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We consider the effect that an upstream cylinder has on the effective inertial collection efficiency of a downstream cylinder. We consider an initially uniform distribution of particles moving past a cylindrical fiber in a potential crossflow and numerically calculate the resulting particle distribution far downstream of the fiber using finite differences. We then investigate the effect that the downstream distribution of particles has on the effective inertial collision efficiency of a downstream test cylinder oriented parallel to the first. We show that the effective collision efficiency of the test cylinder depends on its relative offset in the transverse direction (normal to the flow) with respect to the upstream cylinder. For relatively small offsets there is complete shielding, and no particles collide with the test cylinder. As the offset increases, a growing effective collision efficiency is observed leading to a significant enhancement relative to the collision efficiency of an isolated cylinder for intermediate offsets and Stokes numbers close to unity. Importantly, we observe relative gains in effective collision efficiency above 100% for a range of Stokes number and offset values. For larger offsets and Stokes numbers, the effect of the upstream cylinder on the effective collision efficiency of the test cylinder decreases and eventually becomes negligible. Detailed results are provided for Stokes drag acting on the particles and we also show that a non-linear drag has negligible effect on the observed trends for the conditions relevant to filtration systems. These results suggest that the arrangement of fibers has a substantial effect on inertial particle impaction even when neighboring fibers do not alter the flow field around each individual collector. Moreover, periodic arrangements with specific orientations with respect of the flow could lead to a significant enhancement of the inertial collision of particles on an array of collectors, thus contributing towards a better filtration performance.

Heat and mass transfer analysis of viscous liquid flow generated by rotation of disk has generated prodigious interest due to promising utilizations in numerous processes such as thermal energy generation systems, turbine rotators, geothermal energy preservations, chemical processing, medicinal instrumentations, computing devices and so forth. In view of such extraordinary utilizations in numerous engineering procedures existent exertion is excogitated to disclose flowing phenomenon over rotating disk. To raise the importance of current analysis influential physical aspects like magnetic field, permeability, Dufour and Soret diffusion phenomenon are also incorporated. Subsequently, flow field distributions are analyzed for suction and injection cases. Modelling is structured via PDE’s by obliging constitutive conservation laws. Boundary layer approach is executed to reduce complexity of attained partial differential system. Transformations developed by Karman are implemented to convert developed differential framework into ODE’s. Implicitly finite differenced technique known as Keller Box is engaged to find solution of coupled intricate high order ordinary differential equations. Influence of flow controlling parameters on associated distributions are revealed through graphical and tabular representations. The related quantities of engineering interest like coefficients of wall drag force, along radial and tangential directions are also computed. Credibility of presently computed results is established by constructing comparison with previously published literature. It is inferred that magnetic strength parameter enhances tangential and radial components of velocity whereas contrary trend is depicted in axially directed velocity. In addition, temperature and momentum distributions show up surging attribute versus magnetic field parameter. All associated profiles have exhibited decrementing aspects against suction parameter. It is also revealed that increment in Soret tends to produce depreciation in temperature profile whereas concentration distribution is enhanced.

Due to the existence of the end effect of the vehicle coils in the electrodynamic suspension maglev, the fluctuation of the output parameters of the suspension and guidance system is common, which has an impact on the stability of the motor driving system. In this paper, considering the end effect of vehicle coils, a new magnetomotive force distribution model suitable for the suspension and guidance system of electrodynamic suspension maglev is proposed. Firstly, considering the end effect of vehicle coils, a magnetomotive force model of array of vehicle coils is established. Then, based on space harmonic method and the equivalent circuit of suspension and guidance loop, the expressions of levitation current, guidance current, drag force, levitation force, levitation stiffness, guidance force and guidance stiffness are presented. Finally, the characteristics of the suspension and guidance system are analyzed under different running conditions. The numerical results are compared with the three-dimensional finite element method simulation results and the experimental results of the Yamanashi test line. The relative error is almost within 10%, which verified the feasibility and accuracy of the magnetomotive force model and analytical method.

