High Tip Velocity Research Articles

Enhanced acoustic streaming effects via sharp-edged 3D microstructures.

Acoustofluidic micromanipulation is an important tool for biomedical research, where acoustic forces offer the ability to manipulate fluids, cells, and particles in a rapid, biocompatible, and contact-free manner. Of particular interest is the investigation of acoustically driven sharp edges, where high tip velocity magnitudes and strong acoustic potential gradients drive rapid motion. Whereas prior devices utilizing 2D sharp edges have demonstrated promise for micromanipulation activities, taking advantage of 3D structures has the potential to increase their performance and the range of manipulation activities. In this work, we investigate high-magnitude acoustic streaming fields in the vicinity of sharp-edged, sub-wavelength 3D microstructures. We numerically model and experimentally demonstrate this in fabricating parametrically configured 3D microstructures whose tip-angle and geometry influence acoustic streaming velocities and the complexity of streaming vortices, finding that the simulated and realized velocities and streaming patterns are both tunable and a function of microstructure shape. These sharp-edge interfaces hold promise for biomedical studies benefiting from precise and targeted micromanipulation.

Anisotropic lattice Boltzmann-phase-field modeling of crystal growth with melt convection induced by solid-liquid density change

Density change is ubiquitous in phase transformation, and it can induce melt convection which strongly influences the crystal growth. Here, an anisotropic lattice Boltzmann-phase-field method was extended to predict the dendritic growth under the shrinkage or expansion melt convection by density change induced. A novel LB equation with an anisotropic coefficient was constructed to model the advancement of ordering parameter, coupling with the passive scalar LB equation for convective and diffusive heat transfer during phase transition. We studied dendritic growth and shape selection with melt convection induced by density change in crystal growth. Results show that the melt convection induced by density change affects strongly the dendritic growth. The shrinkage flow results in a higher tip velocity while the expansion flow leads to a slower one. Predicted Péclet number with respect to the relative density change was compared with an analytical solution. Moreover, the modified selection parameter has been verified by numerical simulations.

Phase-field simulation and analytical modelling of CaSiO3 growth in CaO-Al2O3-SiO2 melts

Isothermal crystallization of a hexagonal crystal (Wollastonite) in ternary melts (CaO-Al2O3-SiO2) was simulated by quantitative phase-field simulation and analytical modelling. The dependence of initial composition, undercooling, interfacial energy and anisotropy strength on the growth behavior of Wollastonite was comprehensively investigated. According to simulation results, a transition from flat to dendritic growth of CaSiO3 occurs; the formation of dendritic Wollastonite is favorable at a lower Al2O3 content, a lower temperature and a higher anisotropy. When temperature increases, the transition prefers taking place at lower interface energy. Simulations also show that the tip velocity firstly increases until it reaches a maximum value and then decreases slowly with further decreasing the temperature, while the velocity only increases at a lower interfacial energy level. For anisotropy strength, its increase causes a higher tip velocity. Furthermore, validation of these parameter effects was performed by comparing the simulation results with an analytical model, showing quantitatively good agreement, when solute interaction was taken into account in the analytical model.

A phase-field study on the peritectic phase transition in Fe-C alloys

A quantitative multi-phase-field model, with an anti-trapping current and involving diffusion in the solid, is proposed to simulate the peritectic phase transition in Fe-C alloys. An interface field method with a newly defined step function is adopted to formulate the governing equation of the multi-phase-field variables. The proposed model is applied to simulate the γ-platelet tip growth during the peritectic reaction and the subsequent peritectic transformation (γ-platelet thickness growth) in large computational domains of the experimental length scale. It is found that the local liquid concentration at the triple junction point L/δ/γ is slightly higher than the liquid concentration in equilibrium with the δ-phase, but lower than the liquid concentration in equilibrium with the γ-phase. This leads to slight melting of the δ-phase in the vicinity of the triple junction, while the γ-platelet growth continues. Higher tip velocities at higher undercoolings produce a steeper carbon concentration gradient along the γ-platelet's thickness direction, and thus yield a higher thickness growth velocity. It is also found that the ratio of tip and thickness growth velocity of the γ-platelets increases at higher undercoolings, leading to decreasing tip radius and platelet thickness. Good agreement between the simulations and the experimental data reported in literature is achieved, demonstrating the quantitative prediction capabilities of the proposed model, and confirming the diffusion control for the peritectic phase transition close to equilibrium conditions.

