Upcoming Events

01

2024.04

Enhancing the WMLES prediction with the resolvent analysis

In this talk,we will focus on the physics and modelling of the wall-bounded turbulence. with an emphasis on the WMLES framework.Firstly,we will review our efforts on the physical understanding of compressible wall-bounded turbulence.Then,we will present our latest WMLES approach for high-speed wall-bounded turbulence based on our new compressible law of the wall.At last,within WMLES framework,we will also show how we can predict the missing near-wall turbulence intensities quantitatively with a linear model based on the resolvent analysis.This approach can greatly enhance the prediction capability of WMLES on the small-scale turbulence structures in the near-wall regions.
18

2024.03

Atomistic modeling of hydrogen impact on metals

The study of hydrogen's behavior and its impact on deformation and fracture in metals has been extensive,with numerous models and theories developed.However,direct observation of hydrogen in materials remains challenging,leaving many questions unanswered.Atomistic simulation emerges as a valuable tool for directly investigating hydrogen behaviors and their effects on deformation and fracture.The effectiveness of these simulations largely depends on accurately describing atomic interactions within the iron-hydrogen system. Recent advancements include the proposal of artificial neural network (ANN)atomic interactions for the iron-hydrogen binary system,trained using a dataset based on Density Functional Theory (DFT)calculations of energy,force,and structure.These ANN atomic interactions combine the computational efficiency of empirical models with the accuracy and transferability of DFT,allowing for a quantitative elucidation of phenomena contributing to hydrogen embrittlement.This has led to a clearer understanding of how hydrogen influences vacancy diffusion, dislocation activities,and the mechanisms behind crack formation at both grain boundaries and within grains
07

2024.03

CFD-Based Simulation of Wind Turbines in Complex Terrain

D-Based Simulation of Wind Turbines In Complex Terrain Thorsten Lutz (University of Stuttgart,Institute of Aerodynamics and Gas Dynamics) For the design and load calculation of wind turbines,computationally efficient engineering models are applied,allowing the analysis of numerous load cases to be analyzed in a short time.With these methods, the detailed aerodynamics of the turbines is not captured but modelled in a simplified manner and flat sites are also assumed.However,if the turbine behavior is to be calculated for locations in complex terrain or for inflow conditions with disturbances such as forests,these low-fidelity engineering models reach their limits.Here,numerical CFD (Computational Fluid Dynamics)methods can provide a higher prediction accuracy.However,these high-fidelity methods are computationally expensive and require the use of high-performance computing centres.CFD methods of this kind are being further developed at the Institute for wind energy applications and used for aerodynamic,aeroelastic and aeroacoustic studies. The influence of complex terrain and atmospheric wind fields can also be taken into account.In order to calculate the local wind fields in the area of the turbine,either numerical results from meteorological pre. cursor calculations are fed in at the inflow plane of the simulation domain or synthetically generated wind fields are utilized.In the presentation,the possibilities of today's CFD methods for wind energy applications will be shown and demonstrated using few selected examples ranging from flow physics studies to aeroelastic simulations of flexible turbines in complex terrain.
27

2023.12

When liquid cylinders collide

When two bodies of liquid collide,many interesting dynamics arise from the resulting fragmentation into droplets.Besides their inherent beauty,these dynamics also have relevance to processes of interest to science and engineering ranging from inkjet printing to breaking ocean waves.In this presentation I present direct numerical simulations of an idealised splashing process featuring two mutually colliding cylinders of liquid (in an ambient gas).under conditions characterised by a set of dimensionless parameters including the Weber (We).Laplace (La).and. indirectly,Bond (Bo)numbers,as well as characteristics of the initial perturbation.The collision results in the growth of a liquid rim,which destabilises into a set of ligaments which simultancously fragment and merge,resulting ultimately in a statistical size distribution of small droplets resembling a power law.I will talk about some of the central dynamies and scaling behaviours of the problem,before concluding with a discussion on potential interpretations and applications to breaking occan waves in particular.
11

2023.12

Mechanics-enabled Innovations in Solid State Electrolytes and Environmental Remediation

All forms of life and inanimate matter share a common element for effective development and performance:tiny building blocks.Different configurations of either bio or engineered building blocks are used to make almost anything.Investigation and characterization of such configurations lead to pioneering inventions and scientific advances,including the development of high-performance materials and structures for emerging research areas and sectors,from environmental remediation to energy storage to space exploration.In this context,being able to investigate mechanical behavior at small length scales becomes critical for relevant inventions.
11

2023.12

A rubber band approach to data-based RANS modeling

The constants and functions in Reynolds-averaged Navier-Stokes (RANS)turbulence models are coupled. Consequently,modifications to a RANS model often have a negative impact on its fundamental calibrations, which is why machine-learned enhancements are frequently detrimental beyond the training dataset.A solution to this issue is to identify degrees of freedom that do not affect the fundamental calibrations and only modify these identified degrees of freedom when re-calibrating the baseline model for a specific application.This approach is known as the "rubber-band"approach to RANS modeling.
08

2023.12

Thrust-Vectoring Schemes for Electric Propulsion Systems: A Review

Thrust vectoring capability has become a critical feature for propulsion systems as space missions move from static to dynamic.Thrust vectoring is a well-developed area of rocket engine science.For electric propulsion,however,it is an evolving field that has taken a new leap for- ward in recent years.A review and analysis of thrust vectoring schemes for electric propulsion sys- tems is presented.
17

2023.11

Rheological modelling of dynamically-crosslinked polymer networks–vitrimers and xLCEs

Dynamically-crosslinked polymer networks can be utilized as thermosets with excellent mechanic properties at low temperatures,and as thermoplastics at high temperatures by re-organising the network topology.Among the newly synthesized dynamically-crosslinked polymer networks,two novel classes attract increasing attentions:vitrimers first made in 2011 and xLCEs first made in 2014.By incorporating the microscopic dynamics of the chain exchange reactions,we develop continuum models to study the macroscopic response of vitrimers and xLCEs,including linear viscoelasticity,ramp deformation,creep compliance,etc.We expect these theoretical attempts can help to understand the rheology of these fantastic materials and guide future fabrications with desired viscoelastic properties.
31

2023.10

Turbulence in and out of equilibrium

Kolmogorov postulated in 1941 that the small scales of turbulent flows away from boundaries can be considered universal if the Reynolds number is sufficiently large.Eighty years later we have observed many cases where the prediction of Kolmogorov holds,and certain observations which seem contradictory.In this talk we will illustrate that a number of these seemingly anomalous observations are,in fact,perfectly consistent with Kolmogorov's postulates. We will illustrate this for the special cases of unsteady and inhomogeneous turbulence,using simulations,theory and dynamical systems.
24

2023.10

GPU-based exascale computing for turbulence

Turbulence research is essential for understanding fluid behavior in various physical systems,such as star formation,atmospheric dynamics,and vehicle design.However,accurately simulating ultimate turbulence,where turbulence is independent of diffusivities,poses a significant challenge due to the immense computational power required,beyond the capabilities of current supercomputers.For example,Germany's largest CPU supercomputer, SuperMUC,would require 500 billion grid points and around 400 million CPU hours to simulate the transition to ultimate turbulence for convection.

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