Velocity Size Distribution Research Articles

Experimental and Numerical Simulation of Ejecta Size and Velocity of Hypervelocity Impact Rubble-Pile Asteroid

Rubble-pile asteroids may be the type of near-Earth object most likely to threaten Earth in a future collision event. Small-scale impact experiments and numerical simulations for large-scale impacts were conducted to clarify the size ratio of the boulder/projectile diameter effects on ejecta size–velocity distribution. A series of small-scale impact cratering experiments were performed on porous gypsum–basalt targets at velocities of 2.3 to 5.5 km·s−1. Three successive ejection processes were observed by high-speed and ultra-high-speed cameras. The momentum transfer coefficient and cratering size were measured. A three-dimensional numerical model reflecting the random distribution of the interior boulders of the rubble-pile structure asteroid is established. The size ratio (length to diameter) of the boulder size inside the asteroid to the projectile diameter changed from 0.25 to 1.7. We conducted a smoothed particle hydrodynamics numerical simulation in the AUTODYN software to study the boulder size effect on the ejecta size–velocity distribution. Simulation results suggest that the microscopic porosity on regolith affects the propagation of shock waves and reduces the velocity of ejecta. Experiments and numerical simulation results suggest that both excavation flow and spalling ejection mechanism can eject boulders (0.12–0.72 m) out of the rubble-pile asteroid. These experiments and simulation results help us select the potential impact site in a planetary defense scenario and reduce deflection risk. are comprised primarily of boulders of a range of sizes.

Direct Numerical Simulation of Atomization Characteristics of ECN Spray-G Injector: In-Nozzle Fluid Flow and Breakup Processes

AbstractIn order to sustain applications dealing with various liquid fuels in internal combustion engine (ICE), it is essential to make available prediction methodologies that allow an early evaluation of the potential usefulness of such fuels in terms of favourable mixture preparation process already in realistic configurations. Since the air-mixture formation and subsequent processes are predominantly governed by the fuel injection, a DNS based numerical investigation coupled with VOF as an interface tracking method is carried out in this paper to gain better insight on the fuel injection from an industrial injector "Spray G" configuration. Chosen from Engine Combustion Network (ECN), this is a gasoline direct injector (GDI) featuring 8-holes orifices and operating with high injection pressure (200 bar). Under consideration of the required computational cost associated with DNS, only the 1/8 of the nozzle geometry including one orifice is used. The numerical simulation is accomplished for the quasi-steady injection condition with nozzle needle fully opened. The obtained results are first validated with available experimental data for nozzle mass flow rate and spray spread angle showing a good agreement. Then, a detailed numerical analysis is provided for the in/near nozzle flow evolution especially for flow turbulence, primary and secondary atomization. Furthermore, droplet statistics in terms of droplet shape, and droplet size-velocity distribution together with a breakup regime map are reported. Finally, a 2-D data curation technique is proposed to extract the droplet statistics along selected planes and evaluated by direct comparison with three-dimensional droplet data, which may allow handling of the DNS data in more feasible and economical way especially for time series data with higher frequency. The comprehensive DNS data generated by this DNS-VOF approach enable not only to carry out detailed numerical analysis of in- and near-nozzle physical phenomena for which experimental data are still scarce, but also to provide a hint of more reliable injector boundary conditions useful for lower order spray injection method based on Lagrangian particle tracking.

Spray Drop Size Distribution and Velocity Distribution issued from a Prefilming Airblast Atomizer

Spray Drop Size Distribution and Velocity Distribution issued from a Prefilming Airblast Atomizer

Microscopic spray characteristics of ethanol and methanol blended gasoline in a direct injection spark ignition engine

