This thesis deals with aspects of the dust particles which occur in gaseous products from biomass combustion. The thesis introduces technologies by which solid particles capture from a combustion flow can be implemented. Principles and technical means of dust particles separation in mechanical separators are put in focus primarily. The thesis is concluded with a technical design of a cyclone separator.

This study was concerned with the most common reverse flow type of cyclones where the flow enters the cyclone through a tangential inlet and leaves via an axial outlet pipe at the top of the cyclone. Numerical computations of two different cyclones were based on the so-called Stairmand cyclone. The difference in geometry between these two cyclones was basically characterized by the geometrical swirl number Sg of 3.5 and 4. Turbulent secondary flows inside a straight square channel have been studied numerically by using Large Eddy Simulation (LES) in order to verify the implementation process. Prandtl’s secondary motion calculated by LES shows satisfying agreement with both, Direct Numerical Simulation (DNS) and experimental results. Numerical calculations were carried out at various axial positions and at the apex cone of a gas cyclone separator. Two different NS-solvers (a commercial one, and a research code), based on a pressure correction algorithm of the SIMPLE method have been applied to predict the flow behavior. The flow was assumed as unsteady, incompressible and isothermal. A k − epsilon turbulence model has been applied first using the commercial code to investigate the gas flow. Due to the nature of cyclone flows, which exhibit highly curved streamlines and anisotropic turbulence, advanced turbulence models such as RSM (Reynolds Stress Model) and LES (Large Eddy Simulation) have been used as well. The RSM simulation was performed using the commercial package CFX4.4, while for the LES calculations the research code MISTRAL/PartFlow-3D code developed in our multiphase research group has been applied utilizing the Smagorinsky model. It was found that the k − epsilon model cannot predict flow phenomena inside the cyclone properly due to the strong curvature of the streamlines. The RSM results are comparable with LES results in the area of the apex cone plane. However, the application of the LES reveals qualitative agreement with the experimental data, but requires higher computer capacity and longer running times than RSM. These calculations of the continuous phase flow were the basis for modeling the behavior of the solid particles in the cyclone separator. Particle trajectories, pressure drop and the cyclone separation efficiency have been studied in some detail. This thesis is organized into five chapters. After an introduction and overview, chapter 2 deals with continuous phase flow turbulence modeling including the governing equations. The emphasis will be based on LES modelling. Furthermore, the disperse phase motion is treated in chapter 3. In chapter 4, the validation process of LES implementation with channel flow is presented. Moreover, prediction profiles of the gas flow are presented and discussed. In addition, disperse phase flow results are presented and discussed such as particle trajectories; pressure drop and cyclone separation efficiency are also discussed. Chapter 5 summarizes and concludes the thesis.

<div>Global Navigation Satellite System Reflectometry (GNSS-R) is a remote sensing technique that uses reflected satellite navigation signals from the Earth surface in a bistatic radar configuration. GNSS-R observations have been collected using receivers on stationary, airborne and spaceborne platforms. The delay-Doppler map (DDM) is the fundamental GNSS-R measurement from which ocean surface wind speed can be retrieved. GNSS-R observations can be assimilated into numerical weather prediction models to improve weather analyses and forecasts. The direct assimilation of DDM observations shows potential superiority over the assimilation of wind retrievals.</div><div><br></div><div>This dissertation demonstrates the direct assimilation of GNSS-R DDMs using a two-dimensional variational analysis method (VAM). First, the observation forward model and its Jacobian are developed. Then, the observation's bias correction, quality control, and error characterization are presented. The DDM assimilation was applied to a global and a regional case. </div><div><br></div><div>In the global case, DDM observations from the NASA Cyclone Global Navigation Satellite System (CYGNSS) mission are assimilated into global ocean surface wind analyses using the European Centre for Medium-Range Weather Forecasts (ECMWF) 10-meter winds as the background. The wind analyses are improved as a result of the DDM assimilation. VAM can also be used to derive a new type of wind vector observation from DDMs (VAM-DDM).</div><div><br></div><div>In the regional case, an observing system experiment (OSE) is used to quantify the impact of VAM-DDM wind vectors from CYGNSS on hurricane forecasts, in the case of Hurricane Michael (2018). It is found that the assimilation of VAM-DDM wind vectors at the early stage of the hurricane improves the forecasted track and intensity.</div><div><br></div><div>The research of this dissertation implies potential benefits of DDM assimilation for future research and operational applications.</div>

