Redistribution Of Kinetic Energy Research Articles

Turbulent kinetic energy redistribution in a gravity current interacting with an emergent cylinder

Gravity currents are flows driven by density gradients between two or more contacting fluids and play a key role in nature and industrial environments via global ocean circulations, climate variability and the distribution of airborne pollutants. In the present work, we study, experimentally, the changes induced by an emergent vertical PVC cylinder on the mean and turbulent flow fields of an unsteady bottom-generated lock release gravity current. Tests were carried out, with and without the cylinder, in refractive index matching conditions and instantaneous velocities were acquired with a Particle Image Velocimetry system. The mean velocity field, Reynolds stresses and terms of turbulent kinetic energy (TKE) budget for the currents head were presented and discussed. The results show that the adverse pressure gradient generated by the cylinder induces a uniform deceleration of the current head. Hence, there are no appreciable differences on the spatial distribution of the mean velocities in the current head, compared to the undisturbed current. On the other hand, the changes on the turbulent flow field are remarkable. The total diffusion of TKE decays in the inner part of the head while becoming stronger at the interface between the two fluids, as the current approaches the cylinder. This is associated to an increase of the diffusion term due to pressure fluctuations, that acts against diffusion due to velocity fluctuations and contributes to disrupt the transport of TKE from the interface between the fluids and the inner part of the current. As a result, in the presence of an obstacle, Reynolds stresses are suppressed in the inner part of the current head and enhanced at the interface.

A quantitative study on the turbulent kinetic energy redistribution in the near free-water-surface region of open channel flows

Open channel flows (OCFs) exhibit unique characteristics compared with other wall-bounded flows due to the presence of a free water surface. One of the well-known features is the turbulence kinetic energy (TKE) redistribution phenomenon in the near free-water-surface region. Unlike previous qualitative demonstrations, the present study aims providing a quantitative investigation of this phenomenon. Specifically designed super long domain direct numerical simulations (DNSs) of OCFs and closed channel flows (CCFs) are performed at three low-to-moderate friction Reynolds numbers (Reτ = 180–1000). The numerical configurations of the two flows (i.e., temporal and spatial resolution, domain size, Reynolds number, etc.) at identical Reτ are set to be the same, with the upper boundary being the only difference between them, to allow meaningful comparisons while super long domain sizes are adopted to facilitate fully spectral comparisons of the TKE features between the two flows. With such specifically designed DNS datasets, quantitative investigations of the TKE redistribution phenomenon in OCFs have been made. It is revealed that, as Reτ increases from 180 to 1000, the streamwise and spanwise TKE components of OCFs are higher than those of CCFs by 12%–23% and 28%–17%, respectively, while in the vertical direction OCFs are lower in TKE by 44%–31%. Overall, the TKE of OCFs is higher than that of CCFs by 3%–9% as Reτ increases from 180 to 1000. The comparison of OCFs and CCFs in pre-multiplied energy spectra reveals that VLSMs play a dominant role in the TKE redistribution phenomenon in OCFs.

Development of an untraditional technique to control the structure of the output flow from a vortex chamber

A technique of using coherent vortex formations of the dead-end zone of the vortex chamber of the end type as a controlling factor influencing the structure and characteristics of the output flow has been developed. The kinematic parameters of the flow relative to chambers with elongated and extremely short dead-end parts in the range of Reynolds numbers according to the parameters of the nozzle Re=47080–86530 were investigated. The reaction of the flow structure in the output sections of the vortex chambers was determined experimentally using thermoanemometry. Profiles of time-averaged transversal and axial velocity projections, as well as corresponding values of the relative intensity of velocity pulsations, were obtained. It was found that at Re=86530, the elongation of the dead-end part of the chamber leads to a decrease in the initial cross-section of the transversal component by 15 % with an increase in the axial component by 19.7 %, and, at Re=47080, to a decrease in the transversal component by 21 % with an increase in the axial component by 8.5 %. This indicates the redistribution of kinetic energy from transversal to axial energy motion, which is confirmed by the analysis of the corresponding intensity profiles of the velocity pulsations in the output section of the chamber in the near-wall and near-axis zones of the flow. The integral intensity of the velocity pulsations along the initial cross-section of comparable chamber designs increases in a chamber with an elongated dead-end part with almost no additional energy losses. The obtained results form the basis of a rational method of controlling the macro- and microstructure of flows, which determines the efficiency of mass exchange and heat exchange processes in vortex chambers of the end type. Such designs are characteristic of vortex mixers, burners of industrial furnaces, furnace devices of hot water and steam boilers, and other technological and power equipment

