Kinetic Energy Distributions Research Articles

EXPERIMENTAL CHARACTERISATION OF THE WAKE OF A BOTTOM-MOUNTED TWO TANDEM OF CYLINDERS PLACED IN A HIGH VELOCITY AREA

Following the development of renewable marine energies, the characterization of areas with strong marine currents has become necessary. The Normandy coasts (France) are among the sites suitable for the installation of tidal turbine parks because they have significant energy potential. Projects to install machines in these sites raise questions about various factors affecting the performance of the turbines that would be placed there.
 We are currently working on the understanding of the mechanisms leading to the generation of ambient flow turbulence on the seabed. More particularly, we are interested in the impact of the complexity of the bathymetry on the organization of the wake generated. To simplify the modeling of the bathymetry of the seabed, we use generic cylindrical obstacles of rectangular section. The obstacles are placed on the bottom of the study area of ​​the Hydrodynamic Tunnel of the LUSAC laboratory and occupy its entire width. Measurements are made using Particle Image Velocimetry (PIV-2D) for a velocity flow of 3 m/s.
 In a first time, in a previous contribution, was evaluated the impact of the ratio between the Height and the Width (H/W) of the cross section of the cylinder on the organization of the near wake. Indeed, the average velocity fields obtained for six different obstacles, highlighted the modification of the organization of the flow topology. The variation of this ratio H/W leads to the modification of the length of the average vortex formation zone, implies the presence of two or even three average recirculation zones in the near wake of the cylinder and leads to the possible presence of a recirculation zone average placed upstream of the cylinder.
 Nevertheless, in the seabed the structures are not isolated. In the contrary, on the seabed we can observe successions of structures anchored on the funds, leading to the interaction of a structure with the wake generated upstream by another one structure. The experimental study with the characterization of the flow around a tandem of “long” cylindrical obstacles of square section (side H). The distance between these two cylinders is equal to 2H.
 As expected, in the present study, it can be observed the modifications of the topology of the mean flow and the distribution of the turbulent kinetic energy. Indeed, the interaction between the mean recirculation, generated downstream each cylinder, is shown.

Cooperative Primary Frequency Regulation Strategy of Wind Storage System Based on Variable Inertia Coefficient

Direct-drive permanent magnet synchronous wind turbine-generator (PMSG) is connected to the grid through the rotor side and grid side converter. The rotor speed is decoupled from the grid frequency, so PMSG output power cannot respond to the change in system frequency. However, with the gradual increase of wind power penetration, the static stability of system frequency is weakened, so the new grid-connected wind farm should have the ability of active frequency support. This paper proposes a cooperative primary frequency regulation (PFR) strategy for wind storage systems based on variable inertia coefficient. PMSG provides inertia based on the distribution of rotational kinetic energy and modifies the polarity of the inertia coefficient at the frequency recovery stage to speed up the frequency recovery. Droop control is realized by energy storage and variable power tracking control (VPPT). Energy storage and VPPT respectively suppress the frequency decrease/increase and only participate in the down/up single-side PFR, which can reduce the energy storage configuration capacity. And a safety discharge coefficient considering the state of charge (SOC) is introduced to prevent over-discharge of energy storage devices when outputting energy. Finally, the PFR capability of PMSG under the proposed control strategy is verified by simulation results.

Fission fragment mass distribution of 187Ir

The fission fragment mass and total kinetic energy (TKE) distributions were studied for 187Ir populated using 12C + 175Lu reaction at excitation energies 24.8, 23.3, 20.8, and 16.7 MeV above the saddle point. Fission fragments (FF) were detected using position sensitive MWPC’s kept at a folding angle. The mass of the fragment was calculated using Time-of-Flight (TOF) difference method. The multi Gaussian fit to the extracted mass distributions shows the presence of narrower microscopic components corresponding to Z = 38 and 45 in addition to the liquid drop component at lower excitation energies. The GEF model predicts significant asymmetric components at all the measured energies. The TKE distribution investigations suggest the dominance of macroscopic liquid drop components at all energies.