Renewable fuels are continuously being refined/ upgraded for automotive applications to reduce dependence on conventional fossil fuels. However, optimized use of these renewable fuels in existing and new engines/ vehicles requires comprehensive characterization and understanding of spray atomization and fuel-air mixture formation processes. Spray atomization and mixture formation depends on fuel injection pressure (FIP), fuel injection quantity and ambient conditions. This study is aimed at exploring microscopic spray characteristics of ethanol and methanol blended gasoline for automotive applications, particularly in direct injection Spark Ignition (DISI) engines. Phase Doppler interferometer (PDI) technique was used for comparative microscopic spray characterization in a constant volume spray chamber (CVSC) at ambient pressure condition, to evaluated spray droplet size-velocity distributions and joint probability density function (JPDF) of different test fuels. In this study, two gasohol mixtures [15% v/v ethanol and methanol blended with 85% v/v gasoline] and baseline gasoline were experimentally evaluated for comparing spray droplet size-velocity distributions at two different FIPs of 80 and 160 bars, at two different fuel injection quantities of 12 and 28 mg/injection, which are typical representative conditions for a DISI engines. The results from this experimental investigation are valuable for automotive and fuel industries, and spray community, which are continuously upgrading renewable and oxygenated fuels and engine technologies for efficiency improvement and emission reduction.

Prediction of the Initial Drop Size and Velocity Distribution in the Cold Cryogenic Spray

The polydispersed nature of the spray is captured through the use of probability density functions based on the maximum entropy method to stand for the complete atomization characteristics of spray dynamics. The droplet and velocity size distributions are practical tools for the analysis of sprays cooling. The special benefit of the model is a Eulerian based which is less computationally intensive when compared to models that are based on the Lagrangian approach that tracks droplet parcel. The accuracy of using Lagrangian approach in polydispersed phase is always accurately less than Eulerian approach because it depends on the number of parcels while in Eulerian approach it depends on the proposed continuous distribution function. The main intent of the current work is to evaluate the capability of using the model for the initial predictions of the droplet size and velocity distribution for liquid nitrogen spray of solid-cone pressure swirl nozzle. The use of liquid injection pressure cases of up to 0.6MPa and spray cone angles of just 30◦ from three different sets of experimental data. The results being characterized are spray drop size distribution, liquid volume fraction and spray cone angle values. The unsteady analyses of the effect of injection pressure are studied on the cryogenic liquid nitrogen. The numerical results show that the maximum entropy method applies to liquid cryogenic spray and indicates that the model reacts correctly to changes in different injection pressures. Comparisons are also made with measured drop size distribution data that are reasonably captured and the spray cone angle is found to be in good agreement during initial and far-field spray angles.

Spray Structure and Characteristics of a Pressure-Swirl Dust Suppression Nozzle Using a Phase Doppler Particle Analyze

In order to understand the characteristics of the spray field of a dust suppression nozzle and provide a reference for dust nozzle selection according to dust characteristics, a three-dimensional phase Doppler particle analyzer (PDPA) spray measurement system is used to analyze the droplet size and velocity characteristics in a spray field, particularly the joint particle size–velocity distribution. According to the results, after the ejection of the jet from the nozzle, the droplets initially maintained some velocity; however, the distribution of particles with different sizes was not uniform. As the spray distance increased, the droplet velocity decreased significantly, and the particle size distribution changed very little. As the distance increased further, the large droplets separated into smaller droplets, and their velocity decreased rapidly. The distributions of the particle size and velocity of the droplets then became stable. Based on the particle size-velocity distribution characteristics, the spray structure of pressure-swirl nozzles can be divided into five regions, i.e., the mixing, expansion, stabilization, decay, and rarefied regions. The expansion, stabilization, and decay regions are the effective dust fall areas. In addition, the droplet size in the stabilization region is the most uniform, indicating that this region is the best dust fall region. The conclusions can provide abundant calibration data for spray dust fall nozzles.

Spray droplet size distribution and droplet velocity measurements in a firing optical engine