Direct numerical simulation of turbulent open channel flows at moderately high Reynolds numbers

Well-resolved direct numerical simulations of turbulent open channel flows (OCFs) are performed for friction Reynolds numbers up to $Re_\tau =2000$ . Various turbulent statistics are documented and compared with the closed channel flows (CCFs). As expected, the mean velocity profiles of the OCFs match well with the CCFs in the near-wall region but diverge notably in the outer region. Interestingly, a logarithmic layer with Kárman constant $\kappa =0.363$ occurs for OCF at $Re_\tau =2000$ , distinctly different from CCF. Except for a very thin layer near the free surface, most of the velocity and vorticity variances match between OCFs and CCFs. The one-dimensional energy spectra reveal that the very-large-scale motions (VLSMs) with streamwise wavelength $\lambda _x>3 h$ or spanwise wavelength $\lambda _z>0.5 h$ contribute the most to turbulence intensity and Reynolds shear stress in the overlap and outer layers (where h is the water depth). Furthermore, the VLSMs in OCFs are stronger than those in CCFs, resulting in a slightly higher streamwise velocity variance in the former. Due to the footprint effect, these structures also have significant contributions to the mean wall shear stress, and the difference between OCF and CCF enlarges with increasing $Re_\tau$ . In summary, the free surface in OCFs plays an essential role in various flow phenomena, including the formation of stronger VLSMs and turbulent kinetic energy redistribution.

Redistribution of translational kinetic energy: the surprises of bounces

The topic of collisions is introduced in university education to address the laws of conservation of momentum and energy. In particular, students are asked to classify collisions as either elastic or inelastic. They are often left with the idea that ‘macroscopic energy’ has been transformed into ‘microscopic energy’ in the case of an inelastic collision, but their understanding of the processes of redistribution of kinetic energy to other degrees of freedom, often called ‘dissipation’, is mostly very poor. The aim of this article is to see how to facilitate the understanding of these processes among university students. Firstly, the results of a questionnaire with 27 university students show that they consider mass and material as the most important determinants of the coefficient of restitution of the bounce of a ball on a solid and rigid support, while the notion of internal structure, which is however essential, is not considered. Second, a simple model contextualizes the idea of a temporal sequence of successive events in the rebound of inhomogeneous projectiles. Finally, recent results on bilayered projectiles are exploited to emphasize the non-trivial influence of the structure of a body on the restitution of its initial translational kinetic energy after rebound on a support. These different elements contribute to conceive possible teaching objectives, to propose simple experiments and to address the conditions for progress in this field.

Redistribution of Kinetic Energy in Three-Dimensional Clouds of Charged Dust Grains

Redistribution of Kinetic Energy in Three-Dimensional Clouds of Charged Dust Grains

An improved [formula omitted] turbulence model for FENE-P fluids without friction velocity dependence

An improved k-ω turbulence model for viscoelastic fluids is developed to predict turbulent flows, with polymeric solutions described by the finitely extensible nonlinear elastic-Peterlin constitutive model. The k-ω model is tested against a wide range of direct numerical simulation data in fully-developed channel flow, with different rheological parameter combinations, and can predict all regimes of drag reduction (low, intermediate and high) with good performance. Closures are improved for the NLTij term, which captures the polymer extension due to turbulent fluctuations; a modified damping function, fμ, which accounts for the turbulent kinetic energy redistribution process; and the viscoelastic destruction term, Eτp. The main advantage of the current model is its ability to predict all flow features with model simplicity and without the need for friction velocity dependence, important for flows with reattachment due to their singularity caused by the stagnation points.

Redistribution of Stochastic Kinetic Energy in Ensembles of Non-Identical Charged Particles

The energy exchange processes are studied in the systems of non-identical interacting particles (with different sizes, masses, and charges) with the spatially inhomogeneous distribution of the stochastic kinetic energy sources. To analyze the energy balance in such systems, a theoretical model is considered. The analytical relations are presented that describe the redistribution of the stochastic kinetic energy between two charged particles. The relations proposed are verified by means of simulating numerically the problem for particles with the Coulomb interaction between them. The numerical analysis is performed of the process of the stochastic kinetic energy redistribution in the two-dimensional ensembles with the separated fractions of particles with different sizes and temperatures. The results of this work can be applied to the systems with any type of pair interaction. They can be also used for analyzing the energy exchange processes in inhomogeneous systems that are of interest in plasma physics and in physics of polymers and colloid systems.