<p>Landfalling tropical cyclones bring tremendous coastal and inland hazard, which depends strongly on the evolution of the wind field after the landfall. This work investigates the inland evolution of the tropical cyclone wind field via idealized numerical simulation experiments and existing theories explaining the physics of storms over the ocean. The complicated landfall process is idealized as a transient response of a mature axisymmetric tropical cyclone to instantaneous surface forcings associated with landfall.</p><p><br></p><p>First, idealized landfall experiments are performed in the f-plane Bryan Cloud Model (CM1), where surface drag coefficient and evaporative fraction are individually or simultaneously modified systematically beneath an axisymmetric mature storm. Surface drying stabilizes the eyewall and consequently weakens the overturning circulation, thereby reducing inward angular momentum transport that slowly decays the low-level wind field only within the inner-core. In contrast, surface roughening first weakens the entire low-level wind field rapidly and enhances the overturning circulation dynamically despite the concurrent thermodynamic stabilization of the eyewall; thereafter, the storm gradually decays in a manner similar to drying. As a result, total precipitation temporarily increases with roughening but uniformly decreases with drying. Storm inner size and outer size decrease monotonically and rapidly with surface roughening, while the radius of maximum wind can increase with moderate surface drying.</p><p><br></p><p>Second, the extent to which existing intensity theory formed for tropical cyclones over the ocean can explain the intensity response to idealized landfall is explored in this work. Existing theoretical predictions for the equilibrium response and transient response of storm intensity are compared against the simulated response found in previous idealized simulations. The equilibrium and transient response of storm intensity to combined surface forcings can be reproduced by the product of their individual responses, in line with traditional potential intensity theory. The intensification theory of Emanuel (2012) is generalized for predicting the weakening process and found capable of reproducing the transient intensity decay. Specifically, the rapid initial decay of near-surface wind can be captured by how kinetic energy is instantaneously reduced by surface friction, where the decay is a function of surface roughness.</p><p><br></p><p>Third, existing structural theory and TC radial length scale formed or identified for storms over the ocean are tested against the idealized landfall experiment where surface is individually dried or roughened. The equilibrium storm radial length scale can predict the transient response of storm size to surface roughening throughout the decay evolution. For surface drying experiments, TC size scales with the intensity after around 12h. The E04 wind field model can generally capture the transient response of TC low-level wind field to individual surface drying and roughening, from radius of maximum wind speed to the outer region. The E04 prediction for these two types of experiments exhibits limited dependence on the subsidence cooling rate applied in the model.</p><p><br></p><p>Overall, though results are insufficient to explain the complicated wind field evolution of every real-world landfalling storm, it provides a fundamental understanding of how storm low-level wind fields respond to inland surface properties. This work also indicates the potential for existing theory to predict how tropical cyclone intensity evolves after landfall in the real world, which is essential for improving the forecasts on any timescale and the risk assessments.</p>

Mit dem mesoskaligen nichthydrostatischen Modell 'Lokal Modell' (LM) des Deutschen Wetterdienstes (DWD) werden die Vorgänge in einer Orkanzyklone simuliert. Als Beispiel wird das Tiefdruckgebiet Ginger aus dem Jahr 2000 dargestellt. Die meteorologischen Antriebsdaten wurden durch das globale Modell des DWD erzeugt. Die Auswirkungen von Veränderungen verschiedener Bedingungen auf die Entwicklung der Zyklone, und vor allem auf das Windfeld, sollen untersucht werden. Dazu werden die Antriebsdaten künstlich verändert. Im Beispiel wird der horizontale Temperaturgradient geändert, und die Folge auf Druckverteilung und Windgeschwindigkeit betrachtet. Da das LM nur einen Ausschnitt aus der Atmosphäre simuliert, kommt es durch die Eingriffe in die Antriebsdaten zu Problemen am Rand. Ein Verfahren wird getestet, um diese zu vermeiden. / The development of a cyclone is simulated with the nonhydrostatic limited area model 'Lokal Modell' (LM) of the German Weather Service (DWD). The cyclone Ginger which occurred in 2000 serves as an example. The forcing data were generated by the global model of the DWD. The effects of various conditions were considered contributing to the evolution of Ginger and mainly to its velocity field. For this purpose, the forcing data were artificially varied. As an example the horizontal temperature gradient was changed. The effects on the pressure field and its corresponding velocity field are discussed. As the LM simulates only a limited area, the lateral bounds become problematic because of the manipulated forcing data. A procedure is tested, in order to prevent this problems.

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第18931号 / 工博第3973号 / 新制||工||1612(附属図書館) / 31882 / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 間瀬 肇, 教授 平石 哲也, 准教授 森 信人 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

京都大学 / 0048 / 新制・課程博士 / 博士(地域研究) / 甲第20494号 / 地博第213号 / 未着(附属図書館) / 京都大学大学院アジア・アフリカ地域研究研究科東南アジア地域研究専攻 / (主査)教授 竹田 晋也, 教授 岩田 明久, 准教授 安藤 和雄, 准教授 鈴木 玲冶 / 学位規則第4条第1項該当 / Doctor of Area Studies / Kyoto University / DGAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第21724号 / 工博第4541号 / 新制||工||1708(附属図書館) / 京都大学大学院工学研究科社会基盤工学専攻 / (主査)教授 中川 一, 教授 平石 哲也, 准教授 川池 健司 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

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Standard eddy-viscosity models lack curvature and system rotation sensitized terms in their formulation. Hence they fail to capture the effects of curvature and system rotation on turbulence anisotropy. As part of this effort, an algebraic expression for a characteristic rotation term is developed and tuned with the help of rotating homogeneous shear flow. This formulation is primarily based upon the rotation and curvature sensitized eddy-viscosity coefficient developed by York et al. (2009). A new scalar transport equation loosely based on Durbin’s wall normal turbulent velocity scale (Durbin, 1991) is introduced to account for the modification in turbulence structure due to system rotation and curvature effects. The added transport equation also introduces history effects and stability in the solution with small increase in computational cost. The eddy-viscosity is redefined based on new turbulent velocity scale and hence the effects of rotation and streamline curvature are introduced into the mean momentum equation. A number of canonical test cases with significant curvature and rotation effects along with a cyclone flow, a representative of complex industrial flows, are considered for model validation. Hybrid modeling framework combines the strength of RANS in boundary layers and LES in separated shear layers to alleviate the weaknesses of RANS and limitations of LES model in some complex flows. A recently proposed hybrid RANS-LES modeling framework uses a weighing parameter that dynamically determines the RANS and LES regions based on solution statistics. The hybrid modeling methodology is implemented on a normal jet in crossflow, and a film cooling case for the purpose of model validation and evaluation. The final goal of the proposed effort is to combine advanced RANS modeling capability with LES using the new hybrid modeling framework. Specifically, the curvature and rotation sensitive RANS model developed here is coupled with commonly used LES models to produce a novel model for complex turbulent flows with the potential to improve accuracy of CFD predictions (versus existing RANS models) as well as significantly reduce the computational expense (versus existing LES models). Performance of the model form hence developed is evaluated on a cyclone flow case.