[FLASH-USERS] Growing error in magnetic field when updating fluid variables in wind tunnel simulation

[Rukmani Vijayaraghavan]

Hi Sean,

I just tried both of these, and it doesn't seem to make any noticeable 
difference. Which solver / slope limiter have you used?

Thanks,
Rukmani

On 02/18/2016 06:37 AM, Sean Couch wrote:
> Hi Rukmani,
>
> I’ve seen something similar with the field loop advection test.  Have 
> you tried setting E_modification and E_upwind to .TRUE. in your flash.par?
>
> Sean
>
>
> ----------------------------------------------------------------------------------------------------------
> Sean M. Couch
> Assistant Professor
> Department of Physics and Astronomy
> Department of Computational Mathematics, Science, and Engineering
> National Superconducting Cyclotron Laboratory/Facility for Rare 
> Isotope Beams
> Michigan State University
> 567 Wilson Rd, 3250 BPS
> East Lansing, MI  48824
> (517) 884-5035
> couch at pa.msu.edu <mailto:couch at pa.msu.edu>
>
>
>
>
>> On Feb 17, 2016, at 9:22 PM, Rukmani Vijayaraghavan 
>> <rukmani at virginia.edu <mailto:rukmani at virginia.edu>> wrote:
>>
>> Hi everyone,
>>
>> I've come across an error when updating fluid variables at the inflow 
>> edge of a wind tunnel simulation. I'm running a simulation of a 
>> galaxy (with active dark matter particles, gas, and passive 
>> particles) in a box, whose fluid is initialized to be identical to 
>> the incoming wind (with vx, vy, vz = 600 km/s, 0, 0). There is a 
>> small error (on the order of 1%) when updating grid cells near the 
>> inflow boundary (with both USM and PPM solvers), and this error is 
>> spatially correlated with  block boundaries. While this error itself 
>> is tolerable as far as the density and pressure go, this has bad 
>> consequences for the magnetic field which grows as the wind 
>> propagates through the box (see attached figure, xl_boundary). This 
>> figure shows slices of Bx at two timesteps (annotated with block 
>> boundaries and magnetic field vectors). The dynamic range of Bx in 
>> this image has been reduced to highlight these discontinuities. At 
>> the timesteps shown in the attached image, the fluctuations in Bx are 
>> ~1%, but grow with time up to order unity. I've tried a variety of 
>> Riemann solvers (HLLC, HLLD, Roe, Hybrid), slope limiters (mc, 
>> minmod, etc.), interpolation orders, prolongation methods, turning on 
>> and off specific USM switches, but nothing seems to solve this issue 
>> so far. Has anybody else dealt with and/or successfully solved this 
>> issue?
>>
>> Thanks,
>> Rukmani
>>
>> -- 
>> Rukmani Vijayaraghavan
>> NSF Astronomy & Astrophysics Postdoctoral Fellow
>> University of Virginia
>> rukmani at virginia.edu <mailto:rukmani at virginia.edu>
>>
>> <magxslc_discontinuity.png>
>

-- 
Rukmani Vijayaraghavan
NSF Astronomy & Astrophysics Postdoctoral Fellow
University of Virginia
rukmani at virginia.edu

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