Ratio Of Kinetic Energy Research Articles

Investigation of novel scaling criteria on a reverse-flow combustor

Abstract The present study investigates the scaling of a 3.3-kW laboratory scale combustor (baseline) to 25-kW using Detached Eddy Simulation (DES) with detailed chemistry. The combustor operates on syngas under atmospheric conditions. Two novel scaling criteria, namely, constant volume to jet momentum ratio (CM) and constant volume to jet kinetic energy ratio (CK) have been introduced and applied to the 3.3-kW combustor. Additionally, the constant velocity (CV) and constant residence time (CRT) scaling criteria have also been investigated for comparison. Flow, mixing, temperature, and their effect on the reaction zone and emissions have been compared for the scaled-up combustors with the laboratory scale combustor. The scaling criteria were observed to significantly influence the location and volumetric distribution of the reaction zone. In terms of performance parameters, the CV criterion entails the lowest pressure drop and CO emissions. The performance of the CK and CM criteria closely follows that of the CV criterion, thus offering a promising scaling methodology for reverse-flow combustors. The chamber scaled by the CRT criterion recorded the highest pressure drop and CO emissions. The insights from the present study will aid in sizing lab-scale combustors to industrial requirements.

Turbulence modulation in particle-laden stationary homogeneous isotropic turbulence using one-dimensional turbulence

Turbulence modulation in particle-laden stationary homogeneous isotropic turbulence is investigated using one-dimensional turbulence (ODT), a low-dimensional stochastic flow simulation model. For this purpose, ODT is extended in two ways. First, a forcing scheme that maintains statistical stationarity is introduced. Unlike direct numerical simulation (DNS) of forced turbulence, the ODT framework accommodates forcing that is not directly coupled to the momentum equation. For given forcing the ODT energy dissipation rate is therefore the same in particle-laden cases as in the corresponding single-phase reference case. Second, previously implemented one-way-coupled particle phenomenology is extended to two-way coupling using the general ODT methodology for flow modulation through interaction with any specified energy and momentum sources and sinks. As in a DNS comparison case for Re-lambda = 70, turbulence modulation is diagnosed primarily on the basis of the fluid-phase kinetic-energy spectrum. Because ODT involves subprocesses with straightforward physical interpretations, the ODT mechanisms of particle-induced turbulence modulation are clearly identified and they are plausibly relevant to particleladen Navier-Stokes turbulence. ODT results for the ratio of particle-phase and fluid-phase kinetic energies as a function of particle Stokes number and mass loading are reported for the purpose of testing these predictions in the future when these quantities are evaluated experimentally or using DNS.

Shape model and spin state of non-principal axis rotator (5247) Krylov

Context.The study of non-principal axis (NPA) rotators can provide important clues to the evolution of the spin state of asteroids. However, very few studies to date have focused on NPA-rotating main belt asteroids (MBAs). One MBA known to be in an excited rotation state is asteroid (5247) Krylov.Aims.By using disk-integrated photometric data, we construct a physical model of (5247) Krylov including shape and spin state.Methods.We applied the light curve convex inversion method employing optical light curves obtained by using ground-based telescopes in three apparitions during 2006, 2016, and 2017, along with infrared light curves obtained by the Wide-field Infrared Survey Explorer satellite in 2010.Results.Asteroid (5247) Krylov is spinning in a short axis mode characterized by rotation and precession periods of 368.7 and 67.27 h, respectively. The angular momentum vector orientation of Krylov is found to beλL= 298° andβL= −58°. The ratio of the rotational kinetic energy to the basic spin-state energyE∕E0≃ 1.02 shows that the (5247) Krylov is about 2% excited state compared to the principal axis rotation state. The shape of (5247) Krylov can be approximated by an elongated prolate ellipsoid with a ratio of moments of inertia ofIa:Ib:Ic= 0.36 : 0.96 : 1. This is the first physical model of an NPA rotator among MBAs. The physical processes that led to the current NPA rotation cannot be unambiguously reconstructed.

