Drop Velocity Research Articles

The Iron Spin Transitions in Hydrous Fe3+‐Bearing Bridgmanite and Its Geophysical Properties in the Lower Mantle

AbstractHydrous Fe3+‐bearing bridgmanite (Bdg) is potentially a critical water host in the lowermost mantle. The spin transition behaviors of such materials are pivotal for understanding geophysical heterogeneity in the deep Earth but are poorly understood. Here, we investigated the spin transition and related geophysical properties of Fe3+ with associated H defects [Fe3+‐H] at high P‐T conditions using first‐principles simulations. Our calculations predict that the presence of hydrogen reduces the onset pressure of the spin transition of Fe3+ in Bdg, leading to higher fractions of low spin Fe3+. Along standard geotherms, spin transition is predicted to remain incomplete even at the core‐mantle boundary (CMB), and lateral temperature variations would significantly affect the proportions of high and low spin Fe and related properties like elasticity. The thermoelastic property of hydrous Fe3+‐bearing bridgmanite exhibit stronger softening anomalies at the lower mantle conditions compared to dry system, which potentially enhancing the seismic detectability of the hydrous Bdg in the deep earth. Density profile of hydrous Fe3+‐bearing bridgmanite indicates that the [Fe3+‐H] defect modestly increases the system's density, but much less than that caused by incorporating an equivalent amount of iron alone. This is crucial for understanding regions like Large Low Shear Velocity Provinces (LLSVPs), which exhibits large velocity drops but only minor density changes. The co‐adsorption of Fe and H allows for the introduction of Fe to induce velocity drops without the concomitant sharp increase in density, as pure iron would, thus enabling Fe‐H enrichment as a potential source of LLSVPs.

Analysis of Umbilical Artery Hemodynamics in Development of Intrauterine Growth Restriction Using Computational Fluid Dynamics with Doppler Ultrasound.

Intrauterine growth restriction (IUGR), the failure of the fetus to achieve his/her growth potential, is a common and complex problem in pregnancy. Clinically, IUGR is usually monitored using Doppler ultrasound of the umbilical artery (UA). The Doppler waveform is generally divided into three typical patterns in IUGR development, from normal blood flow (Normal), to the loss of end diastolic blood flow (LDBF), and even to the reversal of end diastolic blood flow (RDBF). Unfortunately, Doppler ultrasound hardly provides complete UA hemodynamics in detail, while the present in silico computational fluid dynamics (CFD) can provide this with the necessary ultrasound information. In this paper, CFD is employed to simulate the periodic UA blood flow for three typical states of IUGR, which shows comprehensive information on blood flow velocity, pressure, and wall shear stress (WSS). A new finding is the "hysteresis effect" between the UA blood flow velocity and pressure drop in which the former always changes after the latter by 0.1-0.2 times a cardiac cycle due to the unsteady flow. The degree of hysteresis is a promising indicator characterizing the evolution of IUGR. CFD successfully shows the hemodynamic details in different development situations of IUGR, and undoubtedly, its results would also help clinicians to further understand the relationship between the UA blood flow status and fetal growth restriction.

An experimental study on self-propulsion of Leidenfrost drops levitating on heated ratchet plates with various orientations and built-in line angles

The self-propelled motion of Leidenfrost drops has become a significant area of interest in recent years. This study introduces diverse combinations of ratchet surfaces in horizontal, angled, and vertical alignments with the aim of augmenting drop speed and manipulating its path in a chosen direction. Four pairs of symmetric ratchet surfaces were machined with different built-in line angles (θ). Each pair of ratchet surfaces was positioned at different plate inclination angles from the ground (α), and the drop motion through these binary surfaces was investigated. A series of experiments were conducted to examine the velocity of Leidenfrost drops levitating on the surface of ratchets with built-in line angles that were positioned at horizontal, inclined, and vertically channeled configurations. It was observed that employing horizontal V-shaped ratchets with built-in line angles resulted in an increased drop velocity when compared to the conventional horizontal ratchets. The effect of three different fluids, including water, ethanol, and methanol on the drop velocity was also studied with water drops demonstrating a superior velocity compared to the others. The results showed that the inclined and vertically channeled configurations can respectively lead to 24.2 % and 33 % higher drop velocities compared to conventional ratchets.