The present study numerically, investigates the aerodynamic characteristics of low speed flow past symmetric NACA airfoils, for various t/c values of 0.10, 0.15, 0.18, 0.21 and 0.24 at chordwise Reynolds numbers of 2 × 105 and 4 × 105, where t is the airfoil thickness and c is the airfoil chord. The presence of laminar separation bubble is indicated by oscillatory behaviour of pressure coefficient on the suction surface beyond peak pressure. The fluctuations in lift/drag are seen at smaller t/c values of 0.10 and 0.15, whereas no fluctuations are seen at a higher t/c value of 0.21. An empirical expression is developed to predict the mean lift, viscous as well as total drag coefficients for symmetric airfoils as a function of t/c only, which varies linearly for both the Reynolds numbers studied. The velocity vectors show the flow separations phenomenon only at smaller t/c values of 0.10 and 0.15, while at a higher t/c value of 0.21, well behaved and steady flow field is seen, which might be the reason for the absence of lift/drag fluctuations. The far-field acoustic measurements of symmetric NACA airfoils for various thickness ratios reveal that thicker airfoil (NACA0021, t/c = 0.21) radiates lower acoustic emissions (i.e., about 2 dB) as compared to the thinner (NACA0010, t/c = 0.10) ones.

A novel method for close-proximity formation flying under differential atmospheric drag using Coulomb forces is investigated for applications in Earth sensing, space-situational awareness (SSA), and aeronomy. Objects in LEO are supersonic with respect to the ambient environment, creating a thinned out wake region behind the craft as it travels through the ionosphere. Objects within this wake experience little drag acceleration and are able to attain voltages much greater than in the ambient ionospheric plasma, creating implications for the design and control of close-proximity leader–follower spacecraft pairs. The proposed system consists of a leader craft with a set of affixed, conducting spheres and a charged follower craft located in the wake of the leader. The differential drag acceleration between the leader and follower craft is countered by a controlled Coulomb repulsion to maintain precise separation. The charged structure on the rear of the leader craft is designed such that the charged follower craft sits in an electrostatic potential well which opposes off-axis perturbations. A conceptual method for controlling such a pair without the use of propellant using a set of charged spheres is investigated, with nonlinear models of the system’s relative motion derived and discussed. Linearized models are used to demonstrate the local controllability of the system to demonstrate the proposed system’s merit. This linear analysis is used to derive conditions on controllability and control performance under different charge geometries and environmental assumptions.

The improvement of thermal-hydraulic analysis techniques is essential to ensure the safety and reliability of nuclear power plants. The one-dimensional two-fluid model has been adopted in state-of-the-art thermal-hydraulic system codes. Current constitutive equations used in the system codes reach a mature level. Some exceptions are the partition method of wall friction in the momentum equation of the two-fluid model and the interfacial drag force model for a horizontal two-phase flow. This study is focused on deriving the partition method of wall friction in the momentum equation of the two-fluid model and modeling the interfacial drag force model for a horizontal bubbly flow. The one-dimensional momentum equation in the two-fluid model is derived from the local momentum equation. The derived one-dimensional momentum equation demonstrates that total wall friction should be apportioned to gas and liquid phases based on the phasic volume fraction, which is the same as that used in the SPACE code. The constitutive equations for the interfacial drag force are also identified. Based on the assessments, the Rassame-Hibiki correlation, Hibiki-Ishii correlation, Ishii-Zuber correlation, and Rassame-Hibiki correlation are recommended for computing the distribution parameter, interfacial area concentration, drag coefficient, and relative velocity covariance of a horizontal bubbly flow, respectively.

In this research, a Graphical Processing Unit (GPU) accelerated Discrete Element Method (DEM) code was developed and coupled with the Computational Fluid Dynamic (CFD) software MFiX to simulate granular and multiphase flows with heat transfers and chemical reactions. The Fortran-based CFD solver was coupled with the CUDA/C++ based DEM solver through inter-process pipes. The speedup to the CPU version of MFiX-DEM is about 130–243 folds in the simulation of particle packings. In fluidized bed simulations, the DEM computation time is reduced from 91% to 17% with a speedup of 78 folds. The simulation of Geldart A particle fluidization revealed a similar level of importance of both fluid and particle coarse-graining. The filtered drag derived from the two-fluid model is suitable for Euler-Lagrangian simulations with both fluid and particle coarse-graining. It overcorrects the influence of sub-grid structures if used for simulations with only fluid coarse-graining.

