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Particles dispersion on fluid-liquid interfaces

Particuology 2011年第1期9卷 1-13页

作者： Sathish Gurupatham Bhavin Dalal Md.Shahadat Hossain Ian S.Fischer Pushpendra Singh Daniel D.Joseph department of mechanical Engineering New Jersey Institute of Technology department of aerospace Engineering and Mechanics University of Minnesota department of mechanical and aerospace Engineering University of California Irvine

This paper is concerned with the dispersion of particles on the fluid-liquid interface. In a previous study we have shown that when small particles, e.g., flour, pollen, glass beads, etc., contact an air-liquid interface, they disperse rapidly as if they were in an explosion. The rapid dispersion is due to the fact that the capillary force pulls particles into the interface causing them to accelerate to a large velocity. In this paper we show that motion of particles normal to the interface is inertia dominated; they oscillate vertically about their equilibrium position before coming to rest under viscous drag. This vertical motion of a particle causes a radially-outward lateral （secondary） flow on the interface that causes nearby particles to move away. The dispersion on a liquid-liquid interface, which is the primary focus of this study, was relatively weaker than on an air-liquid interface, and occurred over a longer period of time. When falling through an upper liquid the particles have a slower velocity than when falling through air because the liquid has a greater viscosity. Another difference for the liquid-liquid interface is that the separation of particles begins in the upper liquid before the particles reach the interface. The rate of dispersion depended on the size of the particles, the densities of the particle and liquids, the viscosities of the liquids involved, and the contact angle. For small particles, partial pinning and hysteresis of the three-phase contact line on the surface of the particle during adsorption on liquid-liquid interfaces was also important. The frequency of oscillation of particles about their floating equilibrium increased with decreasing particle size on both air-water and liquid-liquid interfaces, and the time to reach equilibrium decreased with decreasing particle size. These results are in agreement with our analysis.

关键词： Adsorption Interfacial tension Particle dispersion Fluid–liquid interface Capillary force Viscous drag

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Small is beautiful, and dry

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Science China(Physics,Mechanics & Astronomy) 2010年第12期53卷 2245-2259页

作者： SHERIDAN John department of mechanical and aerospace Engineering Monash University

Thousands of plant and animal species have been observed to have superhydrophobic surfaces that lead to various novel behaviors. These observations have inspired attempts to create artificial superhydrophobic surfaces, given that such surfaces have multitudinous applications. Superhydrophobicity is an enhanced effect of surface roughness and there are known relationships that correlate surface roughness and superhydrophobicity, based on the underlying physics. However, while these examples demonstrate the level of roughness they tell us little about the independence of this effect in terms of its scale. Thus, they are not capable of explaining why such naturally occurring surfaces commonly have micron-submicron sizes. Here we report on the discovery of a new relation, its physical basis and its experimental verification. The results reveal that scaling-down roughness into the micro-submicron range is a unique and elegant strategy to not only achieve superhydrophobicity but also to increase its stability against environmental disturbances. This new relation takes into account the previously overlooked but key fact that the accumulated line energy arising from the numerous solid-water-air intersections that can be distributed over the apparent contact area, when air packets are trapped at small scales on the surface, can dramatically increase as the roughness scale shrinks. This term can in fact become the dominant contributor to the surface energy and so becomes crucial for accomplishing superhydrophobicity. These findings guide fabrication of stable super water-repellant surfaces.

关键词： scale effect line tension wetting contact angle superhydrophobic

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Characteristics of Nanosecond Pulsed Discharges in Atmospheric Helium Microplasmas

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Plasma Science and Technology 2016年第10期18卷 992-997页

作者： Manish JUGROOT department of mechanical and aerospace Engineering Royal Military College of Canada

Microplasmas are very interesting due to their unique properties and achievable regimes maintained at atmospheric pressures. Due to the small scales, numerical modeling could contribute to the understanding of underlying phenomena as it provides access to local parameters — and complements experimental global characteristics. A self-consistent formalism,applied to nanosecond pulsed atmospheric non-equilibrium helium plasmas, reveals that several successive discharges can persist as a result of a combined volume and dielectric surface effects. The valuable insights provided by the spatiotemporal simulation results show the critical importance of coupled gas and plasma dynamics — namely gas heating and electric field reversals.

关键词： microplasmas self-consistent simulations space charge Joule heating nanosecond discharges

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Gaseous plume flows in space propulsion

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Chinese Journal of Aeronautics 2013年第3期26卷 522-528页

作者： Wang Limei Cai Chunpei department of mechanical and aerospace Engineering New Mexico State University

This paper presents a gaskinetic study on high-speed, highly rarefied jets expanding into a vacuum from a cluster of planar or annular exits. Based on the corresponding exact expressions for a planar or annular jet, it is convenient to derive the combined multiple jet flowfield solutions of density and velocity components. For the combined temperature and pressure solutions, extra attention is needed. Several direct simulation Monte Carlo simulation results are provided to validate these analytical solutions. The analytical and numerical solutions are essentially identical for these high Knudsen number jet flows.

