Ratio Of Drag Force Research Articles

Vapor-induced flow and its impact on powder entrainment in laser powder bed fusion

A 2D axisymmetric transient Thermal-Fluid-Evaporation model coupled with melt pool dynamics and gas kinetics is developed to study the formation mechanisms of vapor-induced flow and the resulting powder entrainment in powder bed fusion using laser beam (PBF-LB) for 316 L powders. The interactions between keyhole formation inside the melt pool, vapor plume flow, and vapor-induced shielding gas flow are investigated. Vapor plume flow results in powder spattering with much higher speed, while vapor-induced gas flow significantly contributes to powder denudation with lower speed. It is also reported that powder spattering is stronger in 1 atm argon than that in 1 atm helium because the drag force for spattering is 2.72 times larger in 1 atm argon, but powder denudation becomes greater in 1 atm helium as the ratio of drag force for denudation in 1 atm argon to that in 1 atm helium is only 0.582. Furthermore, the vapor plume results in more spatters with the decrease of ambient pressure from 1 atm to 0.05 atm in argon because the plume is diluted faster with a twofold wider plume head and the two times higher peak velocity as a result of the pressure drop-induced significant reduction of viscosity restriction. A larger divergency angle in 0.05 atm argon is also recorded at the same time for the weaker restriction and faster dilution. In combination with in-situ observations, the proposed model provides insights into the vapor-induced flow, and its impact on powder entrainment under different gas types and ambient pressures.

Computational analysis on free vortex flow with suspension of solid particles

In this research, the rotation of a solid particle in a vortex flow is investigated computationally. The bvp4c MATLAB scheme is employed for mathematical modeling and physical analysis. After solving the governing equations, the influences of some physical parameters like initial values of radius, radial velocity and angular velocity as well as the ratio of drag force to inertia force on the velocity and displacement characteristics of the particle will be analyzed. The findings indicate that increasing [Formula: see text] and [Formula: see text] causes an increase in radial velocity, but increasing [Formula: see text] and [Formula: see text] have conversed treatments. Also, the angular velocity enhances by increasing the ratio of drag-to-inertia forces.

Optimization on pole pitch of magnetic wheels and thickness of metal plate for floating and a propulsion system using permanent magnets

A magnetic-levitation system using a rotating permanent magnet has been developed. Pole pitch of the magnetic wheels and thickness of the metal plates required for levitation were investigated by experiments and computational calculation. To determine the optimum conditions, the levitation force, generated using motors with different torque and rotation speeds, was measured. These measurements clarified differences in the generated levitation force due to the different rotational speed and torque. Parameters, such as skin depth, magnetic density, eddy-current distribution density, the ratio of drag force to levitation force, and levitation force per driving power were numerically calculated from the magnetic field created by the rotating permanent magnet and effective frequency. Magnetic wheels should be designed to be large and the pole pitch of magnets was to be wide, and the levitation force per driving power will be improved in proportion to the root function of the pole pitch between magnets.

A comparison of the aerodynamic characteristics of four kinds of land surface in wind erosion areas of northern China

Aerodynamic characteristics is a crucial factor influencing soil wind erosion, which is closely related to the properties of surface roughness elements. In the expansive arid and semi-arid northern China, grassland, farmland, mobile sandy land, and gobi are the main land surface types that suffer wind erosion to varying degrees. To investigate the aerodynamic characteristics of different surfaces, we used three-dimensional ultrasonic anemometers to observe the near-surface wind speed above grassland, farmland, mobile sand, and two types of gobi surfaces in areas of northern China (a total of five observation sites). We compared the aerodynamic characteristics of the five surfaces and their causes (i.e., the surface roughness length, wind speed pulsation, turbulence intensity, and drag coefficient), and analyzed how surface roughness elements weakened the airflow. The roughness length was greatest for grassland, followed by farmland, sand, fine gobi, and black gobi. The pulsation intensity of near-surface wind speed increased linearly with increasing wind speed at all sites. At a given wind speed, increasing roughness length increased the pulsation intensity of wind speed. The probability distributions for the drag coefficient and turbulence intensity of the five surfaces followed a positively skewed distribution. The drag coefficient and turbulence intensity were greatest for grassland, followed by farmland, sand, fine gobi, and black gobi surfaces. The drag force exerted on the roughness elements increased with increasing wind speed, but the ratio of drag force exerted on the roughness elements to the total drag force (τR/τ) for flexible roughness elements (i.e., plants) increased as the wind speed increased; for rigid roughness elements, τR/τ decreased with increasing wind speed. This confirms that the shelter capability of flexible roughness elements against soil wind erosion increases with the increase of wind speed, while that of rigid roughness elements is opposite.

