Aerodynamic analysis of bullet

Hernus · February 19, 2014, 04:58

Hallo,

I'm currently investigating in the Aerodynamics of a flying bullet. I'm quite comfortable with the set-up I use.

The bullet analysis is for speeds up to 3 Mach, attack angles up to 6 degrees, and a rotational bullet (wall) of up to 22 000 rad/s.

The results I get is almost acceptable, except the force in z direction and moment around y-axis on the centre point of bullet (Magnus force and Magnus moment). These values jump around a lot and never converged to the same value even if the same conditions is run again.

I have a feeling this is about the mesh, I'm currently just using the meshing system inside ANSYS with just the default inflation from the body towards a greater outfield. I tried to refine the mesh around the bullet and inflate more and more gradually with extensive bodies but with no luck. when I ran the simulation in Fluent I get an "Floating point f" error. I really tried a lot of different meshing techniques with no luck

I also know the "floating point f" error can be because of lost units...

Is there anyone that maybe can assist me in the mesh?

Thank you
hernus.groenewald@gmail.com

farzadpourfattah · February 21, 2014, 16:54

hi.
usually Floating Point relate with solution setup.
certainly you used density base solver.Do you check your Courant Number(CFL)?
first set it less than 0.5 and after some iteration increase it to 0.9 and then to 1 and bigger than 3.

Michael-STM · February 24, 2014, 13:40

Hi, can i ask you a question? what kind of setup are you using, what is the domain shape and the BC that you have used in specific...thank you!

February 19, 2014, 04:58	Aerodynamic analysis of bullet	#1
Hernus New Member Hernus Join Date: Feb 2014 Posts: 3 Rep Power: 12	Hallo, I'm currently investigating in the Aerodynamics of a flying bullet. I'm quite comfortable with the set-up I use. The bullet analysis is for speeds up to 3 Mach, attack angles up to 6 degrees, and a rotational bullet (wall) of up to 22 000 rad/s. The results I get is almost acceptable, except the force in z direction and moment around y-axis on the centre point of bullet (Magnus force and Magnus moment). These values jump around a lot and never converged to the same value even if the same conditions is run again. I have a feeling this is about the mesh, I'm currently just using the meshing system inside ANSYS with just the default inflation from the body towards a greater outfield. I tried to refine the mesh around the bullet and inflate more and more gradually with extensive bodies but with no luck. when I ran the simulation in Fluent I get an "Floating point f" error. I really tried a lot of different meshing techniques with no luck I also know the "floating point f" error can be because of lost units... Is there anyone that maybe can assist me in the mesh? Thank you hernus.groenewald@gmail.com

February 24, 2014, 13:40	a question	#3
Michael-STM Member Michele Join Date: Dec 2013 Posts: 32 Rep Power: 13	Hi, can i ask you a question? what kind of setup are you using, what is the domain shape and the BC that you have used in specific...thank you!

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February 21, 2014, 16:54		#2
farzadpourfattah Member farzadpourfattah Join Date: Mar 2013 Posts: 41 Rep Power: 13	hi. usually Floating Point relate with solution setup. certainly you used density base solver.Do you check your Courant Number(CFL)? first set it less than 0.5 and after some iteration increase it to 0.9 and then to 1 and bigger than 3.