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Stuman February 20, 2006 18:20

Hi Mach drag prob
Hi, I am trying to baseline a technique for determining the drag of projectiles at high mach using cfx 10. To achieve this I have a reference projectile design with known drag at various mach numbers.

Thus far I have modelled it in several ways, the most recent using a symmetry plane running half way through the projectile. I have used a very fine mesh around the projectile, and a semi fine mesh in the rest of the domian. The entire domain is approx 30mm by 30mm by 40mm and contain approx 1.2 million elements.

I have set the body to wall no slip, the inlet to supersonic with vel of 680.9 m/s total energy, the outlet to supersonic, and the surrounding walls to wall free slip. Fluid is set to air ideal gas.

The initial values were set at 680.9 m/s and the K E turbulence model, with intensity to 5 or 10%.

During the solve, I get warnings about max continuity loops to 2, what ever that means. It either solves with the wrong force, value is too low ( hence drag ) or it terminates with errors.

Can anyone point me in the right direction as to what I am doing wrong? I have not used any inflation for my cfx mesh as I do not fully understand it. Could it be a mesh problem or am I just setting my solver parameters wrong?

I can email my files if anyone wants to have a look at them.

Any help would be appreciated. Stuman

Bart Prast February 24, 2006 10:03

Re: Hi Mach drag prob
In case of supersonic flow we always use

EXPERT PARAMETERS: max continuity loops = 2 END

works every time!

Stuman February 26, 2006 06:06

Re: Hi Mach drag prob
Yeah I eventually found that and added mesh adaptation as well, now it does not crash but it only gets within 10% of the actual drag value. I think my problems lies in the mesh now.

Thanks for your response


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