[FLASH-USERS] Peaks in RHD solution

[Riccardo Ciolfi]

 Dear all, 

I have experienced similar problems in running in RHD (spikes appearing, e.g., in the density profile). Instead, the equivalent simulation in newtonian HD does not show any problem. 

I would be very interested in the reply to the questions posed by Stefano Ascenzi in the previous message. 
Thanks a lot!

 Best, 
 Riccardo



----- Messaggio originale -----
Da: "ascenzi" <stefano.ascenzi at roma2.infn.it>
A: flash-users at flash.uchicago.edu
Inviato: Venerdì, 28 aprile 2017 19:06:53
Oggetto: [FLASH-USERS] Peaks in RHD solution

Dear all,

I am using FLASH4.4 to simulate an expanding ball of matter with a 
maximum speed of 1.e-4c.

After a preliminary (1D) HD simulation I set up the same problem in RHD 
(taking into account c=1 units), but I obtained a solution with a lot of 
spikes, in spite of the smooth solution of the former case.

When I implemented the same problem in 2D (cylindrical coordinates) I 
found the same behavior passing from the HD to RHD case (figure in 
attachment).

Do you know what could be the origin of these peaks?
I noticed that if I rise the maximum speed to 1.e-2 c  I obtain a smooth 
solution. Is it possible that the RHD solver does not work well because 
when v=1.e-4 c I am too far from the relativistic limit?

I wanted also to try to solve this problem with the artificial 
viscosity. Do you know if it is implemented also for RHD solver or just 
for the HD unsplit solver ?
By the way I tried to rise and lower the parameter cvisc in the 1D HD 
case but I have not seen any difference in the solution. How can I be 
sure that the artificial viscosity is active ?

Thank you very much for your attention.

Best Regards,

Stefano Ascenzi