Macroscopic spray characteristics of a fuel injection system in an internal combustion (IC) engine have a direct impact on engine performance, emissions, and combustion characteristics. Nonintrusive in-cylinder measurements provide insights into the spray formation process for greater understanding of fuel-air mixing and combustion processes in an IC engine. In this paper, there are two parts: (a) procedure and methodology to configure the Artium phase Doppler interferometer (PDI) for in situ measurements through a cylindrical window and (b) comparative macroscopic spray characteristics in a firing Gasoline Direct Injection (GDI) optical engine to a constant volume spray chamber (CVSC) for spray droplet size-velocity distributions. Binned average velocity and average Sauter mean diameter of spray droplets in a firing engine were compared with that of a CVSC. Probability density function of droplet diameters in the CVSC under ambient conditions and in the engine combustion chamber provides an insight into the comparative droplet size distributions and droplet dynamics. Discussion on challenges encountered during PDI measurements in the firing engine environment, safety protocols, and tools required is also included. In addition, shadowgraphy images have been used to discuss the details on spray boundaries and spray evolution. The droplet size distribution inside the engine combustion chamber was found to be significantly different from the one observed in the CVSC. An engine simulation model can be developed/validated by using the data reported in this manuscript for attaining superior accuracy in the model. This paper describes the comparisons of the spray droplet size and velocity distributions in a CVSC and in situ for a working GDI engine. Maximum spray droplet velocity components (Vx, Vy) under engine combustion chamber conditions were 29.8 m/s, 14.2 m/s whereas the corresponding velocities in the CVSC under ambient conditions they were 78.41 m/s, 23.92 m/s, respectively, showing a large difference between the traditional measurements in the CVSC simulating engine conditions, and actual firing engine conditions. This study also reports the very first attempt in the open literature to measure spray droplet size and velocity distribution measurements in a firing IC engine.

Fast Slip Velocity in a High-Entropy Alloy

Due to fluctuations in nearest-neighbor distances and chemistry within the unit cell, high-entropy alloys are believed to have a much higher resistance to dislocation motion than pure crystals. Here, we investigate the coarse-grained dynamics of a number of dislocations being active during a slip event. We found that the time-resolved dynamics of slip is practically identical in Au〈001〉 and an Al0.3CoCrFeNi〈001〉 high-entropy alloy, but much faster than in Nb〈001〉. Differences between the FCC-crystals are seen in the spatiotemporal velocity profile, with faster acceleration and slower velocity relaxation in the high-entropy alloy. Assessing distributions that characterize the intermittently evolving plastic flow reveals material-dependent scaling exponents for size, duration, and velocity–size distributions. The results are discussed in view of the underlying dislocation mobility.

Oil Fragmentation, Interfacial Surface Transport and Flow Structure Maps for Two-Phase Flow in Model Pore Networks. Predictions Based on Extensive, DeProF Model Simulations

In general, macroscopic two-phase flows in porous media form mixtures of connected- and disconnected-oil flows. The latter are classified as oil ganglion dynamics and drop traffic flow, depending on the characteristic size of the constituent fluidic elements of the non-wetting phase, namely, ganglia and droplets. These flow modes have been systematically observed during flow within model pore networks as well as real porous media. Depending on the flow conditions and on the physicochemical, size and network configuration of the system (fluids and porous medium), these flow modes occupy different volume fractions of the pore network. Extensive simulations implementing the DeProF mechanistic model for steady-state, one-dimensional, immiscible two-phase flow in typical 3D model pore networks have been carried out to derive maps describing the dependence of the flow structure on capillary number, Ca, and flow rate ratio, r. The model is based on the concept of decomposition into prototype flows. Implementation of the DeProF algorithm, predicts key bulk and interfacial physical quantities, fully describing the interstitial flow structure: ganglion size and ganglion velocity distributions, fractions of mobilized/stranded oil, specific surface area of oil/water interfaces, velocity and volume fractions of mobilized and stranded interfaces, oil fragmentation, etc. The simulations span 5 orders of magnitude in Ca and r. Systems with various viscosity ratios and intermediate wettability have been examined. Flow of the non-wetting phase in disconnected form is significant and in certain cases of flow conditions the dominant flow mode. Systematic flow structure mutations with changing flow conditions have been identified. Some of them surface-up on the macroscopic scale and can be measured e.g. the reduced pressure gradient. Other remain in latency within the interstitial flow structure e.g. the volume fractions of − or fractional flows of oil through − connected-disconnected flows. Deeper within the disconnected-oil flow, the mutations between ganglion dynamics and drop traffic flow prevail. Mutations shift and/or become pronounced with viscosity disparity. They are more evident over variables describing the interstitial transport properties of process than variables describing volume fractions. Τhis characteristic behavior is attributed to the interstitial balance between capillarity and bulk viscosity.

