LATEST RESEARCH RESULTS

This project collates individual applications from the Fluid Dynamics group at Duisburg-Essen University. The subprojects include the investigation of phenomena from the fields of nanoparticle synthesis, supersonic flows and stratified burners using LES, DNS and direct chemistry.

Quarks are the constituents of the massive basic building blocks of visible matter. These building blocks are the hadrons, more precisely protons and neutrons, which are about 2,000 times heavier than electrons. It was a heroic effort to determine the nature of the phase transition for physical quark masses, which our group carried out in 2006 and published in Nature. This finding has fundamental consequences for the early universe and for the possible remnants we might detect even today. Note however, the result has not only relevance for the early universe (Big Bang) but also for heavy ion collisions (Little Bang), which are carried out at the RHIC (Brookhaven, USA) and LHC (Geneva, Switzerland) accelerators.

Zinc ions have shown antiviral properties, but a key issue for their use for antiviral therapy is its difficulty, as a divalent metal ion, to cross the cell membrane and thus reach its targets inside the cell. A variety of ligands, including the FDA approved drug chloroquine (CQ), form complexes with these ions have been proposed to assist zinc permeation, possibly promoting the combined beneficial action of both zinc ions and the drugs against the virus. Here, we studied the permeation of chloroquine and the interaction of the drug with zinc ions in aqueous solution. For the latter, we take advantage of highly scalable ab initio molecular dynamics simulations to explore the diverse coordination chemistry of zinc ions.

The defining properties of our numerical research in the domain of correlated electron systems are the notions of emergence and criticality. Emergence only occurs in the thermodynamic limit where the volume of the system is taken to infinity at constant particle number. To investigate this phenomena we use the Algorithms for Lattice Fermion implementation of the auxiliary field quantum Monte Carlo algorithm that allows to simulate a large variety of model systems on importance in the solid state.

A tremendous variety of physical phenomena involve turbulence, such as the dynamics of the atmosphere or the oceans, avian and airplane flight, fish and boats, sailing, heating and ventilation, and even galaxy formation. Turbulent flow is characterized by chaotic swirling movements that vary widely in size, from sub-millimeter, over the extent of storm clouds, to galactic scales. The interaction of the chaotic movements on different scales makes it challenging to simulate and understand turbulent flows. Turbulent thermal convection plays an important role in a wide range of natural and industrial settings, from astrophysical and geophysical flows to process engineering.

Turbulence has been a topic of research for many decades and finds its applications in many aspects of life. Still, turbulence is not fully understood up until today. The Navier-Stokes equations, which are used to describe the motion of viscous fluids, do not have a general analytical solution. Consequently, many researchers work with specific canonical cases to understand turbulence better. In the recent years as computers became increasingly powerful, more and more direct numerical simulations (DNS) have been conducted to solve turbulent flows. The goal of this project is to validate the scaling laws that have been derived for a turbulent round jet using Lie-symmetry analysis with numerical data.

Complex magnetic textures and localized particle-like structures on the nanometer scale such as chiral magnetic skyrmions with non-trivial topological properties are nowadays the most studied objects in the field of nanomagnetism. They offer the promise of new data storage and data processing technologies ranging from racetrack memories to memristive switches for neuromorphic computing. In this project we extend the realm of DFT calculations for magnetic systems to significantly larger setups from the basic description provided by our ab-initio code FLEUR

Our Cosmic Home, which is the local volume of the Universe centered on us, contains very prominently visible structures, extending over almost one billion light-years. Such structures, ranging from the Local Group over the Local Void and the most prominent galaxy clusters like Virgo, Perseus, Coma and many more, represent a formidable site where extremely detailed observations exist. Therefore, cosmological simulations of the formation of galaxies and galaxy clusters within the Local Universe, rather than any other, randomly selected part of the cosmic web, are perfect tools to test our formation and evolution theories of galaxies and galaxy clusters down to the details. However, at these detailed levels, such simulations are facing various…

The recent rise of renewable energy sources is promoting the use of hydrogen as a carbon-free energy carrier. One possibility to harness the energy stored in hydrogen is its usage in thermochemical energy conversion processes such as in gas turbines, industrial burners, or internal combustion engines. However, in contrast to conventional fuels, lean hydrogen/air flames are prone to thermodiffusive instabilities, which can substantially change flame dynamics, heat release rates, and flame speeds. To improve prediction capabilities of Large Eddy Simulations of hydrogen/air flames, detailed data of such flames are needed for model development and validation. However, only rare data of three-dimensional thermodiffusively unstable flames that…

Gravitational wave detectors such as LIGO, VIRGO, and KAGRA, have brought about an era of multi-messenger astronomy that has given new insights into the merger of binary compact objects. In all cases, the ability to constrain the characteristics of the compact objects is very limited, especially in the absence of an electro-magnetic (EM) counterpart. Gravitational wave events such as GW190425, however, present a very unique opportunity to study the mass gap regime where the binary could consist of either a black hole and a neutron star (BHNS) or a highly asymmetric neutron star binary (BNS).

