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-   -   Grid generation for conical nose shpe in CFX4 (http://www.cfd-online.com/Forums/cfx/19649-grid-generation-conical-nose-shpe-cfx4.html)

zahid May 25, 2003 01:04

Grid generation for conical nose shpe in CFX4
 
Hi CFX-4 users I want to simulate flow around conical nose shape using CFX4. I generate the conical surface by revolving a line which makes 30 degrees angle with x-axis about x-axis. The problem is that the revolved suface has three edges. Fourth edge has zero lenght. CFX4 requires 4 edges to generate a structured grid. I can generate this type of grid using CFX-TASCgrid. This grid consists of five faces. Sixth face is a collapsed face. In TASCflow a boundary codition called coallescense boundary condition is available. So this problem is easily solved using TASCflow. But CFX-4 does not accept collapsed faces, furthermore theree is no coallescese boundary condition available in CFX-4. How can I solve this problem in CFX-4. Thanks

Glenn Horrocks May 25, 2003 19:14

Re: Grid generation for conical nose shpe in CFX4
 
Hi Zahid,

As you correctly mention, CFX4 does not let you do blocks with other than 6 faces. Your options are:

1) Create a multi-block structure where each block has 6 sides. Your geometry sounds pretty simple so you should be able to do this.

2) If there is a part where you just cannot work out how to get the blocks to join, use an unmatched grid. Unmatched grids are a little less accurate and require significantly more resources than normal interblock boundaries so use them sparingly, but they can be good to get you out of a bind.

3) Use CFX5, its unstructured mesh would make meshing this shape a doddle!

Hope that helps, Glenn

zahid May 26, 2003 09:12

Re: Grid generation for conical nose shpe in CFX4
 
As I had mentioned I can generate grid using CFX-TASCgrid or using Gridgen. But the problem is that I am unalbe to generate structured grid using CFX-Build to be used for CFX-4. I am interested to know that is CFX-4 capable of generating and handling this type of grid or not?

Glenn Horrocks May 26, 2003 19:17

Re: Grid generation for conical nose shpe in CFX4
 
Hi Zahid,

Yes it can. My first post gave three different ways of doing it.

Glenn

zahid May 26, 2003 22:37

Re: Grid generation for conical nose shpe in CFX4
 
Hi Glenn Horrocks! Thank you. Can you please explain how to do it. The problem is that I generate conical nose by revolving a line about x-axis and this line touches x-axis. So the generated surface has only three edges.The fourth edge is of zero length. I do not know any other method to generate conical nose surface. I find no option to create structured grid for 3 edge surfaces. in CFX-4. Of course single block structured grid can be generated using Gridgen using the concept of pole domains or it can also be generated in CFX-TASCgrid using the concept of imaginary zero area surface. But in CFX-4 zero area surfaces are not acceptable. As for as multiblock grid is concerned I can generate multi-block stuctured grid for hemispherical or elliptic type nose. For example using Gridgen I can generate a grid consisting of two blocks, one is H-grid and other is C-grid which wraps around the H-grid. But for conical nose shape this option is not applicalbe. Furthermore I was able to generate above mentioned multiblock grid using Gridgen and was unable to generate in CFX-Build. Please give me more details. Thanks

Bob May 27, 2003 09:40

Re: Grid generation for conical nose shpe in CFX4
 
Hi Zahid, If I understand you correctly, then it shouldn't be a problem. I've just created the 4 sided surfaces for a cone which you could replicate. I'm not sure if I can attach the images, but I'd be willing to send them to you. Unfortunately I'm away as of tomorrow for a week. The secret is to split the cone into sections, rather than build it with one surface. Think of it as a triangle. How do you mesh a triangle in CFX4 ? To do this you need to create a node in the middle of the triangle, which can then be used to split the triangular surface into 3 four sided surfaces. Basically you drop a perpendicular from the central node to each of the 3 curves that make up the edges of the triangle. Now just apply the same principal but in 3D to your cone. I hope this is what you are trying to achieve ? If not I'm sorry. If you want the images you'll need to email me today (funster7@hotmail.com). Good luck Bob

zahid May 28, 2003 09:23

Re: Grid generation for conical nose shpe in CFX4
 
Hi Bob Thank you for giving very useful hint. But still I am unalbe to generate the mesh. I created half cone by revolving a line making 30 deg angle with x-axis about x-axis.. Then I extacted two curves at parametric locations u=0.5 and v=0.5 . Then I created a point at the intersection of these curves and splitted these urves at this point. Then I created 3 surfaces using create-surface-edge with 4 edges option. Two surfaces exactly match the surface of the cone, but the surface at the apex of the cone deviates from the cone surface appreciably. How to solve this problem. Thanks

Bob June 2, 2003 05:31

Re: Grid generation for conical nose shpe in CFX4
 
Hi Does CFX4 allow you to generate a solid ? Sometimes in build, lines or surfaces may look like they do not meet up correctly. This can be due to two things. Firstly, there is something wrong and they actually don't meet up, or secondly it could be due to a display tolerance issue. Build has this tollerance that you can lower or raise enhancing the way the curves are plotted to the monitor. However if you set this too high then moving or rotating a model on screen will become jumpy (if the model is a large or complex one !). So if build allows you to generate the solids then I wouldn't worry about the fact that it doesn't look right. Conversely increase the chordal tollerance. In CFX551 you can find this under display/geometry. Hope this helps ? I've also sent those images you asked for Bob

zahid June 2, 2003 22:51

Re: Grid generation for conical nose shpe in CFX4
 
Hi Bob Thank you very much. Yours suggestion have helped me in solving the problem.


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