Prompt fission neutron multiplicity in the 239Pu(n, f) reaction and its energy dependence

Measuring prompt fission neutrons to high precision is an experimental challenge, especially for radioactive fissioning nuclides. However, accurate average multiplicities, , and kinetic energy distributions of prompt fission neutrons are essential for fundamental and applied nuclear physics. We present here a recent measurement of the 239Pu (n,f) as a function of the incident-neutron energy, over the range 1-700 MeV. The measurement was performed with a cutting-edge setup and an innovative technique, which allowed to minimize and account for the main sources of bias. An unprecedented precision was therefore achieved. Our data are compared to GEF predictions as well as to evaluated libraries. For the first time, at low energies, the ENDF/B-VIII.0 nuclear data evaluation is validated with an independent measurement and the evaluated uncertainty reduced by up to 60%. This work paves the way to precisely measure prompt fission neutron multiplicities on highly radioactive nuclei.

(Invited) Redox Chemistry Driven by Atmospheric Pressure Plasma Jet

Plasmas may be considered as mixed ionic and electronic conductors. From an electrochemical point of view, a conducting gas presents a wonderful opportunity to explore redox reactions without all the restrictions a solvent medium provides. Identifying a plasma medium suitable to allow electrochemical measurements can be technically challenging, often due to the electrical energy used to create the plasma. However, atmospheric pressure plasma jets (APPJ)1&2 have been shown to be accessible and convenient as laboratory plasma sources. They present a medium that may be considered as an electrode, due to the presence of electrons or as electrolytes, due to their electrical conduction.3 Although its definition is not too important, the presence of free electrons gives an opportunity to drive reduction processes.The interesting aspect of non-thermal plasmas, and the root of their interesting chemistry, is partly due to the imbalance of thermal kinetic energy distribution between the electron and all the other species, neutral or ionized. As a consequence plasma jets are found in routine industrial applications such as etching or cleaning of surfaces for adhesion promotion. Furthermore, there is a growing body of evidence to suggest that APPJ may be used for the treatment of solid tumors. These highly energized electrons can drive redox reactions, as well as other chemical reactions, at solid or liquid can be unexpected. In this presentation I will explore the use of APPJ for reduction of metal oxides under potentiostatic control and material synthesis.4-6 References Ratcliffe, L.V., et al., Surface analysis under ambient conditions using plasma-assisted desorption/ionization mass spectrometry. Analytical Chemistry, 2007. 79(16): p. 6094-6101.Golda, J., et al., Concepts and characteristics of the 'COST Reference Microplasma Jet'. Journal of Physics D-Applied Physics, 2016. 49(8).Rumbach, P.; Bartels, D. M.; Sankaran, R. M.; Go, D. B., The solvation of electrons by an atmospheric-pressure plasma. Nature Communications 2016, 6, 7248.Sener, M. E., Quesada Cabrera, R., Parkin, I.P., Caruana, D. J., Facile formation of black titania films using an atmospheric-pressure plasma jet, Green Chemistry 2022 , 24, 2499-2505.Sener, M. E., Palgrave, R., Quesada Cabrera, R., Caruana, D. J., Patterning of Metal Oxide thin Films using H2/He Atmospheric Pressure Plasma Jet. Green Chemistry 2020, 22, 1406-1413.Sener, M. E.; Caruana, D. J., Modulation of copper(I) oxide reduction/oxidation in atmospheric pressure plasma jet. Electrochemistry Communications 2018, 95, 38-42.

Numerical study of the effects of excess air ratio on passive pre-chamber jet performance and ignition mechanism

