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Vortex breakdown occurs in many flow applications such as weather, aerodynamics, swirl combustors, and more, introducing unsteadiness that is often undesired. While vortex breakdown has been previously investigated extensively, researchers have struggled to efficiently characterize these flows due to the flow sensitivity to intrusive probes, and there is no real consensus regarding the process and reason of its formation. Recently, researchers have discovered the blue whirl, a silent and efficient flame which they believe is a mode of vortex breakdown, and suggested mechanisms of stabilization and prevention of it through temperature control. This thesis uses modern time-resolved measurement techniques to investigate breakdown at smaller temporal and spatial scales than previously researched, and shows the effect of heat addition at the inflow of a vortex generator on the onset and behaviour of breakdown modes. Smoke flow visualization experiments were preformed to identify heating and swirl rate effects on vortex flow, and the resulting swirl angle of the flow was measured. Decreasing the incoming swirl was found to delay or fully suppress the formation of a breakdown bubble. Increasing the inlet temperature had a similar effect due to the buoyancy effects on the flow increasing the axial velocity thus reducing the effective swirl. 3D Particle Tracking Velocimetry was used to obtain time-resolved flow fields of the vortex flow and breakdown with and without heating. Individual velocity profiles and velocity fields are presented, showing that flow behavior is dependent on much smaller scales than previously researched. Proper Orthogonal Decomposition is used to isolate energetically dominant modes and determine whether higher order modes are significant to the flow.

The evolution of unforced and weakly damped two-dimensional turbulence over random rough topography presents two extreme states. If the initial kinetic energy [Formula: see text] is sufficiently high, then the topography is a weak perturbation, and evolution is determined by the spontaneous formation and mutual interaction of coherent axisymmetric vortices. High-energy vortices roam throughout the domain and mix the background potential vorticity (PV) to homogeneity, i.e., in the region between vortices, which is most of the domain, the relative vorticity largely cancels the topographic PV. If [Formula: see text] is low, then vortices still form but they soon become locked to topographic features: Anticyclones sit above topographic depressions and cyclones above elevated regions. In the low-energy case, with topographically locked vortices, the background PV retains some spatial variation. We develop a unified framework of topographic turbulence spanning these two extreme states of low and high energy. A main organizing concept is that PV homogenization demands a particular kinetic energy level [Formula: see text]. [Formula: see text] is the separator between high-energy evolution and low-energy evolution.

The concept of a vortex, characterised by the rotational or swirling motion of fluids, lacks a universally accepted definition in the field of fluid mechanics. This ambiguity hampers turbulence research and can lead to confusion and misunderstandings. This thesis addresses this issue by implementing a newly proposed vortex identification criterion, namely the triple decomposition method (TDM), on direct numerical simulation (DNS) data of a linear compressor cascade. The criterion is compared to established techniques, and two different algorithms for its implementation are introduced. Notably, a newer algorithm significantly reduces computational time compared to the original one proposed by Koláˇr (2007), addressing a key limitation of the method. The results obtained through this criterion highlight its main purpose of eliminating shear contamination, which the other methods suffer from. This development expands the potential usage of the TDM in a wider range of cases and can make it more commonly employed in the literature.

We report on the response of magnetic domains in thin magnetite microstructures to weak external magnetic fields. Magnetite islands were grown by high-temperature oxygen-assisted molecular beam epitaxy on Ru(0001). The islands, micrometric wide and tens of nanometers thick are of high structural quality, each having been grown from a single nucleation center. Their magnetic domain structure is dominated by shape anisotropy, i.e., they present Landau flux-closure domain configurations. The magnetic domains of the in situ grown microstructures have been imaged directly by means of x-ray magnetic circular dichroism in photoemission electron microscopy while applying external, in-plane magnetic fields along different directions. Upon application of an external field the Landau state vortex core experiences a displacement along a direction perpendicular to the excitation field. The behavior of the Landau state under the applied magnetic field is quantified and compared with micromagnetic simulations. The results highlight the bulk-like magnetic properties of the nanometer-thick microstructures, opening the way to their possible use in technological applications.

Soft magnetic dots in the form of thin rings have unique topological properties. They can be in a vortex state with no vortex core. Here, we study the magnon modes of such systems both analytically and numerically. In an external magnetic field, magnetic rings are characterized by easy-cone magnetization and shows a giant splitting of doublets for modes with the opposite value of the azimuthal mode quantum number. The effect of the splitting can be refereed as a magnon analog of the topology-induced Aharonov-Bohm effect. For this we develop an analytical theory to describe the non-monotonic dependence of the mode frequencies on the azimuthal mode number, influenced by the balance between the local exchange and non-local dipole interactions.

Magnons are elementary excitations in magnetic materials and undergo nonlinear multimode scattering processes at large input powers. In experiments and simulations, we show that the interaction between magnon modes of a confined magnetic vortex can be harnessed for pattern recognition. We study the magnetic response to signals comprising sine wave pulses with frequencies corresponding to radial mode excitations. Three-magnon scattering results in the excitation of different azimuthal modes, whose amplitudes depend strongly on the input sequences. We show that recognition rates above 95\% can be attained for four-symbol sequences using the scattered modes, with strong performance maintained with the presence of amplitude noise in the inputs.

This data publication contains the numerical and experimental data for our paper "Modification of three-magnon splitting in a flexed magnetic vortex" submitted to Applied Physics Letters. The data contains mumax3 recipes, field- and power-dependent frequency spectra and spatial mode profiles of spin waves in a ferromagnetic disk in the vortex state. All files are sorted according to the figures in which they appear in the paper.