Encased Cantilevers and Alternative Scan Algorithms for Ultra-Gantle High Speed Atomic Force Microscopy

Live cells and many biological samples readily deform under the minimum force required to perform an AFM measurement precluding imaging at high temporal and spatial resolution. We reduced the force noise of the measurement by building a protective encasement around the cantilever. This keeps the cantilever is dry reducing the fluid viscosity and damping but allows the tip to probe the sample in solution. Encased cantilevers have exceptionally high resonance frequency, Q factor, and detection sensitivity and low force noise enabling gentle high speed imaging. Present raster scan techniques are poorly matched to the instrument limitations of Atomic Force Microscopy making data collection slow. We have used advanced image processing tools such as inpainting to recover high-resolution images from sparse quickly collected images to improve temporal resolution without applying more force or increasing bandwidth. We are also using spiral scanning to increase temporal resolution by allowing higher tip velocities without distortion. Inpainting or interpolation is used to quickly create images from the nongrided data.View Large Image | View Hi-Res Image | Download PowerPoint Slide

Ontogeny of lift and drag production in ground birds

The juvenile period is often a crucial interval for selective pressure on locomotor ability. Although flight is central to avian biology, little is known about factors that limit flight performance during development. To improve understanding of flight ontogeny, we used a propeller (revolving wing) model to test how wing shape and feather structure influence aerodynamic performance during development in the precocial chukar partridge (Alectoris chukar, 4 to >100 days post hatching). We spun wings in mid-downstroke posture and measured lift (L) and drag (D) using a force plate upon which the propeller assembly was mounted. Our findings demonstrate a clear relationship between feather morphology and aerodynamic performance. Independent of size and velocity, older wings with stiffer and more asymmetrical feathers, high numbers of barbicels and a high degree of overlap between barbules generate greater L and L:D ratios than younger wings with flexible, relatively symmetrical and less cohesive feathers. The gradual transition from immature feathers and drag-based performance to more mature feathers and lift-based performance appears to coincide with ontogenetic transitions in locomotor capacity. Younger birds engage in behaviors that require little aerodynamic force and that allow D to contribute to weight support, whereas older birds may expand their behavioral repertoire by flapping with higher tip velocities and generating greater L. Incipient wings are, therefore, uniquely but immediately functional and provide flight-incapable juveniles with access to three-dimensional environments and refugia. Such access may have conferred selective advantages to theropods with protowings during the evolution of avian flight.

Abrasion of Particles by a Small Impeller in an Agitated Vessel

There are a number of operations that are carried out in the process industries by a small impeller in an agitated vessel in which particles are suspended, and thus, the possible abrasion of the particles should be considered precisely to understand the operation. To investigate the abrasion of particles in an agitated vessel, an aggregated spherical silica particle, whose diameter was set at about 2.0 mm or 1.0 mm, was prepared purposely, put into a vessel, and agitated by a Rushton turbine impeller (RT) or an edged turbine impeller (ET). The change in the particle diameter with time elapse was measured as an area-equivalent diameter by using a CCD camera. The frequency of the particle passing through the impeller-swept region was also measured by the 3-D PTV method. As a result, it was found that an ET is superior to a RT for the abrasion of particles at the same power input per unit volume. For both the impellers, the power efficiency of particle abrasion at a very high impeller speed was less than that at a low impeller speed. However, it was also found that with increasing impeller speed, the particle abrasion rate per circulation of the particle passing through the impeller-swept region, Rω, increased, especially at a high tip velocity in the case of an ET. At the same maximum impact energy, Rω in the case of an ET was more than that in the case of a RT.

Effect of chemical termination of self-assembled organic monolayers on the tip induced local anodic oxidation of silicon(100)

We evaluated the scanning probe microscope based anodization process of silicon(100) terminated by organic monolayers of the same thickness but with different surface properties. The surface energy of these monolayers with its dispersive and polar component was determined by contact angle measurements. We discovered that the anodization oxide characteristics depend ceteris paribus clearly on the surface properties of the sample. With an increased polar component, and therefore hydrophilic character of the surface, the formed oxide structures became broader and thinner. On the other hand a hydrophilic surface allowed the generation of oxide structures at higher tip velocities and lower applied voltages. The absolute amount of formed oxide is independent of the monolayer indicating a dominating influence of initially formed oxide on the following oxidation process.

