[FLASH-USERS] double rarefraction question

[Dean Townsley]

Hi flash users and developers,

I am working with an undergraduate (cc'd here) on some Riemann solver 
and verification stuff and we got something a bit strange when we tried 
a double-rarefraction wave with flash.  So I thought I would ask around 
about it.

We are just doing the standard double-rarefraction case out of Toro's 
textbook.  I've attached our flash.par for the Sod problem, but 
basically it is:
sim_rhoLeft     = 1.
sim_rhoRight    = 1.
sim_pLeft               = 0.4
sim_pRight              = 0.4
sim_uLeft               = -2.
sim_uRight              = 2.

Broxton has implemented the solver out of Toro to make some comparison 
plots, and they look fine compared to the text solutions.  But I tried 
it with flash and it did something really funky in the internal energy.  
I've attached a plot that compares the energy I get out of flash (blue) 
to that from the explicit riemann solver (red) at a time of 0.15.

This is effectively with flash 3.2, but I tried it with 3.3 and I get a 
slightly weirder structure of similar magnitude.  I attached a plot of 
that too.  I was quite surprised to see this change from one version to 
another.

So my question to anyone who might know:  Is this a known issue with 
PPM?  Perhaps I'm just unfamiliar with it.  I tried turning off the 
steepening, just to try something, and it didn't seem to do anything.  
Am I doing something else dumb?

Any insight would be much appreciated!

(hopefully the attachments will come through, otherwise I'll send links)

Thanks,
Dean
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