Equilibration of energies in a two-dimensional harmonic graphene lattice.

We study dynamical phenomena in a harmonic graphene(honeycomb) lattice, consisting of equal particles connected by linear and angular springs. Equations of in-plane motion for the lattice are derived. Initial conditions typical for molecular dynamic modelling are considered. Particles have random initial velocities and zero displacements. In this case, the lattice is far from thermal equilibrium. In particular, initial kinetic and potential energies are not equal. Moreover, initial kinetic energies(and temperatures), corresponding to degrees of freedom of the unit cell, are generally different. The motion of particles leads to equilibration of kinetic and potential energies and redistribution of kinetic energy among degrees of freedom. During equilibration, the kinetic energy performs decaying high-frequency oscillations. We show that these oscillations are accurately described by an integral depending on dispersion relation and polarization matrix of the lattice. At large times, kinetic and potential energies tend to equal values. Kinetic energy is partially redistributed among degrees of freedom of the unit cell. Equilibrium distribution of the kinetic energies is accurately predicted by the non-equipartition theorem. Presented results may serve for better understanding of the approach to thermal equilibrium in graphene. This article is part of the theme issue 'Modelling of dynamic phenomena and localization in structured media (part 2)'.

The mechanisms of energy transformation in sharp open-channel bends: Analysis based on experiments in a laboratory flume

In sharp open-channel bends, there exists nonlinear interactions between streamwise and cross-stream velocities, which leads to the adjustment of flow energy transport, increases the energy dissipation and eventually influences the development of river bends. However, previous studies have not yet fully understood the mechanisms underlying the transport and dissipation of energy in open-channel bends. In addition, energy dissipation is directly related to the evolution of enstrophy Ω·Ω/2. However, it has not yet received much attention in the study of the resistance in meandering rivers. To gain an insight into these mechanisms, with the aid of detailed experimental data collected in a sharp open-channel bend, this study quantified the impacts of the key terms in the kinetic energy equation and the enstrophy equation. Results show that the term related to the transport of kinetic energy by cross-stream circulation is at least an order of magnitude larger than the other terms in the kinetic energy equation, which contributes significantly to the redistribution of kinetic energy over the cross section. The term related to the production of turbulent kinetic energy in the kinetic energy equation shows the smallest order of magnitude and thus is almost negligible for the time-averaged flow field. Furthermore, over most of the measured area, the term related to the centrifugal force shows values of at least an order of magnitude larger than the other terms in the enstrophy equation, which means that this term exerts the dominant influence on the energy dissipation. The results also revealed that the transformation process is insensitive to the variations in Froude number. These results are expected to improve the understanding of the complete process of energy transformation, especially the resistance caused by secondary flow in meandering rivers.

Reactive mode composition factor analysis of transition states: the case of coupled electron-proton transfers.

A simple method for the evaluation of the kinetic energy distribution within the reactive mode of a transition state (TS), denoted as the Reactive Mode Composition Factor (RMCF), is presented. It allows one to directly map the barrier properties onto the atomic-motion components of the reaction coordinate at the TS, which has potential to shed light onto some mechanistic features of a chemical process. To demonstrate the applicability of RMCF to reactivity, we link the kinetic energy distribution within a reactive mode with the asynchronicity (η) in C-H bond activation, as they both evolve in a series of coupled proton-electron transfer (CPET) reactions between FeIVO oxidants and 1,4-cyclohexadiene. RMCF shows how the earliness or lateness of a process manifests as a redistribution of kinetic energy in the reactive mode as a function of the free energy of reaction (ΔG0) and η. Finally, the title analysis can be applied to predict H-atom tunneling contributions and kinetic isotope effects in a set of reactions, yielding a transparent rationalization based on the kinetic energy distributions in the reactive mode.

