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-   -   Velocity vectors in different planes (http://www.cfd-online.com/Forums/fluent/38301-velocity-vectors-different-planes.html)

Vidya Raja October 19, 2005 11:18

Velocity vectors in different planes
 
Jason- I plotted the velocity vectors using the InPlane option. I did it this way:

1. Selected the X- axis and the In plane option. Got a plot for this.

2. Did the same for the y, z axes.

But all the 3 plots look the same. How can this happen? From my understanding, if I select the X axis along with the in Plane option, all vectors perpendicular to the X axis are removed and only those along the x axis are shown. So how does this explain the reason for all the 3 plots to appear similar?


Jason October 19, 2005 14:19

Re: Velocity vectors in different planes
 
The In-plane option automatically turns off the components that are normal with the surface that you are plotting them on independently of the component selections you make. This option trumps the component selection (in other words, if you have the In-Plane option on then the selections you make for the components doesn't matter, which is why your three plots look the same).

As far as the component selection, the default selection is for all three components to be drawn (x,y, and z). Now if one component overpowers the others (like the main flow is in the x-direction) then you can turn off that component and look at the other components (so if the main flow is in the x-direction, then turning off the x-direction will show the vectors of the flow perpendicular to the main flow). DO NOT use the In-Plane option if you want to turn off specific components. This is because Fluent understands when you're using the In-Plane option that the component normal to the plane should be turned off. The nice thing about the In-Plane option is that if your plane is rotated relative to the x-y-z coordinates, then Fluent turns off the normal component, no matter what the vector direction is of the normal component.

If you want to look at the y-z, the x-z, and then the x-y vectors, then you turn off one component at a time to get these views (for the y-z vectors, only turn off the x-component and plot... for the x-z only turn off the y-component, etc...).

Also, I'm thinking this is a continuation of a conversation we were having previously. You should have posted this as a response to that thread instead of as a new thread. That way I can go back through the conversation if I have to and figure out what was said. Otherwise I end up having to look through the whole forum to try and find our conversation. Not a big deal on this one, but if you look through the forum you'll notice that some of the conversations get pretty involved, and it's easy to lose track if the conversation is spread out all over the forum.

Hope this helps, and good luck, Jason

Vidya Raja October 19, 2005 21:55

Re: Velocity vectors in different planes
 
Hi Jason, Thanks for the help- I understood whatever you said and did accordingly and got the results. But is it possible to get the velocity vectors inside the cylinder. I mean, if you cut open the cylinder along its vertical axis, and look inside. Also the flow region around the solid geometry which is enclosed inside the cylinder is the main region of interest. So is it possible to get this view of the vectors?

Thanks once and again for all the help!!

Vidya

Vidya Raja October 20, 2005 00:44

Re: Velocity vectors in different planes
 
Jason- one more question........... if I want to plot vectors in the xz and yz planes, do I have to turn on the In plane option? That is, I want to plot the vectors only in those directions, so do I go the following way:

1. select x, z components only or x, z, In plane options

2. Similarly for yz plane.

You say that In plane automatically turns off the normal component of the plane. How does this differ from selecting x,z planes only without the In plane option? Here does it plot the y direction vectors?

- Vidya

Jason October 20, 2005 09:38

Re: Velocity vectors in different planes
 
1) only select the x,z components (DO NOT select In Plane option) 2) similar for yz plane

If the plane you are plotting on is parallel to the x,z plane, then it's the same as selecting the x,z components... but lets say your plane has a normal vector of (1,3,4)... then you can't just turn of the x, y, or z components to get the vectors to lie on that plane... but the In Plane option will take care of this for you. That's what it's for. If you're plotting on planes that are orthogonal to the coordinate system, then you can play with the components, otherwise you can use the In Plane option.

Hope this helps, and good luck, Jason

Jason October 20, 2005 09:49

Re: Velocity vectors in different planes
 
You can get vectors anywhere you want. So the answer to "is it possible to get the velocity vectors inside the cylinder" is yes. What I think you're asking is if you have a plane that cuts your cylinder in half, you want to plot the vectors on this plane, correct? For that you create a plane (Surface->Plane). You can create the plane using a point and normal vector, or three points (there's other ways too, but those are the most common). There's lots of other possibilities too (like Iso-Surfaces, or clipping existing surfaces using Iso-Clip). Any existing surface, or any surface you can create can be used to plot contours or vectors. Once you create your plane, you can clip it so it's local to the region of interest, or you can simply zoom-in on the region of interest to create your images.