This data publication contains the data for our publication "Pattern recognition in reciprocal space with a magnon-scattering reservoir" published in Nature Communications. The dataset is structured in folders corresponding to the different figures in the paper. Folder Fig2 and Fig2 contain the experimental data measured with Brillouin-light-scattering microscopy. The files contain the data integrated for the measurement positions described in the methods section in a csv format. Forlder Fig4 contains the evaluated numerical data presented in the corresponding figure. The raw data generated with micromagnetic simulations is too large for this dataset and is available upon request by the authors.

© 2010 Optical Society of America. The financial support of the Spanish Ministry of Science and Innovation under project TEC2008-04105 and the Santander-Complutense project PR-34/07-15914 is acknowledged., Based on the analysis of second-order moments, a generalized canonical representation of a two-dimensional optical signal is proposed, which is associated with the angular Poincare sphere. Vortex-free ( or zero-twist) optical beams arise on the equator of this sphere, while beams with a maximum vorticity ( or maximum twist) are located at the poles. An easy way is shown how the latitude on the sphere, which is a measure for the degree of vorticity, can be derived from the second-order moments. The latitude is invariant when the beam propagates through a first-order optical system between conjugate planes. To change the vorticity of a beam, a system that does not operate between conjugate planes is needed, with the gyrator as the prime representative of such a system. A direct way is derived to find an optical system ( consisting of a lens, a magnifier, a rotator, and a gyrator) that transforms a beam with an arbitrary moment matrix into its canonical form., Spanish Ministry of Science and Innovation, Santander-Complutense, Depto. de Óptica, Fac. de Ciencias Físicas, TRUE, pub

This document contains the final Master Thesis Report to obtain the Master of Science on Aerospace Engineering (Flight Performance & Propulsion - Propulsion & Power) at the Delft University of Technology. The research work focuses on characterizing the interaction of a radial inlet turbine with a downstream diffuser through the size of the rotor tip gaps. In the implementation of power turbines it is common to add a diffuser downstream of it to lower the rotor exhaust pressure and thus increase power extraction for the same inlet conditions. However, diffusersare bulky and take a lot of space in the assembly. This lowers the power density of the machine, increases installation weight in transport applications, and installation costs in ground based operations. In the quest to obtain compact diffusers, researchers noticed that the non-dimensional static pressure recovery (Cp) of this device was higher when operating downstream of a turbine than with uniform inlet conditions. The publications in this field are relatively scarce, and thus there is a knowledge gap with immediate practical application. Some researchers have focused on the interaction of turbine vortical structures with the boundary layer of the diffuser. They have found out that under this conditions the boundary layer can support steeper pressure gradients without detaching. This is only applicable in very steep diffusers that would stall in isolation. Notably, all the publications in this field deal with axial machines, and as the text will show the picture changes considerably when applying the theory to radial turbines. This work studies another side of the problem. The text will focus on stable diffusers, and thus there is no boundary layer that needs reinforcement. Turbine rotor tip gaps generate an increase of entropy and reduce turbine power generation. However, these gaps also cast powerful vortexes that affect the diffuser flowfield. This project will study th, Aerospace Engineering | Flight Performance and Propulsion

The work presented throughout this file provides a study of the methods currently available for the identification of vortex within the fluid dynamics field. Particularly, this work presents a set of routines based on the methods aimed at being test and integrated so as to promote, later, its usage as a new powerful tool in research. The routines are intended to bring the advantages presented with third generation of vortex identification methods, as well as to overcome problems identified in previous generation methods. The usage of this brand-new methods might boost the research and understand slightly better the functioning of nature in this field, providing a clean view of flow features for a further implementation in industry. Concepts such as turbulence, coherent structures, vorticity, vortex or Rortex, among others are reviewed and have great relevance in the work. The study presents a complete literature review so as to establish a reference frame. Methodology comparison between the major methods, the mathematical and physical bases and procedures which are the bases of those, and the methods themselves. Moreover, the document includes the own development of Rortex and Omega methods routines and their testing in research cases in collaboration with Barcelona Supercomputing Center as part of MAESTRO project. The results presented evidence the clear ease of Ω to identify the correct vortex structures with 0.52 value and provide insight about the vortex core. As well, it is seen that the Rortex definition provides a huge amount of information about the structures if a proper rotational strength value is selected. Also, Rortex is seen to properly capture the rotation axis corresponding to determined structures.

Full-shell nanowires are hybrid nanostructures consisting of a semiconducting core encapsulated in an epitaxial superconducting shell. When subject to an external magnetic flux, they exhibit the Little-Parks (LP) phenomenon of flux-modulated superconductivity, an effect connected to the physics of Abrikosov vortex lines in type-II superconductors. We show theoretically that full-shell nanowires can host subgap states that are a variant of the Caroli-de Gennes-Matricon (CdGM) states in vortices. These CdGM analogs are shell-induced Van Hove singularities in propagating core subbands. We elucidate their structure, parameter dependence, and behavior in tunneling spectroscopy through a series of models of growing complexity. Using microscopic numerical simulations, we show that CdGM analogs exhibit a characteristic skewness towards higher flux values inside nonzero LP lobes resulting from the interplay of three ingredients. First, the orbital coupling to the field shifts the energy of the CdGM analogs proportionally to the flux and to their generalized angular momentum. Second, CdGM analogs coalesce into degeneracy points at flux values for which their corresponding radial wavefunctions are threaded by an integer multiple of the flux quantum. And third, the average radii of all CdGM-analog wavefunctions inside the core are approximately equal for realistic parameters and are controlled by the electrostatic band bending at the core/shell interface. As the average radius moves away from the interface, the degeneracy points shift towards larger fluxes from the center of the LP lobes, causing the skewness. This analysis provides a transparent interpretation of the nanowire spectrum that allows to extract microscopic information by measuring the number and skewness of CdGM analogs. Moreover, it allows to derive an efficient Hamiltonian of the full-shell nanowire in terms of a modified hollow-core model at the average radius.