Spectral Analysis of Gravity Waves from Near Space High-Resolution Balloon Data in Northwest China

Using a set of near space high-resolution balloon data released in Hami, Xinjiang, we explored the spectral characteristics of temperature fluctuations and three-dimensional wind field fluctuations. As different from previous studies, which were based on radiosondes, we have increased the height range of spectral analysis to the stratosphere (38 km), which can explore the variation of spectral features with altitude, and can analyze higher wavenumber regions. The results show that horizontal wind field disturbances are isotropic, meridional and zonal winds have relatively consistent spectral structures, while vertical wind fluctuations have completely different spectral structures, which cannot be explained by the existing “universal spectrum” theory. The observed spectrum of horizontal wind field can be explained well by the “wind-shifting” theory. The ratio of spectral kinetic energy to potential energy is approximately constant only in the high wavenumber region but it varies at different height intervals. This study is a necessary extension of the observation for the characteristics of the vertical wavenumber spectrum in northwestern China, and it is also an experimental observation of spectral characteristics using radiosonde data at higher altitudes.

Energy conversion and deposition behaviour in gravitational collapse of granular columns

The high-density gravitational collapse of granular columns is very similar to the movements of large collapsing columns in nature. Based on the development of dangerous columnar rock mass in fields, granular column collapse boundary condition in the physical experiments of this study is a new type of boundary conditions with a single free face and a three-dimensional deposit. Physical experiments have shown that the mobility of small particles during the collapse of granular columns was greater than that of large particles. For example, when particle size was increased from 5 to 15 mm, deposit runout was decreased by about 16.4%. When a column consisted of two particle types with different sizes, these particles could mix in the vicinity of layer interfaces and small particles might increase the mobility of large particles. In the process of collapse, potential and kinetic energy conversion rate is fluctuated. By increasing initial aspect ratio a, the ratio of the initial height of column to its length along flow direction, potential and kinetic energy conversion rate is decreased. For example, as a was increased from 0.5 to 4, the ratio of maximum kinetic energy obtained and total potential energy loss was decreased from 47.6% to 7.4%. After movement stopped, an almost trapezoidal body remained in the column and a fanlike or fan-shaped accumulation was formed on the periphery of column. Using multiple exponential functions of the aspect ratio a, the planar morphology of the collapse deposit of granular columns could be quantitatively characterized. The movement of pillar dangerous rock masses with collapse failure mode could be evaluated using this granular column experimental results.

Quantum kinetic energy and isotope fractionation in aqueous ionic solutions.

At room temperature, the quantum contribution to the kinetic energy of a water molecule exceeds the classical contribution by an order of magnitude. The quantum kinetic energy (QKE) of a water molecule is modulated by its local chemical environment and leads to uneven partitioning of isotopes between different phases in thermal equilibrium, which would not occur if the nuclei behaved classically. In this work, we use ab initio path integral simulations to show that QKEs of the water molecules and the equilibrium isotope fractionation ratios of the oxygen and hydrogen isotopes are sensitive probes of the hydrogen bonding structures in aqueous ionic solutions. In particular, we demonstrate how the QKE of water molecules in path integral simulations can be decomposed into translational, rotational and vibrational degrees of freedom, and use them to determine the impact of solvation on different molecular motions. By analyzing the QKEs and isotope fractionation ratios, we show how the addition of the Na+, Cl- and HPO42- ions perturbs the competition between quantum effects in liquid water and impacts their local solvation structures.

Lagrangian Drifter to Identify Ocean Eddy Characteristics

Deterministic–stochastic empirical mode decomposition (EMD) is used to obtain low-frequency (non-diffusive; i.e., background velocity) and high-frequency (diffusive; i.e., eddies) components from a Lagrangian drifter‘s trajectory. Eddy characteristics are determined from the time series of eddy trajectories from individual Lagrangian drifters such as eddy radius, eddy velocity, eddy Rossby number, and the eddy–current kinetic energy ratio. A long-term dataset of the Sound Fixing and Ranging (RAFOS) float time series obtained near the California coast by the Naval Postgraduate School from 1992 to 2004 at depth between 150 and 600 m is used as an example to demonstrate the capability of the deterministic–stochastic EMD.

