Fluid Drag Research Articles

CFD-DEM simulation of proppant pack stability during flowback in a rough fracture using supercritical CO2

The destabilization of proppant packs during flowback, leading to undesirable consequences such as choke points (fracture closure near the wellbore) and proppant production, is a critical concern in fracturing operations. Despite its significance, comprehensive investigations into proppant pack stability during flowback remain limited, particularly in supercritical CO2 (Sc-CO2) fracturing. This study addresses this gap by employing an experimentally validated coupled Computational Fluid Dynamics–Discrete Element Method (CFD–DEM) model, integrated with a heat transfer model, to analyze proppant pack stability in Sc-CO2 fracturing near the wellbore. An authentic proppant pack for flowback analysis is generated by simulating proppant pack development during the pumping stage and subsequent compression during the fracture closure stage in a synthetic rough fracture. The findings reveal that the flowback stage can be subdivided into three stages: translation-controlled, rolling-controlled, and stable. Proppant pack stability is intricately governed by factors such as fluid drag force, inter-particle contact force, and pre-flowback pack shape. Due to the reduced fluid drag force, the retained proppant ratios rise under varied conditions: from 47.6% to 95.7% with a decrease in flowback rate from 0.3 m/s to 0.1 m/s, from 50.0% to 67.8% with an increase in fluid temperature from 40 °C to 160 °C, and from 16.5% to 80.8% with an increase in proppant size from 0.4 mm to 0.8 mm. In comparison, due to the increased inter-particle contact force, the retained proppant ratio increases by 16.4% as the closure width increases from 0.15 mm to 0.3 mm. Additionally, a longer proppant pack with a front characterized by a higher inclination angle and curved zone exhibits higher stability during flowback. These insights significantly enhance the understanding of proppant pack stability during flowback, offering crucial guidance for designing Sc-CO2 fracturing processes.

Particle erosion in 90-Degree elbow pipe of pneumatic conveying System: Simulation and validation

In this paper, a new comprehensive numerical model is proposed to investigate the particle erosion behaviors (PEBs) in 90-degree elbow pipe (90° EP) of pigsty feed pneumatic conveying system (PFPCS) for gas–solid two-phase flow (GSPF). Calculations of the Re-normalisation group (RNG) k-ε equation, pipeline heat transfer (PHT) equation, and particle tracking (PT) equation are coupled and solved in our model via computational fluid dynamics and discrete phase model (CFD-DPM). Notably, temperature effect, which is the thermophoretic force (FT) is considered and verified for enhancing the prediction accuracy of the erosion rate (η) in this model. Subsequently, this model is used to analyze the η influence of various factors, such as the impact angle (θ), the particle mass flow rate (mp), the particle injection velocity (v), the particle shape factor (κp), the particle diameter (Dp), on the performance of 90° EP of PFPCS. Simultaneously, a visual experimental system for temperature and pressure drop gradient of 90° EP is established for verification. The prediction results via our proposed erosion model are remarkably close to the experimental values by calculating, evaluating and comparing eight kinds of previous erosion models. Furthermore, ηmax increases as the surface temperature of (Text) increases, revealing the interaction between thermophoretic forces, gravity, and fluid drag. Moreover, ηmax initially decreases with the increase of Dp, and then increases when Dp is from 50 μm to 1000 μm, and ηmax increases linearly with the increase of mp. In addition, ηmax first increases with the increase of κp, and then decreases, and ηmax is 1.18 mg·m−2·s−1 at Text = 25℃, κp = 0.8. Therefore, this study provides a theoretical basis and high-performance numerical model for developing a real-time data transmission software, which forms a health monitoring system with the components of PFPCS.

Navigating the microenvironment with flip and turn under quadrupole magnetophoretic steering control: Nanosphere- and nanorod-coated microbead.

