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Michal Marcinkowski January 17, 2001 07:09

Calculation of forces
 
Hi I hope nobody is offended that I am using this group for "technical details" but I couldn't get the response on Phoenics forum /for beginner like me :))/

I would like to know what is the most efficient way for integrate pressures on some shape for getting the forces /like lift and drag/ in Phoenics V 3.2. I found two examples / Y113, Y114/ on Cham sites but I can't run them and check the results /some errors during EARTH's run/. Is it possible automatically ?

Thank you in advance

MM

John C. Chien January 17, 2001 21:12

Re: Calculation of forces
 
(1). I guess everything is possible, if you know what you are looking for. (2). First of all, you must have the wall geometry, because that the input to your code. And from the computed pressure distribution on the wall, you can compute the local lift force per cell surface on the wall. By the way, the pressure force is always normal to the wall surface. So, the local wall slope such as cos, and sin of the local wall angle is all you need to find the lift force component. (3). You also have to define the lift and the drag first. For example, the lift can be defined as the vertical component of the total pressure force acting on the surface. For the drag, it can include the other horizontal component of the total pressure force and the viscous component. So, you need to find the wall surface local skin friction, which is tangent to the surface of the wall. (4). So, try to resolve these forces on the local wall surface first. Once you have it, just sum it over the complete wall surface. Then you will have the total lift and the total drag forces. (5). By the way, nothing is automatic on a computer, someone has to write the program to compute it first. (Sometimes, it is included in the commercial program. In that case, all you have to do is to identify the wall boundary and the code will calculate the total lift and drag for you. If it is not included in the code, you can still do it by hand or write a small piece of code to compute the forces.)

Michal Marcinkowski January 18, 2001 04:37

Re: Calculation of forces
 
I am afraid that I chose wrong group,anyhow. Sorry. But thanks for little repetition : ) from Mr Chien. My problem is how to "just sum" the pressures over, let's say, 10000 cells of some complex, curvlinear geometry having Phoenics output file.

Everything is possible so... maybe something will happen on my computer "automatically"...

MM


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