Wind farm control is an area of research that looks to maximise the performance of individual but most importantly the collective performance of wind farms. The performance of turbines located in a wind farm is heavily dependent on the effects of turbine wakes, and improving the efficiency of wind farms by mitigating the wake effects is an ongoing and promising field of research. Simulating the wake effects of a turbine is generally done with computationally expensive physics based modelling techniques like CFD simulations. The computational complexity of these models limits the scope of optimisation that can be performed on wake mitigating controls strategies such as dynamic induction control. A substitute engineering model like the free vortex wake model could provide better insight into dynamic induction control by virtue of its computational efficiency allowing a wider optimisation parameter space. In this thesis an optimisation framework based on a 2D implementation of the free vortex wake model and genetic algorithm optimisation is used to investigate dynamic induction control for a simple two turbine wind farm beyond the research that has been done up to this point. While yet to be confirmed with higher fidelity simulations, initial results corroborate earlier findings for simple dynamic induction signals and additionally indicate that dynamic induction control could benefit from multiple harmonics. The optimisation framework achieves its goal in allowing a wider parameter space to be searched for optimisation, even on consumer grade desktop hardware, and shows potential as a tool for further investigation of dynamic induction control., Mechanical Engineering | Systems and Control

Humans have always looked at the heavens and wondered about the nature of the objects seen in the night sky. Discovering the secrets of space has been and is one of humanity’s greatest desires, however, each rocket launch involves a great economic cost. With the development of lighter rockets and the advances in electronics and other technologies in the 20th century, it became possible to lower costs and make rocket launches a common practice. Several methods to reduce the weight of the rockets have been proposed. This document is based on the Vortex-Cooling technique, a variant of film cooling which aims to cool the walls of the combustion chamber by means of a vortex flow in order to reduce its thickness. The main objective is to study the flow behavior of such a simplified vortex-cooled rocket engine in different configurations through numerical simulations. Firstly, a 3D model of Rocketdyne RS-25 (SSME) geometry is created from data sheets published by NASA. Besides, six different geometries of vortex-cooled rocket engines (VCRE) have been 3D modeled in order to carry out four analyses. Secondly, the characteristics of the mesh, a turbulent model for high-velocity flows, as well as the boundary conditions and all the parameters that allow computing the simulations of the SSME and vortex-cooled rocket engine have been selected. Using computational fluid dynamics (CFD) studies on the SSME it has been possible to verify the simulations obtained with Ansys Fluent. Once the parameters used in Fluent have been verified, it is proceeded to compute the simulations of 8 VCRE, modifying the number of inlets that generate the vortex; the angle of incidence of the inlets with respect to the axial direction; the diameter of the inlets; and finally, inlet velocity. After drawing conclusions from each analysis, the VCRE configuration chosen among the 8 cases studied is presented in more detail. The choice is based on the characteristics of the generated vortex, being the one t

The helicity is a key ingredient of the Nambu-bracket for the Euler equation for motion of an ideal fluid. This conference focuses on the helicity, as the common structure of the non-canonical Hamilton structure and the Nambu bracket for the ideal fluid motion, and deepens its mathematical and physical significance that transcends the subjects, by enlightening the symmetry behind its preservation. With interdisciplinary fusion, we explore a new theoretical framework and seek new applications of the helicity.

A slender-bodied vehicle with asymmetrically arranged protuberance generates strong side force due to asymmetric vortices, even at a low angle-of-attack. We investigated effects of the well-known RANS turbulence models [SA-R (Crot = 0.0, 1.0, and 2.0), SST, and SST-2003] by comparing the numerically obtained side force values on supersonic slender-body, along with the flow structure. As a result, all the SA-R models showed good agreement with the experiment regardless of the Crot (which controls the degree of modification from the original SA model), although a separation point on the protuberance side slightly changed depending on the Crot value. On the other hand, as for the SST models, when the vorticity was used to evaluate eddy viscosity (original SST) the side force exhibit 44% deviation from the experiment, whereas SST-2003, in which the strain rate was employed instead, significantly reduced the discrepancy to 0.7%.

Vertically stacked exchange coupled magnetic heterostructures of cylindrical geometry can host complex noncolinear magnetization patterns. By tuning the interlayer exchange coupling between a layer accommodating magnetic vortex state and an out-of-plane magnetized layer, one can efficiently realize new topological chiral textures such as cone state vortices and circular stripe domains. We study how the number of circular stripes can be controlled by both the interlayer exchange coupling and the sample geometrical parameters. By varying geometrical parameters, a continuous phase transition between the homogeneous state, cone state vortex, circular stripe domains, and the imprinted vortex takes place, which is analysed by full scale micromagnetic simulations. The analytical description provides an intuitive pictures of the magnetization textures in each of these phases. The possibility to realize switching between different states allows for engineering magnetic textures with possible applications in spintronic devices.