Three-way coupled numerical simulations of particle-laden fluid flow around a square obstacle are performed by a coupled finite-volume and discrete-element method, taking account of the collisions between particles. The fluid flow is described by the Eulerian formalism, while the Lagrangian formalism is used for the solid particles. The dynamics of each phase and the modulation mechanism of the flow field by the inertial particles are explored. The Reynolds number based on the side length of the obstacle is 100, which leads to a typical periodic flow pattern of vortex shedding. Under the action of particles, the flow tends to be chaotic even in the upstream region, and the vortex shedding occurs earlier. The intensity of the vortex is attenuated due to particle dissipation. At sufficiently small Stokes numbers, the particles exhibit flow tracer behavior with relatively high fidelity. However, as the Stokes number and mass loading increase, the interaction between the particles and fluid becomes important, especially in the core region of the channel. With the increase of the particle response time, the spanwise velocity fluctuation is attenuated, while the influence on the streamwise velocity fluctuation seems complicated. No particles are observed to hit the rear surface of the obstacle or deposit in the domain during the flow. When the Stokes number and mass loading are elevated from 0.0036 and 0.065 to 0.5 and 9.024, respectively, the distribution of the particles near the channel centerline varies from being filled in the shedding vortices to surrounding them. Meanwhile, the particle-free zones centered on these vortices become larger. For the Stokes number and mass loading up to 1.5 and 27.073, respectively, the particles are scattered in the downstream area, and the flow pattern of the Karman vortex street is modified. Within the range of the Stokes number considered, the drag and lift coefficients, and the Strouhal number also show a certain trend of variation.

This work presents the effect of wingtip-mounted propellers on the aircraft drag polar, identified from in-flight measurements. In previous wind-tunnel experiments, significant reductions in drag a...

The motion of blood conveying gold nanoparticles on a curved surface when suction, thermal radiation, and Lorentz force are significant is explored in this report with the aim to announce the increasing effects of Williamson fluid parameter, volume fraction, radius of curvature, thermal radiation, and Lorentz force on such a transport phenomenon. This report was designed to explore the upper and lower solutions of the model suitable to study the enhancement of the aforementioned variables. The similarity solution of the dimensional governing equation was sought for using the appropriate similarity variables. These dimensionless forms of ODEs are numerically solved using the 3-stage Lobatto formula, also known as bvp4c. The validation of the numerical scheme was considered. The drag force decelerated and then upsurges owing to the volume fraction of nanoparticles in the corresponding UBS and reduces in LBS, while the rate of heat transfer drastically decreases. The temperature and velocity gradient escalate and decelerate, respectively for both branches of results owing to the effect of higher curvature parameter. The temperature distribution decelerates in both outcomes due to the strengthened of mass suction while the velocity weakened in the lower branch solution (LBS) and augments in the upper branch solution (UBS).

Wakes of aircraft and automobiles with relatively flat slanted aftbodies are often characterized by a streamwise-oriented vortex pair, whose strength affects drag and other crucial performance parameters. We examine the stability characteristics of the vortex pair emerging over an abstraction comprised of a streamwise-aligned cylinder terminated with an upswept plane. The Reynolds number is fixed at 5000 and the upsweep angle is increased from 20deg to 32deg. At 20deg, the LES yields a steady streamwise-oriented vortex pair, and the global modes are also stable. At 32deg, the LES displays unsteady flow behavior. Linear analysis of the mean flow reveals different unstable modes. The lowest oscillation frequency is an antisymmetric mode, which is attached to the entire slanted base. At the highest frequency, the mode is symmetric and has the same rotational orientation as the mean vortex pair. Its support is prominent in the rear part of the slanted base and spreads relatively rapidly downstream with prominent helical structures. A receptivity analysis of low- and high-frequency modes suggests the latter holds promise to affect the vortical flow, providing a potential starting point for a control strategy to modify the vortex pair., 10 pages, 4 figures

Atmospheric mass density (AMD) plays a vital role in the drag calculation for space objects in low Earth orbit (LEO). Many empirical AMD models have been developed and used for orbit prediction and...