Effect of tip velocity on weld solidification process of hot-work tool steel

In order to clarify the effect of tip velocity on the weld solidification process of hot-work tool steel (SKD61) during welding, information about microstructure evolution was obtained by the combination of a liquid tin quenching and time resolved X-ray diffraction technique using intense synchrotron radiation. From the experimental results, it was found that the solidification mode was changed from FA mode (L → L+δ → L+δ+γ → L+γ → γ) to A mode (L → L+γ → γ) at high tip velocity. Moreover, the effect of tip velocity on the microstructure selection during solidification between the primary δ, ferrite and the primary γ, austenite was theoretically proven by the Kurz, Giovanola and Trivedi model. Therefore, it was understood that the solidification cracking susceptibility of hot-work tool steel (SKD61) weld metal was increased due to the δ to γ transition of the primary phase.

Mass transport and heterogeneous electron transfer of a ferrocene derivative in a room-temperature ionic liquid

Electrochemical and mass-transport properties of a redox-active ionic liquid, 1-(ferrocenylmethyl)-3-methylimidazolium bis(trifluoromethanesulfonyl)amide (FcEmiTFSI), were investigated for the pure compound and for solutions in acetonitrile (ACN) and in a room-temperature ionic liquid, 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EmiTFSI). Cyclic voltammetry data were compared with those obtained for the oxidation of ferrocene (Fc) in EmiTFSI and ACN. The half-potential of FcEmiTFSI/Fc +EmiTFSI is higher than that of Fc/Fc + in both media. The apparent heterogeneous rate constants k app ° of FcEmiTFSI and Fc were determined in both solvents. The values of k app ° for these two redox probes in the same solvent are of the same order of magnitude. However, k app ° is lower in EmiTFSI than in ACN. Comparison of k app ° in these solvents indicates that the decrease in k app ° cannot be explained in terms of Marcus–Hush theory. The electrochemical and mass-transport properties of FcEmiTFSI in EmiTFSI were investigated by means of scanning electrochemical microscopy (SECM). The tip current depends upon the tip velocity. With high tip velocity, one observes that the tip current increases as the distance between the tip and insulating substrate decreases. This behavior is not due to a positive feedback mechanism. It is interpreted in terms of mixed diffusion and convective mass transfer control.

Jet Projectiles Penetration into Multilayer Metal Targets with Large Interval

At long standoff, a shaped charge with small cone angle will produce a jet with a high tip velocity and a low tail velocity, causing it to stretch and break up, so its penetration ability into multilayer metal targets is very weak, while the penetration depth of explosively formed projectiles is too low to penetrate into multilayer metal targets. On account of this, the large cone angle shaped charge, whose internal cone angle is about 100 degree, is proposed and designed in the paper. The sensitivity of penetration effect into targets to the cone angle of the liner is investigated by experiment. The results reveal that the shaped charge penetration into multilayer metal targets with large interval is more optimistic than that of the shaped charge with small cone angle and explosively formed projectiles. In numerical simulation, based on interface tracking algorithm known as markers on cell line to reconstruct material interfaces, jet penetration into metal targets is simulated in a two-dimensional multi-material Eulerian code. The numerical results are in good agreement with the experimental ones and also indicate the interface tracking algorithm has much better resolution for moving interfaces, especially effective for large deformation.

High-Temperature Superconducting Homopolar Inductor Alternator for Marine Applications

This paper describes a high power density high-temperature superconducting (HTS) electric machine topology that is scalable for marine propulsion and power generation. The design, currently being pursued for airborne applications, is based on homopolar inductor alternator (HIA) technology, which is new within HTS applications. The basic machine design configuration of the HTS HIA is based on a stationary HTS field excitation coil, a solid rotor, and an advanced but conventional stator comprising liquid-cooled air-gap armature winding and an advanced iron core. High power density is obtained by the enhanced magneto-motive force capability of the HTS coil, the increased airgap flux density and armature current loading, and the high tip velocity of the rotor. Preliminary scaled up designs look attractive for three marine applications: propulsion drive, primary ship power generation, and power generation modules. The generators are driven directly by the turbines without the additional complexity of a clutch and gear system. A conceptual design study of a 36-MW 3600-r/min generator, a 4-MW 7000-r/min auxiliary generator, and a 36-MW 120-r/min and 4-MW 132-r/min propulsion motor are summarized.