Exergy analysis of supersonic steam jet condensed into subcooled water

Exergy analysis of supersonic steam jet condensed into subcooled water was conducted via a numerical method. A thermal phase-change model was employed by Ansys, and considering turbulence interaction and turbulent dispersion force, three-dimensional simulations were conducted to simulate supersonic steam jet at different test conditions. Results indicated that the exergy flow of steam jet was mainly affected by water temperature and inlet steam pressure. The total physical exergy flow decayed monotonically due to the significant irreversible losses caused by heat and momentum transfer. For under-expanded supersonic steam jet, the peak distributions of steam kinetic exergy flow were obtained. The peak distributions of the water enthalpy exergy flow were also obtained at low water temperatures (293.15 K and 303.15 K). In addition, water temperature was found to be the main factor in the damping-energy properties of the supersonic steam jet. The damping-energy ratio and decay rate of the time-averaged kinetic energy decreased with the increase in water temperature, and a correlation was proposed to predict the time-averaged kinetic energy decay ratio.

The Horizontal Spectrum of Vertical Velocities near the Tropopause from Global to Gravity Wave Scales

Abstract Vertical motions are fundamental for atmospheric dynamics. Compared to horizontal motions, the horizontal spectrum of vertical velocity w is less well known. Here, w spectra are related to spectra of horizontal motions in the free atmosphere near the tropopause from global to gravity wave scales. At large scales, w is related to vertically averaged horizontal divergent motions by continuity. At small scales, the velocity energy spectra reach anisotropy as in stably stratified turbulence. Combining these limits approximates the w spectrum from global to small scales. The w spectrum is flat at large scales when the divergent spectrum shows a −2 slope, reaches a maximum at mesoscales after transition to −5/3 slopes, and then approaches a fraction of horizontal kinetic energy. The ratio of vertical kinetic energy to potential energy increases quadratically with wavenumber at large scales. It exceeds unity at small scales in stratified turbulence. Global and regional simulations and two recent aircraft measurement field campaigns support these relationships within 30% deviations. Energy exchange between horizontal and vertical motions may contribute to slope changes in the spectra. The model allows for checking measurement validity. Isotropy at large and small scales varies between the datasets. The fraction of divergent energy is 40%–70% in the measurements, with higher values in the stratosphere. Spectra above the tropopause are often steeper over mountains than over oceans, partly with two −5/3 subranges. A total of 80% of w variance near the tropopause occurs at scales between about 0.5 and 80 km.

Floquet-engineered light-cone spreading of correlations in a driven quantum chain

We investigate the light-cone-like spread of electronic correlations in a laser-driven quantum chain. Using the time-dependent density matrix renormalization group, we show that high-frequency driving leads to a Floquet-engineered spread velocity that determines the enhancement of density-density correlations when the ratio of potential and kinetic energies is effectively increased both by either a continuous or a pulsed drive. For large times we numerically show the existence of a Floquet steady state at not too long distances on the lattice with minimal heating. Intriguingly, we find a discontinuity of dynamically scaled correlations at the edge of the light cone, akin to the discontinuity known to exist for quantum quenches in Luttinger liquids. Our work demonstrates the potential of pump-probe experiments for investigating light-induced correlations in low-dimensional materials and puts quantitative speed limits on the manipulation of long-ranged correlations through Floquet engineering.