The system of vortices created by the hub and tip vortices of rotors and propellers is composed of two subsystems of helical vortices that have different radii and pitches. A similar system of external and internal vortices is created by some blade devices proposed to destabilize the tip vortices of helicopters. The steady solution of these systems of vortices was recently described. However, their stability was not studied. The stability of a system of multiple helical vortices was studied in this work using a complex-step technique to linearize the Biot-Savart law and the vorticity transport equations. It was noted that the hub and tip vortices do not interact and their linear stability can be treated separately, if the velocity field induced by one system is considered in the stability of the other. For a ratio of radius of 0.8, strong interaction between the vortices was observed, with an out-of-phase mechanism appearing as one of the main phenomena., Part of ISBN 9781713871163QC 20230801

This study is an inquiry into the experience of “vectorial” (i.e., directional) motion in music. It proposes a conceptual model for the experience of directional motion. It then applies the model interculturally, examining the relationship between Western and Eastern linear and cyclic cultural representations of time and corresponding compositional organisation. In its conclusion, it proposes geometrical models of Western and Eastern musical forms as helix and vortex, respectively, presenting musical works that exemplify these concepts. The major research question of the dissertation is “What is the nature of the experience of directional movement in music, and how can this experience be conceptually represented?”. It examines this question via the principal methodological process of a thought experiment. There are four research areas — music as phenomenological mechanics, composition as intercultural metaphor, applications to musical performance and analysis, and newly imagined instruments and novel compositional processes — and 12 research propositions — three primary, three secondary (two exegetical), two tertiary, and four artefactual. The primary research propositions examine the experience of vectorial motion in music, proposing a phenomenologically determined, hierarchically organised, multi-parameter, form-void vector field model. Referencing this model, the dissertation proposes that the experience of directional motion in music can be compared to principles from mechanics, albeit at a purely phenomenological level — a proposition that gives rise to the concept of phenomenological mechanics. In the application of the concept of phenomenological mechanics to composition, the dissertation proposes a novel characterisation of musical development as a phenomenological representation of the first and second laws of thermodynamics — as the phenomenological “organisation of sound” from low to high potential energy states, and from chaos to order. The secondary res

This paper presents an extended form of the blade element momentum theory (BEMT) for a co-axial rotor during hover. This extended form is an adaptation of the BEMT to fit the co-axial rotor working condition by iteratively solving the upstream and downstream rotor induced velocities. The downstream rotor influences the upstream rotor induced velocity, thrust and wake structure, whereas the upstream rotor induced velocity influences the downstream rotor. The extended form of the BEMT predicts the performance of the co-axial rotor as a function of blade size, pitch angle, angular velocity and the axial displacement between individual rotors. It is shown that the extended form of the BEMT accurately captures the trends and magnitudes of the co-axial rotor performance as a function of pitch angle and axial displacement in comparison with experimental and computational results. The sensitivity and limitations of this extended form are determined by adjusting relevant parameters and comparing the output with CFD results.*****This paper presents an extended form of the blade element momentum theory (BEMT) for a co-axial rotor during hover. This extended form is an adaptation of the BEMT to fit the co-axial rotor working condition by iteratively solving the upstream and downstream rotor induced velocities. The downstream rotor influences the upstream rotor induced velocity, thrust and wake structure, whereas the upstream rotor induced velocity influences the downstream rotor. The extended form of the BEMT predicts the performance of the co-axial rotor as a function of blade size, pitch angle, angular velocity and the axial displacement between individual rotors. It is shown that the extended form of the BEMT accurately captures the trends and magnitudes of the co-axial rotor performance as a function of pitch angle and axial displacement in comparison with experimental and computational results. The sensitivity and limitations of this extended form are determined by adjusti

We present acoustic drill beams, structured sound beams exhibiting a dynamic intensity distribution that matches the shape of a helix. The intensity distribution rotates along the beam axis with controlled direction and angular frequency, resembling in this way the shape of a mechanical drill bit. Acoustic drill beams emerge as the spatiotemporal interference of two confocal, detuned vortex beams. The beam parameters are fully tuneable. The detuned frequency, the detuned wavenumber and the detuned topological charge of the composing beams can be tuned to control the drill parameters such as the number of drill arms, the winding period, the rotational speed, and their direction. We show that elongated drill beams are obtained using two confocal high-order Bessel beams, allowing analytical solutions for optimal overlap. In addition, drill beams can also be synthesised using focused ultrasound vortices. Analytical, numerical, and experimental results are shown in the ultrasound regime using a low-cost device based on two 1-MHz confocal piezoelectric transducers and 3D printed acoustic holograms. This exotic structured wavefront opens new avenues for wave-matter interaction, such as contactless particle manipulation, matter processing or biomedical applications., Postprint (published version)