Numerical insights into magnetic particle enrichment and separation in an integrated droplet microfluidic system

Particle concentration and manipulation inside droplets hold great potential in expanding lab-in-a-droplet applications ranging from biological to chemical assays. Herein, we present a numerical model that provides sufficient insights into magnetic particle enrichment in an integrated microfluidic system considering the most possible interactions and forces. The proposed system comprises three distinct interconnected modules: droplet generator, spacer, and splitter with a permanent magnet placed under the splitting zone. Two approaches are developed to predict the particle trajectories inside the droplet, namely, magnetohydrophoretic streamline (static) and multi-particle tracing (dynamic). It is found that although the presence of an external magnetic force may help to improve the separation/enrichment of the magnetic particles in such microfluidic systems, however, the location of the magnet must be carefully determined to avoid the inverse effect of the magnetic field on the separation/enrichment efficiency. Moreover, the full particle enrichment is obtained at a maximum magnetic force to drag force ratio of >0.8% and a magnetophoretic velocity to the mean fluid velocity ratio of >6% for both 2.83 µm and 4.4 µm magnetic beads. The presented accurate numerical model, together with its unique features of low computational cost and broad applicability, such as separating particles with different properties, can further broaden utility in droplet microfluidics.

Drag and heat transfer characteristics around and through two interactive porous particles

When the concentration of porous particles reaches a certain level, the interactions between the particles can't be ignored. Therefore, this paper numerically investigated the interactions between two porous particles using the lattice Boltzmann method. In this paper, two-dimensional steady flow and heat transfer around and through two porous particles with the same diameters (D) was studied numerically. The effects of Reynolds number (Re), Darcy number (Da), center-to-center distance (expressed as dimensionless form L/D), angle between two porous particles (β) and particles with different permeability on the flow and heat transfer characteristics were investigated in detail. The investigated ranges of the parameters were 10 ≤ Re ≤ 40, 10−6 ≤ Da ≤ 10−2, D ≤ L ≤ 4D and 0° ≤ β ≤ 90°. It is observed that these parameters have significant effects on the flow and temperature fields, drag coefficient and average Nusselt number. The drag coefficient and average Nusselt number of the leading particle (P1) is much larger than those of the trailing particle (P2) in most instances. And the two porous particles show different change tendency to the same changes of these parameters. The effects of Da on P1 are more prominent compared with P2 while the effects of L/D on P2 are more obvious compared with P1. Besides, the drag coefficient of P2 increases with β increasing. In addition, we define drag force ratio and heat transfer enhancement ratio to compare the sensitivity of particles to the changes of Re and/or Da when two particles coexist and when one particle exists alone. The results indicate the heat transfer efficiency of P1 is more sensitive to changes in Da and Re compared with a single porous particle.

OPTIMIZATION OF FLOATING HORIZONTAL AXIS WIND TURBINE (FHAWT) BLADES FOR AERODYNAMIC PERFORMANCE MEASUREMENT

Wind power is one of the most important sources of renewable energy which extract kinetic energy from the wind. Currently much research has concentrated on improving the aerodynamic performance of wind turbine blade through wind tunnel testing and theoretical studies. However, wind turbine simulation through Computational Fluid Dynamics (CFD) software offers inexpensive solutions to aerodynamic blade analysis problem. The purpose of this paper is to find the effect of angle of attack towards the blade of Floating Horizontal Axis Wind Turbine (FHAWT) and optimize to get the best blade performance in between twisted and untwisted blade which will give maximum lift and drag force ratio. The optimization of the FHAWT blades are carried out by analysing, modelling and simulation by using simplified spreadsheet method, CFD analysis in ANSYS WORKBENCH 2020 R1 software and wind tunnel testing. The blades are evaluated regarding their lift and drag force ratio in different angle of attack and wind speed. The results, obtained from both computer programs, wind tunnel testing and the initial hand calculations, are comparable and satisfying. Finally, the model was implemented to optimize blades performance, especially at low wind velocities, which is crucial to produce power during operating in offshore environment.