Variable density and viscosity, miscible displacements in capillary tubes

The displacement of a more viscous fluid by a miscible, less viscous one of lower density in a horizontal capillary tube is studied by means of Stokes flow simulations. Both axisymmetric and three-dimensional simulations are conducted at Péclet numbers up to 10 4, in order to resolve discrepancies between earlier simulations by [C.Y. Chen, E. Meiburg, Miscible displacements in capillary tubes. Part 2. Numerical simulations, J. Fluid Mech. 326 (1996) 57] and corresponding experiments of [P. Petitjeans, T. Maxworthy, Miscible displacements in capillary tubes. Part 1. Experiments, J. Fluid Mech. 326 (1996) 37] and [J. Kuang, T. Maxworthy, P. Petitjeans, Miscible displacements between silicone oils in capillary tubes, Eur. J. Mech. B Fluids 22 (2003) 271–277]. An initial set of simulations addresses the influence of different viscosity–concentration relations on the quasisteady finger tip velocity. The results indicate that steeper relations generally result in a higher tip velocity. However, the effect is too small to explain the above discrepancies. Further simulations show that a concentration-dependent diffusion coefficient results in a slight reduction of the tip velocity at moderate Pe, but again the effect is too small to fully account for the observed differences. Three-dimensional simulations that include gravitational forces yield a much more significant effect. Consistent with the experiments of [P. Petitjeans, T. Maxworthy, Miscible displacements in capillary tubes. Part 1. Experiments, J. Fluid Mech. 326 (1996) 37], at moderate Pe the tip slows down as the gravity parameter increases, an effect that becomes more pronounced as Pe decreases. However, the three-dimensional simulations do not produce the longitudinal splitting phenomenon observed by [P. Petitjeans, T. Maxworthy, Miscible displacements in capillary tubes. Part 1. Experiments, J. Fluid Mech. 326 (1996) 37]. In order to check for the existence of gravitational instabilities that might cause such a splitting, additional two-dimensional simulations are conducted in cross-sections of the tube. A comparison of these two-dimensional results with corresponding three-dimensional simulations demonstrates that for a wide range of parameters the evolution of the trailing finger sections is governed by a two-dimensional balance between gravitational and viscous forces. However, a gravitational instability along the lines suggested by [P. Petitjeans, T. Maxworthy, Miscible displacements in capillary tubes. Part 1. Experiments, J. Fluid Mech. 326 (1996) 37] was not observed. On the other hand, for some parameter combinations the evolution of a 'dimple' is observed on the lower side of the finger, and close to its tip. This dimple may signal the evolution of a splitting phenomenon after long times, which are beyond the reach of the current simulations. Taken together, the two- and three-dimensional simulations suggest that the splitting phenomenon observed by [P. Petitjeans, T. Maxworthy, Miscible displacements in capillary tubes. Part 1. Experiments, J. Fluid Mech. 326 (1996) 37] likely is caused by the gravity-induced modification of the flow around the tip of the finger, rather than by a gravitational instability per se.

Radial fingering in viscoelastic media, an experimental study

We report measurements of two dimensional radial fingering in viscoelastic concentrated suspensions (pastes) of colloidal particles, in small surface tension conditions. The displacement efficiency, the average finger width and the fractal dimension for growth have been measured in a broad range of paste viscosity and driving pressure. The growth process appears to be fractal in all the experimental conditions, with fractal exponents, D G , covering the whole range from 1.3 at very small tip velocity to 2.0 at very high tip velocity. The displacement efficiency, δ, defined as the volume fraction of paste displaced by water when water flows out of the paste, is almost zero at very low velocity, and seems to tend toward an asymptotic value close to 0.25 at high velocity, δ is almost entirely dominated by the velocity dependence of the tip-splitting cascade. The average finger width has very little influence Realisation d'experiences de digitation viscoelastique en geometrie radiale, dans des suspensions concentrees de particules colloidales (des argiles) en conditions de tension interfaciale tres faible