Simulation of a hypersonic astrophysical jet with Mach=2156.91 moving through a medium at rest.

The simulation was performed on a 256 × 256 quadrilateral grid with a nodal fourth-order entropy-stable Discontinuous Galerkin (DG) scheme. Local bounds on the density and specific entropy are imposed by blending the DG scheme locally (at the node level) with a second-order Finite Volume (FV) method. Both the DG and the FV methods use the Harten-Lax-van Leer-Einfeldt (HLLE) Riemann solver.

The simulation results were obtained with the open-source code FLUXO (https://github.com/project-fluxo/fluxo).

The numerical methods used to perform the simulation are described in our preprint:
Rueda-Ramírez, A. M., Pazner, W., Gassner, G.J. (2022). Subcell Limiting Strategies for Discontinuous Galerkin Spectral Element Methods. Submitted. https://arxiv.org/abs/2202.00576.

Simulation of the viscous flow past a cylinder with a discontinuous Galerkin spectral element method on a hierarchical Cartesian mesh with adaptive mesh refinement (AMR). The polynomial degree is N = 3 and the mesh uses five refinement levels. The cylinder boundary is imposed with an immersed boundary method (IBM) based on volume penalization [1], which adds a source term to the compressible Navier-Stokes equations,
$$
\partial_t \mathbf{u} + \nabla \cdot \vec{\mathbf{f}} (\mathbf{u},\nabla \mathbf{u}) = \underbrace{\beta (\mathbf{u}_s – \mathbf{u})}_{\text{IBM source}},
$$
where $\mathbf{u}$ is the vector of conservative quantities, $\vec{\mathbf{f}}$ is the Navier-Stokes flux, $\beta$ is the penalty parameter, and $\mathbf{u}_s$ is an imposed state. For this simulation, $\mathbf{u}_s$ mimics an isothermal no-slip wall boundary condition.

The simulation was obtained with the open-source code FLUXO (https://github.com/project-fluxo/fluxo).

References
[1] Kou, J., Joshi, S., Hurtado-de-Mendoza, A., Puri, K., Hirsch, C., & Ferrer, E. (2022). Immersed boundary method for high-order flux reconstruction based on volume penalization. Journal of Computational Physics, 448, 110721.

Simulation of an asymmetric two-dimensional stiff multi-species reacting flow for the compressible Euler equations. The computation domain [0,6]x[0,2] of this detonation problem is split into three zones. Zone A [0,0.5]x[0,2] as well as zone B (0.5,6]x[1.2,2] is filled with burnt gas, namely O2,OH and H2O. The last zone C (0.5,6]x[0,1.2) contains unburnt gas, namely H2 and O2.

The reacting model consists of two reactions H2+O2->2OH, 2OH+H2->2H2O and five species H2,O2,OH,H2O,N2 whereas reaction 1 has a smaller ignition temperature as well as a much faster chemical rate than reaction 2. Species N2 acts as a dilute catalyst here.

This example has been calculated using Trixi.jl with a P4est mesh using 3072x1024=3.145.728 elements, Dirichlet boundary conditions in x-direction as well as solid wall boundaries in y-direction. The final time is T = 0.1. The convection part is solved with FV whereas the chemical network is solved with KROME. (Note: Not all of these features are currently available in the main code of Trixi.jl.)

Pressure distribution at final time T=0.1:

Temperature distribution at final time T=0.1:

Density distribution at final time T=0.1:

OH-fraction distribution at final time T=0.1:

Earth’s climate is changing due to human activity. Therefore, the ability to predict future climate change is of utmost importance if we want to reduce the human interference with the climate system (climate change mitigation) and our vulnerability to the harmful effects of climate change (climate change adaptation).