Radar Attenuation and Reflectivity Measurements of Snow With Dual Ka-Band Radar

There is insufficient understanding of backscattering and attenuation for the radiowave remote sensing of snow because ground measurements of snow in the Ka-band are limited. This study estimates the equivalent radar reflectivity factor $(Z_e)$ and specific attenuation $(k)$ of snow using a dual Ka-band radar (KaR) system comprising two identical Ka-band instruments. To evaluate the estimations, estimated $k{-}Z_e$ plots of rain events are compared with plots estimated from the raindrop size distribution. The two $k{-}Z_e$ plots have similar power-law relations. In contrast, $k{-}Z_e$ plots of snow have complex tendencies. Among snow events, the tendencies of $k{-}Z_e$ relations depend on surface temperature. When surface temperature exceeds 0 °C during snow events, $k{-}Z_e$ data are scattered and there are $k$ values higher than those of rain. In contrast, when surface temperature is below 0 °C during snow events, both $k$ and $Z_e$ are low and the $k{-}Z_e$ plots show no relation. In the former (latter) cases, wet (dry) snow is probably dominant. The differences in $k{-}Z_e$ relations of snow are attributed to the differences in backscattering and attenuation characteristics between wet and dry snow. To confirm the existence of wet/dry snow, snow particle data obtained using a two-dimensional video disdrometer on the ground are analyzed. Velocity–size distributions are clearly different in wet- and dry-snow cases. For dry-snow cases, snow particles of dry snow and graupel occasionally coexisted.

Mass-velocity and size-velocity distributions of ejecta cloud from shock-loaded tin surface using atomistic simulations

The mass (volume and areal densities) versus velocity as well as the size versus velocity distributions of a shock-induced cloud of particles are investigated using large scale molecular dynamics simulations. A generic three-dimensional tin crystal with a sinusoidal free surface roughness (single wavelength) is set in contact with vacuum and shock-loaded so that it melts directly on shock. At the reflection of the shock wave onto the perturbations of the free surface, two-dimensional sheets/jets of liquid metal are ejected. The simulations show that the distributions may be described by an analytical model based on the propagation of a fragmentation zone, from the tip of the sheets to the free surface, in which the kinetic energy of the atoms decreases as this zone comes closer to the free surface on late times. As this kinetic energy drives (i) the (self-similar) expansion of the zone once it has broken away from the sheet and (ii) the average size of the particles which result from fragmentation in the zone, the ejected mass and the average size of the particles progressively increase in the cloud as fragmentation occurs closer to the free surface. Though relative to nanometric scales, our model may help in the analysis of experimental profiles.

Secondary craters from large impacts on Europa and Ganymede: Ejecta size–velocity distributions on icy worlds, and the scaling of ejected blocks

We have mapped fields of secondary craters around three large primary craters on Europa and Ganymede and estimated the size and velocity of the fragments that formed the secondaries using updated scaling equations for ice impacts. We characterize the upper envelope of the fragment size–velocity distribution to obtain a function for the largest fragments at a given ejection velocity. Power-law velocity exponents found in our study of icy satellite secondary fields are compared to the exponents found for similar studies of mercurian, lunar, and martian craters; for all but basin-scale impacts, fragment size decreases more slowly with increasing ejection velocity than on rocky bodies. Spallation theory provides estimates of the size of ejected spall plates at a given velocity, but this theory predicts fragments considerably smaller than are necessary to form most of our observed secondaries. In general, ejecta fragment sizes scale with primary crater diameter and decrease with increasing ejection velocity, υej, by 1/υej or greater, and point-source scaling implies a relation between the two. The largest crater represented in any of these studies, Gilgamesh on Ganymede, exhibits a relatively steep velocity dependence. Extrapolating the results to the escape speed for each icy moon yields the size of the largest fragment that could later re-impact to form a so-called sesquinary crater, either on the parent moon or a neighboring satellite. We find that craters above 2km in diameter on Europa and Ganymede are unlikely to be sesquinaries.

