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Spectra of atmospheric motions describe the distribution of kinetic and potential energy as a function of scales. The spectrum of horizontal motions in the free troposphere and the lower stratosphere at horizontal scales from a few 10 m to several 1000 km has often been shown to follow a power law with logarithmic spectral slopes near -3 at large scales and near -5/3 at smaller scales. The motions are highly anisotropic. Inertial subrange turbulence occurs only occasionally. The horizontal spectrum of vertical velocity has been discussed relatively little. Vertical wind drives conversion between potential and kinetic energy, vertical fluxes, cloud formation and turbulence. This study started from measurements of velocity and temperature spectra in field campaigns investigating atmospheric dynamics over oceans and mountains with the DLR research aircraft HALO. Accurate measurements are demanding because the wind speed is often small compared to the aircraft speed. The measured spectrum of vertical velocity showed unexpected peaks at scales corresponding to the depth of the atmosphere. We discuss the Helmholtz decomposition of horizontal velocity in rotational and divergent velocity components. We then show that the horizontal spectrum of vertical velocity is kinematically connected to the spectrum of horizontal divergent motions. The observed peaks occur when the divergent motions are vertically coherent and when the horizontal spectrum of divergent velocity reaches spectral slopes larger than -2. Details can be found in a recent publication (J. Atmos. Sci., 2019, doi: 10.1175/JAS-D-19-0160.1). This lecture is dedicated to Ludwig Prandtl (1875-1953) who contributed fundamentally to fluid mechanics, including meteorology.

Trajectory optimisation is one option to reduce air traffic impact on environment. A multidimensional environmental assessment framework is needed to optimize impact on climate, local air quality and noise simultaneously. An interface between flight planning and environmental impact information can be established with environmental cost functions. In a feasibility study such multidimensional assessment can be applied to the European Airspace. The project ATM4E within the frame of SESAR2020 has spelled out the objective to develop such a concept and to study changing traffic flows due to environmental optimisation. Aircraft Noise and Climate Effects

In times of a rising share of fluctuating renewables in the worldwide energy mix, there is a great need for energy storage units allowing harmonization of electricity production and consumption. Using phase change materials (PCM) to store heat for a flexible electricity generation with direct steam generating solar thermal power plants promises a good overall efficiency due to small temperature gradients that occur. This good efficiency, however, is associated with the need for expensive heat transfer structures (HTS) because of a poor thermal conductivity in PCMs. The required ratio of HTS and PCM to achieve an acceptable effective thermal conductivity is constant, and upscaling a storage unit is not expected to reduce costs significantly. With respect to the local fixation of the PCM, the system is defined as a static system. While discharging, the maximum heat flux decreases with time due to a growing and isolating layer of solidified PCM on the heat exchanger modules. One possibility to overcome this problem is the development of new dynamic concepts of PCM storage systems with moving PCM. In such systems, the isolating layer of PCM is slid away from areas with the highest heat transfer. The heat flux can thereby be controlled accurately by the PCM`s velocity. In this paper, PCM Flux as a completely new PCM storage concept is presented. PCM Flux is compared to other dynamic concepts and to the state-of-the-art static PCM storage system regarding possible heat flux and performance. The comparison outlines the outstanding properties of PCM Flux. Simulations with a specifically developed finite difference method tool modeling the movement of PCM, aluminum and steel, show a fully controllable heat flux with a peak power of 10 kW/m2 at a ΔT of 10K. Additionally, a negligible parasitics share of 0.13% arises in this storage system. The heat exchanger with its HTS only has to be designed for the nominal power output independent of the storage capacity. That is why the relative costs decline is inversely proportional to the storage size. The PCM Flux concept represents a PCM storage system with strict separation of power and capacity reducing the specific electricity costs of direct steam generating solar thermal power plants significantly.

Wind energy is a growing industry, and in an effort to reduce costs and increase turbine efficiency, rotor blades are becoming increasingly large in size. To facilitate this effort, the SmartBlades2 research project has designed, built, and tested a set of prototype research blades. As part of the SmartBlades2 project, high sensor density modal testing has been conducted on the research blades. The analysis of the modal tests showed good agreement of the global vibration modes with the finite element model predictions. However, the test analysis also identified low frequency vibration modes, referred to as breathing modes, which were not predicted by the finite element models. These vibration modes were found on all of the blades and are characterised by out-of-plane trailing edge panel motion. The objective of this thesis is to identify and predict the aforementioned breathing modes using finite element analysis. To achieve this, three model characteristics are analysed to determine their influence on the breathing mode prediction, namely, model topology, shell element configuration, and material properties. To characterise the affect of model topology, a cut section from the SmartBlades2 prototype blade is modelled with shell elements and continuum element glue joints. To validate the blade section model, a modal test is conducted which identifies breathing modes analogous to the full blade. Various topology features are investigated with the focus on the shell glue joints and spar web joints of the blade section. The analysis shows that while these changes significantly effect the mode shapes and frequencies, none of them predict the experimentally identified breathing modes. To investigate the source of this discrepancy, the modal behaviour of a sample plate structure with the same materials is used to remove the variability of topology. The effects of shell element size and configuration are analysed with mutual comparisons. The analysis shows that higher fidelity element configurations offer no advantage ...