This article investigates the side-mirror base position effect on the aerodynamic forces generated and acoustics generated along the vehicle body, using the finite element analysis method in ANSYS. The model of simulation used is K-Omega steady-state conditions. The relation is investigated using Reynolds Average Navier Strokes steady-state simulation in CFD software. Results depict base position has little or no effect on aerodynamic forces (Drag and Lift). However, the horizontal base position generated noticeably higher noise than the angular placement of the mirror base.

The quasi-steady translational motion of an incompressible couple stress fluid confined between two eccentric spherical surfaces is investigated. It is assumed that the motion is generated by allowing the internal sphere to translate with a constant velocity. The Stokesian assumption of low Reynolds numbers is considered so that the nonlinear terms of the equation of motion are neglected. The superposition principle is employed to construct the general solution of the governing equations in the presence of spherical surfaces using two spherical systems of coordinates relative to the centers of the two spherical surfaces. The no-slip boundary conditions on the spherical boundaries are applied. In addition, the conditions of vanishing couple stresses on the bounding surfaces are imposed. The boundary collocation technique is utilized numerically to satisfy the boundary conditions on the spherical surfaces. The drag force experienced by the fluid flow on the spherical particle is obtained and represented numerically through table and graphs. The numerical results show that the values of the drag force increases monotonically with the increase in the radii ratio. It increases also with the increase of the couple stress viscosity parameter. The obtained results are consistence with the results available in the literature for viscous fluids.

Extreme drag and aerodynamic heat are the main penalties for blunt forebody of supersonic vehicles. This results in shorter flight range and higher fuel consumption, and aerodynamic heat seriously affects the performance of internal electronics. In the current study, the flow field mechanism of a blunt body model with a supersonic opposing jet in a supersonic flow field is numerically study. The physical model is a two-dimensional axisymmetric blunt forebody model with a convergent nozzle structure, and the numerical calculation model is a coupling of the two-dimensional axisymmetric Reynolds average method and the shear stress transport(SST) turbulence model. The calculation results in this paper are compared with the experimental data in the literature, which verifies the accuracy, and the calculation verifies the grid independence. An active flow control method that controls a single pressure parameter is proposed, and the formation process of the opposing jet in the convergent nozzle is considered, and the flow field structure of the opposing jet formed by the convergent nozzle with different nozzle sizes is studied. The results show that a single pressure parameter can control the formation of a supersonic opposing jet to form a long penetration mode and a short penetration mode. The ratio of the ambient pressure to the jet pressure at the stagnation point of the blunt body can directly affect the flow field structure of the opposing jet, and reasonable control of opposing jet parameters is an effective way for thermal protection and drag reduction of blunt body structures.

This study presents an untethered magnetic manipulation technique for controlling a microrobot position under high rate laminar flows up to 4.5 mL/min. An increase in flow rate exponentially increases the drag force on the microrobot and negatively impacts its positioning accuracy. Increasing the longitudinal force generated by the microrobot's driving apparatus helps in overcoming the disruptive effects of the fluid flow and increases longitudinal motion stability. To this end, we propose a magnetic configuration with two ring-shaped magnets, one above and the other below the microfluidic channel. This configuration causes the magnetic field lines emanating from the ring-shaped magnets to converge on both sides of the microrobot. Thus, the magnetic trapping forces that hold the microrobot in position are increased. To the best of our knowledge, no prior study exists on investigating the longitudinal motion for high flow velocities (>5 mm/s). Investigating the longitudinal forces (along the x-axis) that affect a magnetically-driven microrobot is a novel research topic that has many potential application areas such as cell research, micromanipulation, and lab-on-a-chip systems. The microrobot's dynamical motion is modeled as a second-order system, and using this model as a guideline, we demonstrate the ability of a microrobot in a square-shaped microfluidic channel 900 m 900 m to follow a linear trajectory with a relative velocity up to 132.6 mm/s. A straight and longitudinal trajectory of 4000 m has been successfully followed in the same and opposite directions to the flow for different flow rates (1-4.5 mL/min) and different robot speeds (10-50 mm/s).