Pre-chamber (PC) ignition is a promising lean-burn technology to improve the efficiency of spark ignition (SI) engines while achieving ultra-low NOx emissions. However, the significant effects of the excess air ratio (λ) on the PC jet performance and ignition mechanism were still not fully unraveled. The current study numerically investigated the jet characteristics and combustion behaviors of a narrow-throat PC with two rows of orifices on a passive PC engine fueled with methane. The numerical model was validated extensively by the pressure, heat release rate, and natural flame luminosity (NFL) imaging of the PC flame jet. A detailed comparison of the NFL images of the jets and the simulated flame iso-faces presented excellent matching in the flame jet penetration and propagation process. The results reveal that the λ = 0.9 case has the best jet performance, but it doesn’t lead in every jet characteristic. For instance, the jet temperature is highest under λ = 1.0, and OH concentration is most under λ = 1.1. The transition from cold jet to flame jet produces noticeable jet non-uniformity, which is reported for the first time. This observation can be remarked as a more accurate indication of the initiation of pre-chamber flame jet discharge. The asymmetrical mixture inflow from the main chamber produces asymmetrical turbulent kinetic energy (TKE) and temperature distributions; these result in different flame propagation in the PC, jet non-uniformity, and varied stages of jet discharge. The upper jets are quenched in every case because of the much higher TKE, while the lower jets don’t present quenching when the λ ranges from 0.9 to 1.3; especially, the λ = 1.1 case has the best ignition performance for its most OH radicals. The “jet ignition regime”, in which flame quenching takes place, results in highly non-uniform flame propagation and low flame propagation speed. The ultra-rich case shows more signs of jet ignition and thus exhibits worse jet performance than the lean cases. This study uncovers the mechanisms and the optimal λ value for the pre-chamber ignition of the main chamber charge, providing valuable guidance for PC design.

Large eddy simulation of plunging solitary wave: Understanding the breaking and turbulent mechanisms along shoaling region

A large eddy simulation (LES) is conducted to investigate the distribution of turbulence kinetic energy (TKE) under a plunging solitary wave over a 1:15 slope. This study provides a novel contribution to the field by examining the roles of resolved and sub-grid scale TKE in plunging solitary waves at the different stages of wave breaking. Furthermore, comparing the performances of two sub-grid scale (SGS) models in simulating the distribution of TKE was carried out to identify their performances. The separate investigation of these components in the context of wave breaking and recognizing the importance of an appropriate sub-grid scale model to consider the effects of small-scale eddies provide a significant advancement in understanding coastal morphological changes and nearshore sediment transport. Both the zero-equation and one-equation SGS models demonstrated acceptable performance in simulating water surface and kinematic properties. The one-equation SGS model, however, provided more accurate results on TKE transport during the breaking process and as the wave approaches its collapsing point. The study’s results reveal that an SGS model’s inability to simulate TKE transport (such as in the zero equation model) leads to inaccurate simulations of the TKE level and breaking location in the breaking zone. Additionally, the results of the one-equation model demonstrated that the maximum horizontal fluid velocity around the wavefront surface is a better predictor of breaking wave onset than the horizontal fluid velocity at the wave crest.

Double layer acceleration of ions with differently charged states in a laser induced plasma

The electric field driven acceleration of plasma ions is an intrinsic effect in laser-induced plasma plumes and is responsible for the generation of high-energy ions. At high laser fluences (≥ 2 J/cm2), multiply charged ions are formed and affect the plume expansion dynamics. In this paper, we used kinetic energy-resolved mass spectrometry to investigate the relative abundance and kinetic energy distributions of singly- and doubly-charged ions produced by KrF-laser ablation of nine different oxide targets. The doubly charged metal ions with a lower mass-to-charge (m/z) ratio show narrow energy distributions at high average kinetic energies coinciding with the cutoff energies for the singly-charged ion distributions. The observation suggests that the recombination of higher charged ions plays a prominent role in the formation of the high-energy tail for singly-charged ions. The results are discussed in terms of component volatility and a dynamic double layer, where ions with different m/z values experience different accelerations.

Electron circular dichroism in hot electron emission from metallic nanohelix arrays.

We investigate the electron emission from 3D chiral silver alloy nanohelices initiated by femtosecond laser pulses with a central photon energy of hν = 1.65eV, well below the work function of the material. We find hot but thermally distributed electron spectra and a strong anisotropy in the electron yield with left- and right-circularly polarized light excitations, which invert in signbetween left- and right-handed helices. We analyze the kinetic energy distribution and discuss the role of effective temperatures. Measurements of the reflectance and simulations of the absorbance of the helices based on retarded field calculations are compared to the anisotropy in photoemission. We find a significant enhancement of the anisotropy in the electron emission in comparison to the optical absorption. Neither simple thermionic nor a multiphoton photoemission can explain the experimentally observed asymmetries. Single photon deep-UV photoemission from these helices together with a change of the work function suggests a contribution of the chirally induced spin selectivity effect to the observed asymmetries.

