Numerical modeling and simulations

Entry missions into the atmospheres of planets and those of other celestial bodies represent future goals in space travel. They can only be safely accomplished with improved knowledge of the behavior, properties, and effects of gas flows around spacecrafts. Additionally, the design of advanced space propulsion systems requires a sound knowledge of the behavior of the engine exhaust gas stream. Numerical methods enable the possibility to simulate flows, where suitable experiments are usually very limited or associated with high costs. Therefore, numerical investigation methods are gaining more importance.

Simulationen of the DLR-REX-Free Flyer

One focus of the "Numerical modeling and simulation" group is modeling non-equilibrium effects in gases and plasmas. These always occur when large local differences in surrounding conditions are involved, e.g. large temperature differences. Examples related to space travel have been mentioned considering entry missions or space propulsion systems. However, understanding these effects also becomes increasingly important in other industrial sectors. The spectrum ranges from micro- and nanotechnology, including plasma-based coating processes for nanotechnology production itself, to next-generation lithography.

Within a cooperation between the Institute of Space Systems (IRS) and the Institute of Aerodynamics and Gas Dynamics (IAG), the particle code "PICLas" is being developed as a flexible simulation tool to calculate three-dimensional gas and plasma flows. Meanwhile, the company "boltzplatz" has established itself as a university spin-off, founded by former employees of the numerics departments of IRS and IAG. This ensures a direct exchange between industry and university as well as a continuously growing number of users of PICLas in either field. More information and contact details can be found at the boltzplatz homepage.

Simulation of an atmospheric entry at Titan

PICLas couples different field and particle solvers to provide numerically efficient solution methods in different gas and plasma regimes. Since PICLas historically started as a tool for simulating diluted gases and plasmas, its two largest components are the Particle-In-Cell (PIC) and the Direct Simulation Monte Carlo (DSMC) modules. While the PIC part models electromagnetic interactions of particles in plasmas, the DSMC part models collisions and chemical reactions. Both methods have been used for many years in a wide range of numerical applications and are constantly being developed.

Another development of PICLas deals with the numerical investigation of flows and plasmas in the context of multiscale phenomena. This includes for example extremely large density gradients as they occur in nozzle expansions. Another example are large temporal gradients of the physical effects occurring in the flows. The time scales of plasma oscillation and advection of ions, which is relevant in electric space propulsion systems, can be several orders of magnitude apart. For these purposes, different particle-continuum methods like the Bhatnagar-Gross-Krook (BGK) or the Fokker-Planck method are being coupled with PIC and DSMC. In addition, various implicit procedures are being developed to further increase the effectiveness of the implemented methods.
Furthermore, in some of the flows under investigation, radiation effects play an important role. Therefore, the working group also deals separately with the further development of radiative energy transfer solvers.

Current projects

ERC Starting Grant "MEDUSA" (Multiscale Fluid and Plasma Dynamics using Particles 899981)

The objective is to develop particle-based multiscale methods for thermo-chemical non-equilibrium gas and plasma flows, which for the first time enable the simulation of a large number of high-tech applications.

The International Research TrainingGroupe "Droplet Interaction Technologies" (GRK 2160/2: DROPIT)

DROPIT is a research training group that deals with the investigation of droplet interaction phenomena. The aim is to understand how microscale transport processes influence macroscopic flow properties.

GRK 2160/2: DROPIT

Numerical methods

Particle methods

Stochastic particle methods are the focus of the numerics group at the IRS. They often offer advantages, especially for higher-dimensional problems such as the solution of the Boltzmann equation.

Particle methods

Discrete-Velocity-Methods

The development of noise reduction methods for stochastic particle methods is of great importance for slow or low-mach flows.

Discrete-Velocity-Methods

Radiation solver and radiative energy transfer solver

Surface chemistry

Heat shields are essential for atmospheric spacecraft entry. The choice of material is crucial for extreme conditions and weight minimization. Heterogeneous processes between gas and surface influence the heat flow. A catalytic reaction model developed in PICLas estimates this influence, as experiments are cost-intensive.

Surface chemistry

Gas-Surface Interactions in Very Low Earth Orbit

Very Low Earth Orbit (VLEO), typically defined as altitudes below 450 km, presents unique challenges and opportunities for satellite missions. One of the critical aspects of operating in VLEO is understanding gas-surface interactions, which significantly impact satellite the design and operation of satellites.

GSI-Model in VLEO

Particle-based multiphase methods

Particle-based multiphase methods offer an efficient way to visualize non-equilibrium effects in multiphase flows.

Particle-based multiphase methods

Particle-In-Cell

Plasma effects play a major role in highly enthalpy flows. The Particle-In-Cell method is therefore used to simulate non-equilibrium effects in plasmas.

Particle-In-Cell

Plasma Kinetic Code PICLas

All models developed within the numerics group are available on GitHub in the open source code PICLas. In addition, detailed documentation can be found at piclas.readthedocs.io.