Studying the redistribution of kinetic energy between the morphologically distinct parts of the fragments cloud formed from high-velocity impact fragmentation of an aluminum sphere on a steel mesh

Numerical simulations of experiments (Shumikhin et al., 2014) on the fragmentation of aluminum spheres with diameter of 6.35 mm on single steel-mesh bumpers of different specific mass are carried out in the present work. Specific mass of the mesh bumpers in these experiments was varied by changing the diameter of the wire from which was woven the mesh. The spatial distribution of fragments, their mass and kinetic energy (KE) are determined. The results of the numerical simulations are in good agreement with the experimental data showing that the cloud of fragments composes of two morphologically distinct groups of fragments, which differ greatly in mass: the central group, consisting mainly of four large fragments, and four groups of linearly-distributed chains of smaller fragments. The numerical simulations in agreement with the experiments show that KE of the central group of fragments decreases relative to the total KE of the fragments cloud with increasing the specific mass of the mesh, while the relative KE of other smaller fragments increases.

Shockwave generates < 100 > dislocation loops in bcc iron

The formation mechanism of < 100 > interstitial dislocation loops in ferritic steels stemming from irradiation remains elusive, as their formations are either too short for experiments, or too long for molecular dynamics simulations. Here, we report on the formation of both interstitial and vacancy dislocation loops in high energy displacement cascades using large-scale molecular dynamics simulations with up to 220 million atoms. Riding the supersonic shockwave generated in the cascade, self-interstitial atoms are punched out to form < 100 > dislocation loops in only a few picoseconds during one single cascade event, which is several orders of magnitude faster than any existing mechanisms. The energy analysis suggests that the formation of the interstitial loops depends on kinetic energy redistribution, where higher incidence energy or larger atom mass could improve the probability of the direct nucleation of interstitial dislocation loops.

Influence of the horizontal component of Earth’s rotation on wind turbine wakes

Wind turbines with large rotor diameters create wakes which are affected by the rotation of the earth. Aside from creating horizontal mean velocity veer, the Coriolis force, caused by earth’s rotation, also results in wake deflection and turbulence kinetic energy redistribution. In atmospheric turbulence, the horizontal component of Earth’s rotation is often neglected since its forcing magnitude is small compared to buoyant forces. However, at lower latitudes, the horizontal component will cause vertical deflection and redistribution of the same order as the horizontal wake deflection and distribution imposed by the vertical component. Large Eddy Simulations (LES) using uniform laminar inflow, along with more realistic neutrally and stably stratified atmospheric boundary layer inflow conditions are used to study the effect of the horizontal component. Simulations performed at a latitude of 450 suggest that the horizontal component cannot be neglected in the study of wind farms since the horizontal component’s effect in wind turbine planetary boundary layer flows manifests most directly in the vertical entertainment of kinetic energy. A low-order Coriolis force-induced wake deflection model is proposed and tested against numerical results for uniform inflow conditions.

Energy Redistribution Between the Reservoir and Liquid with Free Surface for Angular Motions of the System

We study the problem of motion of a cylindrical reservoir (on a pendulum suspension) partially filled with an ideal liquid. At the initial time, the deviation of reservoir from the equilibrium position is described by a certain angle. We analyze the redistribution of kinetic energy in the system and explain the decay of the surface wave motion. The accumulated results qualitatively agree with the available experimental data.

Deciphering environment effects in peptide bond solvation dynamics by experiment and theory.

Most proteins work in aqueous solution and the interaction with water strongly affects their structure and function. However, experimentally the motion of a specific single water molecule is difficult to trace by conventional methods, because they average over the heterogeneous solvation structure of bulk water surrounding the protein. Here, we provide a detailed atomistic picture of the water rearrangement dynamics around the -CONH- peptide linkage in the two model systems formanilide and acetanilide, which simply differ by the presence of a methyl group at the peptide linkage. The combination of picosecond pump-probe time-resolved infrared spectroscopy and molecular dynamics simulations demonstrates that the solvation dynamics at the molecular level is strongly influenced by this small structural difference. The effective timescales for solvent migration triggered by ionization are mainly controlled by the efficiency of the kinetic energy redistribution rather than the shape of the potential energy surface. This approach provides a fundamental understanding of protein hydration and may help to design functional molecules in solution with tailored properties.