The purpose of this work is the development and validation of a Large Eddy Simulation (LES) model for the Aerodynamic’s Section at ESEIAAT in-house Vortex Cloud Method (VCM) fluid mechanics solver. The previous version of the program allowed for a less computationally expensive way to model 2D flow where separation or viscosity effects are important. The addition of a LES subroutine to this program allows studies in conditions where turbulence plays an important role. The subroutine was initially intended to be developed for a Fortran version of the ESEIAAT solver, which was optimised for performance. However, some problems with the Fortran version appearing at the testing stage required a switch to an older MATLAB version. The subroutine was rewritten in MATLAB code and the MATLAB version of the code adapted to accommodate it. Unfortunately, the MATLAB program had a much greater computational cost, which entailed a reduction of the scope of the validation of the program. Consequently, only preliminary validation of the program is carried out in the present work, comparing its performance with bibliographic data, both numerical and experimental. The results obtained are satisfactory and showed that the new LES version of the solver matches closely the results obtained by other similar programs. Despite this, there are still some aspects of the methodology that need more testing and adjustments before it could have full research use. Some questions also arose regarding the adequacy of the implemented LES turbulence model that are discussed in this work. This work has also highlighted the need of properly adjusting the program to each flow situation and has provided information on the different variables to be adjusted. Both physical and numerical (program stability and computational cost) considerations have to be taken into account for a successful adjustment.

With the increasing number of wind farm projects, a growing interest is seen towards the extension of wind turbine durability and the optimisation of energy production. A promising technology in this direction, is the use of lidars for remote sensing of wind fields and particularly for lidar-assisted control of wind turbines. Many investigations have been carried out to study the performance of lidars for measuring global wind statistics and test out lidar-assisted control strategies. However there appears to be less research efforts towards identifying and characterising localised and specific flow structures within the wind field, which is the aspect of focus in this study. Whilst the main objective is to detect flow structures, this study also dives into the lidar measurement process. A striking feature of this process is the extensive data processing procedure applied to reduce noise and provide a final output in the form of the line-of-sight velocity. As this consists on relatively large data reduction and condensing steps, the question therefore arises, is useful information lost during this process? To investigate the different stages of the lidar measurement process, a continuous wave lidar emulator was developed and served as the main tool for simulating lidar operation under controlled conditions. The first part of the investigation was performed on the Lamb-Oseen vortex, and was aimed at finding traces of the vortex within the lidar outputs. Besides, the line-of-sight velocity output, the Doppler spectrum was also analysed in a statistical sense with the use of moments. Three main indicators of the presence of the vortex were identified in the velocity envelope and the variations of the Doppler spectrum standard deviation and skewness across the vortex core. Tests were performed to see the effects of varying conditions (core size, noise, line-of-sight effects, etc.) on these patterns. From these sensitivity tests, a possible approach at, European Wind Energy Masters (EWEM) | Rotor Design Track

The added drag on a buoyant body traveling in a solid-body rotation flow has been rigorously studied over the last century with G.I. Taylor being the first one to describe it in 1922, a hundred years ago. A recent publication by Duinmeijer (2021) investigated the capacity of free-surface vortices to transport solids as a practical application to avoid solids accumulation in wastewater pump sumps. In that research, the assumption was made that a Taylor column exists upstream and downstream of the solids body, aiding the downward motion in the vortex core. This has however never been experimentally confirmed for free-surface vortex flows. The goal of this research is to experimentally check whether or not the Taylor-column induced drag force is the main mechanism for the downward motion of buoyant particles in a free surface vortex core. An experimental set-up consisting of a 600 x 1000mm (diameter x height) Perspex tank is used, in which controlled vortices can be generated. A novel combination of Laser Doppler Velocimetry (LDV) and Particle Tracking Velocimetry (PTV) is deployed simultaneously to obtain synchronised data of both the flow velocities and particle motion. The LDV device measures the tangential and axial flow components in a small measurement volume. Many point-measurements along a horizontal line through the vortex enable us to create the tangential and axial velocity profiles. A deconvolution process is applied on the LDV data to account for the spatial averaging effect of the LDV measurement volume and the wandering of the vortex core. The PTV system is used to determine the particle location over time, from which the velocity is obtained. For simplicity, only one type of particle - a buoyant sphere of 25 mm in diameter - is considered in this study. To obtain repeatability of the experiments, a particle dropping device is introduced to insert the sphere in the vortex core without entrapping air. A PID control system is added to the set-up to keep th, Civil Engineering | Hydraulic Engineering

The helicity is a key ingredient of the Nambu-bracket for the Euler equation for motion of an ideal fluid. This conference focuses on the helicity, as the common structure of the non-canonical Hamilton structure and the Nambu bracket for the ideal fluid motion, and deepens its mathematical and physical significance that transcends the subjects, by enlightening the symmetry behind its preservation. With interdisciplinary fusion, we explore a new theoretical framework and seek new applications of the helicity.

A slender-bodied vehicle with asymmetrically arranged protuberance generates strong side force due to asymmetric vortices, even at a low angle-of-attack. We investigated effects of the well-known RANS turbulence models [SA-R (Crot = 0.0, 1.0, and 2.0), SST, and SST-2003] by comparing the numerically obtained side force values on supersonic slender-body, along with the flow structure. As a result, all the SA-R models showed good agreement with the experiment regardless of the Crot (which controls the degree of modification from the original SA model), although a separation point on the protuberance side slightly changed depending on the Crot value. On the other hand, as for the SST models, when the vorticity was used to evaluate eddy viscosity (original SST) the side force exhibit 44% deviation from the experiment, whereas SST-2003, in which the strain rate was employed instead, significantly reduced the discrepancy to 0.7%.