Seasonal Variability of Ice Motion for Hubbard and Valerie Glaciers, Alaska

Hubbard Glacier is a large fast-flowing tidewater-terminating glacier in the St. Elias Mountains and is connected at its terminus to Valerie Glacier. Although Hubbard Glacier has been shown to experience large intra-annual velocity changes and a long-term deceleration, previous seasonality studies have had limited timescale without a dense record of motion. Valerie Glacier’s variability has also been understudied, with only one study reporting its seasonal behaviour. The goal of this study was to combine ITS_LIVE, RADARSAT-2, RADARSAT Constellation Mission, and TerraSAR-X/TanDEM-X derived velocity data to create the densest record of motion ever constructed for Hubbard and Valerie glaciers from July 2013-April 2022 in order to explore seasonal velocity variability of both glaciers. Air temperature (NCEP-NCAR Reanalysis) was used to estimate surface melt on the glaciers, which was explored as a potential driver for seasonal velocity changes. Valerie Glacier had a seasonal pattern of fast flow in May, with minimum flow between August-November before accelerating again. Hubbard Glacier displayed a unique seasonal pattern that has not been previously observed on this glacier, with two periods of fast motion: one in May and one in December-February. It is inferred that the spring peaks and late summer/fall minimums on both glaciers are due to meltwater reaching the glacier bed and influencing the subglacial hydrology. The cause of the winter peak and slight velocity drop before the spring peak on Hubbard Glacier has not been determined and should be a topic for future studies, although it is hypothesized to influenced by its geometry.

Heterogeneous high frequency seismic radiation from complex ruptures

Fault geometric heterogeneities such as roughness, stepovers, or other irregularities are known to affect the spectra of radiated waves during an earthquake. To investigate the effect of normal stress heterogeneity on radiated spectra, we utilized a poly(methyl methacrylate) (PMMA) laboratory fault with a single, localized bump. By varying the normal stress on the bump and the fault-average normal stress, we produced earthquake-like ruptures that ranged from smooth, continuous ruptures to complex ruptures with variable rupture propagation velocity, slip distribution, and stress drop. High prominence bumps produced complex events that radiated more high frequency energy, relative to low frequency energy, than continuous events without a bump. In complex ruptures, the high frequency energy showed significant spatial variation correlated with heterogeneous peak slip rate and maximum local stress drop caused by the bump. Continuous ruptures emitted spatially uniform bursts of high frequency energy. Near-field peak ground acceleration (PGA) measurements of complex ruptures show nearly an order-of-magnitude higher PGA near the bump than elsewhere. We propose that for natural faults, geometric heterogeneities may be a plausible explanation for commonly observed order-of-magnitude variations in near-fault PGA.

A novel approach to designing compact cyclones for efficient natural gas filtration

This paper presents an innovative method to design cyclone separators based on geometrical principles, and incorporates a coupling iterative algorithm to obtain crucial parameters. The proposed approach allows for simultaneous variation of multiple key parameters, including inlet velocity, inlet height, and pressure drop. Thus, effects of varying one parameter on the others are accounted for. The innovative methodology is utilized to design a novel, high-performance cyclone potentially applicable in natural gas filtration. The introduced cyclone has a uniquely large inlet length to diameter ratio and a small curved cone, making it compact and usable in clusters to handle large flow rates. The cyclone is experimentally tested to evaluate its filtration performance. The results indicate that six micron or larger particles are completely separated, and a cut point diameter of 1 μm is achieved. Finally, the introduced cyclone is numerically investigated to analyze the gas flow behavior and visualize particle trajectories.

Precursors of rock failure under cyclic loading and unloading: From the perspective of energy and acoustics

The precursor characteristics of rock failure under cyclic loading and unloading are crucial to the prevention of underground engineering disasters. Taking sandstone as an example, this work conducted rock failure experiments under uniaxial cyclic loading and unloading combined with active wave velocity and passive acoustic emission (AE). The damage evolution process of rock was analyzed from the perspectives of energy, AE, and wave velocity. The results show that as the cyclic load stress level increases, the rigidity of the rock continuously increases, the proportion of elastic energy may reach a peak, and there will be an extreme time difference between the wave velocity and stress. The occurrence of the peak point of elastic energy proportion is a sufficient and unnecessary condition for the precursor characteristics of rock failure. The appearance of numerous AE events with high amplitude and high count is an effective precursor characteristic of rock failure. The stress continues to increase while wave velocity decreases is a key precursor characteristic of rock failure. There is a clear linear relationship between wave velocity drop and dissipated energy, it implies that both the which can quantitatively evaluate the rock damage under cyclic loading and unloading. The variation of wave velocity exhibits obvious anisotropic characteristics. This paper is not only a beneficial supplement to the theoretical system of rock failure precursors, but also provides new ideas and methods for rock stability monitoring and failure disaster early warning in underground engineering.

Size and velocity of jet drops produced by bursting bubbles at the interface of a water jet

Bursting bubbles at the free surface of aerated faucet water jets may spread pathogens through the released droplets. Many studies focused on the production of jet drops from bursting bubbles at a planar interface, particularly for the first jet drop. The extent to which previous findings apply to bubbles in aerated jets remains unknown. In this study, we produce a wide range of bubble size distributions within different jet diameters and characterize the diameter and velocity of jet drops released from individually bursting bubbles. Several similarities with the planar case are recovered, such as the overall dependence of the jet drop diameter and bursting dynamics on the bubble diameters and the formation of secondary jet drops. However, we observe asymmetries in the ejection of the droplets, and droplets ejected horizontally appear to have the highest ejection velocity among all jet drops. By modeling the evolution of the ejected drops for the different bubble size distributions, we find that for a mean Laplace number Labub=ρwσwRbubμw2≲6×104, a fraction of the drops ejected can become airborne. Droplets deposit within 9 cm for a mean Labub≲2.1×104 and within 33 cm for a mean 2.1×104≲Labub≲1.8×105 from a faucet jet, assuming a countertop situated 20 cm below the faucet outlet. A bubble size distribution with a mean Labub of 6×104 would minimize both the risk of airborne pathogen transmission and that resulting from surface contamination.

Splashing impact of a falling liquid drop

The splashing phenomenon associated with the impact of a liquid drop on a liquid pool is investigated in this study using the volume of fluid method. The different outcomes of this phenomena largely depend on the height (/depth) of a liquid pool and the impinging drop velocity. The impingement angle, drop shape, fluid properties, and other non-isothermal effects also play a role, but we have eliminated those dependencies by considering no variation in these parameters. The different phenomena that are observed when a drop impacts a liquid pool are controlled by (i) crater depth and wave-swell (rim of the crater) expansion, (ii) wave-swell retraction followed by crater side retraction, and (iii) crater base retraction. During splashing, a deep crater is produced in the receiving liquid after the drop impact. At its rim, a crown-like cylindrical liquid film is ejected out of the crater. Small droplets are normally shed from this rim. It is seen that the depth of the pool has dramatic effects on the dynamics of the crown formed during splashing. When observed even more comprehensively, the physical attributes of the crown, such as crown height and crown radius, are found to strongly relate to the velocity of the falling drop. Finally, we try to demarcate the regions of splashing with and without the formation of secondary droplets on the regime map of Weber number–dimensionless pool depth.

Effect of chemical reaction on MHD Casson natural convection flow over an oscillating plate in porous media using Caputo fractional derivative

Fractional calculus is a branch of mathematics that extends the traditional definitions of calculus to include non-integer exponents. It has been successfully used to model a variety of physical processes, including the coiling of polymers, viscoelasticity, traffic flow, diffusive transport, fluid dynamics, electromagnetic theory, and electrical networks. However, fractional calculus has not yet been widely used to study the physical properties of non-Newtonian fluids flowing over accelerating porous plates. The present research examines the unsteady Casson flow over an infinitely horizontal porous plate, MHD and porosity impacts on fluid velocity are also discussed. The major goal here is to develop analytical outcomes for the tran-sient incompressible MHD Casson flow over an accelerating porous plate. This plate is oscillating in the x-direction and infinitely large in the y-direction and fluids flowing over it at y > 0 due to oscillation. Choosing the right choice of dimensionless variables allows the model's governing equations to become dimensionless. These dimensionless differential equations of the Casson fluid are calculated by applying the Laplace transform method. On velocity, the impacts of different factors are investigated. They are time, porosity parameter, oscillation frequency of plate, magnetic parameter, and Casson fluid parameter. As we rise the Casson flow parameter values, magnetic parameter, and Prandtl number we observe that the velocity drops. In contrast to other factors, the effects of Grashof number, oscillation frequency, fractional parameter, and porosity on the velocity profile are reversed. Using Mathcad software, graphs are sketched for various values of these parameters and are thoroughly described. The fluid properties discovered signif-icant findings and disclosed several characteristics for a range of flow parameters and fractional parameter values. Increasing the values of fractional parameters is shown to improve the characteristics of fluids, and this is beneficial in fitting experimental data related to heating and cooling processes, particularly in electronic equipment.

Energy Absorption Behavior of Carbon-Fiber-Reinforced Plastic Honeycombs under Low-Velocity Impact Considering Their Ply Characteristics.

Honeycomb structures made of carbon-fiber-reinforced plastic (CFRP) are increasingly used in the aerospace field due to their excellent energy absorption capability. Attention has been paid to CFRP structures in order to accurately simulate their progressive failure behavior and discuss their ply designability. In this study, the preparation process of a CFRP corrugated sheet (half of the honeycomb structure) and a CFRP honeycomb structure was illustrated. The developed finite element method was verified by a quasi-static test, which was then used to predict the low-velocity impact (LVI) behavior of the CFRP honeycomb, and ultimately, the influence of the ply angle and number on energy absorption was discussed. The results show that the developed finite element method (including the user-defined material subroutine VUMAT) can reproduce the progressive failure behavior of the CFRP corrugated sheet under quasi-static compression and also estimate the LVI behavior. The angle and number of plies of the honeycomb structure have an obvious influence on their energy absorption under LVI. Among them, energy absorption increases with the ply number, but the specific energy absorption is basically constant. The velocity drop ratios for the five different ply angles are 79.12%, 68.49%, 66.88%, 66.86%, and 60.02%, respectively. Therefore, the honeycomb structure with [0/90]s ply angle had the best energy absorption effect. The model proposed in this paper has the potential to significantly reduce experimental expenses, while the research findings can provide valuable technical support for design optimization in aerospace vehicle structures.

Numerical assessment of using various outlet boundary conditions on the hemodynamics of an idealized left coronary artery model.

Vascular diseases are greatly influenced by the hemodynamic parameters and the accuracy of determining these parameters depends on the use of correct boundary conditions. The present work carries out a two-way fluid-structure interaction (FSI) simulation to investigate the effects of outlet pressure boundary conditions on the hemodynamics through the left coronary artery bifurcation with moderate stenosis (50%) in the left anterior descending (LAD) branch. The Carreau viscosity model is employed to characterise the shear-thinning behaviour of blood. The results of the study reveal that the employment of zero pressure at the outlet boundaries significantly overestimates the values of hemodynamic variables like wall shear stress (WSS), and time-averaged wall shear stress (TAWSS) compared with human healthy and pulsatile pressure outlet conditions. However, the difference between these variables is marginally low for human healthy and pulsatile pressure outlets. The oscillatory shear index (OSI) remains the same across all scenarios, indicating independence from the outlet boundary condition. Furthermore, the magnitude of negative axial velocity and pressure drop across the plaque are found to be higher at the zero pressure outlet boundary condition.