Quantum Chromodynamics (QCD) is the sector of the standard model describing the strong nuclear force, which binds quarks and gluons inside hadrons. The theory confines these constituents, which are never observed directly in experiment. In this project the researchers study charmonium, a system containing a charm quark-anti-quark pair.

As a carbon-free fuel, hydrogen has the potential of emerging as the leading energy carrier for next-generation, zero-carbon power generation, and hence has received considerable attention. Hydrogen can offer significant benefits over hydrocarbon fuels, such as wide flammability range, low ignition energy, and high diffusivity. However, the use of hydrogen in gas turbines poses considerable challenges, such as the risk of flashback due to its high flame speed, which adversely affects the performance of hydrogen combustion. Flashback, a problem that occurs in premixed combustors, is the upstream propagation of the flame from the combustor into the premixing tube due to the change in mass flow rate, which could change the combustion process…

G-protein coupled receptors (GPCRs) are membrane proteins that transmit the effects of extracellular ligands to effect changes in the intracellular G-protein signaling system. Approximately 800 GPCRs are encoded in the human genome and approximately half of all marketed drugs target GPCRs. Crystal structures often deviate from the natural system: Proteins, especially membrane-bound ones, do not necessarily crystallize in their biologically active structures and the measures needed to obtain suitable GPCR crystals tend to increase the diversity between the natural environment and the crystal. It is within this context that molecular-dynamics simulations play a special role in GPCR research as a full-value complement to experimental studies.

The amazing progress in observational cosmology over the last decades has brought many surprises. Perhaps the most stunning is that we live in a Universe where most of the matter (~85%) is comprised of yet unidentified collisionless dark matter particles, while ordinary baryons produced in the Big Bang make up only a subdominant part (~15%). The real physical nature of dark energy, as well as the mass of the neutrinos which contribute a tiny admixture of “hot” dark matter, are profound and fundamental open questions in physics. To make further progress, this firmly established standard cosmological model will be subjected to precision tests in the coming years that are far more sensitive than anything done thus far.

Today, car manufacturers rely on CFD tools to design and optimise spark-ignition engines. However, current models of turbulent combustion—which are built based on the assumptions of the flamelet regime—lose their predictivity when used to simulate a highly diluted or ultra-lean combustion involving high turbulent intensities. Yet the combustion in a diluted boosted spark-ignition engine shifts from the flamelet to the thin reaction zone (TRZ) regime. This research project performed direct numerical simulations of premixed C₈H₁₈/air statistically flat flame interacting with a turbulent flow field. Results were analysed to develop a combustion model suitable for combustion in the TRZ regime based on the formalism of the coherent flame model.

This ongoing project aims at investigating the long-term evolution of a merging binary system of two neutron stars. The investigation conducted within this project is well aligned with the past research conducted by the Relastro group in Frankfurt and is motivated by the gravitational-wave detection GW170817 and its electromagnetic counterpart, the
so-called kilonova. This kilonova signal is produced by the nuclear processes within the dense and neutron rich mass that is ejected during the merger. Since a lot of mass is ejected during the longterm postmerger evolution, it is crucial to investigate this part via state-of-the-art simulations in order to fully understand the observation.

Deceleration of a supersonic flow in a channel by shocks and interaction with the turbulent boundary layer leads to the formation of a complex array of shocks, subsonic and supersonic regions, and recirculation zones. In this project, high-fidelity and well-resolved large-eddy simulations (LES) of such a fully turbulent (Reδ≈105) pseudo-shock system were performed and compared with experimental data. Particular attention is paid to the occurrence of flow instabilities (such as shock motion, shock-boundary layer interaction, and symmetry breaking of the shock system), mixing behaviour in the transonic shear layer, and a comparison with sophisticated RANS turbulence models.