Investigation of heat transfer and damage characteristics of high pressure abrasive water jet impacting high temperature sandstone

ABSTRACT Efficient breaking of hard mineral rocks is an important prerequisite for deep metal mining. In order to study the rock breaking mechanism of abrasive water jet erosion of high-temperature hard rock in deep ground, the temperature deformation evolution law during the process of jet impact on rocks was simulated and experimentally studied. The results show that the distribution of jet pressure, jet velocity, and jet turbulent kinetic energy near the residence point of the jet impingement wall is generally high in the middle and low in the outside. The heat transfer distance r on the rock surface is approximately (1.5–2.0) times the nozzle diameter, and the heat transfer distance inside the rock is (1.0–1.5) times the nozzle diameter. The maximum heat flux density at the jet cooling wetting boundary can reach 450 W/mm2. Within 0–3 seconds of the erosion process, the average surface temperature sharply decreases and exhibits a downward trend of jet stagnation point radiating outward. The radius of jet cooling influence gradually increases. Due to the impact cooling effect, tensile stress is generated at the top of the rock sample, and the tensile stress in the lower part of the rock is converted into compressive stress. With the increase of jet pressure and treatment temperature, the area and range of erosion pits significantly increase, and there is a significant phenomenon of thermal cracking around the erosion pits. The research conclusion can provide new ideas and basis for hydraulic breaking of high-temperature hard rocks in deep ground.

Study of the erosion and redeposition of W considering the kinetic energy distribution of incident ions through a semi-analytical model

In today’s nuclear fusion devices, erosion of high-Z metallic plasma-facing materials (PFMs) is mainly caused by physical sputtering. That is, by the exchange of energy between plasma ions and the atoms in the walls. In most of the numerical codes currently in use impinging plasma is approximated as a fluid. By averaging the incident particles’ energy distribution the high-energy population of the eroded material is underestimated. For heavy materials such as W, high-energy eroded particles tend to ionize far from the wall and they are less affected by the sheath electric field hence, not being attracted back to the wall, they have a higher chance to contaminate the core plasma. This could in turn result in an underestimation of the net erosion sources. In this work, a semi-analytical model was developed to include the energy distribution of the incident particles. Then, by Monte Carlo method, the net erosion of tungsten from a smooth PFM was calculated. The results show that the kinetic description in energy is important only for incident particles ionized once. For instance, it is particularly important for plasma ions such as Deuterium. It is seen that Deuterium contribution to the W net sources is not always negligible if compared to light impurities or to tungsten self-sputtering in the range of plasma parameters tested. Finally, results show that the difference between the fluid and kinetic models becomes more pronounced for high-screening plasma conditions.

Multiple pendulum and nonuniform distribution of average kinetic energy.

Multiple pendulums are investigated numerically and analytically to clarify the nonuniformity of average kinetic energies of particles. The nonuniformity is attributed to the system having holonomic constraints and it is consistent with the generalized principle of the equipartition of energy. With the use of explicit expression for Hamiltonian of a multiple pendulum, approximate expressions for temporal and statistical average of kinetic energies are obtained, where the average energies are expressed in terms of masses of particles. In a typical case, the average kinetic energy is large for particles near the end of the pendulum and small for those near the root. Moreover, the exact analytic expressions for the average kinetic energy of the particles are obtained for a double pendulum.

On the distributed blowing control of flow around a square cylinder at a low Reynolds number

This paper numerically investigates the distributed blowing control of the flow around a square cylinder at a low Reynolds number of Re=200. The air holes are placed at the windward or leeward stagnation points. The control effect of the unsteady aerodynamic forces is notably different with different spanwise distributions of air holes, which is represented by the dimensionless air hole area ratio G. The simulation results indicate that the windward blowing control (WBC) shows better control effect than the leeward blowing control (LBC) in reducing the time-averaged drag coefficient Cd¯ of the square cylinder while the fluctuating lift coefficient Cl′ can be significantly suppressed by the LBC. Besides, the surface pressure distribution, the turbulence kinetic energy (TKE) and Reynolds shear stress (RSS) distributions and the shedding vortices in the wake are analysed and compared in detail under different control conditions. Finally, through the instantaneous 3D vortex structures and the spanwise fluctuating velocity w′ distribution in the flow field, the suppression of the unsteady aerodynamic forces is mainly related to the 3D vortex pairs induced by the blowing jet.