Impact of an initial random magnetic field on the evolution of two-dimensional shearless mixing layers

The impact of an initial random magnetic field on the temporal evolution of a two-dimensional incompressible turbulent shearless mixing layer is investigated using direct numerical simulation. Different intensities of the initial random magnetic field are imposed with uniform probability distribution on an identical flow field. The initial flow field condition is the turbulent shearless mixing layer with different kinetic energy ratio (E_{H}/E_{L}=6.7) and identical integral length scale. Simulations are carried out in a moderate magnetic Reynolds number, which causes a two-way interaction between the velocity and magnetic fields. In order to analyze the effect of the initial random magnetic field on the mixing characteristics, the intermittency inside the mixing layer and the mixing evolution parameters are investigated. It is found that with small initial magnetic field intensity, the intermittency in both large and small scales are larger than those values in hydrodynamic flow. However, increasing the intensity of the initial magnetic field reduces the intermittency in the mixing region to lower values compared to the hydrodynamic flow. The mixing layer growth rate and the mixing efficiency both show reduction by increasing the initial magnetic field intensity, which is attributed to the reduction of the averaged Reynolds number of both homogenous isotropic turbulent regions due to the suppressing effect of the Lorentz force on the velocity fields of these regions.

Improving Conductivity in Nano-Conduit Flows by Using Thermal Pulse-Induced Brownian Motion: A Spectral Impulse Intensity Approach

Inter-particle and particle-wall connectivity in suspension flow has profound effects on thermal and electrical conductivity. The spectral impulse generation and the imparting of kinetic energy on the particles is shown through a mathematical analysis to be effective as a means of achieving an approximate equivalent of a Langevin thermostat. However, with dilute suspensions, the quadratic form of the thermal pulse spectra is modified with a damping coefficient to achieve the desired Langevin value. With the dense suspension system, the relaxation time is calculated from the non-linear differential equation, and the fluid properties were supported by the viscosity coefficient. A “smoothed” pulse is used for each time-step of the flow simulation to take care of the near-neighbor interactions of the adjacent particles. An approximate optimal thermostat is achieved when the number of extra pulses introduced within each time step is found to be nearly equal to the co-ordination number of each particle within the assembly. Furthermore, the ratio of the particle kinetic energy and the thermal energy imparted is found to be never quite equal to unity, as they both depend upon the finite values of the pulse duration and the relaxation time.

Quasi-static analysis and multi-objective optimization for tape spring hinge

Mechanical attributes of interest are always mutually exclusive in the design process of tape spring hinge. Here we present a complete optimization framework consisting of computational mechanics, optimization design, engineering application, and experimental research to compromise mechanical attributes such that an optimal solution set can be obtained to provide design strategies for engineering practices. Tape spring hinge in folding and unfolding processes with large non-linearity is firstly simulated using quasi-static analysis technique. During the quasi-static process, the ratio of kinetic energy to strain energy is observed to determine mass scaling parameters that measure the precision of analysis. Based on the parameters analyzed, moment-rotation responses of tape spring hinge in quasi-static folding and unfolding processes are investigated and experimentally verified. Yield theory derived from the combination of thin shell theory and Tresca yield criterion is introduced to control the yield of the hinge during folding and deploying processes. In addition, tape spring hinge is released transiently when in spatial conditions; thus the fundamental frequency is calculated and selected herein to be a measurement of stiffness that is maximized to avoid the vibration. Then a multi-objective optimization model is established using the derived yield theory control equation and critical moment as optimization constraints, with the fundamental frequency and strain energy as objectives. The non-dominated sorting genetic algorithm is used to solve the optimization model, and then feasible solution distribution and Pareto frontier are obtained. These results are compared and discussed with two additional single-objective optimizations. Ultimately we achieve the optimal design for tape spring hinge, which is verified well with numerical simulation.