We investigate the impact of the DC current-induced Ampère–Oersted feld on the dynamics of a vortex based spin-torque nano-oscillator. In this study we compare micromagnetic simulations performed using mumax3 and our analytical model based on the Thiele equation approach. The latter is improved by adding two important corrections to the Thiele equation approach. The frst is related to the magneto-static contribution and depends on the aspect ratio of the magnetic dot. The second is a full analytical description of the Ampère–Oersted feld contribution. The model describes quantitatively the simulation results in the resonant regime as well as the impact of the Ampère–Oersted feld. Depending on the relative orientation between the vortex in-plane curling magnetisation (chirality) and the Ampère–Oersted feld a strong splitting phenomenon appears in the fundamental properties (frequency and vortex core position) of the nano-oscillator. Thus, we show that the Ampère–Oersted feld should not be neglected as it has a high impact on the spin-torque vortex oscillator dynamics.

The use of the complex velocity potential and the complex velocity is widely disseminated in the study of two-dimensional incompressible potential flows. The advantages of working with complex analytical functions made this representation of the flow ubiquitous in the field of theoretical aerodynamics. However, this representation is not usually employed in linear stability studies, where the representation of the velocity as real vectors is preferred by most authors, in order to allow the representation of the perturbation as the complex exponential function. Some of the classical attempts to use the complex velocity potential in stability studies suffer from formal errors. In this work, we present a framework that reconciles these two complex representations using bicomplex numbers. This framework is applied to the stability of the von Karman vortex street and a generalized formula is found. It is shown that the classical results of the symmetric and staggered von Karman vortex streets are just particular cases of the generalized dynamical system in bicomplex formulation., QC 20221003

The limiting factor for most gas turbines has been the turbine inlet temperature. Furthermore, higher pressure ratios and turbine inlet temperatures improve the efficiencies on the gas turbine. A big focus has been on new schemes of internal cooling designs of turbine blades, using pressurized air from the engine compressor, and break-through in blade metallurgy, in order to achieve higher turbine inlet temperatures. Significant research has been ongoing for decades to design an internal cooling system for the first stage of the turbine blade consequently higher turbine inlet temperatures can be achieved. The challenging engineering intricacies related to improving the efficiency of a gas turbine engine come with the need to maximize the efficiency of the internal cooling of the turbine blade to withstand the high turbine inlet temperature. Understanding the fluid mechanics and heat transfer of internal blade cooling is therefore of paramount importance. This dissertation presents the impact of swirl flow cooling on the heat transfer of a gas turbine blade cooling passage to understand the mechanics of internal blade cooling. The focus is the continuous cooling flow that must be maintained via nonstop injection of tangential flow, whereby swirl flow is generated. The experimental investigation is presented first with three-dimensional (3-D) Stereo-Particle Image Velocimetry (Stereo-PIV) and second Thermochromic Liquid Crystal (TLC) of a swirl flow that models a gas turbine blade internal cooling configuration. The study is intended to provide an evaluation of the developments of swirl flow cooling methodology utilizing 3-D Stereo-PIV and liquid crystals. The objective of the experimental models is to determine the critical swirl number that has the potential to deliver the maximum axial velocity results with the highest heat transfer at three different Reynolds numbers, 7,000, 14,000, and 21,000. The swirl flow cooling methodology comprises of cooling air channeling

Solitons are a class of solution to equations that appear in the study of physics, particularly the study of fields and field theory. In the study of quantum field theory, solitons often present themselves as heavy degrees of freedom, and are therefore approached from a semi-classical perspective. Traditionally, the soliton is considered as the background field with which perturbative quantum states are defined with respect to. In this dissertation, we present the position that this approach is flawed. In particular, we suggest that using classical solitons as a starting point of analysis only narrowly covers the scope of the possibilities for solitons to manifest in quantum field theories. We show that there are classical solitons of infinite mass which in the quantum theory have their mass rendered finite. We additionally describe circumstances where quantum effects are large enough to significantly alter the net forces which act upon solitons, compared to the classical case. The conclusion is simple: quantum field theory generically contains a much larger space of dynamically accessible field configurations than classical field theory, and this facilitates the existence of quantum solitons that would not exist in the classical case.

Horizontal axis wind turbines (HAWTs) experience yaw misalignments due to the physical limitations of yaw controllers and various novel active yaw controls. Moreover, the motion of floating offshore wind turbines (FOWTs) accelerates yaw misalignment. The blade element momentum (BEM) method is widely used due to its computational efficiency for the design of HAWTs. Momentum theory, the basis of BEM, assumes steady flow and uniform induction field at the disc. Those assumptions are relaxed by engineering models to capture yaw and unsteady effects. Current yaw engineering models, however, are inaccurate since they do not capture the asymmetric wake expansion effect. Dynamic inflow models have been developed for non-yawed flow. Furthermore, the AVATAR project shows that BEM using fully coupled engineering models, the current yaw, dynamic inflow and various engineering models, suffers from significant deficiencies. This purpose of this paper, therefore, is to investigate dynamic effects for yawed flow, and determine if current dynamic inflow models are applicable in yawed conditions. The Glauert’s modified momentum theory is applied to dynamic inflow models to couple the two models. Among all coupled models, Øye, Yu PWVM and Yu FWVM DIM can capture asymmetric trends. However, the results show the significant deficiencies in phase delay on the actuator disc., Wind Energy