In this paper, we discuss the solution of the magneto hydrodynamics (MHD) thermal boundary layer flow of Casson liquid over a penetrable extending wedge with ohmic heating and convective boundary condition (BC). Important applications of such flows and condition include the MHD pump, radiation therapy, MHD generator, soil mechanics, melt spinning process, thermal insulation and many others. Practical applications of convective BC are often encountered in laser damage or laser processing. The problem is non dimensionalized and computational solutions are achieved for the governing nonlinear coupled ordinary differential equations (PDEs) by using homotopy analysis method (HAM) and influence of various emerging parameters on momentum and temperature field are examined. A table containing computational data for the wall shear stress f ′ ′ ( 0 ) and local Nusselt - θ ′ ( 0 ) number is also provided. Major findings/objectives of the present study are: an increasing in Casson fluid parameter δ decreases velocity when wedge stretches faster than free stream velocity for R = 2 . However, velocity increases for R = 0.1 case. Temperature velocity decreases for R = 2 or R = 0.1 cases for δ escalations. Enhancing B i for convective heat transfer increases the momentum and thermal boundary layer thickness in the presence of suction C. Computational outcomes for velocity, drag force, temperature velocity and heat transfer rate are discussed through tables numerically. Results are verified with varied choices of suction parameter C. It is noted that the convective parameter magnified the heat transfer rate.

Two-body point absorbers are useful for wave energy conversion in high energetic and high wave period sea locations. Analysis and simulation show that the two-body point absorbers have high efficiencies which makes them a potential candidate to promote wave energy harvesting technology towards commercialization and implementation. The submerged body of the two-body point absorbers has a large effect on their performance, hence the question arises: which geometric shape of the submerged body will lead to the best performance of the two-body wave energy harvesters? This paper presents a comprehensive study that analyses the different shapes of the submerged bodies based on the numerical wave tank simulated viscous drag coefficient and hydrodynamic property parameters of the oscillating device. A set of transient and three-dimensional computational fluid dynamic simulations of a numerical wave tank were carried out in Ansys Fluent to determine the viscous drag coefficients of the different submerged body shapes. And then the boundary element hydrodynamic simulation and linear dynamic frequency-domain modeling have been applied to identify the optimized PTO damping. Finally, non-linear time-domain modeling has been applied with the identified viscous damping drag coefficient and PTO damping coefficients to predict and compare the power output performance of different large-scale devices with different shapes of submerged bodies. It is found that each submerged body shape is suitable for a different range of wave frequencies, as one must establish a balance between the hydrodynamic properties and the viscous drag of the submerged body based on the sea location. It is also found that the typical viscous drag coefficient values used in the past studies underestimate the drag coefficient, and the linearized model widely adopted in frequency domain models is non-accurate for the devices with large viscous drag forces.

An opto-electronic readout of the memory state in spin transfer torque random access memory (STT-RAM) cells is proposed. A single optical beam illuminating an array of STT-RAM cells creates electrical potential along each STT-RAM cell due to optical rectification that can be further enhanced through plasmon drag effect (PLDE). Then, the photo-induced voltage is assumed to be measured by conventional electronics. Here, a theoretical modeling is performed, where the results provide an estimate of the photo-induced voltage in each memory cell and its variation with respect to the changes in state of the memory cell (parallel vs anti-parallel). Our study shows that the plasmonic enhancement facilitates ${\sim }$ 20 times enhancement in the voltage change due to state change of the each memory cell, compared to the case of out-of-resonance excitation. This enhancement potentially improves the memory readout rate if a proper supporting electronic circuit is available.