Effects of tributary floodplain on confluence hydrodynamics

Confluences are common components of river networks and are characterized by a highly complex flow structure. Two confluence geometries, without and with the floodplain in the tributary, were comparatively investigated to highlight the effects of floodplain on confluence hydrodynamics. The three-dimensional velocity field and the spatial distribution of turbulent kinetic energy and Reynolds shear stresses were analysed. In the second geometry, a tilted shear layer was observed, which was related to the flow expansion from the main channel into the tributary. Significant secondary motions are mainly related to the fluid upwelling in the lee of the floodplain step and streamline curvature. A wider flow separation zone was found, while the length of the separation zone was not affected by the floodplain flow. The results could be useful to understand the complex hydrodynamics of the large confluence between the Yangtze River and the Poyang Lake, characterized from a floodplain under high flow conditions.

Direct numerical simulations of turbulent flow over the converging and diverging riblets

Different from conventional streamwise-aligned riblets, converging and diverging (C–D) riblets are arranged obliquely along the main-flow direction, intending to induce a large-scale secondary flow that modulates or controls the existing large-scale vortical structures in wall turbulence. In this study, we perform direct numerical simulations of turbulent flow over the C–D riblets at a low Reynolds number and investigate the impacts of the C–D riblets on aerodynamic forces, turbulence statistics, and coherent structures. The results show that the C–D riblets can reduce the skin-friction drag, but at the expense of a significantly increased pressure drag in the diverging region, which leads to an increase in the total drag. We present detailed mean and statistical flow-fields to assess the flow characteristics in the presence of the C–D riblets, including modifications on the distributions of velocities, pressure, Reynolds stresses, and turbulence kinetic energy. Moreover, the re-arrangement of turbulence structures over the C–D riblets is examined in terms of instantaneous flow-fields and two-point correlations. The findings provide more insight into the physics of flow over C–D riblets and may contribute to the further development of this flow control strategy.

Large eddy simulation study of the airflow characteristics in a human whole-lung airway model

Studying airflow characteristics in the human respiratory system is important for understanding the properties of the aerosol transport and deposition. This study first constructed a human whole-lung airway model (WLAM) with random features extending from the mouth to the 13th generation bronchus. The large eddy simulation method is utilized to investigate the features of both the averaged airflow fields and flow unsteadiness under inspiratory flow rates of 15 and 30 l/min, respectively. The results reveal the following novel findings: (1) secondary flow strength is not monotonically changing throughout the respiratory tract, depending on the local flow state and geometry, which allows for strong secondary flow motion even in the G13 bronchial airway. (2) In the upper airway, the peak distribution of turbulent kinetic energy (TKE) is due to in-plane secondary flow shear and longitudinal flow shear; local kinetic energy plays a vital role in the persistence of unsteadiness throughout the bronchial tree, which allows instability to still exist even in the bronchial airway with low Reynolds number. (3) TI is more dependent on the local flow state and geometric structure than TKE. These findings indicate that secondary flow and airflow unsteadiness in the thin bronchial airway are far stronger than previously reported and cannot be neglected. Therefore, further studies should investigate airflow unsteadiness in the thin bronchial airway using a suitable WLAM instead of a segmented bronchial airway model.

Vortex evolution and merging mechanism across 180° sharp bend for laminar inflow

The present study deals with the fundamentals of vortex evolution and merging across a 180° sharp bend for laminar inflow (Re = 800). A three-dimensional flow and pressure distribution across the bend are analyzed by using particle image velocimetry measurements. The results show that the sudden flow redirection and adverse pressure gradient create a recirculation region in the vicinity of the divider wall. The vorticity and turbulent kinetic energy distribution highlight the presence of a shear layer between the recirculation and mainstream turning flow. A Rayleigh instability analysis shows the existence of centrifugal instabilities outside the shear layer in the mainstream turning flow. The imbalance of centrifugal and pressure forces act in unison to produce a net force that creates Dean instability across the mainstream turning flow. Consequently, two pairs of counter-rotating Dean vortices develop after the first turn, possibly merging into a single pair after the subsequent 90° turn. Finally, the evolution and merging of Dean vortices are explained with the help of a conceptual diagram illustrating the force interaction and the formation of counter-rotating currents.