Intermittent multijet sprays for improving mixture preparation with low-pressure injection systems

In this work, the characteristics of droplets produced by a multijet impingement atomization process are measured with a Phase-Doppler Interferometer and statistically described using finite mixtures of weighted probability density functions. Through this statistical tool, drop size and axial velocity distributions are involved in the physical interpretation of the flow, instead of limiting it to first- and second-order distribution moments. Each group of droplets with similar size characteristics has been modeled by lognormal distributions and normal distributions relatively to drop axial velocity. The analysis based on finite mixtures identified three groups of droplets with similar size characteristics, although the group with smaller sizes is negligibly represented in the statistical finite mixture. Also, the lognormal standard deviation in all groups is well correlated with the corresponding geometric mean diameter allowing to simplify the description of the spray. In terms of axial velocity, mainly one distribution has been identified with a relatively constant standard deviation, and a characteristic velocity slightly dependent on the duty cycle associated with the spray intermittent condition. Furthermore, droplets characteristics are correlated with the heat transfer rate obtained for several operating conditions that maintain the surface temperature in steady-state at 125 °C. The effect of the time between consecutive injections is analyzed. Concerning the potential use of multijet impingement sprays for fuel injection systems, results evidence the importance of an interaction between thin liquid film heat transfer and droplets axial velocity for enhancing heat transfer and promote evaporation. This would decrease the amount of fuel deposited on interposed surfaces, thus, improving mixture preparation in low-pressure injection systems for internal combustion engines.

Pipeline Flow of Heavy Crude Oil Emulsions

Abstract Using a 53 mm test pipeline, emulsions containing up to 67% Lloydminster heavy crude oil in water have been transported in laminar and turbulent flow. Pressure drops, droplet size distributions, viscometry and velocity distribution measurements were made. The results showed that a homogeneous model was appropriate for emulsions with median droplet sizes near 30 microns. Introduction Pipeline flow of oil in water emulsions occurs widely in field operations and has also been studied systematically in laboratory conditions. Zakin et al.(1), used oils with specific gravities between 0.78 and 0.923 in emulsions formed in a colloid mill. The emulsions were non-Newtonian at oil concentrations of 50% by weight and above. Turbulent flow pressure drops were between 8% and 26% lower than values predicted using their laminar flow behaviour. These predictions used the Dodge and Metzner(2) correlation for turbulent non-Newtonian friction which has been largely supplanted by those of Wilson and Thomas(3) and Thomas and Wilson(4). Pal and Rhodes(5) used a mineral oil of comparatively low viscosity and inferred effective viscosities from the laminar and turbulent flow pressure gradients, assuming Newtonian fluid behaviour. With 45% and 55% oil in water emulsions, laminar flow effective viscosities were significantly lower than those in turbulent flow. The droplet size was unknown, however. With heavy crudes, inversion(6,7) of an oil-in-water emulsion to a water-in-oil emulsion can occur during pipeline flow with a catastrophic increase in pipeline pressure drop if the oil wets the pipe wall. On the other hand Layrisse et al.(8), found stable emulsions for a wide range of concentrations (to 65% oil) and shear rates with droplets whose mean diameters ranged between 6 and 86 ?m. Good agreement was found between viscosities inferred from pipeline pressure drops and values measured with Couette viscometers. The rheology was strongly dependent on droplet size, however, and non-Newtonian behaviour was evident for smaller diameters, low shear rates and high oil concentrations. Turbulent flow pressure drops appeared to be within 20% of the predicted values. In contrast with these results, Wyslouzil et al.(9), found pipeline pressure drops to be significantly lower than values predicted using measured viscosities, in both the laminar and turbulent flow regions. The disparity was attributed to droplet migration away from the wall, producing a region of depleted concentration. With prolonged recirculation in a closed loop, an instability occurred which resembled the inversion reported by Gillies et al.(6) The initial droplet size in the Wyslouzil experiments was in the range of 5 – 10 µm. Gillies and Shook(7) have reported experiments conducted with high oil concentrations in laminar pipe flow. Differences between the apparent viscosities in pipe flow and those measured in a Couette viscometer were also attributed to droplet migration and evidence for this was obtained in the form of velocity distributions measured with a pitot tube. In contrast with the droplets in the Wyslouzil et al. experiments, the droplets were too large to allow their diameters to be determined photographically.