Aeration is one of the most cost intensive steps in water and wastewater treatment due to the large energy requirement for the creation of large surfaces for sufficient gas exchange as well as for providing efficient liquid transport in order to exchange saturated liquid elements at the surface with unsaturated ones from the bulk. In this work we show that geometrically constrained vortices in a hyperbolic funnel are a promising aeration technique as they meet these criteria and allow oxygen transfer coefficients up to 50 h−1, a number significantly higher than that of comparable methods like air jets or impellers (<10 h−1)., Energy Technology

A superconducting nanowire single-photon detector (SNSPD) is an emerging, and today commercially available technology, for photon-counting and quantum cryptography. Yet, the photon detection event is not fully understood and current modeling efforts require substantial computational resources which motivates studies of simpler models. This thesis introduces a model for vortex dynamics in thin-layered superconductors, such as SNSPDs, using a simplified approach, which leads to a 2D Coulomb gas model where the vortices are modeled as electrostatic charges. The model is carefully constructed from the method of images to describe a wire with open boundary conditions and an applied supercurrent. Subsequently, equilibrium and non-equilibrium properties are sampled with the Metropolis-Hastings algorithm and further analyzed and discussed. The suggested model is shown to be effective and successfully reproduces expected SNSPD behavior; most importantly critical behavior and voltage pulses which are directly measured during detection events. In conclusion, a 2D Coulomb gas model can be a preferred alternative for modeling vortex dynamics in SNSPDs at a small computational cost, motivating further development and studies., Supraledande nanotråd-enfotondetektorer (SNSPD:er) är en framväxande och idag kommersiellt tillgänglig teknologi som används för räknande av fotoner samt inom kvantkryptografi. Ändå är fotondetektionshändelsen inte helt förstådd och de nuvarande modelleringar kräver substantiell datorkraft vilket motiverar studier av enklare modeller. Det här examensarbetet introducerar en model för vortexdynamik i tunnskiktade supraledare såsom SNSPD:er genom ett förenklat tillvägagångssätt som leder till en 2D Coulombgas-modell där ett vortex modelleras som en elektrisk laddning. Modellen är noggrant konstruerad med öppna randvillkor och den så kallade frysta spegelbildsmetoden samt en pålagd superström. Då samlas mätvärden in på jämvikts- samt icke-jämviktsegenskaper hos systemet som vidare analyseras, jämförs och diskuteras. Den föreslagna modellen visas vara effektiv och reproducerar framgångsrikt förväntat beteende hos SNSPD:er; framför allt kritiskt beteende och spänningstoppar som direkt uppmäts i en fysisk detektionshändelse. Sammanfattningsvis, kan en 2D Coulombgas-modell vara ett föredraget alternativ för att modellera vortexdynamik hos SNSPD:er för en liten beräkningskostnad, vilket motiverar fler studier av detta.

The helicity is a key ingredient of the Nambu-bracket for the Euler equation for motion of an ideal fluid. This conference focuses on the helicity, as the common structure of the non-canonical Hamilton structure and the Nambu bracket for the ideal fluid motion, and deepens its mathematical and physical significance that transcends the subjects, by enlightening the symmetry behind its preservation. With interdisciplinary fusion, we explore a new theoretical framework and seek new applications of the helicity.

The helicity is a key ingredient of the Nambu-bracket for the Euler equation for motion of an ideal fluid. This conference focuses on the helicity, as the common structure of the non-canonical Hamilton structure and the Nambu bracket for the ideal fluid motion, and deepens its mathematical and physical significance that transcends the subjects, by enlightening the symmetry behind its preservation. With interdisciplinary fusion, we explore a new theoretical framework and seek new applications of the helicity.

With the increasing number of wind farm projects, a growing interest is seen towards the extension of wind turbine durability and the optimisation of energy production. A promising technology in this direction, is the use of lidars for remote sensing of wind fields and particularly for lidar-assisted control of wind turbines. Many investigations have been carried out to study the performance of lidars for measuring global wind statistics and test out lidar-assisted control strategies. However there appears to be less research efforts towards identifying and characterising localised and specific flow structures within the wind field, which is the aspect of focus in this study. Whilst the main objective is to detect flow structures, this study also dives into the lidar measurement process. A striking feature of this process is the extensive data processing procedure applied to reduce noise and provide a final output in the form of the line-of-sight velocity. As this consists on relatively large data reduction and condensing steps, the question therefore arises, is useful information lost during this process? To investigate the different stages of the lidar measurement process, a continuous wave lidar emulator was developed and served as the main tool for simulating lidar operation under controlled conditions. The first part of the investigation was performed on the Lamb-Oseen vortex, and was aimed at finding traces of the vortex within the lidar outputs. Besides, the line-of-sight velocity output, the Doppler spectrum was also analysed in a statistical sense with the use of moments. Three main indicators of the presence of the vortex were identified in the velocity envelope and the variations of the Doppler spectrum standard deviation and skewness across the vortex core. Tests were performed to see the effects of varying conditions (core size, noise, line-of-sight effects, etc.) on these patterns. From these sensitivity tests, a possible approach at, European Wind Energy Masters (EWEM) | Rotor Design Track

