[FLASH-USERS] Rapid oscillations near density discontinuity - negative c^2 and/or 3T errors

[Chesler, Paul - 0991 - MITLL]

Dear FLASH users,


I am running laser-slab-like simulations, with a planar Al target and a He filled chamber. Depending on the equation of state I use, I see rapid oscillations develop in the temperature near the Al-He interface, where there is a jump in density, even if no laser is turned on. These oscillations can grow suitably large such that FLASH dies with either a c^2<0 error or negative 3T error. I believe that these errors are due to a breakdown in the numerical evolution, with the discontinuity not well handled, and not the EoS, which I’ve verified only has positive energy and positive c^2. Notably, I see the same errors develop with a simple solid-like equation of state,


P = K/rho_0 (rho/rho_o - 1) 


with the internal energy determined by the thermodynamic relation rho^2 dE/drho = P. Note the above pressure is negative, but c^2 = dP/drho > 0.


I’d love to hear if anybody out there has had similar experiences and about any remedy. I’ve tried obvious remedies like increasing artificial viscosity to no avail. 


Thanks for reading!


Best,
Paul
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://flash.rochester.edu/pipermail/flash-users/attachments/20260508/7ced004f/attachment.htm>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: smime.p7s
Type: application/x-pkcs7-signature
Size: 8296 bytes
Desc: not available
URL: <http://flash.rochester.edu/pipermail/flash-users/attachments/20260508/7ced004f/attachment.bin>