Metal ion filtering of vacuum arc ion source through an inclined-aperture extraction grid

The paper reports a novel method of increasing the fraction of H+ ions produced by vacuum arc ion sources with metal hydride cathodes, which applies the ionic selectivity of an inclined-aperture extraction grid to separate and filter heavy metal ions. A simple theoretical model is built to describe the filtering mechanism. Since H+ ions and Tin+ (n = 1 ∼ 3) ions produced by vacuum arc discharge have a great difference in the ratio of charge state and kinetic energy, H+ ions are easy to pass through the inclined-aperture grid, while most of the Ti ions are blocked and absorbed by the grid wall. Using a 2D particle-in-cell simulation, the ionic selectivity of an inclined-aperture extraction grid is demonstrated. The numerical simulation results show that after ion filtering through the extraction grid, the fraction of H+ ions is increased from 39% to more than 80%. The increased amplitude of H+ ion fraction depends on the thickness of the grid and the angle of grid apertures. In addition, an extraction grid with different aperture angles for the extraction of divergent vacuum arc plasma is proposed.

Numerical simulation of turbulent flow over a backward facing step using partially averaged Navier-Stokes method

This paper presents some key features of partially averaged Navier-Stokes (PANS) method in the simulation of turbulent flow over a backward facing step at Reh = 5100. Both fixed and spatially variable values for the unresolved-to-total ratio of kinetic energy (fk) are adopted in the present PANS simulations. Different model parameters relevant to PANS have been assessed. Detached eddy simulation (DES) is also adopted and the results from DES are compared in detail with PANS and the available experimental data. Variable fk PANS gives overall acceptable predictions but it is slightly less accurate than DES. The defects of PANS simulation with fixed fk throughout the entire computational domain are highlighted in this investigation. An improved step is to introduce variable fk to ensure the near-wall Reynolds averaged Navier-Stokes (RANS) solution. This paper provides encouraging results for PANS simulations of this wall-bounded flow involving separation.

Solid particle erosion of epoxy matrix composites reinforced by Al2O3 spheres

The solid particle erosion of a spherical alumina particle-reinforced epoxy matrix composite was investigated. Three dimensionless parameters were demonstrated to play key roles in the erosion resistance: r1, the ratio of the abrasive to reinforcement particle size; r2, the ratio of the abrasive particle size to the average edge-to-edge distance between reinforcements; and r3, the ratio of the abrasive particle kinetic energy to a threshold kinetic energy. At perpendicular incidence, modest improvements in erosion resistance could be obtained at intermediate r2 values (1 < r2 < 3) when r1 was intermediate (0.2 < r1 < 0.35). At oblique incidence, the erosion resistance of the composites was significantly higher than the neat epoxy in all cases. The results may have important implications for the design of polymeric composite coatings.

Synthetic jet vortex rings impinging onto a porous wall: Reynolds number effect

The interaction of synthetic jet vortex rings with a porous wall was investigated using laser-induced fluorescence (LIF) and particle image velocimetry (PIV) techniques. The synthetic jet Reynolds number (Resj) varied from 309 to 1238, where the vortex rings underwent transition from laminar to turbulent flow. For the lowest Reynolds number (Resj = 309), the flow is almost laminar; the primary vortex ring (VR1) induces and pairs with a well coherent secondary vortex ring (VR2) in the upstream side of the porous wall, leading to a conventional “rebound” and “reversal” in VR1’s trajectory. As Resj increases, the induced VR2 becomes weaker and loses coherence quickly after rolling up; even at Resj = 1238, VR2 becomes indistinguishable. During the vortex ring interacting with the porous wall, some fluid penetrates through the wall to form a transmitted vortex ring (VRT) in the downstream region. The circulation of VRT increases with the growth of Resj. In particular, for a higher Resj, the synthetic jet tends to pass through a porous wall more easily with less losses in both vortex ring circulation and jet momentum. Velocity triple decomposition shows that VRT for all tested cases has lost coherence completely before it moves out of the field of view. Moreover, for Resj = 309, the incoherence of VRT is caused by the vorticity diffusion and viscous dissipation since both the upstream and downstream flow are almost laminar. But for the high Resj (619, 928 and 1238), VRT lost coherence is mainly due to the transition, which results in a relatively large ratio of the fluctuation kinetic energy (FKE) to the total flow kinetic energy (KE). In particular, for Resj = 928 and 1238, it is observed that some small-scale Kelvin-Helmholtz vortices are formed in the trailing jet, and entrained into the primary vortex core, which accelerates the loss of coherence for the primary vortex ring. This observation can explain why the vortex ring at high Reynolds number is less coherent.

