathematical quantities the size of vectors represent？

Best gratitude.

[NickFL]

Also keep in mind that vectors are 3D quantities. This means that you could have a vector pointing at you and it would appear as a dot.

[Rob]

The size is usually linked to the speed, so we can look at vectors coloured by something else: since replaced by the Scene option. 

Please can you post the Vector Display and Vector Options panels. 

[Dato]

Hi,

Sorry to reponse so late.

I still didn't comprehend the size of the velocity vector in fluent so far. The Vector Options panels is shown below.

You have said that the size is linked to speed. But it's unreasonable that the calculated cell which have lower speed colored with blue almost have the same large size as high speed colored with red. 

Besides, if you enlarge the graphic, you can see main flow region have red color but tiny vector size. So I don't think the size of vector is related to speed. I know I can use fixed length to make all vector the same size but I still want to know how does the size of velocity vector  is defined in Fluent.

Regard,

LEE

[NickFL]

Your vectors are colored by velocity magnitude will be the three components of velocity. But your velocity vectors are showing the x & y directions. What is the velocity in the z-direction?

Do you want to have flow going through that narrow region on the bottom? You only have one cell through that neck, and the results will be questionable under such conditions.

[Dato]

Hi NickFL,

1. Yes, my vectors are colored by velocity magnitude, but my vector graphic is the vector of velocity. I choose x and y direction vector in Vector Options panel and it will only show the resultant vectors of x and y velocity components.

2. It's the mesh that are deficiencies in my simulations. Let the gap alone and look at the red circle I drew in velocity vector graphic. I am questionable for the size of velocity vector. The size is so small colored red in main flow region while the velocity vector near the wall is much more larger with lower speed.

[NickFL]

Have you defined your own Velocity Magnitude? Because the one used in Fluent is uses all three components, whereas your vectors are only showing the x and y components. Those vectors in your circle are red despite being small because these cells have a large component of velocity in the z direction. If you were to create your own variable for the velocity magnitude using only v_x and v_y, then you would see these vectors be blue.

[Dato]

Oh, I get it.  I misunderstood what color and vectors represent.  The vectors are colored by velocity magnitude of x, y and z components while in the plane, it only shows the x and y components whose resultant vectors represent the size of vectors in my graphics. No wonder the size of vectors is small away from the wall. 

Highly appreciated for your patiently explanations!!!

Best regards.

 

[Rob]

Please replot with the z component on too.