Hope this helps, and good luck, Jason

Vidya Raja October 20, 2005 12:37

Re: Velocity vectors in different planes
 
That's exactly what I want...... cutting the cylinder in half and looking at the vectors inside. But how do you clip a plane? Which option do you use for that?

Jason October 20, 2005 13:35

Re: Velocity vectors in different planes
 
First you create the plane in Surfaces->Plane. Then you can clip the plane by going to Surfaces->Iso-Clip. There you pick the surface you want to clip, the variable you want to clip it by (you'll want the variables under grid most likely) and then you pick the max and min values. Anything outside of the range is removed from the surface.

Hope this helps, and good luck, Jason

Vidya Raja October 20, 2005 21:20

Re: Velocity vectors in different planes
 
I tried using the Iso clip option........ but nothing happened. On what criteria are the points selected? Also when I used the Mouse Buttons on option, again worked. What may be the reason.

The bottom line is that I want to slice the cylinder and look at the vectors in the XZ and YZ planes- the flow being in the Z direction. Also if I slice the cylinder, will I get the cross section of the symmetrical solid geometry contained within the cylinder? If you remember, I had earlier subtracted the volume of the solid from the volume of the cylinder to create and mesh the flow field. I want to see the behavior of the vel vectors around the geometry, and this is the main area of interest. Also, when meshing the volumes, I meshed both the geometry and the flow field after subtraction of the volumes and had turned on the RETAIN VOLUME for both (solid and flow field) while subtracting. Is this correct?

Thanks a million for all the help and advice.

Regards, Vidya


Jason October 21, 2005 09:41

Re: Velocity vectors in different planes
 
The only reason you would keep and mesh the solid is if you were interested in the heat transfer through it. If you're not concerned with the HT through the solid, then you don't need to mesh or even keep that volume. You can just do the subtract command without the Retain Volume option. The retain volume option keeps the original volumes. Like I said, if you're not interested in the HT through the solid, then you don't need that volume, and the original volume for the control volume was simply a cylinder... no point in keeping that. You're only interested in the control volume that has the solid portion subtracted from it, so don't bother keeping or meshing the other volumes.

To get a slice of the cylinder, use the Surface->Plane command. Now you can create a plane by inputing a point and normal vector, or you can put three points. The Iso-Clip function will not create a surface for you. It's only good for modifying a surface that you already created within Fluent. Here's what you do to visualize the vectors on the XZ plane:

Go to Surface->Plane Change the options to Point and Normal In the bottom portion of the window, input the point (0,0,0) towards the right of this input the normal vector [0,1,0]. This will create a plane that passes through the origin and has a normal vector along the y-axis (in other words a plane coincident with the XZ plane).

For a YZ plane, use the normal vector [1,0,0].

You can input any point and any normal you want to create different planes, I just used the XZ and YZ planes because that's what you mentioned you wanted.

Once you've created your surfaces, then you can go to Display->Vectors and choose whichever plane you want to see.

Hope this helps, and good luck, Jason

Vidya Raja October 21, 2005 10:30

Re: Velocity vectors in different planes
 
Thanks a lot Jason......... that wasextremely helpful.

Cheers, Vidya

Vidya Raja October 31, 2005 17:06

Re: Velocity vectors in different planes
 
Jason -

Can you tell me if the IsoClip option will create velocity profiles only along certain parts of the plane? I have the cylinder sliced in half and then have the velocity vectors on it. Now I want to see the vectors on certain regions only and also the regions which have the same velocity profiles. Can the IsoClip option do this?

Thanks, Vidya

Jason November 1, 2005 10:06

Re: Velocity vectors in different planes
 
The iso-clip will "trim" a surface based on flow (u, v, w, P, T, etc...) or geometry (x-coord, y-coord, radial coord, etc...) variables. I think you can trim the surface using Custom Field Function variables as well, but I'm not 100% sure on that one, you'll have to try it out to see. So what happens, is you select the surface you want to trim, then the variable you want to trim it by, and the max and min values for that variable.

So I'm not entirely sure what you're trying to accomlpish, but as long as you can define "the same velocity profiles" with the existing flow variables, then I think the iso-clip is what you're looking for.

Another option... if you want more of a 3D representation, you can create an iso-surface. Here you don't need to start from an existing surface. You can simply create a surface based on a flow, geometry, or custom-field variable.

Hope this helps, Jason


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