The spatiotemporal accuracy of microscale magnetophoresis has improved significantly over the course of several decades of development. However, most of the studies so far were using magnetic microbead composed of nanosphere particle for magnetophoretic actuation purpose. Here, we developed an in-house method for magnetic sample analysis called quadrupole magnetic steering control (QMSC). QMSC was used to study the magnetophoretic behavior of polystyrene microbeads decorated with iron oxide nanospheres-coated polystyrene microbeads (IONSs-PS) and iron oxide nanorods-coated polystyrene microbeads (IONRs-PS) under the influence of a quadrupole low field gradient. During a 4-s QMSC experiment, the IONSs-PS and IONRs-PS were navigated to perform 180° flip and 90° turn formations, and their kinematic results (2s before and 2s after the flip/turn) were measured and compared. The results showed that the IONRs-PS suffered from significant kinematic disproportion, translating a highly uneven amount of kinetic energy from the same magnitude of magnetic control. Combining the kinematic analysis, transmission electron microscopy micrographs, and vibrating sample magnetometry measurements, it was found that the IONRs-PS experienced higher fluid drag force and had lower consistency than the IONSs-PS due to its extensive open fractal nanorod structure on the bead surface and uneven magnetization, which was attributed to its ferrimagnetic nature.

Multiflagellarity leads to the size-independent swimming speed of peritrichous bacteria.

To swim through a viscous fluid, a flagellated bacterium must overcome the fluid drag on its body by rotating a flagellum or a bundle of multiple flagella. Because the drag increases with the size of bacteria, it is expected theoretically that the swimming speed of a bacterium inversely correlates with its body length. Nevertheless, despite extensive research, the fundamental size-speed relation of flagellated bacteria remains unclear with different experiments reporting conflicting results. Here, by critically reviewing the existing evidence and synergizing our own experiments of large sample sizes, hydrodynamic modeling, and simulations, we demonstrate that the average swimming speed of Escherichia coli, a premier model of peritrichous bacteria, is independent of their body length. Our quantitative analysis shows that such a counterintuitive relation is the consequence of the collective flagellar dynamics dictated by the linear correlation between the body length and the number of flagella of bacteria. Notably, our study reveals how bacteria utilize the increasing number of flagella to regulate the flagellar motor load. The collective load sharing among multiple flagella results in a lower load on each flagellar motor and therefore faster flagellar rotation, which compensates for the higher fluid drag on the longer bodies of bacteria. Without this balancing mechanism, the swimming speed of monotrichous bacteria generically decreases with increasing body length, a feature limiting the size variation of the bacteria. Altogether, our study resolves a long-standing controversy over the size-speed relation of flagellated bacteria and provides insights into the functional benefit of multiflagellarity in bacteria.

Quantitative analysis of thin metal powder layers via transmission X-ray imaging and discrete element simulation: Roller-based spreading approaches

A variety of tools can be used for spreading metal, ceramic, and polymer feedstocks in powder bed additive manufacturing (AM) methods. Rollers are often employed when spreading powders with limited flowability, as arises in powders comprising fine particle sizes or high surface energy materials. Here, we study roller-based powder spreading for powder bed AM using the unique combination of a purpose-built powder spreading testbed with a proven method for X-ray mapping of powder layer depth. We focus on the density and uniformity of nominally 100 μm thick layers of roller-spread Ti-6Al-4V and Al-10Si-Mg powders. Our results indicate that when rotation is too rapid, roller-applied forces including shear and medium fluid drag impede the creation of dense and uniform layers from powders of high innate flowability, or where inertial forces driven by particle density dominate cohesive forces. Roller counter-rotation augments the uniformity of cohesive powder layers, primarily though reducing the influence of particle clusters in the flowing powder, which are otherwise shown to cause deep, trench-like streaks. Companion discrete element method (DEM) simulations further contextualize the experiments through isolation of the effects of cohesion on layer attributes. Results suggest that roller motion parameters could apply a strategic level of additional shear force to the flowing powder, thereby mitigating the clumping behavior characteristic of highly cohesive feedstocks while maintaining high layer uniformity.