Development and testing of a three‐dimensional ballistics model for bat strikes on wind turbines

AbstractBats colliding with spinning wind turbine blades result in bat mortality. Carcass surveys at individual wind turbines vary from daily to once a week and from large cleared plots to only the road and pad area. A physics‐based model is proposed to guide carcass surveys, for designing curtailment studies to detect treatment fatalities and for improving fatality estimates by accounting for unsearched areas. The model considers the effects of carcass size, weight, and drag, and it accounts for the turbine rotor size and rotation rate to simulate the trajectory of a carcass after it is struck by a wind turbine blade. A carcass parameter is defined as the ratio of drag force to body weight, which accounts for the relative effect of bat biophysical and aerodynamic characteristics. By applying restrictions on carcass survey and turbine yaw data, a limited sample of bat fatalities was obtained, and the analysis revealed that bats fall downwind of wind turbines, indicating wind drift significantly influences carcass fall trajectories. The new ballistics model includes the effect of wind drift on fall trajectory of a carcass. The model was used to investigate the sensitivity of carcass fall trajectories to variability of the input parameters. The tests showed that larger values of the carcass parameter, that is, when drag dominates, such as for small carcasses, resulted in larger downwind drift, whereas large carcasses with smaller carcass parameter values resulted in larger distances within the rotor plane. The relationship of wind speed and RPM was found to influence the carcass downwind distance more compared to the within rotor plane distance. Using carcass survey data, turbine operation data, and wind speed records, for seven bats surveyed the day after colliding with a wind turbine, modelled back‐trajectories were used to identify the likely strike location on the rotor. The model can be improved by validating the modelled trajectories with the recorded bat‐blade strikes in thermal videos. It should be noted that the findings of the present study are based on the bat fatalities that met strict criteria leading to small sample size and hence requires further evaluation for testing the robustness of the model.

Aerodynamic Investigation on Performance Enhancement of NACA 2412 Airfoil with Suction Assistance

Advanced transport aircraft concept has active boundary-layer control by slot suction which reduces drag by stabilizing the laminar boundary. Thus, the prevention of transition and delaying the boundary layer separation will lead to a higher lift co-efficient. The influence of location and position of suction, suction flow rate and suction hole width on aerodynamic performance have greater influence. These examine the potential payoff for boundary-layer control as applied to the advanced-concept wings. An experimental work deals with the continuous normal suction from the wing upper surface effects on the aerodynamic forces. The wing model with NACA-2412 has been made to achieve normal suction from the wing upper surface by means of four slot channels. The results showed that the continuous normal suction can significantly increase the lift to drag force ratio and this ratio is increasing as the strength of suction increases. There is a convincing decrease in drag and pressure loss and an increase in max lift, which in turn improves the overall performance of the aircraft. While multi-hole suction control can reduce drag much more efficiently than single hole suction control, the position of the suction hole has a greater effect on reducing pressure losses than the suction flow rate.

The Effects of Different Shaped Baffle Blocks on the Energy Dissipation

Stilling basins can be defined as energy dissipaters constructed of the irrigation systems. This study aims at investigating the performance of the new seven baffle blocks design in terms of reducing the dimensions of stilling basins in irrigation systems. In order to assess the hydraulic efficiency of a new model for baffle block used in stilling basins, a Naval Research Laboratory (NRL) has conducted. The results of this study demonstrate that the performance of the new baffle block, in term of hydraulic jump length reduction and hydraulic energy dissipation, it's better than standard blocks. However, the ratios of the drag resistance attributed to the new baffles block (FB / F2) have been larger than that applied on the normal block. It was found that the new block dissipates the energy by 9.31% more than the concrete block, and decreases the length of the hydraulic jump by 38.6% in comparison with the standard blocks. However, the new block maximizes the drag force ratio by 98.6% in comparison with the standard baffle blocks. The findings indicated that in terms of energy reduction and dissipation in the length of the hydraulic jump, the new block is superior to the other kinds.

Experimental and numerical analysis on the hydrodynamic behaviors of permeable microbial granules

The microbial granules are found to be porous and permeable, which leads to a different drag force coefficient from the rigid sphere granules. Discrete element method (DEM) was employed to establish geometric models of porous microbial granules for the first time in this study. And computational fluid dynamics (CFD) was applied to simulate the effects of porosity and Reynolds number on the fluid flow, shear stress, pressure and drag force based on the established geometric models. The results showed that both the Reynolds number and the porosity of microbial granules significantly affect the fluid velocity distribution inside the granules. The porosity shows less effect on maximum shear stress than Reynolds number. It s well known that drag force consists form drag and skin drag. The ratio of form drag to drag force increased, while the skin drag force ratio decreased with the increasing Reynolds number. The porosity will enhance the skin drag and weaken the form drag at the same Reynolds number. A drag force coefficient equation was established based on the simulated results in order for engineering application. The correctness of the equation was confirmed by comparing with experimental results. The results from this study may provide valuable information for operation and designing of a granule-based bioreactor in wastewater treatment.