Energy conversion during the crown evolution of the drop impact upon films

The energy conversion is proposed to analyze the effects of inertial force, surface tension, gravitational force and viscous force during the crown evolution of the drop impact phenomena. The incompressible laminar Navier–Stokes equations coupled with the volume of fluid model are solved numerically in the axisymmetric frame to simulate the impact process. The influences of both the ratio of the initial kinetic energy to the surface tension energy of the drop as well as the initial film thickness on the energy conversion during the impact process are studied in detail. The ratio of the initial kinetic energy to the surface tension energy of the drop can affect the energy conversion at a very early stage of the impact process, thus it can affect the occurrence of prompt splash significantly; while the initial film thickness can affect the energy conversion process during the whole impact process, and it is related to the occurrence of delayed splash. The energy conversion process corresponds to the type of impact phenomena, which is affected by the film depth significantly. according to the differences in energy curves and flow characteristics, the impact phenomenon is divided into three types: the drop impacts on shallow, medium and deep films. A typical impact process of the medium film is analyzed in detail. The impact process is divided into five stages, namely, crown formation, crown growth, crown stabilization, crown collapse and central jet formation. In the crown formation and growth stages, inertial force promotes the deformation of the liquid-gas interface and surface tension prevents the deformation; while in the crown collapse stage, inertial force prevents the deformation and surface tension does the opposite effect. During the whole process, the viscous force plays a prevention effect.

Investigation of the anchor layer formation on different substrates and its feasibility for optical properties control by aerosol deposition

The effect of particles' kinetic energy and particle-substrate relative hardness ratio on anchor layer formation during aerosol deposition (AD) were investigated in this work. Fast anchor layer formation was observed using a substrate with a low relative hardness ratio (copper) while alumina fragments were generated using high relative hardness ratio substrates (alumina and sapphire). Using a room temperature AD method, novel formation of nanocomposite films exhibiting optical properties control was demonstrated. The desired nanocomposite particles were first formed by a facile electrostatic adsorption method prior to AD. Optical transmittance in the ultra-violet (UV) and infra-red (IR) regions could be controlled using the nanocomposite films while exhibiting good transmittance in the visible region. The feasibility of this nanocomposites thick film formation at room temperature would be beneficial for the development of optical-related nanocomposite ceramic films.

An application of quadrant and octant analysis to the atmospheric surface layer

The quadrant and octant analysis methods are used to investigate the characteristic of the atmospheric surface layer (ASL) turbulent flow based on the field observation data obtained from the Qingtu Lake Observation Array (QLOA). The results indicate that a stronger thermal convection intensity can lead to a larger intensity ratio of Reynolds stress from each quadrant to the total Reynolds stress. In the near-neutral ASL, the time ratios of Reynolds stress from each quadrant against the total Reynolds stress at different heights and friction velocities are approximately constant, i.e., DQ1≈0.19, DQ2≈0.296, DQ3≈0.2 and DQ4≈0.314. And the turbulent kinetic energy (TKE) ratios of each quadrant against the total TKE (streamwise or vertical) for the ejection events and sweep events are pretty similar at different wall-normal heights. The flow characteristics tend to be isotropic with the increasing of the vertical distance. Moreover, a threshold value is also applied to separate the most important events from the less significant ones. Last, the contribution of Octant 2 and Octant 8 is dominant to the Reynolds stress, and the intensity ratios of Octant 2 and Octant 8 to the total Reynolds stress will be increased with the thermal convection intensity. The abundant dynamics behaviors revealed by the quadrant and octant analysis could benefit us a wider understanding of the ASL coherent structures.