COVID-19 bei einer Großveranstaltung: Erfahrungen aus der Kieler Woche 2022

Im Juni 2022 fand die Kieler Woche ohne pandemiebedingte einschränkende Maßnahmen statt. Im Anschluss daran verdreifachte sich binnen weniger Tage die lokale Sieben-Tage-Inzidenz der SARS-CoV-2-Infektionen. Im selben Zeitraum war bei den COVID-19-bedingten Hospitalisierungen, schweren Erkrankungen und Todesfällen allenfalls ein schwacher Anstieg zu verzeichnen. Dagegen kam es aufgrund der Absonderungsmaßnahmen zu umfangreichen Personalausfällen unter anderem in Krankenhäusern sowie damit auch zu einem starken Rückgang der Anzahl der belegbaren Krankenhausbetten auf Normalstationen. Der Erfahrungsbericht fasst die verfügbaren, quantifizierbaren epidemiologischen Auswirkungen der Kieler Woche 2022 zusammen.Peer Reviewe

Hybrid RANS/LES Simulation Strategy for High-Lift Applications with Disturbed Inflow

The prediction of gust loads during take off and landing is relevant for the safety of an airplane and should be already considered during the design process. Therefore, we present a framework to investigate the effects of atmospheric gusts on high-lift airfoils with the help of hybrid RANS/LES models (HRLM). To estimate the relevance of different turbulent length scales in the gust, the method relies on the ADDES, which uses algebraic sensors to distinguish RANS and LES regions. The model is used in combination with a vorticity-based LES filter scale and a numerical scheme with low dissipation. High-quality experimental data, which include PIV measurements, are used to validate the simulation results. We will focus on the effects that prevent the flow separation at the flap in the HRLM

A Grid-Adaptive Algebraic Hybrid RANS/LES Method

The present thesis considers the compressible Navier-Stokes equations to simulate the flow of air about basic and complex test cases. As numerical solution method the unstructured finite-volume solver DLR-TAU is used. The aim of the work is to provide a hybrid RANS/LES simulation strategy for the reliable numerical prediction of the stall behavior of high-lift airfoils under the influence of turbulent inflow. The focus is on the development of an improved modeling technique based on the Detached Eddy Simulation (DES) method. The DES combines two complementary modeling concepts: the Large Eddy Simulation (LES) with high fidelity at a high computational effort, which is directly coupled to the flow Reynolds number, and the statistical approach to solve the Reynolds-Averaged Navier-Stokes (RANS) equations with lower fidelity for separated flows but at a considerably lower computational effort. In the present thesis the Algebraic Delayed DES (ADDES) is extended, improved, and validated for several fundamental flow cases and application challenges. In the ADDES the distinction between RANS and LES zones is controlled by algebraic sensors, which detect the flow state by evaluating boundary layer velocity profiles. To allow for complex application cases, the evaluation of the boundary-layer properties is implemented in a fully parallelized algorithm, which can handle complex geometries. Furthermore, the ADDES is coupled with wall-modeled LES capabilities to provide a model for attached boundary layers with turbulent onflow. In order to mitigate the so-called grey-area problem at the RANS-to-LES interface, a vorticity-based LES filter width was adopted and reformulated for the unstructured dual-grid approach of TAU, in order to stimulate the generation of resolved turbulent structures. Moreover, a grid-resolution sensor for Large-Eddy Simulations is proposed, which enables assessing the grid from a single LES solution. This sensor can be used to control an automatic local grid adaptation in order to provide an appropriate spatial resolution for the respective flow problem. In the target application of the present thesis, the interaction of a generic airfoil generated vortex with a two-element high-lift airfoil is simulated. In a preliminary investigation the generation and transport of the onflow disturbance is isolated to determine the required level of modeling. In combination with the improved high-fidelity ADDES approach, the mean influence of the disturbance on the high-lift airfoil is successfully reproduced in the final target application. During the development of the improved simulation strategy, intermediate results were published at several work stages, as listed below. The publications [A]-[F] with major own contributions are attached in the appendix of the thesis

PROGRESS IN SCALE-RESOLVING SIMULATIONS WITH THE DLR-TAU CODE

This paper provides an overview of the recent development of scale-resolving simulation methods in the DLR-TAU code for flow simulations near the border of the flight envelope. On the numerical side, a hybrid low-dissipation low-dispersion discretization scheme is presented that allows for accurate wall-resolved and wall-modelled LES computations and is shown to provide satisfying hybrid RANS/LES predictions of a Delta wing flow on a unstructured mesh. In the field of physical modelling, the grey-area issue of non-zonal hybrid RANS/LES is addressed through a vorticity-sensitive sub-grid filter scale which is shown to improve the prediction of a backward-facing step flow. Moreover, an embedded-LES functionality based on the Synthetic Eddy Method is implemented in TAU and applied to a complex multi-element airfoil flow

Scale-resolving simulations of wall-bounded flows with an unstructured compressible flow solver

The fully-developed channel flow at Re_tau ≈ 395 is used to validate scaleresolving simulations with the unstructured compressible DLR-TAU code. In a sensitivity study based on wall-resolved LES a low-dissipative spatial scheme is derived, which allows to predict the channel flow in fair agreement with DNS. Then the scheme is used in ImprovedDelayed DES computations in order to assess TAU’s capabilities for wall-modelled LES. Spatial-resolution requirements for obtaining acceptable mean-flow results are pointed out in a grid study. Besides, the combination of IDDES with an advanced vorticity filter is verified, and the effect of the underlying RANS approach, including Reynolds-stress modelling, is analysed

Best Practice for starting a detached eddy simulation on the F15 geometry

Several approaches to generate an initial field for a DES computation are compared. The generation of turbulent content is investigated

Hybrid RANS/LES simulations of a three-element airfoil

For a three element airfoil three different hybrid RANS-LES approaches namely DDES, zonal DDES and IDDES are compared in terms of mean pressure distribution and resolution of turbulent structures and stresse

Hybrid RANS/LES simulations of a three-element airfoil

In this paper a the Spalart-Allmaras based Delayed Detached Eddy Simulation (DDES [1]) and Improved Delayed Detached Eddy Simulation (IDDES [2]) are used to simulate the flow about an industrially relevant airfoil-configuration with deployed high-lift devices. Here, the potential advantage of the computationally very challenging hybrid approaches over pure RANS simulations in the case of in-cipient separation is investigated

Assessment of Local LES-Resolution Sensors for Hybrid RANS/LES Simulations

Different sensors that provide a measure for the resolution of the LES content in hybrid RANS/LES computations are proposed and investigated. In an apriori test on isotropic turbulence a suitable sensor is identified. Based on that sensor an automatic local mesh refinement is performed for an IDDES of the flow over a backward facing step. The results obtained on locally adapted grids are compared to results on globally refined grids. It is shown, that the proposed sensors can detect underresolved LES regions and that the local mesh refinement can help to reduce resolution errors caused by a too coarse grid spacing