2D CFD Modeling of H-Darrieus Wind Turbines Using a Transition Turbulence Model

AbstractIn the present paper, the authors describe the strategy to develop a 2D CFD model of H-Darrieus Wind Turbines. The model was implemented in ANSYS Fluent solver to predict wind turbines performance and optimize its geometry. As the RANS Turbulence Modeling plays a strategic role for the prediction of the flowfield around wind turbines, different Turbulence Models were tested. The results demonstrate the good capabilities of the Transition SST turbulence model compared to the classical fully turbulent models. The SST Transition model was calibrated modifying the local correlation parameters through a series of CFD tests on aerodynamic coefficients of wind turbines airfoils. The results of the tests were implemented in the 2D model of the wind turbine. The computational domain was structured with a rotating ring mesh and the unsteady solver was used to capture the dynamic stall phenomena and unsteady rotational effects. Both grid and time step were optimized to reach independent solutions. Particularly a high quality 2D mesh was obtained using the ANSYS Meshing tool while a Sliding Mesh Model was used to simulate rotation. Spatial discretization algorithm, interpolation scheme, pressure - velocity coupling and turbulence boundary condition were optimized also.The 2D CFD model was calibrated and validated comparing the numerical results with two different type of H-Darrieus experimental data, available in scientific literature. A good agreement between numerical and experimental data was found.The present work represents the basis to develop an accurate 3D CFD unsteady model and may be used to validate the simplest 1D models and support wind tunnel experiments

The true story of Yeti, the "abominable" heterochromatic gene of drosophila melanogaster

The Drosophila Yeti gene (CG40218) was originally identified by recessive lethal mutation and subsequently mapped to the deep pericentromeric heterochromatin of chromosome 2. Functional studies have shown that Yeti encodes a 241 amino acid protein called YETI belonging to the evolutionarily conserved family of Bucentaur (BCNT) proteins and exhibiting a widespread distribution in animals and plants. Later studies have demonstrated that YETI protein: (i) is able to bind both subunits of the microtubule-based motor kinesin-I; (ii) is required for proper chromosome organization in both mitosis and meiosis divisions; and more recently (iii) is a new subunit of dTip60 chromatin remodeling complex. To date, other functions of YETI counterparts in chicken (CENtromere Protein 29, CENP-29), mouse (Cranio Protein 27, CP27), zebrafish and human (CranioFacial Development Protein 1, CFDP1) have been reported in literature, but the fully understanding of the multifaceted molecular function of this protein family remains still unclear. In this review we comprehensively highlight recent work and provide a more extensive hypothesis suggesting a broader range of YETI protein functions in different cellular processes

Evaluation of the Radial Flow Effects on Micro HAWTs through the Use of a Transition CFD 3D Model – part I: State of the Art and Numerical Model Review

Abstract The radial flow along a rotating blade is a fluid dynamic behavior that specifically affects the flow field of HAWTs. The physical effects of such flow on the rotor performance are not yet fully understood due to the complexity of the phenomenon and its high dependence on three dimensionality and Reynolds numbers. In the first part of this paper the authors reviewed the State of the Ar tof physics and modeling of radial flows. Some researchers have proposed empirical models to take into account the centrifugal pumping inside 1D codes. It was found in general, that the radial flow acts on the blades, increasing the forces and delaying the stall. Compared to a simple 2D condition, the aerodynamic coefficients are hence increased. Obviously, this phenomenon is heavily dependent on rotational speed as the centrifugal force increases with the square of the angular velocity and only linearly with the radial distance. So, due to higher rotational speed, the aerodynamics of mini and micro rotors is mostly influenced by the radial flow rather than the large rotors. The combined effects of both transitional and radial flow were evaluated in the present work using an accurate CFD 3D model as there was no specific literature in this particular field. This model, developed by the authors, was based on a RANS, four equations, transition turbulence model and it was calibrated and validated on a suitably designed micro rotor. The rotor was tested in the subsonic wind tunnel owned by the University of Catania. A review of the modeling and validation strategy is presented in the first part of this paper while the extrapolated data and the post-processing is presented in the second part, thus finding results of significant interest

Evaluation of the Radial Flow Effects on Micro HAWTs through the Use of a Transition CFD 3D Model – Part II: Post-processing and Comparison of the Results☆

Abstract The importance and the complexity of the phenomena related to the development of radial flows is demonstrated in the first part of this paper. In order to further study the radial flow effects and to extend the analysis to laminar and transitional flows, the authors used a CFD 3D model, validated in the wind tunnel owned by the University of Catania. In the second part of this paper, the authors describe the strategy which was used to post-process the simulation results. Furthermore, a comparison of the results was made. Several simulations were first carried out at various wind and rotational speeds. Angles of Attack and aerodynamic coefficients were evaluated on cylindrical surfaces at different radial stations using the ANSYS Fluent Solver and ANSYS Post. Local velocities and forces, related to the sectional airfoil, were obtained in each cylindrical surface along with pressure coefficient distributions. In this way, it was possible to demonstrate the close relationship between radial flows and the strong depressurization of the suction side of the blade. Moreover, the results proved that the increase of lift and drag coefficients is linked to rotational speed and Angle of Attack as well. The radial effects were found to be enforced by laminar and transitional flows related to low Reynolds numbers. This will affect both design and analysis of wind rotor performance, more so than that which was originally suggested by empirical stall delay models