The configuration of new type of turbine is the Archimedes wind turbine with a spiral structure whose design is inspired by logarithmic spirals. This type of wind turbine uses lift and drag to harness the kinetic energy of the wind. The eccentric design has aerodynamic characteristics that have been the focus of previous research. The design is made from the arrangement of the Fibonacci sequence (1x1, 2x2, 3x3, 5x5, 8x8) or commonly known as the golden ratio. This study aims to analyze the coefficient of lift (C L ) and coefficient of drag (C D ) with variations opening angle of 35°, 45°, 65°, air fluid, turbulent flow, Re 1200, pressure distribution 1 atm, wind speed 5, 5 and 15 m/s. The results is at wind speed of 5.5 m/s, an angle of 35°, the C L value is 1.07E+02, the C D value is 4.02E+04. At wind speed of 5.5 m/s, an angle of 45°, the C L value is 1.08E+04, the C D value is 1.77E+01. At wind speed of 5.5 m/s, an angle of 65°, the C L value is 1.84E+06, the C D value is 3.68E+04. At wind speed of 15 m/s, an angle of 35°, the C L value is 2.20E+03, the C D value is 9.76E+02. At wind speed of 15 m/s, an angle of 45°, the C L value is 5.51E+04, the C D value is 4.12E+02. At wind speed of 15 m/s, an angle of 65°, the C L value is 5.96E+01, the C D value is 1.33E+03. Based on this, it can be concluded that at wind speed of 5.5 m/s the higher the opening angle, the higher C L produced. At wind speed of 15 m/s the larger the opening angle the C D increases. This is because the higher the angle, the more it receives sweeps or catches the wind. While the unstable value generated in this simulation is generally a weakness in the wind turbine design.

A numerical model is investigated representing counter-current spontaneous imbibition of water to displace oil or gas from a core plug. The model is based on mass and momentum conservation equations in the framework of the theory of mixtures. We extend a previous imbibition model that included fluid–rock friction and fluid–fluid drag interaction (viscous coupling) by including fluid compressibility and Brinkman viscous terms. Gas compressibility accelerated recovery due to gas expansion from high initial non-wetting pressure to ambient pressure at typical lab conditions. Gas compressibility gave a recovery profile with two characteristic linear sections against square root of time which could match tight rock literature experiments. Brinkman terms decelerated recovery and delayed onset of imbibition. Experiments where this was prominent were successfully matched. Both compressibility and Brinkman terms caused recovery deviation from classical linearity with the square root of time. Scaling yielded dimensionless numbers when Brinkman term effects were significant.Article Highlights Spontaneous imbibition with viscous coupling, compressibility and Brinkman terms. Viscous coupling reduces spontaneous imbibition rate by fluid–fluid friction. Brinkman terms delay early recovery and explain seen delayed onset of imbibition. Gas compressibility accelerates recovery and can be significant at lab conditions. Gas compressibility gives recovery with two root of time lines as seen for shale.

The axisymmetric motion of a spherical particle in the presence of a porous interface is considered in the limit of small Reynolds and capillary numbers where the interface is of negligible deformation. We consider the translation along and the rotation about an axis perpendicular to the interface. The flow through the porous medium is modeled by Brinkman equation with a tangential stress jump condition applied at the interface and a slip boundary condition is used at the surface of the particle. A semi-analytical approach based on a collocation technique is used. Due to the linearity of the present problem, the flow variables for the two flow regions are constructed by superposing basic solutions in both cylindrical and spherical coordinate systems. The collocation solutions for the normalized hydrodynamic drag force and torque acted on the particle are calculated with good convergence for various values of the separation parameter, the stress jump coefficient, viscosity ratio and the permeability parameter. The results for the normalized drag and torque coefficients are in good agreement with the available solutions in the literature for the limiting cases.

While scholars are aware of the suction force of particles (FDn) in gas-solid flow, until recently, most researchers have considered the drag force (FD) to be FDn, and there are few application functions for the calculation of FDn; this will affect the design of air-suction seeders, check valves, or other machines based on particle absorption. Therefore, it is necessary to re-build an applicable function of FDn and verify the equivalence between FDn and FD. In the present study, the empirical formula of FDn, which includes the suction hole diameter (D), particle diameter (dp), distance from the particle center to the suction hole (Lp), pressure difference (ΔP), gas density (ρg), and gas viscosity (μg), is established via dimensional analysis, and the application scope is 0.571 ≤ D/dp ≤ 1, 0.5 ≤ L/dp ≤ 0.634, and 3000 Pa ≤ ΔP ≤ 5000 Pa. Some conjectures are provided based on the comparison of the results of CFD simulations and experiments. For instance, FDn may be a combination of multiple forces, one of which is the dominant force FD. This research introduces a new method and device for measuring FDn for use by other researchers, and contributes to the existing research on particle absorption.

