Aerodynamic analysis of moving projectile using CFX
 

Hi
I am trying to move the projectile inside the barrel and to simulate the shock waves. I am not sure what type of boundary conditions should I use. Any suggestion on this. Any kind of help on this will be really appreciated.

sathish

Are you modeling the combustion and using that to move the projectile down bore? Are you using prescribed velocity? Do you need it to exit the muzzle?

Thank you for your reply. I am not modelling the combustion. I am trying to give the velocity to the projectile and to move till the exit of the barrel. I am not getting shock waves (Though the projectile is moving at supersonic speed) Yes, i need to exit the muzzle. What type of boundary conditions should i give. I want to simulate the pressure distribution at the exit of the muzzle and to capture shock waves. I appreciate your help

sathish

This is rather easy:

Model a large portion of the air outisde the muzzle including the barrel. Use a subdomain for the barrel core, including the outside air part. Use specified mesh deformation on that subdomain (using CEL to fix the end towards the muzzle and a linear ramp up to full deformation at the projectile side), to "squash" up this core. You can get away with a course mesh at the muzzle end at the start, since nothing is happening there until later (you might have to remesh at some point if you dont get the distribution of the core mesh correct enough to accomodate the flow as it get squashed and the pressure wave hits the squashed part).

I would also model a section in the front of the projectile with a pretty fine mesh and exclude that from the linear ramp, but rather, use the front end of that section as the end of the ramp, and keep the deformation in that region as unity (full motion). This allows you to capture the physics at that interface while keeping the mesh fixed (but translating) allowing you to fully control the mesh quality in that region.

The section around the muzzle exit needs to be large enough to accomodate the blast without interference from the sides. I just put openings on my sides at that end, with the sides rather far away from the muzzle exit.

i have been working on moving projectile i barrel. I need udf for dynamic mesh(Six degree of freedom solver). can anyone help me?

CFX does not need a UDF for 6DOF motion. It is built in.

If you are talking about Fluent then try the Fluent forum.

Thank u for the fast reply. In CFX an experssion is not needed?

The 6DOF solver is built in. No need for you to write equations of motion.

Thank u. do you have information about 6DOF in Fluent? I need a UDF to run in Fluent.

Let me quote post #6: