Drop Velocity Research Articles

Numerical simulation of Darcy–Brinkman oscillatory flow of dissipative fluid: Utilization of finite difference method

This study investigates viscous flow behavior in a Darcy–Brinkman porous medium, considering the effects of porous dissipation and frictional heating. The fluid is flowing over a flat plate, oscillating in its plane. The velocity and temperature profiles are simulated using a mathematical model that includes linear convection and considers the effects of porous and viscous dissipation. After performing mathematical transformations, the governing equations are modified into coupled and nonlinear dimensionless PDEs. The forward time centered space method numerically solves the modeled dimensionless equations. The acquired results are explicitly validated against the findings of the literature in a situation where limits are considered. The numerical results are presented graphically, providing a comprehensive analysis of the variables impacting fluid characteristics, including temperature and velocity. Interestingly, this work shows that a rise in the porosity parameter causes temperature profiles to rise and velocity to decrease. Moreover, a drop in velocity is linked to a rise in the Prandtl number. Furthermore, the influence of surface friction is diminished by including the porosity parameter. Moreover, a rise in the heat transmission rate at the surface can be observed.

Analytical solutions for airborne droplet trajectory: Implications for disease transmission

Airborne droplets containing viruses from infected persons can present long range disease transmission risks. In this study, we examine the trajectory of an airborne droplet based on a point force model. The interplay between gravity, drag, inertia and deformation are factored in, for drop sizes ranging from micrometer to millimeter size. In particular, we propose an expression for the drag force which enables analytical solutions for cases of practical interest, such as the transient velocity behavior and spreading distances. This allows us to obtain physical insights which are not obvious from direct numerical simulations. Effects such as droplet deformation, breakup and evaporation are also considered. Our analytical solutions compare favorably with numerical and experimental data. The evaporation rate was determined experimentally with a levitating device and some experimental drop velocity versus time data were obtained with falling millimeter sized droplets.

Analyzing possible seismic velocity changes in Mexico City using seismic noise interferometry

The seismic response of the Mexico City basin has received plenty of attention as one of the most relevant cases of ground motion amplification. A recent study showed possible velocity variations of the deposits in both the lake bed and firm ground. A clear drop in seismic velocity was observed during the 2017.09.19 earthquake (Mw 7.1) in addition to more subtle seismic velocity changes related to seasonal temperature and precipitation. We use continuous seismic noise data recorded in a 29 broadband seismograph network in and around Mexico City to investigate Rayleigh wave group velocity structure and velocity changes. We estimate Green's functions (GF) between station pairs using seismic noise cross-correlation. An average estimate is computed for each of three five-day periods of recording. GFs are dominated by a Rayleigh pulse at low frequencies (between 0.1 and 0.2 Hz). Velocity changes are investigated through the comparison between GF's for different five-day periods. No velocity variations are observed. Station pairs separated at a distance smaller than 20 km also show some Rayleigh wave energy at higher frequencies, between 0.3 and 1.2 Hz. We repeated the analysis in a higher frequency band (up to 5 Hz) and show that again no velocity variation can be observed. In addition, we used horizontal-to-vertical spectral ratios computed for both earthquake and seismic noise records to identify possible non-linear effects during the 2017 earthquake. The results showed that significant non-linear effects during that event are to be discarded. Finally, we present preliminary results of a tomography of Rayleigh wave group velocity at the center of the array. Lateral structure variations below the geotechnical zonation are significant. Our data will be useful to constrain the structure of the volcanic deposits of the Transmexican Volcanic Belt (TVB).

MFiX-TFM simulation of hydrodynamics of a dual fluidized bed system

The abundance and replenishable nature of biomass make it a suitable fuel for power generation. Among the various technologies, dual fluidized bed gasification (DFBG) is a suitable technology to generate high-quality syngas from biomass. However, the complexity of hydrodynamics and heat transfer with bed geometry, flow conditions as well as feedstock demands effective research for the design of such system. This study, therefore, focuses on the simulation of hydrodynamics of a dual fluidized bed gasification system. The 2-D two-fluid model (TFM) simulations were performed using Multiphase Flow with Interphase eXchanges (MFiX) software by varying the superficial air velocities for both the gasifier and riser. The influence of superficial air velocity on static pressure, pressure drop, axial and radial voidage, solid velocities, and granular temperature was evaluated. From the simulations, it was observed that with the increase in superficial air velocities, there was an increase in the effective height of pressure drop (66%), voidage, and solid velocities of the gasifier. For the simulation of the riser, similar trends in the profile of hydrodynamic parameters were also observed. The optimum velocity for the gasifier and riser has been suggested to be between 0.15 and 0.35 m/s and 6–7 m/s, respectively.

Optimization and Analysis of Clutch Switching Timing for Hybrid Tractors Equipped with Hydraulic Mechanical Combined Transmission

The working environment of tractors is harsh and the working conditions are very complicated. To cope with this complex and changeable working environment, this paper presents a hybrid tractor powertrain loaded with hydraulic mechanical combined transmission (HMCVT). The powertrain can switch modes according to different operating environments. During mode switching, impact loads can cause wear and even damage to the transmission components. Interrupting the power transmission will reduce the tractor’s operational efficiency. In this paper, the orthogonal experimental range analysis method was proposed to optimize the quality of mode switching. Mode switching involves interactions between clutches. Orthogonal table L16 (215) was selected to design the orthogonal table head. SimulationX was used for simulation. Employing MINITAB range analysis yielded the optimal results. The simulations indicated a reduction in the output shaft’s velocity drop amplitude from 17.647% to 6.591%. The dynamic load coefficient decreased from 2.743 to 1.857. The impact strength was reduced from 14.125 to 5.67 m/s3. The switching time was reduced from 2.13 to 1.71 s. We built a model-in-the-loop (MIL) test platform to validate the results. The MIL test results were compared with the simulation results. Our findings indicate a degree of discrepancy between the simulated and the experimental results, yet the overall trends remain largely consistent. The correctness of the optimal scheme obtained from the orthogonal experiment is verified. This study provides a theoretical basis for the optimization of powertrain mode switching in hybrid tractors equipped with HMCVT.

Is There a Carbonated Mid‐Lithosphere Discontinuity in Cratons?

AbstractThe mid‐lithosphere discontinuity (MLD), identified by a sharp velocity drop at ∼70–100 km depths within the cratonic lithosphere is key to comprehending the chemical composition and thermal structure of the cratonic lithosphere. The MLD is widely accepted to be caused by composition anomalies, such as hydrous minerals, which show low velocities and high electrical conductivities. However, noticeable high‐electrical conductivity anomalies have not been detected in the most cratonic lithosphere. Dolomite has an electrical conductivity similar to olivine and can be originated by carbonatitic melts trapped at ∼80–140 km depths. Here we investigated the elasticity of dolomite under mantle conditions using ab initio calculations and found dolomite exhibits significantly lower velocities than the primary minerals in the lithospheric mantle. Therefore, the dolomite enrichment might provide a good explanation for the observed velocity drop of the MLD in cratonic regions where no high‐conductivity anomaly has been detected, such as the northern Slave craton.

Energy-saving characteristics of pneumatic conveying based on the Dune model of elbow installation with different radius of curvature

Abstract During pneumatic conveying, particles undergo rapid horizontal movement and experience significant wear and collision when changing direction at the elbow pipe due to inertia. Consequently, to minimize energy consumption in transportation, a Dune model has been developed specifically for bends with varying radii of curvature. In this paper, the pressure drops the additional pressure drop coefficient, and the energy loss coefficient of the system are studied. At the minimum pressure drop velocity, PIV is used to capture the particle velocity at different locations in the vertical pipe. The findings reveal that the Dune model installation successfully minimizes the minimum pressure drop velocity, and the maximum pressure drop velocity is reduced by 10.36%. In addition, the energy loss coefficient decreased by 11.56%. Particles in vertical pipes have greater axial velocity than particles in pipes without dunes.

Magnetohydrodynamic bioconvective flow past an elongated surface with convective heat transport, and velocity slip in a non‐Darcian porous regime

AbstractIn recent times, bioconvection has numerous uses, like, biological and biotechnological problems. The present study describes the magnetic bioconvective Buongiorno's flow model with microorganisms in a stretchable area with convective heat transfer and second‐order velocity slip in a non‐Darcian porous regime. Here, the influence of variable viscosity, viscous dissipation, Joule heating, and heat source/sink are considered in the occurrence of higher‐order chemical reactions. Employing proper similarity transformations leading equations are transformed to dimension‐free form. The transformed equations are solved via MATLAB bvp4c problem solver. This study's main objective is to graphically analyze the effects of different pertinent factors on the density of motile microorganisms, velocity, concentration, temperature, number of motile microorganisms' density, skin friction, mass transport rate, and heat transport rate. The main findings drawn from this study are viscosity and magnetic parameter lowers the fluid velocity. Biot number increases fluid temperature, but reduces heat transport rates and skin friction. Schmidt and Eckert numbers reduce the fluid concentration. A rise of 0.3 in bioconvective Rayleigh number and 0.2 in buoyancy ratio number causes a percentage drop in velocities of 8.79% and 3.91% (approximately), respectively, in the neighborhood of the sheet. Furthermore, the increase in Peclet number by 0.2 lowers the density number of microorganisms by 28%. Additionally, the profile of motile microorganisms is improved by thermophoresis impact, while it is diminished by chemical reaction.

Thermocapillary migration of a compound drop in an arbitrary viscous flow

The thermocapillary migration of a concentric compound drop in an arbitrary viscous flow under the consideration of negligible Reynolds number is investigated. The thermocapillary effect refers to the migration of a drop under the influence of a temperature gradient. The thermal and hydrodynamic problems are examined. The thermal field is governed by the heat conduction equation whereas the hydrodynamic fluid velocities are governed by the linearized Navier–Stokes equations. Presence of temperature gradient results in variation of the interfacial tension which is assumed to depend on temperature linearly. Variation of interfacial gradient leads to the coupling of the hydrodynamic problem with the thermal problem through the boundary condition. A complete general solution of Stokes equations is utilized to obtain closed-form expressions for the velocity vector and pressure. The hydrodynamic forces acting on the compound drop are obtained and expressed in terms of Fax́en’s law. Some important asymptotic limiting cases of hydrodynamic drag are also derived. The hydrodynamic drag for cases of uniform flow, shear flow, and heat source with the known ambient flow are derived and it is found that in the case of shear flow, the hydrodynamic drag is contributed only by the thermal component and the shear flow has no effect on it. The obtained results for drag and torque in the limiting cases are in agreement with the existing results in the literature. Furthermore, the migration velocity of the compound drop is obtained by equating the hydrodynamic drag force to zero. The results obtained for migration velocity are explained with the aid of graphs. The migration velocity is found to be a monotonic function of the Marangoni number and the radius of the innermost drop.

A quasi-realistic computational model development and flow field study of the human upper and central airways.

The impact of drug delivery and particulate matter exposure on the human respiratory tract is influenced by various anatomical and physiological factors, particularly the structure of the respiratory tract and its fluid dynamics. This study employs computational fluid dynamics (CFD) to investigate airflow in two 3D models of the human air conducting zone. The first model uses a combination of CT-scan images and geometrical data from human cadaver to extract the upper and central airways down to the ninth generation, while the second model develops the lung airways from the first Carina to the end of the ninth generation using Kitaoka's deterministic algorithm. The study examines the differences in geometrical characteristics, airflow rates, velocity, Reynolds number, and pressure drops of both models in the inhalation and exhalation phases for different lobes and generations of the airways. From trachea to the ninth generation, the average air flowrates and Reynolds numbers exponentially decay in both models during inhalation and exhalation. The steady drop is the case for the average air velocity in Kitaoka's model, while that experiences a maximum in the 3rd or 4th generation in the quasi-realistic model. Besides, it is shown that the flow field remains laminar in the upper and central airways up to the total flow rate of 15l/min. The results of this work can contribute to the understanding of flow behavior in upper respiratory tract.

Effect of Double Stratification on MHD Williamson Boundary Layer Flow and Heat Transfer across a Shrinking/Stretching Sheet Immersed in a Porous Medium

The present study aims to provide a mathematical model of the Williamson fluid flow via a permeable stretching/shrinking sheet in the MHD boundary layer in the presence of a heat source, chemical reaction, and suction. This study is novel because it investigates the physical effects of thermal and solutal stratification on convective heat and mass transport using thermal radiation. The flow’s PDEs are numerically solved using the BVP4c approach and the pertinent similarity variables until a stable solution is found. Through visual analysis, the effects of dimensionless factors on temperature, velocity, and concentration profiles are examined. This encompasses the mass transfer rate, the heat transfer rate, and the coefficient of friction. The results of the present analysis are found to be consistent with those of previously published studies. The findings demonstrate that enhanced temperature and concentration profiles cause the Williamson, magnetic, and permeability parameters to rise in conjunction with a drop in the dimensionless velocity. In relation to temperature, the thermal stratification parameter exhibits the opposite tendency. Regarding the solutal stratification parameter, concentration profiles are seen to show the opposite trend. Lastly, the current work will have important implications for the removal of dust and viruses from viscoelastic fluid in bioengineering, the medical sciences, and medical equipment.

New insight and experimental study of ineffective void in hydrodynamic performance of countercurrent‐flow packing column

AbstractExtensive experimental research and hydrodynamic models have been proposed to guide the design of superior packings. However, most research has concentrated on the effective void (ε − H) of packing while ignoring the ineffective void (ε − H − HL), which causes discrepancies in hydrodynamic performance compared to actual observations. This study evaluated the hydrodynamic performance under diverse conditions considering the liquid holdup (H), pressure drop (ΔP), and gas flooding velocity (uf). A novel approach to hydrodynamic model construction is introduced by incorporating an ineffective void. The results indicate that at a constant hold‐up area, liquid flow (L) and viscosity (μ) significantly influence liquid hold up, moderated by the gas velocity in the flooding area. The pressure drop rises as the viscosity, gas flow rate, and liquid flow rate increase. Notably, a considerable pressure drop initiates flooding at the bottom of the absorber. Elevated liquid flow rates and viscosities correlate with higher ineffective void values (HL) in the packing column. At low gas flow rates, the gas flow rate marginally affects HL values. However, after the flooding point was achieved, the values of HL rapidly increased as the gas flow rate increased. Moreover, a linear relationship emerges between the liquid holdup and HL, as evidenced by the consistent variation in the liquid holdup and the F‐factor. Utilizing the ineffective void yields a more accurate fit for the experimental data, reducing the average absolute relative deviation to 10.2%, 7.4%, and 10.8%, respectively.

Formation and evolution of apple (Malus pumila Mill.) bruising based on high-speed camera verification and finite element method

To analyse the characteristics and internal mechanical changes of bruising formed on apples under different working conditions, this paper explored the formation mechanism of bruising using finite element method. A composite model of peel and flesh was established by reverse engineering, and the accuracy of the apple model was validated two aspects: drop velocity and bruise volume, with a maximum error of 2.51 %. The collision velocity, contact force, stress, and energy of apple bruising were analysed using commonly used contact materials (wood and rubber) at falling heights of 600, 900, 1200, 1500, 1800, and 2100 mm. The characteristics of apple bruising after formation were analysed and the susceptibility of apple bruising were explored. The findings suggest that as the height increased, so does the maximum stress and bruise susceptibility. At a height of 2100 mm, the apple’s bruise susceptibility was measured at 24955.87 mm3 J−1 (wood) and 24710.18 mm3 J−1 (rubber), respectively. This study offers valuable insights into understanding the mechanism behind bruising in fruits, and has a guiding role in the control of bruising and the optimal design of related machinery.

Numerical treatment for radiative hybrid nanofluid flow over a stretching sheet

Artificial neural networks (ANNs) have brought a huge transformation to the machine learning regime by furnishing unparalleled abilities for modeling intricate phenomena and coping with a variety of challenges. In the oneiric field of ANNs, the essential approach for training ANNs is backpropagation. However, optimization is crucial when handling the complex fluid flow phenomenon through backpropagation. The current article implements the Levenberg Marquardt Technique with ANN backpropagation (LMT-BP-ANN) to investigate the radiative flow of a hybrid nanofluid (RHNF) addressing a Cattaneo-Christov flux system past a stretching sheet (SS). Fe2O3 with single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT) hybrid nanofluid is considered. The base fluid is ethylene glycol. Physical parameters of nanofluidic system, including the magnetic parameter M, the solid volume fractions φ1 and φ2, the velocity slip parameter λ, the relaxation time parameter Ω, the Biot number ϒ, and the thermal radiation parameter Gr are evaluated through appropriate variations that effectively accomplish the dynamics of the fluid model. These are utilized to create the dataset for LMT-BP-ANNs using the renowned deterministic Adam's numerical technique in Mathematica software. In MATLAB software, 70 % of data is kept for preparing, 15 % for checking, and 15 % for validating the neural network. The performance plot, regression graphs, and error histograms are constructed to demonstrate the suggested LMT-BP neural network scheme's high efficiency, efficacy, and exactness. When ANN performs, a mean squared error (MSE) of order 10−11 is observed. The observed R squared value is 1. As the magnetic parameter estimate grows, the fluid velocity declines, although the thermal profile shows increasing behavior. As the velocity slip parameter increases, the velocity of the fluid drops. Key findings of this study are anticipated to have a noteworthy bearing on sectors that require local refrigeration and heating by contravention.

Ancient Craton‐Wide Mid‐Lithosphere Discontinuity Controlled by Pargasite Channels

AbstractThe mechanisms governing a commonly observed seismic velocity drop in the cratonic lithosphere, referred to as the mid‐lithospheric discontinuity (MLD), have been widely debated. To identify the composition and seismic structure of MLDs, we have analyzed Sp receiver functions (SRF) and mantle xenocrysts for six regions across Australia. We utilize locations where seismic stations and kimberlite‐hosted mantle xenocrysts are both available, allowing for comparison between seismological and petrological constraints. Our results show negative SRF phases indicative of the MLD coincide with clinopyroxene‐depleted zones at 60–140 km depth. Clinopyroxenes with different chemical compositions across the MLD define a litho‐chemical discontinuity. Modeling and experimental data show that MLDs may be explained by modified lherzolite with 10%–20% modal pargasite. Pargasite MLDs may form when rising H2O‐bearing melts cross the amphibole dehydration curve and react with clinopyroxene in lherzolite. Because the amphibole dehydration curve is isobaric at 80–120 km, pargasite will be precipitated as horizontal channels.

Numerical modelling of earthquake sequences involving valving and pumping of fluids

SUMMARYFaults in the upper crust are sometimes thought to act as self-sealing valves, episodically releasing highly overpressured fluids trapped at greater depth during earthquakes. They are also often considered to be capable of actively pumping fluids into or out of faults in response to coseismic volumetric strain, thermal pressurization or other mechanisms. In this study, we investigate how these different types of behaviour (i.e. valve versus pump) are manifested in earthquakes. We do this using a 2-D plane strain model where frictional sliding on a thrust fault that is fed by a fluid source at its base is coupled to porous flow, thermal pressurization and strong variations in permeability. Our results show that thermal pressurization leads to dramatic dynamic weakening that produces earthquakes that propagate as slip pulses producing large stress drop, large slip and high slip velocities. On the other hand, valve-type behaviour typically produces smaller, less energetic earthquakes that commonly arrest before rupturing the entire fault. In some valve models, we observe complex compound ruptures and swarm activity, which is linked to the ascent of a propagating fluid pressure pulse driven by a large increase in permeability during sliding. Both pump and valve mechanisms can produce anomalously weak faults, though they are each associated with distinctly different fluid pressure and strength evolution over the seismic cycle and during rupture. Our models highlight the complex way in which fluids may interact with earthquakes, especially if valve and pump models coexist.

RESEARCH ON THE WEAR CHARACTERISTICS OF HORIZONTAL TO VERTICAL BENDS OF DILUTE-PHASE PNEUMATIC CONVEYING BASED ON CFD-DEM METHOD

To solve the problem that thin phase pneumatic conveying elbow is easy to wear, the particle mass flow rate, gas velocity, bending diameter ratio and particle size are selected as the influencing factors. The orthogonal test of four factors and four levels is carried out by using CFD-DEM coupled numerical simulation. The results of bending pipe wear, particle velocity and system pressure drop under different conditions are obtained. The results show that the particle mass flow and gas velocity have significant effects on the above three evaluation indexes, while the bending diameter ratio and particle size have no significant effects on the particle velocity and bending wear. Under the discussed conditions, the factors corresponding to the minimum wear are: mass flow rate of 0.5kg/s, gas velocity of 30 m/s, bending diameter ratio of 4.5D, particle size of 2.5mm.