Silicon surface characteristics in vibration-assisted machining process via molecular dynamics

This study investigates the impacts of vibration amplitude, vibration frequency, and sliding velocity on the characteristics of the machined silicon substrate. The results show that increasing the vibration amplitude increases atomic strain, stress, and kinetic energy distributions while decreasing subsurface damage thickness, potential energy distribution, and especially surface roughness. The surface roughness values are 7.5 Å, 6.4 Å, 6.9 Å, and 6.0 Å corresponding to vibration amplitude of 15 Å, 20 Å, 25 Å, and 30 Å. Moreover, increasing the vibration frequency results in increased atomic strain, stress, and kinetic energy levels. The surface roughness values are 7.1 Å, 7.1 Å, 6.5 Å, 6.4 Å, and 6.0 Å corresponding to the vibration frequencies of 16.7 GHz, 33.3 GHz, 50 GHz, 66.7 GHz, 100 GHz, and 200 GHz. Furthermore, increasing the sliding velocity lowers the surface quality of the silicon sample. The surface roughness values of the silicon substrate are 6.5 Å, 6.7 Å, 6.9 Å, 6.9 Å, and 7.1 Å corresponding to 50 m/s, 100 m/s, 150 m/s, 200 m/s, and 250 m/s. Improving the vibration amplitude and frequency while decreasing the sliding velocity improves surface quality by increasing the collision between the diamond tips and the substrate. Remarkably, the vibration movement of the diamond tips could leave wave marks on the substrate surface. In general, the optimal parameters that generate a good surface are 30 Å, 200 GHz, and 50 m/s.

Inelastic scattering of OH from a liquid PFPE surface: Resolution of correlated speed and angular distributions.

Inelastic collisions of OH with an inert liquid perfluoropolyether (PFPE) surface have been studied experimentally. A pulsed molecular beam of OH with a kinetic energy distribution peaking at 35 kJ mol-1 was directed at a continually refreshed PFPE surface. OH molecules were detected state-selectively with spatial and temporal resolution by pulsed, planar laser-induced fluorescence. The scattered speed distributions were confirmed to be strongly superthermal, regardless of the incidence angle (0° or 45°). Angular scattering distributions were measured for the first time; their reliability was confirmed through extensive Monte Carlo simulations of experimental averaging effects, described in Paper II [A. G. Knight et al., J. Chem. Phys. 158, 244705 (2023)]. The distributions depend markedly on the incidence angle and are correlated with scattered OH speed, consistent with predominantly impulsive scattering. For 45° incidence, the angular distributions are distinctly asymmetric to the specular side but peak at sub-specular angles. This, along with the breadth of the distributions, is incompatible with scattering from a surface that is flat on a molecular scale. New molecular dynamics simulations corroborate the roughness of the PFPE surface. A subtle but unexpected systematic dependence of the angular distribution on the OH rotational state was found, which may be dynamical in origin. The OH angular distributions are similar to those for kinematically similar Ne scattering from PFPE and hence not strongly perturbed by OH being a linear rotor. The results here are broadly compatible with prior predictions from independent quasiclassical trajectory simulations of OH scattering from a model-fluorinated self-assembled monolayer surface.

Моделювання та аналіз складного руху автономного безпілотного підводного апарата

Ensuring autonomy, maneuverability and organization of movement control along complex trajectories of a maneuverable multi-purpose autonomous unmanned underwater vehicle (AUUV) is a complex scientific research and engineering task, for the solution of which it is necessary to know the behavior of the vehicle in the environment and the influence of the environment on the dynamics of the vehicle. Plots of the distribution of speed, pressure and kinetic energy of turbulence during the complex movement of the AUUV were obtained, in accordance with the chosen trajectories. Simulation and numerical modeling of AUUV under complex motion was carried out. The obtained results were compared with the results of rectilinear movement. showed that the construction of the ABPA model is acceptable both for straight-line movement and for movement along complex trajectories. A comparative analysis of the obtained values of speed, pressure and kinetic energy of turbulence shows the ability of the developed model of the device to perform quick maneuvers in limited areas (turning around, avoiding obstacles, etc.). The selected and designed ABPA model is suitable for further research in order to develop an automatic control system for a maneuverable multi-purpose AUUV.