关键词： Free molecular flow Gasdynamics Gaskinetics jets Monte Carlo methods Plume flow

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Experimental study of flow field distribution over a generic cranked double delta wing

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Chinese Journal of Aeronautics 2016年第5期29卷 1196-1204页

作者： Mojtaba Dehghan Manshadi Mehdi Eilbeigi Mohammad Kazem Sobhani Mehrdad Bazaz Zadeh Mohammad Ali Vaziry department of mechanical and aerospace Engineering Malek Ashtar University of Technology

The flow fields over a generic cranked double delta wing were investigated. Pressure and velocity distributions were obtained using a Pitot tube and a hot wire anemometer. Two different leading edge shapes, namely ＂sharp＂ and ＂round＂, were applied to the wing. The wing had two sweep angles of 55° and 30°. The experiments were conducted in a closed circuit wind tunnel at velocity 20 m/s and angles of attack of 5°- 20° with the step of 5°. The Reynolds number of the model was about 2 - 105 according to the root chord. A dual vortex structure was formed above the wing surface. A pressure drop occurred at the vortex core and the root mean square of the measured velocity increased at the core of the vortices, reflecting the instability of the flow in that region. The magnitude of power spectral density increased strongly in spanwise direction and had the maximum value at the vortex core. By increasing the angle of attack, the pressure drop increased and the vortices became wider; the vortices moved inboard along the wing, and away from the surface; the flow separation was initiated from the outer portion of the wing and developed to its inner part. The vortices of the wing of the sharp leading edge were stronger than those of the round one.

关键词： Cranked double delta wing Flow field Hot wire Leading edge shape Vortical flow

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Momentum and heat transfer of a special case of the unsteady stagnation-point flow

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Applied Mathematics and Mechanics(English Edition) 2020年第1期41卷 51-82页

作者： T.G.FANG F.J.WANG mechanical and aerospace Engineering department North Carolina State University

This paper investigates the unsteady stagnation-point flow and heat transfer over a moving plate with mass transfer,which is also an exact solution to the unsteady Navier-Stokes(NS)*** boundary layer energy equation is solved with the closed form solutions for prescribed wall temperature and prescribed wall heat flux *** wall temperature and heat flux have power dependence on both time and spatial *** solution domain,the velocity distribution,the flow field,and the temperature distribution in the fluids are studied for different controlling *** parameters include the Prandtl number,the mass transfer parameter at the wall,the wall moving parameter,the time power index,and the spatial power *** is found that two solution branches exist for certain combinations of the controlling parameters for the flow and heat transfer *** heat transfer solutions are given by the confluent hypergeometric function of the first kind,which can be simplified into the incomplete gamma functions for special *** wall heat flux and temperature profiles show very complicated variation *** wall heat flux can have multiple poles under certain given controlling parameters,and the temperature can have significant oscillations with overshoot and negative values in the boundary *** relationship between the number of poles in the wall heat flux and the number of zero-crossing points is *** difference in the results of the prescribed wall temperature case and the prescribed wall heat flux case is *** given in this paper provide a rare closed form analytical solution to the entire unsteady NS equations,which can be used as a benchmark problem for numerical code validation.

关键词： unsteady stagnation point flow Navier-Stokes(NS)equations analytical solution heat transfer

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Aircraft robust multidisciplinary design optimization methodology based on fuzzy preference function

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Chinese Journal of Aeronautics 2018年第12期31卷 2248-2259页

作者： Ali Reza BABAEI Mohammad Reza SETAYANDEH Hamid FARROKHFAL department of mechanical and aerospace Engineering Malek-Ashtar University of Technology

This paper presents a Fuzzy Preference Function-based Robust Multidisciplinary Design Optimization(FPF-RMDO) methodology. This method is an effective approach to multidisciplinary systems, which can be used to designer experiences during the design optimization process by fuzzy preference functions. In this study, two optimizations are done for Predator MQ-1 Unmanned Aerial Vehicle(UAV):(A) deterministic optimization and(B) robust optimization. In both problems, minimization of takeoff weight and drag is considered as objective functions, which have been optimized using Non-dominated Sorting Genetic Algorithm(NSGA). In the robust design optimization, cruise altitude and velocity are considered as uncertainties that are modeled by the Monte Carlo Simulation(MCS) method. Aerodynamics, stability and control, mass properties, performance, and center of gravity are used for multidisciplinary analysis. Robust design optimization results show 46% and 42% robustness improvement for takeoff weight and cruise drag relative to optimal design respectively.