Experimentally validated numerical study of gas-solid vortex unit hydrodynamics

A three-dimensional numerical analysis of the flow in a Gas-Solid Vortex Unit (GSVU) is carried out. The numerical model is first validated by comparing the bed pressure drop and solids velocity with experimental data. Next, the influence of gas flow rate, solids density, and particle diameter on the pressure drop, solids velocity, bed void fraction and slip velocity between the two phases is studied. A stable, solids bed is achieved for the entire range of gas flow rates tested (0.1–0.6Nm3/s). No particle entrainment is observed when varying the solid density (1800–450kg/m3) or the particle diameter (2–0.5mm). A shift to bubbling fluidization regime is observed for small particle diameters (0.5mm). The observed changes in the GSVU flow patterns are discussed by analyzing the changes in the cumulative centrifugal to drag force ratio over the bed.

Direct Simulation of Drag Force on Fractal Flocs during Settling

Zhang, J. and Zhang, Q., 2015. Direct simulation of drag force on fractal flocs during settling.The hydrodynamic drag force of fractal flocs during settling is examined by the Lattice Boltzmann method. Fractal flocs formed by Diffusion-Limited Aggregation (DLA) and diffusion-limited-cluster-cluster aggregation (DLCCA) models settle down in the quiescent water and drag forces are directly calculated. The numerical simulations are consistent with the analytical results. The ratio of drag force on fractal flocs and floc size shows a linear relationship with the floc settling velocity when the flow filed around the flocs is Stokes flow. The drag coefficient experienced by flocs is significantly different from the spheres. Moreover, drag forces on flocs formed by DLCCA are larger than flocs formed by DLA, when the flocs are composed of the same primary particles.

Enzymatic hydrolysis suspension cross-flow diafiltration using polysulfone hollow fiber module

Glucose and enzyme in a high concentration enzymatic hydrolysis suspension were separated using hollow fiber cross-flow diafiltration. The operating condition effects on the filtration performance are discussed. Over 86% of the enzymes were retained using a 10kDa polysulfone membrane. Most glucose molecules penetrated through the membrane into the filtrate. The major filtration resistances are due to the cake formation on the membrane surface and enzyme blocking in the membrane pores in addition to the appreciable virgin membrane resistance. The cake mass is correlated with the drag force ratio tangential to the filtration directions and the average specific cake filtration resistance is expressed as a power-function of the transmembrane pressure with a cake compressibility of 0.3. The empirical equation related the resistances due to internal membrane fouling to the operating conditions established by conducting experimental data regression. The filtration flux can be estimated accurately by substituting the results calculated using the empirical equations into the basic filtration equation. An increase in cross-flow velocity or transmembrane pressure leads to higher filtration flux. The filtration flux increases ca 2-fold as the cross-flow velocity increases from 0.3 to 1.5m/s under a transmembrane pressure of 60kPa. The filtration flux increases over 3-fold as the transmembrane pressure increases from 20 to 100kPa. Two kinds of modified operating methods are used to improve the filtration flux. A pulse feeding method may increase the filtration flux by 25%, while the step-increase pressure method improves the filtration flux by over 34%. Forming a thin cake under low pressure in the early filtration period has great potential to significantly mitigate membrane pore blocking and enhance filtration flux.

Effect of seepage on initiation of cohesionless sediment transport

This paper presents theoretical analyses and experimental results of seepage effects, especially downward seepage, on the initiation of cohesionless sediment particles. The theoretical analysis examines how the additional seepage force acts to modify the critical shear stress for sediment entrainment. Laboratory experiments were conducted using medium sand with diameter of 0.9 mm with downward seepage to quantitatively show suction effects on sediment entrainment. The critical shear stresses with different suction rates were calculated using the experimental results. The measured data together with published results provide an overall view on seepage effects on the initiation of cohesionless sediment transport. Depending on whether seepage is in the form of injection or suction, it will either increase or decrease the critical shear stress. The result reveals that the ratio of drag force at the threshold condition with seepage to that without seepage is dependent on the ratio of the hydraulic gradient with seepage to its value at the quick condition.