Subgrid scale modeling of droplet bag breakup in VOF simulations

The mesh-dependency of the breakup of liquid films, including their breakup length scales and resulting drop size distributions, has long been an obstacle inhibiting the computational modeling of large-scale spray systems. With the aim of overcoming this barrier, this work presents a framework for the prediction and modeling of subgrid-thickness liquid film formation and breakup within two-phase simulations using the volume of fluid method. A two-plane interface reconstruction is used to capture the development of liquid films as their thickness decreases below the mesh size. The breakup of the film is predicted with a semi-analytical model that incorporates the film geometry captured through the two-plane reconstruction. The framework is validated against experiments of the bag breakup of a liquid drop at We=13.8 through the comparison of the resulting drop size and velocity distributions. The generated distributions show good agreement with experimental results for drop resolutions as low as 25.6 cells across the initial diameter. The presented framework enables these drop breakup simulations to be performed at a computational cost three orders of magnitude lower than the cost of simulations utilizing adaptive mesh refinement.

Optimization design of hydrocyclone with overflow slit structure based on experimental investigation and numerical simulation analysis

This study aims to address the issue of high energy consumption in the hydrocyclone separation process. By introducing a novel slotted overflow pipe structure and utilizing experimental and response surface optimization methods, the optimal parameters were determined. The research results indicate that the number of slots, slot angles, and positioning dimensions significantly influence the performance of the hydrocyclone separator. The optimal combination was found to be three layers of slots, a positioning dimension of 5.3 mm, and a slot angle of 58°. In a Φ100mm hydrocyclone separator, validated through multiple experiments, the separation efficiency increased by 0.26% and the pressure drop reduced by 24.88% under a flow rate of 900 ml/s. CFD simulation verified the reduction in internal flow field velocity and pressure drop due to the slotted structure. Therefore, this study provides an effective reference for designing efficient and low-energy hydrocyclone separators.

Effect of Thermal Radiation on Fractional MHD Casson Flow with the Help of Fractional Operator

This study examines the effects of Newtonian heating along with heat generation, and thermal radiation on magnetohydrodynamic Casson fluid over a vertical plate. At the boundary, the Newtonian heating phenomena has been employed. The problem is split into two sections for this reason: momentum equation and energy equations. To transform the equations of the given model into dimensionless equations, some particular dimensionless parameters are defined. In this article, generalized Fourier’s law and the recently proposed Caputo Fabrizio fractional operator are applied. The corresponding results of non-dimensional velocity and heat equations can be identified through the application of Laplace transform. Moreover, Tzou’s algorithm as well as Stehfest’s algorithm is implemented to recognize the inverted Laplace transform of heat and momentum equations. Finally, a graphical sketch is created using Mathcad 15 software to demonstrate the results of numerous physical characteristics. It has been reported that the heat and velocity drop with rising Prandtl number values, whereas the fluid’s velocity has been seen to rise with increasing Grashof number values. Additionally, current research has shown that flow velocity and temperature increase with rising values of a fractional parameter.

Experimental Investigation of Threshold Velocities for Air-Water Two-Phase Flow in a Vertical Tube and Annular Channels

This work presents an experimental study of five threshold velocities for air-water flow in three different vertical channels. The measured threshold velocities included onset flooding (OF), end flooding (EF), onset deflooding (OD), end deflooding (ED), and minimum pressure (MP) velocities. The experimental system includes a transparent vertical tube of 52.5 mm inner diameter and 1500 mm length. The test channel can be easily changed from a tube to an annular shape by inserting a cylindrical test element. A counter-current or concurrent upward flow was achieved by blowing air upward from the channel’s bottom and flowing water from its top. The threshold velocities were determined by analyzing the pressure drop versus air superficial velocity. Findings revealed evident hysteresis between the end flooding and onset deflooding velocities. In contrast, the end deflooding and onset flooding velocities were found to be identical. The end flooding velocity was indifferent to the water’s superficial velocity for all three channel geometries. A generalized gas-liquid flow state diagram for vertical channels is developed based on the present empirical analysis for different threshold velocities.