Transient Model for the Hydrodynamic Force in a Hydraulic Capsule Pipeline Transport System

The hydraulic capsule pipeline (HCP) is an eco-friendly and sustainable pipeline transport option. The freight-carrying capsule is driven by hydraulic pipe flow. Fluid drag is generated by the principal dynamic force effect on the capsule, which could influence the capsule’s motion speed. To make the HCP more efficient, a transient model for the hydrodynamic force in an HCP was developed in this study. From a numerical simulation, the coherent vortex structures of fluctuating modes were observed, and the velocity iso-surfaces of the coherent vortex of the wake flow exhibited an annular trend in circumferential connection. Then, the hydrodynamic force was analyzed: the steady component and transient component were resolved, and the general trend in forces in terms of the transient components was that the maximum amplitude of forces reduced with an increase in mode order. Through short-term Fourier transform, the frequency components and their variations in terms of the entire time range could be acquired. The transient model in this study provided a perspective to build the connection between the flow structures and the hydrodynamic force. By the transient model, the transient component of hydrodynamic force can be explained as the fluctuation of coherent vortex structures.

CFD-DEM investigation of the effects of aperture size for a capsule-based dry powder inhaler

Capsule based dry powder inhalers (DPIs) often require piercing of the capsule before inhalation, and the characteristics of the apertures (punctured holes) affect air flow and the release of powders from the capsule. This work develops a numerical model based on the two-way coupling of computational fluid dynamics and discrete element method (CFD-DEM) to investigate the effect of aperture size on powder dispersion in the Aerolizer® device loaded with only carrier particles (lactose). Powders (carrier particles) in the size range 60–140 μm (d50: 90 μm and span: 0.66) were initialized in a capsule which had a circular aperture at each end. Boundary conditions corresponding to an air flow rate of 45 L/min were specified at each inlet to the mixing chamber (i.e., a total flow rate 90 L/min), and a capsule spin speed of ∼ 4050 rpm. The velocity magnitudes inside the capsule were considerably lower than those in the mixing chamber in the vicinity of the rotating capsule, with the exception of the capsules featuring 2.5 mm and 4 mm apertures. Larger apertures reduced the capsule emptying time and increased the particle evacuation velocity; the fluid drag force on the particles issuing from the capsule peaked for an aperture of 1.3 mm. Inside the capsule, particle–particle (PP) collisions were more frequent than particle–wall (PW) collisions due to high concentration of powder, but PP collisions had smaller (median) impact energy than PW collisions. Larger apertures resulted in fewer collisions in the capsule with higher PW and virtually unchanged PP collision energies. Outside the capsule (i.e., in the inhaler mixing chamber), PW collisions occurred more frequently than PP collisions with median collision energies typically two orders of magnitude higher than inside the capsule. Larger apertures resulted in more collisions with slightly reduced collision energy, but this effect plateaued for aperture sizes larger than 1.3 mm. Powder dispersion, expressed as the fine particle fraction (FPF) of the powder, was predicted using an empirical equation based on carrier PW collisions. Therefore, consistent with the model prediction of the effect of aperture sizes on the chamber collision frequency, FPF increased with aperture size but plateaued beyond 1.3 mm.

Effects of polymer and dust particles inclusion on drag and heat transfer characteristics in Non-Newtonian dusty fluids

The objective of this article is to examine the simultaneous incorporation of polymers and dust particles, a previously unexplored topic according to the available literature. Understanding these effects is essential for industrial processes and biomedical engineering applications where the manipulation of drag and heat transfer characteristics is desired. This research looks at how including polymers in a viscous non-Newtonian FENE-P dusty fluid alters the flow and heat transfer characteristics of the boundary layer over a non-linearly stretched surface. By employing an appropriate similarity transformation method, we transform the nonlinear system of equations into an equivalent form that exhibits similarity. The resulting boundary layer equations are then numerically solved to investigate the effect of flow factors on the drag force and Nusselt number. This analysis allows us to investigate how various flow parameters influence the forces experienced by the fluid and the rate of heat transfer. In our investigations, we observe a decrease in velocity and an increase in heat transfer when both polymers and dust particles are present. These results suggest that the presence of polymers and dust particles simultaneously has a positive effect on fluid dynamics and increases the system’s thermal exchange efficacy.