Experimental Study of Lift/Drag Ratio Enhancement Using Continuous Normal Suction

An experimental work of continuous normal suction from the wing upper surface effects on the aerodynamic forces is carried out, as well as, the effect of normal suction slot channels location and the mass flow rate sucked strength are involved in this study. The wing model with NACA-0015 has been made to achieve normal suction from the wing upper surface by means of four slot channels. The satisfaction of the suction is done by using vacuum pump. The tests are to be done for incompressible flow over wing with and without a continuous normal suction for three different angle of attack 8, 12 and 16 Deg., and for three different Reynolds numbers 13.6×104, 20.4×104 and 24.5×104. The results showed that the continuous normal suction can significantly increase the lift to drag force ratio, and this ratio is increasing more as the strength of the suction increases. Keywords : Aerodynamic – Incompressible Flow – Boundary Layer Control – Normal Suction– Experimental work – Lift and Drag Coefficient

1217 埋め込み境界法によるGeldart粉体分類が抗力と流れの方向に横向きの力の比に及ぼす影響の検討(流体力学IX)

1217 埋め込み境界法によるGeldart粉体分類が抗力と流れの方向に横向きの力の比に及ぼす影響の検討(流体力学IX)

Sensitivity Study of Hydrodynamic Parameters During Numerical Simulations of Tsunami Inundation

This paper describes the analysis of a parameter, “hydrodynamic demand,” which can be used to represent the potential for tsunami drag force related damage to structures along coastlines. It is derived from the ratio of drag force to hydrostatic force caused by a tsunami on the structure. It varies according to the instantaneous values of the current velocities and flow depths during a tsunami inundation. To examine the effects of a tsunami in the present study, the analyses were performed using the tsunami numerical model in two altered regular-shaped basins having different bottom slopes. The simulations were implemented using a single sinusoidal wave with particular initial conditions, such as leading elevation wave and leading depression wave profiles with different wave periods. Two different initial wave amplitudes were employed to assess the diversity in the distribution of the square of the Froude number Fr 2 along the coastline. The numerical results were compared quantitatively.

Advective flow of permeable sphere in an electrical field

Advective flow of a permeable sphere in an electrical field is comprehensively studied. The sphere has a uniform permeability and is subject to an incoming Newtonian flow. The electrical field generates an electro-osmotic flow inside the sphere, which markedly affects sphere flow dynamics. A numerical model elucidates the effects of flow dynamic parameters on the drag coefficient and ratio of drag forces to a permeable and solid sphere. The model solves the Navier–Stokes equations both inside and outside the porous sphere. The unique flow field and pressure patterns of the permeable sphere flow are characterized in detail, and utilized to interpret the distinguishing flow behaviors of spheres induced by electro-osmotic flow. Drag force decreases and or reverses in direction when the intensity of the electro-osmotic flow in the sphere increases. When the electro-osmotic flow is counter to the incoming flow, drag force increases significantly, and vortices form near the sphere. As the sphere becomes highly permeable, the influence of the electro-osmotic flow and incoming flow velocity are reduced markedly.

Stratified propelled wakes

This paper presents experimental results on the wake of a propelled bluff body towed at a constant horizontal speed in a linearly stratified fluid. Three regimes of the wake have been found, depending on the angle of attack and on the ratio of drag force to propeller thrust. Most of the experiments were obtained in a first regime where a strong momentum flux is created in the wake, which can be oriented backward or forward depending on the ratio of drag force to thrust of the propeller. The velocity amplitude, wake width and Strouhal number of the wake can be predicted by defining a momentum thickness based on the drag coefficient of the bluff body and the thrust of the propeller. A second regime is obtained for a narrow band of towing velocities, with a relative width of 4%, in which the momentum flux is found to vanish. The wake is characterized by the velocity fluctuations; the scaling exponents of the velocity, vorticity and width of the wake are measured. A third regime is obtained for wakes with a small angle of attack, with a null momentum flux. The mean profile of the wake is found to be asymmetric and its amplitude and wake width are measured. Finally, the relevance of these results to the case of a real self-propelled bluff body is discussed. The presence of weak internal waves or of weak fluctuations of background velocity would lead to a wake in the regime with momentum flux, and would allow prediction of the amplitude, width and Strouhal number of the wake.