[soona57]

Subject : I’ve made numerical simulation for transient incompressible flow around an axisymmetric projectile using ESI-CFD-ACE+ V2008.2 and in model option screen, I chose transient time step as “Standard” , No. of Steps as “800” and Time Step as “1E -005”. This simulation is done twice, one using structure mesh and the other using un-structure mesh. Taking into Consideration all solver parameters are the same for both mesh types.
Observation : Both cavities are formed in structure grid case and un-structure grid case but are not similar in time step period i.e. one is started to form in time step 30 ∆t and the other starts to form say at 50 ∆t .

Structure Case Blunt projectile
No. of Cells 106,266
Faces 6
2D Blocks 3



Un-structure Case Blunt projectile
No. of Cells 22,180
Surfaces 1
Loops 1

Queries :
1. Why did the cavity in unstructured grid case formed faster than that one in structure grid case?
2. Why is the cavity in unstructured case more detailed than that one in structure case?
3. Is “Transient Time Step” a real time step in projection simulation of projectile?
If answer is “yes”, why the cavity formation simulation is different in both in spite of the same projectile velocity and same solver parameters.