A superconducting nanowire single-photon detector (SNSPD) is an emerging, and today commercially available technology, for photon-counting and quantum cryptography. Yet, the photon detection event is not fully understood and current modeling efforts require substantial computational resources which motivates studies of simpler models. This thesis introduces a model for vortex dynamics in thin-layered superconductors, such as SNSPDs, using a simplified approach, which leads to a 2D Coulomb gas model where the vortices are modeled as electrostatic charges. The model is carefully constructed from the method of images to describe a wire with open boundary conditions and an applied supercurrent. Subsequently, equilibrium and non-equilibrium properties are sampled with the Metropolis-Hastings algorithm and further analyzed and discussed. The suggested model is shown to be effective and successfully reproduces expected SNSPD behavior; most importantly critical behavior and voltage pulses which are directly measured during detection events. In conclusion, a 2D Coulomb gas model can be a preferred alternative for modeling vortex dynamics in SNSPDs at a small computational cost, motivating further development and studies., Supraledande nanotråd-enfotondetektorer (SNSPD:er) är en framväxande och idag kommersiellt tillgänglig teknologi som används för räknande av fotoner samt inom kvantkryptografi. Ändå är fotondetektionshändelsen inte helt förstådd och de nuvarande modelleringar kräver substantiell datorkraft vilket motiverar studier av enklare modeller. Det här examensarbetet introducerar en model för vortexdynamik i tunnskiktade supraledare såsom SNSPD:er genom ett förenklat tillvägagångssätt som leder till en 2D Coulombgas-modell där ett vortex modelleras som en elektrisk laddning. Modellen är noggrant konstruerad med öppna randvillkor och den så kallade frysta spegelbildsmetoden samt en pålagd superström. Då samlas mätvärden in på jämvikts- samt icke-jämviktsegenskaper hos systemet som vidare analyseras, jämförs och diskuteras. Den föreslagna modellen visas vara effektiv och reproducerar framgångsrikt förväntat beteende hos SNSPD:er; framför allt kritiskt beteende och spänningstoppar som direkt uppmäts i en fysisk detektionshändelse. Sammanfattningsvis, kan en 2D Coulombgas-modell vara ett föredraget alternativ för att modellera vortexdynamik hos SNSPD:er för en liten beräkningskostnad, vilket motiverar fler studier av detta.

The aerodynamic complexity of the underbody surfaces of conventional road vehicles is a matter of fact. Currently available literature is focused mainly on very simple Ahmed-body geometries as opposed to realistic car shapes, due to their complexity and computational cost. We attempted to understand the flow behaviour around different realistic conventional road car geometries, and we provide an extensive evaluation of the aerodynamic loads generated. The key findings of this article could potentially set a precedent and be useful within the automotive industry’s investigations on drag-reduction mechanisms or sources of downforce generation. The novelty of the work resides in the realistic approach employed for the geometries and in the investigation of barely researched aerodynamic elements, such as front diffusers, which might pave the way for further research studies. A baseline flat-underfloor design, a 7¿ venturi diffuser-equipped setup, a venturi diffuser with diagonal skirts, and the same venturi diffuser with frontal slot-diffusers are the main configurations we studied. The numerical predictions evaluated using RANS computational fluid dynamics (CFD) simulations deal with the aerodynamic coefficients. The configuration that produced the highest downforce coefficient was the one composed of the 7¿ venturi diffuser equipped with diagonal sealing skirts, achieving a CL value of -0.887, which represents an increase of around 1780% with regard to the baseline model. That achievement and the gains in higher vertical loads also entail a compromise with an increase in the overall air resistance. The performance achieved with diffusers in the generation of downforce is, as opposed to the one obtained with conventional wings, a cleaner alternative, by avoiding wake disturbances and downwash phenomena., Peer Reviewed, Postprint (published version)

Aeration is one of the most cost intensive steps in water and wastewater treatment due to the large energy requirement for the creation of large surfaces for sufficient gas exchange as well as for providing efficient liquid transport in order to exchange saturated liquid elements at the surface with unsaturated ones from the bulk. In this work we show that geometrically constrained vortices in a hyperbolic funnel are a promising aeration technique as they meet these criteria and allow oxygen transfer coefficients up to 50 h−1, a number significantly higher than that of comparable methods like air jets or impellers (<10 h−1)., Energy Technology

The added drag on a buoyant body traveling in a solid-body rotation flow has been rigorously studied over the last century with G.I. Taylor being the first one to describe it in 1922, a hundred years ago. A recent publication by Duinmeijer (2021) investigated the capacity of free-surface vortices to transport solids as a practical application to avoid solids accumulation in wastewater pump sumps. In that research, the assumption was made that a Taylor column exists upstream and downstream of the solids body, aiding the downward motion in the vortex core. This has however never been experimentally confirmed for free-surface vortex flows. The goal of this research is to experimentally check whether or not the Taylor-column induced drag force is the main mechanism for the downward motion of buoyant particles in a free surface vortex core. An experimental set-up consisting of a 600 x 1000mm (diameter x height) Perspex tank is used, in which controlled vortices can be generated. A novel combination of Laser Doppler Velocimetry (LDV) and Particle Tracking Velocimetry (PTV) is deployed simultaneously to obtain synchronised data of both the flow velocities and particle motion. The LDV device measures the tangential and axial flow components in a small measurement volume. Many point-measurements along a horizontal line through the vortex enable us to create the tangential and axial velocity profiles. A deconvolution process is applied on the LDV data to account for the spatial averaging effect of the LDV measurement volume and the wandering of the vortex core. The PTV system is used to determine the particle location over time, from which the velocity is obtained. For simplicity, only one type of particle - a buoyant sphere of 25 mm in diameter - is considered in this study. To obtain repeatability of the experiments, a particle dropping device is introduced to insert the sphere in the vortex core without entrapping air. A PID control system is added to the set-up to keep th, Civil Engineering | Hydraulic Engineering