Centrifugal failure mechanism analysis for ferrofluid seals based on a bidirectional coupled multi-physics model

In this paper, we propose a bidirectional coupled multi-physics (BCM) model to study the centrifugal failure mechanism of ferrofluid seals, employing a hybrid finite volume–finite element method. In this model, the evolution of the flow field is described by the two-phase incompressible Navier-Stokes (NS) equations with Kelvin force. The volume of fluid (VOF) method is used to capture the gas-ferrofluid interface. Magnetic scalar potential is introduced to solve for the magnetostatic field. We conducted secondary development on the OpenFOAM and Elmer software packages, which are based on the finite volume method (FVM) and finite element method (FEM), respectively, to calculate the flow field and magnetic field in ferrofluid seals. By developing interpolation methods between FEM and FVM grids based on the parallel bidirectional coupler EOF-Library[1], field information exchange between the flow field and magnetic field is achieved. The BCM model executes iterative computations on the flow and magnetic fields in an alternating way, continuously synchronizing the information of each, thus facilitating bidirectional coupling between the FVM and FEM frameworks. We employ the BCM model to investigate the failure mechanisms of ferrofluid seals under different conditions, including various load pressure and rotational velocity. The results indicate that the ferrofluid will leave the surface of the shaft along the pole teeth under the action of centrifugal forces, with the highest radial velocity occurring at the boundary of the liquid film. Under varying conditions of rotational velocity and pressure drop, the centrifugal failure modes of ferrofluid seals exhibit distinct differences. Moreover, two dimensionless numbers are proposed to quantitatively evaluate the effects of load pressure and centrifugal force, thereby augmenting the efficacy of seal design.

Numerical Analysis of Sedimentation in Open Channels Using Computational Fluid Dynamics

This study investigates sedimentation in open channels utilizing Computational Fluid Dynamics (CFD). The validation indicates a strong agreement between the simulation and the reference data. Flow velocity substantially decreases in the branched channel post-bifurcation. Similarly, at a 90o bend, there is a notable drop in flow velocity after the curve. A vortex forms in areas where the velocity decreases. Sedimentation prediction can be achieved by observing these velocity reductions in specific channel sections. In the branched channel, low velocities and localized water eddies are found after the bifurcation point. In a channel with a 90o bend, the velocity diminishes on the inner side of the curve, with vortices forming, acting as potential sediment traps. This study highlights the utility of CFD as an effective method for enhancing the understanding of sedimentation processes in river systems.

Pressure drop and bubble velocity in Taylor flow through square microchannel

Interface tracking simulations of gas–liquid Taylor flow in horizontal square microchannels were carried out to understand the relation between the pressure drop in the bubble part and the curvatures at the nose and tail of a bubble. Numerical conditions ranged for 0.00159 ≤ CaT ≤ 0.0989, 0.0817 ≤ WeT ≤ 25.4, and 8.33 ≤ ReT ≤ 791, where CaT, WeT, and ReT are the capillary, Weber, and Reynolds numbers based on the total volumetric flux. The dimensionless pressure drop in the bubble part increased with increasing the capillary number and the Weber number. The curvature at the nose of a bubble increased and that at the tail of a bubble decreased as the capillary number increased. The variation of the curvature at the tail of a bubble was more remarkable than that at the nose of a bubble due to the increase in the Weber number, which was the main cause of large pressure drop in the bubble part at the same capillary number. The relation between the bubble velocity and the total volumetric flux was also discussed. The distribution parameter of the drift-flux model without inertial effects showed a simple relation with the capillary number. A correlation of the distribution parameter, which is expressed in terms of the capillary number and the Weber number, was developed and was confirmed to give good predictions of the bubble velocity.

The IACOB project

The properties of blue supergiants are key for constraining the end of the main sequence (MS) of massive stars. Whether the observed drop in the relative number of fast-rotating stars below ≈21 kK is due to enhanced mass-loss rates at the location of the bistability jump, or the result of the end of the MS is still debated. Here, we combine newly derived estimates of photospheric and wind parameters with Gaia distances and wind terminal velocities from the literature to obtain upper limits on the mass-loss rates for a sample of 116 Galactic luminous blue supergiants. The parameter space covered by the sample ranges between 35–15 kK in Teff and 4.8–5.8 dex in log(L/L⊙). Our results show no increase in the mass-loss rates over the bistability jump. Therefore, we argue that the drop in rotational velocities cannot be explained by enhanced mass loss. Since a large jump in the mass-loss rates is commonly included in evolutionary models, we suggest an urgent revision of the default prescriptions currently in use.