Heat transfer analysis in hybrid nano-composite flow in a stretchable convergent/divergent channel in the preaence of Darcy-Forchheimer law and Lorentz force

The hybrid nano-composite fluid transportation in Jaffery-Hemal flow (JHF) has important uses in various technologies, like converging dies, hydrology, automobiles, etc. Such significant applications motivated us to work on the current problem. Therefore, the purpose of the current work is to inspect the energy efficiency analysis of hybrid nanofluids via convergent/divergent channels using porous space. The hybrid nanofluid consists of polyethylene glycol water, nanoparticles ZrO2 and MgO. To understand the porosity features, the Darcy-Forchheimer law is used. Solar radiation is considered for a more comprehensive analysis of the thermal field. The strong ODEs are obtained using a suitable similarity transformation. The NDSolve technique is used to simulate numerical results, which are then compared with previous published results. Plots and tables are used to report physical investigations of the related parameters. For higher solid volume fractions, the divergent channel’s velocity drops. Whereas it increases for a convergent channel. In the presence of variables, Eckert number, and porosity parameter, skin friction increases in divergent channels and decreases in convergent channels for both nanofluids and hybrid nanofluids. Furthermore, it is noticed that hybrid nanocomposite has more dominant features than nanocomposite for both scenarios of narrowing/expanding channels.

Numerical contact line behavior prediction for drop-wall impact using Basilisk

Drop-wall impact and spray cooling have a wide technical application. There are still fundamental problems associated with wettability and its effect on the drop spreading. Experiments and direct numerical simulations are performed in a wide range of initial drop velocities (0.2–3.6 m/s). The 3D simulation is implemented by solving the incompressible Navier-Stokes equations along with the volume-of-fluid method in the Basilisk software. An adaptive mesh refinement near the interfacial surface provides a cell size of 5 µ m. The effect of the contact angle calculated using the Hoffman function on the minimum drop height and its maximum spreading is explored. The contact angle affects the dynamics of the contact line. Moreover, the mesh cell size and the initial velocity of a water drop before impact define the development of the drop rim instability when compared with experimental results. Experimental and numerical findings are compared to estimate quantitatively numerical model capabilities.

Fluid-driven fault nucleation, rupture processes, and permeability evolution in oshima granite — Preliminary results and acoustic emission datasets

This study investigated the fault nucleation and rupture processes driven by stress and fluid pressure in fine-grained granite by monitoring acoustic emissions (AEs). Through detailed analysis of the spatiotemporal distribution of the AE hypocenter, P-wave velocity, stress-strain, and other experimental observation data under different confining pressures for stress-driven fractures and under different water injection conditions for fluid-driven fractures, it was found that fluid has the following effects: 1) complicating the fault nucleation process, 2) exhibiting episodic AE activity corresponding to fault branching and the formation of multiple faults, 3) extending the spatiotemporal scale of nucleation processes and pre-slip, and 4) reducing the dynamic rupture velocity and stress drop. The experiments also show that 1) during the fault nucleation process, the b-value for AEs changes from 1 to 1.3 to 0.5 before dynamic rupture, and then rapidly recovers to around 1–1.2 during aftershock activity and 2) the hydraulic diffusivity gradually increases from an initial pre-rupture order of 0.1 ​m2/s to 10–100 ​m2/s after dynamic rupture. These results provide a reasonable fault pre-slip model, indicating that hydraulic fracturing promotes shear slip before dynamic rupture, as well as laboratory-scale insights into ensuring the safety and effectiveness of hydraulic fracturing operations related to activities such as geothermal development, evaluating the seismic risk induced by water injection, and further researching the precursory preparation process for deep fluid-driven or fluid-involved natural earthquakes. The publicly available dataset is expected to be used for various purposes, including 1) as training data for artificial intelligence related to microseismic data processing and analysis, 2) predicting the remaining time before rock fractures, and 3) establishing models and assessment methods for the relationship between microseismic characteristics and rock hydraulic properties, which will deepen our understanding of the interaction mechanisms between fluid migration and rock deformation and fracture.