Research on topological grinding of bionic structured scale surface for reducing contact friction and fluid drag resistance

The structured scale surface is an important functional surface that reduces the drag resistance of fluids and contact friction resistance. In order to grind the bionic scale structure on the workpiece, based on the topological theory and the principle of grinding kinematics, a novel topological grinding strategy was proposed. To this end, the topological feature vectors of the structured scale surface and the grinding wheel surface were established by analyzing the biomimetic structured scale surface; The Topological space of grinding process is constructed and the topological mapping equation of grinding process is established; The feasibility of this grinding strategy was verified through simulation and grinding experiments. The research results indicate that the established topological mapping equation is correct; Under the condition of maintaining design parameters, the errors of the feature parameters of the ground structured scale surface are between 2.8% and 8%; As the grinding parameters change, the feature parameters of the ground scale surface will also change, but they can still maintain the same topological attributes as the designed scale surface. Therefore, the proposed topology grinding strategy is feasible.

A self-propelling clapping body

We report an experimental study of the motion of a clapping body consisting of two flat plates pivoted at the leading edge by a torsion spring. Clapping motion and forward propulsion of the body are initiated by the sudden release of the plates, initially held apart at an angle $2\theta _o$ . Results are presented for the clapping and forward motions, and for the wake flow field for 24 cases, where depth-to-length ratio ( $d^* = 1.5,1\text { and }0.5$ ), spring stiffness per unit depth ( $Kt$ ), body mass ( $m_b$ ) and initial separation angle ( $2\theta _o = 45^{\circ }\text { and }60^{\circ }$ ) are varied. The body initially accelerates rapidly forward, then slowly retards to nearly zero velocity. Whereas the acceleration phase involves a complex interaction between plate and fluid motions, the retardation phase is simply fluid dynamic drag slowing the body. The wake consists of either a single axis-switching elliptical vortex loop (for $d^* = 1\text { and }1.5$ ) or multiple vortex loops (for $d^* = 0.5$ ). The body motion is nearly independent of $d^*$ and most affected by variation in $\theta _o$ and $Kt$ . Using conservation of linear momentum and conversion of spring strain energy into kinetic energy in the fluid and body, we obtain a relation for the translation velocity of the body in terms of the various parameters. Approximately 80 % of the initial stored energy is transferred to the fluid, only 20 % to the body. The experimentally obtained cost of transport lies between 2 and $8\ \mathrm {J}\ \mathrm {kg}^{-1}\ \mathrm {m}^{-1}$ .

A computational investigation of occlusive arterial thrombosis.

The generation of occlusive thrombi in stenotic arteries involves the rapid deposition of millions of circulating platelets under high shear flow. The process is mediated by the formation of molecular bonds of several distinct types between platelets; the bonds capture the moving platelets and stabilize the growing thrombi under flow. We investigated the mechanisms behind occlusive thrombosis in arteries with a two-phase continuum model. The model explicitly tracks the formation and rupture of the two types of interplatelet bonds, the rates of which are coupled with the local flow conditions. The motion of platelets in the thrombi results from competition between the viscoelastic forces generated by the interplatelet bonds and the fluid drag. Our simulation results indicate that stable occlusive thrombi form only under specific combinations for the ranges of model parameters such as rates of bond formation and rupture, platelet activation time, and number of bonds required for platelet attachment.

Magnetically assisted soft milli-tools for occluded lumen morphology detection.

Methodologies based on intravascular imaging have revolutionized the diagnosis and treatment of endovascular diseases. However, current methods are limited in detecting, i.e., visualizing and crossing, complicated occluded vessels. Therefore, we propose a miniature soft tool comprising a magnet-assisted active deformation segment (ADS) and a fluid drag-driven segment (FDS) to visualize and cross the occlusions with various morphologies. First, via soft-bodied deformation and interaction, the ADS could visualize the structure details of partial occlusions with features as small as 0.5 millimeters. Then, by leveraging the fluidic drag from the pulsatile flow, the FDS could automatically detect an entry point selectively from severe occlusions with complicated microchannels whose diameters are down to 0.2 millimeters. The functions have been validated in both biologically relevant phantoms and organs ex vivo. This soft tool could help enhance the efficacy of minimally invasive medicine for the diagnosis and treatment of occlusions in various circulatory systems.