The majority of wind power is currently produced on high wind speed sites by large wind turbine, whereas small wind turbines often operate in light wind conditions. Small capacity wind turbines have not received the same engineering attention as their larger counterparts. This is partially due to a number of unique problems that small wind turbines experience. The most relevant are: low operating Reynolds number ( R e 500 , 000 ) , and poor performance at high angles of attack. Low and medium wind speed sites (Class II–IV) are more common than high wind speed sites, meaning there is a large source of energy not being taken advantage of. Several studies have suggested that flow control devices such as the spherical tubercle could be used to increase lift before stall and generate more power in such situations. The aim of this study is to determine the effect of tubercle amplitude on aerodynamic performance of an airfoil at low-Re numbers ( R e = 300 , 000 & R e = 400 , 000 ) . Three amplitudes were considered in this study: A 1 = 0 . 005 c , A 2 = 0 . 01 c , and A 3 = 0 . 03 c . A detailed 2D simulation study is carried out, using FLUENT (a commercial CFD software) and the T r a n s i t i o n S S T k − ω turbulence model, to obtain aerodynamic coefficients and flow characteristics. Results indicate that small tubercles perform better overall than larger tubercles. The airfoil with the smallest tubercle outperforms the unmodified airfoil at both studied Reynolds numbers at angles of attack 0° – 4 °. Moreover, the airfoil with the largest tubercle outperformed all of the airfoils at an angle of attack of 0° and R e = 300 , 000 . The analysis of the aerodynamic coefficients indicates that the improvement of the aerodynamic performance of airfoils with tubercles is due to the reduction of the drag coefficient. Pressure, intermittency and wall shear stress contours suggest that the overall drag reduction is achieved through the decrease of friction drag. The decrease in friction drag is attributed to the thickening of the laminar boundary layer, caused by a more favorable pressure distribution around the airfoils with the aerodynamic improvements. Moreover, the drastic deterioration in aerodynamic performance at higher angles of attack is attributed to the turbulence generated by the tubercles. This study suggests that spherical tubercles could have a potential application in small wind turbines.

We present results from Euler–Lagrange simulations of turbulent flow over an erodible monodisperse bed of particles at a shear Reynolds number of R e τ = 180 . The Galileo number G a and the ratio of Shields to the critical Shields number Θ / θ c r were varied in the range 11.4 to 29.8 and 1.32 to 5.98, respectively. Two drag force models were investigated along with the influence of lift, particle rotation, and tangential collision forces for each model. Both models give similar results as far as mean particle flux and Shields stress are concerned, however we find that excluding particle rotation, without ignoring the associated tangential collisional force, significantly reduces the particle flux with little influence on Shields stress. On the other hand, when both particle rotation and tangential collision forces are not taken into account, the particle flux is practically unchanged, but the excess Shields stress slightly increases compared to the case where both effects are considered. We also find the lift force to substantially influence particle flux. Additionally, we show the importance of spatial coarse graining and time averaging for Euler–Euler simulations and quantify the reduction in scatter for space and time dependent variables such as sediment flux, Shields stress, and bed surface fluid velocities.

This paper presents steady axisymmetric creeping motion of a conducting, incompressible viscous fluid past a weakly permeable slightly deformed sphere in the presence of transverse magnetic field. The Stokes approximation of momentum equation and Darcy’s law together with Lorentz force are used for the flow outside and within the semi-permeable particle. The governing equations are changed into dimensionless form, and resulting equations are solved using separation of variables method. We have determined the resistance force exerted on the oblate spheroid in the presence of magnetic field as a particular case of an approximate sphere. The impact of Hartmann numbers, permeability and deformation parameter on the coefficient of drag and the streamline pattern is exhibited graphically. Some special cases are deduced from the current study and compared with some previous results. The outcome clarifies that the Hartmann numbers enhance the drag on the oblate spheroid in comparison with prolate spheroid.