A quantitative test suite for codes used in Astrophysics


Riemann Shock Tube Problem

The test set-up consists of two fluids of different densities and pressures separated by a membrane that is then removed. The resulting solution shows all three types of fluid discontinuties; a shock wave moving from the high density fluid to the low density one, a rarefraction (sound) wave moving in the opposite direction and a contact discontinuity which marks the current location of the interface between the two fluids.

Initial conditions


This test is commonly performed in one-dimension, but here we extend this to consider two three-dimensional set-ups; the first of these has the fluid membrane at 90 degrees to the x-axis of the box ([1,0,0] plane), causing the shock to propogate parallel to this axis. The second set-up aligns the membrane at 45 agrees to each of the x, y and z axes ([1,1,1] plane).

In both cases, the intial density and pressure jump either side of the membrane are:



and we used a polytropic index of 5/3. In 2D, the projected initial conditions look like the image below, with black and white regions representing fluids of different densities. The left-hand image shows the shock face oriented along the [1,0,0] plane, while the right-hand image shows it oriented along the [1,1,0] plane. In actuality, this second one needs to be oriented in the [1,1,1] plane i.e. oblique to all the axes.


Code Specifics


The SPH codes Hydra and Gadget2 were run with 1 million particles formed from two glasses containing 1.6 million and 400,000 particles. The AMR codes Enzo and Flash used an initial grid of 1003 with two levels of refinement. The box size was 1 (since no gravity is present here, there are no units) and periodic boundary conditions were used. The results were analyzed at t=0.12.

Planer shock results



Enzo (PPM)
Enzo (Zeus)
Flash
Gadget2
Hydra



Enzo (PPM)
Enzo (Zeus)
Flash
Gadget2
Hydra


Oblique shock results



Enzo (PPM)
Enzo (Zeus)
Flash
Gadget2
Hydra


Enzo (PPM)
Enzo (Zeus)
Flash
Gadget2
Hydra


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