Project, Bachelor and Master theses

At high Reynolds numbers in the order of 10 000 000, which are frequently encountered in aerospace applications, the size of turbulent structures is so small that high-fidelity large-eddy simulations (LES) become unfeasible even on modern supercomputers. However, high resolution of the near-wall region is necessary to accurately predict wall-shear stress and guarantee a proper development of the boundary layer. To overcome this problem various wall-modeling approaches have been developed, that compute the correct wall-shear stress from the outer boundary layer and therefore allow for a significant reduction of the number of cells in the computational mesh. Simply computing the local wall-shear stress based on instantaneous data from the outer boundary layer transfers the dynamics of the outer layer turbulence to the boundary surface. In reality, however, the dynamics at the wall are supressed significantly by the viscous sublayer. Therefore, the wall-model introduces a modeling error in the instantaneous behaviour of the wall-shear stress while giving correct predictions with respect to the temporal mean. In this thesis various time-filtering procedures with respect to the sampled data from the outer boundary layer and their effect on the predicted wall-shear stress will be analyzed. This requires the implementation of the filtering procedures into the multiphysics framework m-AIA. The implemented filtering strategies will then be evaluated by conducting multiple LES of a turbulent channel flow on the RWTH High Perfomance Computer CLAIX and analyzing characteristic properties of the boundary layer flow with respect to the literature.

Pulmonary infectious diseases are a growing challenge of human health. Therefore, investigations of alternative curative therapies and new strategies are essential. As the literature indicates, allicin (diallyl thiosulfinate) has antifungal, antibacterial activity, even against multiple drug resistance (MDR) strains of human lung bacteria as well as antiviral properties. To better understand the deposition mechanism of aerosols, experimental investigations are mandatory. Hence, a detailed analysis of the drug-loaded and infectious aerosol particle deposition in the respiratory system is necessary. A combined approach of biology, medicine and experimental fluid dynamics allows realistic in vitro measurements of the human airways.

Methods to diagnose pathologies in the human respiratory system have evolved recently from mainly focusing on medical imaging data to the consideration of computational fluid dynamics (CFD). In the past, the thermal lattice-Boltzmann (TLB) solver of the simulation framework multiphysics Aerodynamisches Institut Aachen (m-AIA) has been frequently used to numerically qualify the nasal cavity by analyzing the fluid mechanical properties of the respiratory flow, such as the pressure loss, the temperature distribution, and the mass flux distribution. However, an important quantity that has not been considered so far in these studies is the humidity of the inhailed air. Dry nasal passages can lead to discomfort and irritated sinuses and in the worst case to lung infections.

Fast alle Strömungen, die in der Umwelt und Technik vorkommen, sind turbulent. Jedoch ist bereits die numerische Simulation einphasiger turbulenter Strömungen aufwendig, wobei es viele erfolgreiche Modellierungsansätze gibt. Eine noch größere Herausforderung besteht hingegen in der numerischen Analyse partikelbeladener turbulenter Strömungen. Trotz ihrer hohen Relevanz in Umwelt und Technik, sind vorhandene Modelle nur für vereinfachte Bedingungen gültig und eine Validierung steht oft noch aus. Ein wichtiger Anwendungsfall ist die numerische Auslegung einer Biomasse-Brennkammer. Dabei ist die Bestimmung der Aufheizraten, der Dynamik, und der turbulenten Durchmischung nicht-sphärischer Partikel entscheidend um den gesamten Verbrennungsprozess zuverlässig auszulegen. Die Generierung von hoch-aufgelösten Referenzdaten mit Hilfe von Simulationen und die Entwicklung von genauen Modellen für Anwender, sowie deren Validierung sind aktuelle Forschungsvorhaben, die am Aerodynamischen Institut intensiv verfolgt werden. Für dieses Projekt sind wir auf der Suche nach motivierten Masterarbeitern.