Evaluation of the potential to dispose of sewage-sludge. 2. Potential for off-site movements of solids and solutes

This paper reports a study of the potential for off-site movements of pollutants from sewage sludge broadcast onto the soil surface in Pinus plantations established on the coastal lowlands of south-east Queensland. Laboratory studies of size and settling velocity distributions of rainfall-wetted sludge showed that it is relatively coarse and non-erodible. Field rainfall simulation studies at three sites in pine forests near Beerburrum found no significant increase in interrill erosion due to broadcasting of sludge. (Most or all of the sediment was observed to come from mineral soil exposed when a gutter to collect runoff was installed at the downslope ends of the plots.) However, there was considerable movement of solutes in runoff from rainfall simulator plots that had received sludge-either freshly applied or 'consolidated' sludge (that had been broadcast on the plots 6 months prior to the rainfall simulation study and exposed to rain and weathering). Electrical conductivity (EC) of runoff from freshly applied sludge was initially high but decreased steadily during the 30 min rainfall event. Runoff from consolidated sludge had lower ECs, though significantly (P < 0.05) higher than those of runoff from control plots. Concentrations of nitrate-N and ammonium-N were initially high in runoff from freshly applied sludge, but decreased rapidly during the rainfall event. In contrast, concentrations of mineral N in runoff from consolidated sludge were low throughout the rainfall event. These results indicate a significant risk of off-site N pollution if runoff occurs during the first rains following broadcasting of sludge. By contrast, concentrations of total phosphorus, copper, and zinc in runoff from both fresh and consolidated sludge were relatively high, and showed only small decreases during the rainfall event applied. This suggests that sludge will contribute significant quantities of these elements to runoff for extended periods after broadcasting. The implications of these findings become important in terms of the timing and method of sludge application to the soil.

Effect of an impact-generated gas cloud on entrained surface boulders and spall ejecta

The purpose of this investigation is to study the effect of an impact-generated gas cloud on the size-velocity distribution of large, solid ejecta fragments that become entrained in it, with particular reference to the possible Martian origin of the SNC meteorites. The entrainment both of loose surface boulders and of the early-time, large-size, high-velocity spall component of the crater ejecta is modeled numerically. Surface boulders from as far as 40 km from the center of impact can be accelerated by the high velocity leading edge of the gas cloud to velocities in excess of Martian escape velocity (5 km/s), but are generally crushed by the acceleration. Spall fragments become entrained later and nearer the center of the gas cloud, where gas velocities are much less. High velocity spalls are decelerated by the gas and low velocity spalls are accelerated by the gas, but no spalls ejected at < 5km/s are accelerated to velocities 5km/s. An impact-generated gas cloud is thus expected to scour the pre-existing surface of loose material and to change the size-velocity distribution of spall ejecta, but does not sufficiently enhance the velocities of crater ejecta to explain the Martian origin of SNC meteorites as large rocks.

Bubble properties and mixing characteristics in an airlift bubble column with redistributor

The effects of gas velocity liquid velocity redistributor and their free surface area on bubble properties (size rising velocity size distribution) and mixing characteristics (mixing time circulation time) were studied in an internal airlift bubble column Bubble properties were measured by resistivity probe method, and mixing characteristics were obtained by salt-base impulse method in air-water system. The empirical correlations between bubble properties, mixing characteristics and various operating parameters were proposed The disk type redistnbutor was more effective to redisperse coalesced bubbles than the perforated plate type Especially, the disk type with 19.5% free surface area had given the best result.

Size-velocity distribution of large ejecta fragments

The size-range distributions of secondary craters around three large primary craters on the Moon and Mars were measured. Ejection velocities of the fragments that produced the secondaries were estimated from the ranges of the secondaries from the primary. These velocities were then used in the Schmidt-Holsapple scaling relations to estimate the size of the ejecta fragments. Since it is unclear whether the secondary cratering events lie in the strength-dominated regime or in the gravity-dominated regime (or in the transition between the two), the data were reduced separately for both regimes in order to bracket the “true” answer. Furthermore, Schmidt and Holsapple have defined two scaling relations for the gravity regime, one appropriate for porous rock or regolith, and the other for nonporous target rocks. Since the nature of the target rock is unknown, both gravity scaling relations were used to reduce the data. The inferred size-velocity distributions of ejecta are compared to the predictions of the Melosh spallation model for 10 and 20 km/sec impacts of andesite onto andesite. The maximum inferred ejecta sizes are much greater than the maximum predicted spall sizes. This is consistent with the corresponding secondary craters having been produced by clustered impactors, with the inferred impactor diameter approximating the effective diameter of the cluster (Schultz and Gault, 1985). The inferred velocities show cutoffs at ⪅1 km sec . Whether this cut-off is real or is due to the inability to recognize secondary craters at greater ranges is unknown.