It is possible to model the time-dependent local temperatures on the globe using a simple two-dimensional energy balance model [1,2],
$$ C(\vec{x}) \frac{\partial T}{\partial t} + A + BT = \nabla \cdot \left( D(\vec{x}) \nabla T \right) + Q S(\vec{x},t) (1-a(\vec{x})), $$
where $T$ is the local temperature; $C(\vec{x})$ is the local heat capacity for a column of air on land, water or ice; the term $A+BT$ models the outgoing long-wave radiation, where $A$ depends on the amount of green-house gases in the atmosphere and $B$ models several feedback effects; $D$ is a latitude-dependent diffusion coefficient; and the last term includes the heat input in the system, where $Q$ is the solar radiation at earth’s position in the solar system, $S$ is the seasonal and latitudinal distribution of insolation, which depends on orbital parameters, such as the eccentricity of earth’s orbit, and the precession and tilt of earth’s rotation axis, and $a(\vec{x})$ is the local albedo, which measures the reflection of solar radiation and depends on the surface cover.

We developed a julia code that implements the EBM model on the sphere surface and used it to describe the mean temperatures on the globe assuming a constant atmospheric CO$_2$ concentration (of year 1950). The results are presented in the animation.

[1] North, G.R.; Mengel, J.G.; Short, D.A. (1983). Simple Energy Balance Model Resolving the Seasons and the Continents’ Application to the Astronomical Theory of the Ice Ages. Journal of Geophysical Research.
[2] Zhuang, K.; North, G.R.; Stevens, Mark J. (2017). A NetCDF version of the two-dimensional energy balance model based on the full multigrid algorithm. SoftwareX.

Io is the most volcanically active body of the solar system. Furthermore, it is embedded in Jupiter’s magnetic field, the largest and most powerful planetary magnetosphere of the solar system. Due to its strong volcanic activity, Io expels ions and neutrals, which are in turn ionized by ultraviolet and electron impact ionization, forming a plasma torus around Jupiter [1,2]. As Io moves inside the plasma torus, elastic collisions of ions and neutrals inside its atmosphere generate a magnetospheric disturbance that propagates away from Io along the background magnetic field lines at the Alfvén wave speed. This phenomenon creates a pair of Alfvén current tubes that are commonly called Alfvén wings, which have been observed by several flybys [1].

The figure shows the momentum (non-dimensional) and magnetic field of the plasma that surrounds Io, obtained with the magneto-hydrodynamic (MHD) plasma model of FLUXO*. The Alfvén wings can be observed as disturbances of both the background magnetic and momentum fields. In yellow is the trajectory of the I31 flyby of the Galileo spacecraft, which visited Io in 2001 [1]. The Galileo spacecraft is also depicted (not to scale). A 3D model of the moon’s surface developed by NASA [3] was superposed on the simulation results.

*FLUXO (www.github.com/project-fluxo/fluxo) is an MPI parallel high-order Discontinuous Galerkin code, which supports unstructured curvilinear hexahedral grids, and is able to perform Adaptive Mesh Refinement (AMR).

[1] M. Kivelson, K. Khurana, C. Russell, R. Walker, S. Joy, J. Mafi, GALILEO ORBITER AT JUPITER CALIBRATED MAG HIGH RES V1.0, GO-J-MAG-3-RDR-HIGHRES-V1.0, Technical Report, NASA Planetary Data System, 1997.
[2] J. Saur, F. M. Neubauer, J. E. P. Connerney, Plasma interaction of Io with its plasma torus, 2004.
[3] https://solarsystem.nasa.gov/resources/2379/io-3d-model/

[1] Machida, Mami, Mitsuru R. Hayashi, and R. Matsumoto.
“Global simulations of differentially rotating magnetized disks:
Formation of low-beta filaments and structured coronae.”
The Astrophysical Journal Letters 532.1 (2000): L67.
[2] Markert et al. “A Discontinuous Galerkin Method with Sub‑Cell Adaptive Shock Capturing for
FLASH” (in preparation)
[3] http://flash.uchicago.edu/

Here we are simulating a gingerbread man, whereby the gingerbread man itself has 861 unstructured quadrilateral elements. For the run parameters, we used polydeg = 10 with the compressible Euler equations and the manufactured (convergence test) solution. The visualization is done on nvisnodes=12 uniform points in each direction, on each element.

We thank Prof. Dr. Andrew Winters (https://liu.se/en/employee/andwi94) for providing this video/simulation.