关键词： Fuzzy logic Multidisciplinary design optimization Preference function Robust design Unmanned Aerial Vehicle(UAV)

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The energy transfer mechanism of a perturbed solid-body rotation flow in a rotating pipe

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Acta Mechanica Sinica 2017年第2期33卷 274-283页

作者： Chunjuan Feng Feng Liu Zvi Rusak Shixiao Wang School of Aeronautics Northwestern Polytecrhnical University department of mechanical and aerospace Engineering University of California department of mechanical Aerospaceand Nuclear EngineeringRensselaer Polytechnic Institute department of Mathematics University of Auckland

Three-dimensional direct numerical simulations of a solid-body rotation superposed on a uniform axial flow entering a rotating constant-area pipe of finite length are presented. Steady in time profiles of the radial, axial, and circumferential velocities are imposed at the pipe inlet. Convective boundary conditions are imposed at the pipe outlet. The Wang and Rusak (Phys. Fluids 8:1007-1016, 1996.) axisymmetric instability mechanism is retrieved at certain operational conditions in terms of incoming flow swirl levels and the Reynolds number. However, at other operational conditions there exists a dominant, three-dimensional spiral type of instability mode that is consistent with the linear stability theory of Wang et al. (J. Fluid Mech. 797: 284-321, 2016). The growth of this mode leads to a spiral type of flow roll-up that subsequently nonlinearly saturates on a large amplitude rotating spiral wave. The energy transfer mechanism between the bulk of the flow and the perturbations is studied by the Reynolds-Orr equation. The production or loss of the perturbation kinetic energy is combined of three components: the viscous loss, the convective loss at the pipe outlet, and the gain of energy at the outlet through the work done by the pressure perturbation. The energy transfer in the nonlinear stage is shown to be a natural extension of the linear stage with a nonlinear saturated process.

关键词： Vortex instability Incompressible viscous flow Cylindrical coordinates

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Numerical evaluation of passive control of shock wave/boundary layer interaction on NACA0012 airfoil using jagged wall

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Acta Mechanica Sinica 2016年第5期32卷 792-804页

作者： Mojtaba Dehghan Manshadi Ramin Rabani mechanical and aerospace Engineering department Malek-Ashtar University of TechnologyEsfahan Iran department of mechanical Engineering Yazd University

Shock formation due to flow compressibility and its interaction with boundary layers has adverse effects on aerodynamic characteristics, such as drag increase and flow separation. The objective of this paper is to appraise the practicability of weakening shock waves and, hence, reducing the wave drag in transonic flight regime using a two-dimensional jagged wall and thereby to gain an appropriate jagged wall shape for future empirical study. Different shapes of the jagged wall, including rectangular, circular, and triangular shapes, were employed. The numerical method was validated by experimental and numerical studies involving transonic flow over the NACA0012 airfoil, and the results presented here closely match previous experimental and numerical results. The impact of parameters, including shape and the length-to-spacing ratio of a jagged wall, was studied on aerodynamic forces and flow field. The results revealed that applying a jagged wall method on the upper surface of an airfoil changes the shock structure significantly and disintegrates it, which in turn leads to a decrease in wave drag. It was also found that the maximum drag coefficient decrease of around 17 % occurs with a triangular shape, while the maximum increase in aerodynamic efficiency（lift-to-drag ratio）of around 10 % happens with a rectangular shape at an angle of attack of 2.26？.

关键词： Jagged wall Passive flow control Shock wave/boundary layer interaction Aerodynamic efficiency

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Effects of nanoscale features on infrared radiative properties of heavily doped silicon complex gratings

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Science China(Technological Sciences) 2010年第8期53卷 2207-2214页

作者： HSU PeiFeng department of mechanical and aerospace Engineering Florida Institute of Technology

The infrared radiative properties of one heavily doped silicon complex grating and its corresponding four modified complex gratings with attached features at transverse magnetic wave incidence were numerically investigated by employing the finite-difference time-domain *** the complex grating,by properly choosing the carrier concentration and geometry,it exhibited a broadband absorptance peak at wavelengths between 7 and 12μm resulting from the excitation of surface plasmon *** for the four modified complex gratings,though absorptance spectra of the gratings almost remained unchanged, their locations shifted towards longer ***,the spectral absorptance peaks of two modified complex gratings were wider than that of the grating without attached *** broadened peaks could be partly attributed to the cavity resonance within the grating structures demonstrated by the electromagnetic fields and Poynting vectors ***,through comparing the spectral absorptances of complex gratings with two symmetrical square features in three sizes,it was shown that the peak wavelength shifted toward longer wavelengths with enlarged feature *** work theoretically laid a foundation for the optimized design and application of the infrared detector with high performance.

关键词： cavity resonance effect finite-difference time-domain modified complex gratings radiative property surface plasmon polaritons

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