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Turbulent flow consists of structures with a wide range of spatial and temporal scales which are hard to resolve numerically. Classical numerical methods as the Large Eddy Simulation (LES) are able to capture fine details of turbulent structures but come at high computational cost. Applying generative adversarial networks (GAN) for the synthetic modeling of turbulence is a mathematically well-founded approach to overcome this issue. In this work, we investigate the generalization capabilites of GAN-based synthetic turbulence generators when geometrical changes occur in the flow configuration (e.g. aerodynamic geometric optimization of structures such as airfoils). As training data, we use the flow around a low-pressure turbine (LPT) stator with periodic wake impact obtained from highly resolved LES. To simulate the flow around a LPT stator, we use the conditional deep convolutional GAN framework pix2pixHD conditioned on the position of a rotating wake in front of the stator. For the generalization experiments we exclude images of wake positions located at certain regions from the training data and use the unseen data for testing. We show the abilities and limits of generalization for the conditional GAN by extending the regions of the extracted wake positions successively. Finally, we evaluate the statistical properties of the synthesized flow field by comparison with the corresponding LES results.

The dynamics occurring at the terrestrial magnetopause are investigated by using Geotail and THEMIS spacecraft data of magnetopause crossings during ongoing Kelvin&ndash, Helmholtz instability. Properties of plasma turbulence and intermittency are presented, with the aim of understanding the evolution of the turbulence as a result of the development of Kelvin&ndash, Helmholtz instability. The data have been tested against standard diagnostics for intermittent turbulence, such as the autocorrelation function, the spectral analysis and the scale-dependent statistics of the magnetic field increments. A quasi-periodic modulation of different scaling exponents may exist along the direction of propagation of the Kelvin&ndash, Helmholtz waves along the Geocentric Solar Magnetosphere coordinate system (GSM), and it is visible as a quasi-periodic modulation of the scaling exponents we have studied. The wave period associated with such oscillation was estimated to be approximately 6.4 Earth Radii ( R E ). Furthermore, the amplitude of such modulation seems to decrease as the measurements are taken further away from the Earth along the magnetopause, in particular after X ( G S M ) ≲ &minus, 15 R E . The observed modulation seems to persist for most of the parameters considered in this analysis. This suggests that a kind of signature related to the development of the Kelvin&ndash, Helmholtz instabilities could be present in the statistical properties of the magnetic turbulence.

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020; Aachen : RWTH Aachen University 1 Online-Ressource : Illustrationen, Diagramme (2021). = Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020, The formation and subsequent reaction of CO in a flame is a measure of the combustion quality. The aim of this experimental work is to answer the question, whether it is possible to perform planar quantitative measurements of CO by means of laser-induced fluorescence under the realistic conditions of a combustion chamber in an aeronautical engine. For this purpose, a measuring system was set up and applied in a single sector test rig under pressure. With a laser system, both the excitation and the emission spectra were examined using an atmospheric laboratory combustor. The influence of pressure on the LIF emission was studied in a pressurized laboratory combustor. The results of this study were used to develop a quantitative 2-photon-PLIF measurement technique, which was used at a combustion chamber test rig for aircraft engines with realistic pressures and temperatures. The results of these measurements are discussed in the context of previous results of velocity and OH measurements., Published by RWTH Aachen University, Aachen