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May 25, 2003, 00:04 
Grid generation for conical nose shpe in CFX4

#1 
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Hi CFX4 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 xaxis about xaxis. 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 CFXTASCgrid. 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 CFX4 does not accept collapsed faces, furthermore theree is no coallescese boundary condition available in CFX4. How can I solve this problem in CFX4. Thanks


May 25, 2003, 18:14 
Re: Grid generation for conical nose shpe in CFX4

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Hi Zahid,
As you correctly mention, CFX4 does not let you do blocks with other than 6 faces. Your options are: 1) Create a multiblock 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 

May 26, 2003, 08:12 
Re: Grid generation for conical nose shpe in CFX4

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As I had mentioned I can generate grid using CFXTASCgrid or using Gridgen. But the problem is that I am unalbe to generate structured grid using CFXBuild to be used for CFX4. I am interested to know that is CFX4 capable of generating and handling this type of grid or not?


May 26, 2003, 18:17 
Re: Grid generation for conical nose shpe in CFX4

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Hi Zahid,
Yes it can. My first post gave three different ways of doing it. Glenn 

May 26, 2003, 21:37 
Re: Grid generation for conical nose shpe in CFX4

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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 xaxis and this line touches xaxis. 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 CFX4. Of course single block structured grid can be generated using Gridgen using the concept of pole domains or it can also be generated in CFXTASCgrid using the concept of imaginary zero area surface. But in CFX4 zero area surfaces are not acceptable. As for as multiblock grid is concerned I can generate multiblock stuctured grid for hemispherical or elliptic type nose. For example using Gridgen I can generate a grid consisting of two blocks, one is Hgrid and other is Cgrid which wraps around the Hgrid. 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 CFXBuild. Please give me more details. Thanks


May 27, 2003, 08:40 
Re: Grid generation for conical nose shpe in CFX4

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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


May 28, 2003, 08:23 
Re: Grid generation for conical nose shpe in CFX4

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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 xaxis about xaxis.. 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 createsurfaceedge 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


June 2, 2003, 04:31 
Re: Grid generation for conical nose shpe in CFX4

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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


June 2, 2003, 21:51 
Re: Grid generation for conical nose shpe in CFX4

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Hi Bob Thank you very much. Yours suggestion have helped me in solving the problem.


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