A non-Darcy flow CFD–DEM method for simulating ground collapse induced by leakage through underground pipeline defect

Ground collapse due to soil erosion near pipeline defects involves soil loss and orifice outflow, which may lead to non-Darcy flow, but it is often ignored in numerical simulations. In this study, a computational-fluid-dynamics and discrete-element-method (CFD–DEM) coupling method is developed considering the non-Darcy flow. In contrast to the Darcy Equation, which tends to overestimate fluid velocity and drag force at high Reynolds numbers, the newly developed CFD-DEM method has been validated and found to be applicable across a wide range of Reynolds numbers. Utilizing the capabilities of this method, the investigation of ground collapse mechanism is conducted. Results show that the trajectories of lost particles approximately form a straight line from their initial positions towards the defect, with higher velocities for particles closer to the defect. It is likely the main reason that the evolution of particle loss closely resembles a progressive contraction of an ellipse, while the evolution of the loosening zone resembles an upward movement and expansion of an ellipse. The soil settlement is uneven both in the horizontal and vertical direction. As the particle loss increases, the shape of the surface settlement curve transitions from a normal distribution to a logarithmic function.

Effects of Shape and Size on Microplastic Atmospheric Settling Velocity.

Microplastics (MPs) have been found in all terrestrial, marine, and riparian environments, including remote regions. This implies that atmospheric transport is an important pathway when considering MP sources and global budgets. However, limited empirical data exist to aid in effective development and parameterization of MP atmospheric transport models. This study measured the atmospheric settling and horizontal drift velocities of various sizes and shapes of MPs in two specially designed settling columns using a laser Doppler anemometer. The settling velocities were generally lower than modeled values, while shape exerted the most significant influence on the rate of settling. Rather than conforming to well-established, power-law models, each class of MP exhibited a linear but different relationship between MP size and settling velocity, with markedly higher slopes for the spheres and cylinders as compared to the films and fibers. Shape also had a substantial influence on particle drift, with the fibers and films exhibiting the greatest horizontal motion, as suggestive of their changing orientation in response to particle interactions and fluid drag. As a consequence, microplastic particles identified within atmospheric deposition samples collected at a single point may derive from entirely different sources representing a wide range in transport distance.

Studying Liquid-Infused Surfaces with Affordable Surface Features Infiltrated with Various Lubricants from Corrosion, Biofouling, and Fluid Drag Viewpoints

Studying Liquid-Infused Surfaces with Affordable Surface Features Infiltrated with Various Lubricants from Corrosion, Biofouling, and Fluid Drag Viewpoints

Drag and uncertainty of power-law fluid flows in fractal multiparticle systems

In this study, new approaches are developed to predict the drag and assess its potential uncertainty of a non-Newtonian fluid in a multiparticle system. First, a new and simpler approximate solution of power-law fluid flow is developed using the free surface cell model. Second, the uncertainty of drag in a fractal multiparticle system is investigated by treating the heterogeneous voidage in the system as a truncated power-law fractal distribution. The results demonstrate that the developed simpler approximate solution works well compared to the analytical solutions and experimental data. Incorporating truncated power-law fractal voidage can better capture the experimental data. The voidage heterogeneity increases the drag of the power-law fluid moving through the multiparticle system. Strong shear-thinning effects of power-law fluids and high mean voidage diminish the effect of voidage heterogeneity. The flow drag of power-law fluid in the heterogeneous multiparticle system decreases with increasing fractal dimension.

The application of bionics in optimizing ship resistance reduction

Since humans and nature have a shared destiny, harmony is the way for the two to get along. Learning from nature can lead to long-term and steady development for humans. Bionics is an emerging discipline that learns from nature modestly. The structure and products of the best organisms in species evolution work as a beacon for scientific and technological progress. In the field of ship fluid mechanics, the combination of bionics and ship and ocean engineering provides many simple and effective design schemes for the fluid performance optimization of ship materials and structures. This paper mainly summarizes and discusses the research and application status of bionics in the field of ship fluid drag reduction from four aspects, namely the imitation of biological shape, biological epidermal texture, biological function, and biological structure. Conclusions can be drawn that bionics can used to improve a ships shape, structure, surface materials, and marine coatings to optimize ship fluid performance and effectively reduce ship drag.