Migdal effect and photon Bremsstrahlung: improving the sensitivity to light dark matter of liquid argon experiments

The search for dark matter weakly interacting massive particles with noble liquids has probed masses down and below a GeV/c^2. The ultimate limit is represented by the experimental threshold on the energy transfer to the nuclear recoil. Currently, the experimental sensitivity has reached a threshold equivalent to a few ionization electrons. In these conditions, the contribution of a Bremsstrahlung photon or a so-called Migdal electron due to the sudden acceleration of a nucleus after a collision might be sizable. In the present work, we use a Bayesian approach to study how these effects can be exploited in experiments based on liquid argon detectors. In particular, taking inspiration from the DarkSide-50 public spectra, we develop a simulated experiment to show how the Migdal electron and the Bremsstrahlung photon allow to push the experimental sensitivity down to masses of 0.1 GeV/c^2, extending the search region for dark matter particles of previous results. For these masses we estimate the effect of the Earth shielding that, for strongly interacting dark matter, makes any detector blind. Finally, we show how the sensitivity scales for higher exposure.Comment: 30 pages, 13 figures, 2 table

Mechanical design and deployment of a quasi-rhombic pyramid drag sail for safe de-orbit of a 3U CubeSat

Orbital debris is rapidly becoming a more prevalent and alarming obstacle that, without immediate intervention, will undoubtedly become disastrous for human activity in space. The University of Glasgow’s microsatellite society, GU Orbit, has taken action to equip its 3U CubeSat ASTRAEUS-01 with a drag sail de-orbit device. This payload represents a simple and low-cost solution for the mitigation of debris in Low Earth Orbit (LEO) and is expected de- orbit the CubeSat within 12 to 24 months, depending on solar activity. These aspects are deemed fundamental for the mission and align with GU Orbit’s ethics of promoting space sustainability and accessibility. As a student society, the aim of this research is to demonstrate the viability of a drag sail technology in the absence of large monetary investment.a In this article, the studies on the structure, material and Hold-Down and Release Mechanism (HDRM) of the drag sail system are evaluated and briefly discussed. The discussion starts by illustrating the 7m2 quasi-rhombic drag sail that will deploy to increase the satellite's atmospheric drag and allow the spacecraft to lose altitude and re-enter the atmosphere. Various aspects of the geometry and folding technique used to fit the drag sail on the CubeSat are analysed. Phenomena of material degradation such as thermal and oxygen degradation have been accounted for in the design to mitigate their effect over the duration of the mission. Tape spring booms coiled around a spool will release the drag sail from its folded state maintained throughout the mission. These have been dimensioned through a mathematical model in order to provide optimum deployment dynamics for the drag sail. The paper describes also how a simple and economic nichrome burn-wire HDRM has been integrated with the drag sail design to trigger the release sequence of the cover doors and the drag sail itself

Developing Inorganic Approaches to Polymerization and Bioconjugation

Multi-disciplinary approaches to problem solving are needed given the increasing complexity of fundamental scientific questions. This dissertation undertakes a holistic approach to research and tackles challenges spanning the biology, chemistry, and materials interface. The central theme for most projects involves applying inorganic and main group chemistry to develop new bioconjugation strategies or polymerization methodologies to access novel materials. Chapter One describes efforts in understanding the effects of trehalose polymers towards protein stabilization. The stabilization capability of polymers made from a set of styrenyl-based trehalose monomer regioisomers were studied. Polymers of each trehalose monomer regioisomer and one polymer which contained all three isomers combined were synthesized. All polymer regioisomers stabilized insulin to a similar degree towards agitation and heat stress.Chapter Two details the initial discovery that icosahedral boron-rich cluster compounds of the type B12(OR12)—where “R” can be any alkyl or aryl group— could be utilized as strong one-electron photooxidants thereby initiating the polymerization of olefins. The perfunctionalized clusters are able to initiate polymerization of a range of styrene substrates under blue LED irradiation. Also demonstrated, is the visible light initiated, metal free cationic polymerization of isobutylene into poly(isobutylene).Chapter Three introduces a new class of carborane-based chain-transfer agents (CTA’s) to be used in reversible addition-fragmentation chain-transfer (RAFT) polymerization. The carborane-based CTA’s mediate the controlled polymerization of monomers such as styrene, N-isopropylacrylamide, and methyl acrylate to produce monodisperse carborane terminated polymers. The carborane-based scaffold, appended on the polymer chain end, serves as a general 1H NMR spectroscopic handle used to elucidate polymer molecular weight. Binding of carborane into the hydrophobic cavity of β-cyclodextrin was demonstrated by isothermal titration calorimetry thereby validating its potential use as an affinity label. The carborane RAFT agents also act as Raman active probes.Chapter Four explores the reactivity of gold(III) organometallic complexes in the context of bioconjugation chemistry. The gold(III) organometallic complexes mediated the conjugation of small molecule substrates which included heterocycles, an anti-cancer drug, biotin, and low molecular weight PEG to cysteine residues on biomolecules. The bioconjugation reactions proceeded rapidly, with high efficiency, and in a broad pH range