The effect of nonreciprocal interaction on the redistribution of kinetic energy in the system of particles

Dynamical properties of particles in the chain-like and layered structures are studied with the help of Langevin MD approach. We considered infinite, confined chain-like structures, and extended layered structures with vertical (chain-like) and hexagonal ordering of particles in adjacent layers over a wide range of parameters, corresponding to the experimental conditions in the laboratory dusty plasmas. The nonreciprocal anisotropic interparticle interaction leads to a growth of kinetic energy of stochastic motion of particles especially its vertical component. Efficacy of the heating depends on the thermal particle motion, the anisotropy of the considered interparticle interaction and with decreasing the friction coefficient.

Kinetic energy in a system of particles with a nonreciprocal interaction

We present a theoretical model for the description of the heating mechanism and the redistribution of kinetic energy in a system of particles with nonreciprocal interactions that occur in disperse systems of different nature. To verify the theory, we carried out the numerical simulations of two-particle systems with a nonreciprocal “quasi-dipole–dipole” interaction that is similar to the interaction due to the effect of ion focusing in a laboratory complex plasma under experimental conditions. The proposed model of heating can explain various features of dust dynamics in anisotropic complex plasma.

Budgets of turbulent kinetic energy, Reynolds stresses, variance of temperature fluctuations and turbulent heat fluxes in a round jet

The self-preserving region of a free round turbulent air jet at high Reynolds number is investigated experimentally (at$x/D=30$,$\mathit{Re}_{D}=1.4\times 10^{5}$and$\mathit{Re}_{{\it\lambda}}=548$). Air is slightly heated ($20\,^{\circ }\text{C}$above ambient) in order to use temperature as a passive scalar. Laser doppler velocimetry and simultaneous laser doppler velocimetry–cold-wire thermometry measurements are used to evaluate turbulent kinetic energy and temperature variance budgets in identical flow conditions. Special attention is paid to the control of initial conditions and the statistical convergence of the data acquired. Measurements of the variance, third-order moments and mixed correlations of velocity and temperature are provided (including$\overline{vw^{2}}$,$\overline{u{\it\theta}^{2}}$,$\overline{v{\it\theta}^{2}}$,$\overline{u^{2}{\it\theta}}$,$\overline{v^{2}{\it\theta}}$and$\overline{uv{\it\theta}}$). The agreement of the present results with the analytical expressions given by the continuity, mean momentum and mean enthalpy equations supports their consistency. The turbulent kinetic energy transport budget is established using Lumley’s model for the pressure diffusion term. Dissipation is inferred as the closing balance. The transport budgets of the$\overline{u_{i}u_{j}}$components are also determined, which enables analysis of the turbulent kinetic energy redistribution mechanisms. The impact of the surrogacy$\overline{vw^{2}}=\overline{v^{3}}$is then analysed in detail. In addition, the present data offer an opportunity to evaluate every single term of the passive scalar transport budget, except for the dissipation, which is also inferred as the closing balance. Hence, estimates of the dissipation rates of turbulent kinetic energy and temperature fluctuations (${\it\epsilon}_{k}$and${\it\epsilon}_{{\it\theta}}$) are proposed here for use in future studies of the passive scalar in a turbulent round jet. Finally, the budgets of turbulent heat fluxes ($\overline{u_{i}{\it\theta}}$) are presented.

A statistical study into the spatial distribution and dawn‐dusk asymmetry of dayside magnetosheath ion temperatures as a function of upstream solar wind conditions

AbstractThe magnetosheath contains the shocked solar wind and behaves as a natural filter to the solar wind plasma before it reaches the magnetosphere. The redistribution of kinetic energy at the bow shock results in significant thermalization of the solar wind plasma, resulting in a magnetosheath temperature profile which is highly nonhomogeneous and nonisotropic and differs between the dawn and dusk flanks. The present study attempts to study the spatial distribution of magnetosheath ion temperature as a function of upstream solar wind conditions. We pay particular attention to the dawn/dusk asymmetry in which we attempt to quantify using experimental data collected over a 7 year period. We also compare these data to simulated data from both the Block‐Adaptive‐Tree‐Solarwind‐Roe‐Upwind‐Scheme (BATS‐R‐US) MHD code and a kinetic hybrid model. We present evidence that the dawn flank is consistently hotter than the dusk flank for a variety of upstream conditions. Our statistical data also suggest a dependency on solar wind speed such that the level of asymmetry increases with faster speeds. We conclude that the dawn‐favored asymmetry of the magnetosheath seed population is insufficient to explain the dawn asymmetry (30–40%) of cold component ions in the cold, dense plasma sheet, and therefore, other mechanisms are likely required.