Numerical studies on aerodynamic performance of NACA 0018 profile in fundamental and research application of the aerospace industry

For a good functioning of the activities carried out within research institutions both at managerial level and for fulfilling the technical requirements, we aim to determine the aerodynamic characteristics of the standard profiles used in the aerospace field by testing in the subsonic tunnel. We also intend to conduct a study based on numerous experimental tests performed in wind tunnels that can be compared to the actual scale of the aircraft for structural integrity and improving its performance. The purpose of this paper is to evaluate the dynamics of fluid separation, lift and drag. This allows us to further improve the profiles so that it is essential to improve the efficiency and performance of an aircraft in terms of improving lift and reducing drag. In the present research, numerical and experimental studies are performed on a finite geometry of the NACA0018 wing at different angles of attack and Reynolds numbers. This paper aims to improve the performance, accuracy and quality of testing, increase the competitiveness of similar installations on the world market, ensure the national research and development capacity of new products in the aeronautical and defense industry.

Comparison of reduced order models based on dynamic mode decomposition and deep learning for predicting chaotic flow in a random arrangement of cylinders

Three reduced order models are evaluated in their capacity to predict the future state of an unsteady chaotic flow field. A spatially fully developed flow generated in a random packing of cylinders at a solid fraction of 0.1 and a nominal Reynolds number of 50 is investigated. For deep learning (DL), convolutional autoencoders are used to reduce the high-dimensional data to lower dimensional latent space representations of size 16, which were then used for training the temporal architectures. To predict the future states, two DL based methods, long short-term memory and temporal convolutional neural networks, are used and compared to the linear dynamic mode decomposition (DMD). The predictions are tested in their capability to predict the spatiotemporal variations of velocity and pressure, flow statistics such as root mean squared values, and the capability to predict fluid forces on the cylinders. Relative errors between 15% and 20% are evident in predicting instantaneous velocities, chiefly resulting from phase differences between predictions and ground truth. The spatial distribution of statistical second moments is predicted to be within a maximum of 5%–10% of the ground truth with mean error in the range of 1%–2%. Using the predicted fields, instantaneous fluid drag force predictions on individual particles exhibit a mean relative error within 20%, time-averaged drag force predictions to within 5%, and total drag force over all particles to within 1% of the ground truth values. It is found that overall, the non-linear DL models are more accurate than the linear DMD algorithm for the prediction of future states.

Effects of Ti3C2Tz MXene nanoparticle additive on fluidic properties and tribological performance

Nanoparticle additives are known to enhance a range of fluidic properties, including thermal conductivity, heat capacity, and viscosity. Ti3C2Tz nanosheets exhibit high thermal conductivity, electrical conductivity, and mechanical strength, making them promising candidates as lubricant additives. In this work, we evaluate the performance of Ti3C2Tz as an additive to enhance the heat transfer, rheological properties, and tribological performance of silicone and Polyalphaolefin (PAO) oils. The acid-etched Ti3C2Tz nanosheets were synthesized and characterized by SEM, XRD, and XPS to confirm etching. The nanofluids were produced by dispersing the Ti3C2Tz nanosheets in silicone and PAO oils at different loadings. Experimental results showed that adding Ti3C2Tz improved thermal conductivity by 16 % and 23 % in silicone and PAO oils, respectively. The rheological data revealed that adding Ti3C2Tz nanosheets reduced the viscosity by 12.3 % (at 0.09 wt%) and 18.1 % (0.04 wt%) in silicone and PAO oil, respectively. This non-Einstein viscosity reduction can be attributed to the disruption of intermolecular bonding of base oil molecule. The addition of Ti3C2Tz reduced the friction by 23 % (0.09 wt%) and 65 % (0.04 wt%) in silicone and PAO oils, respectively. The improved properties and reduced fluidic drag in viscosity and friction lead to potential applications in (electrical) vehicles that will be helpful in attaining improved fuel economy.