Fluid Phenomena Research Articles

Apresentação. O retorno a Aby Warburg no discurso historiográfico artístico contemporâneo

A presença de escritos referenciais de Aby Warburg é emblemática do crescente movimento de retorno a teóricos e historiadores da arte do início do século XX, pelo menos em dois diferentes âmbitos. Um deles se dedica a seus pressupostos teórico-metodológicos sob uma revisão epistemológica da história da arte, cuja especificidade nos coloca a pensar a possibilidade de acesso a uma região de saberes e não saberes sobre a diversidade cultural do Renascimento e de seu olhar sobre a Antiguidade, entendendo sua temporalidade como um fenômeno complexo. O outro âmbito é suscitado por questões oriundas da arte moderna e contemporânea, que impõem agenciar deslocamentos de sentido, conceitos operatórios e categorias de análise para considerar a produção visual (recente ou não) e problematizar constrangimentos classificatórios e modelos teóricos fundados por teorias que se pretendiam objetivas. A ordem epistemológica desse retorno, em ambos os âmbitos, parece questionar o próprio discurso historiográfico da arte em sua consideração da imagem e do tempo, pensados a partir de diálogos transdisciplinares abertos pela obra de Warburg (e de estudiosos warburguianos). Trata-se de considerar a abertura desse retorno face à consciência de uma inquietação, algo que poderíamos chamar de uma ausência fundamental: uma dúvida constituinte do próprio regime discursivo dessa disciplina quando ela assume a insistente perturbação que, de fundo, seria provocada pela região intervalar entre o objeto de investigação, a natureza de sua escolha e o próprio historiador da arte, que interdita narrativas totalizantes. O presente dossiê apresenta textos que refletem sobre a fertilidade e a potência política do pensamento warburguiano, no que concerne às lógicas de aproximação ou associação de imagens, de obras, de referências artísticas e culturais em curadorias de exposições, de coleções e acervos de arte já constituídos e em constituição, dos trânsitos e migrações de imagens de diferentes épocas e contextos em outras constelações, antes impensáveis, que doam às próprias imagens renovados sentidos em diferentes áreas.

Lax pairs, infinite conservation laws, Darboux transformation, bilinear forms and solitonic interactions for a combined Calogero-Bogoyavlenskii-Schiff-type equation

Calogero-Bogoyavlenskii-Schiff-type (CBS-type) equations have been used to describe certain nonlinear phenomena in fluids and plasmas. Under investigation in this paper is a combined CBS-type equation. Lax pairs in the differential and matrix forms are derived respectively. Infinite conservation laws, which are different from those in the existing literatures, and n-fold Darboux transformation are constructed through the matrix-form Lax pair, where n is a positive integer. Bilinear forms are constructed. Parallel solitons can be derived from the bilinear forms, which are caused by a constraint in the linearization process. Waveforms for the parallel solitons have the no superposition, nonlinear superposition and linear superposition forms. Bell-to-anti-bell-shaped solitons and oblique solitonic interactions are discovered via the n-fold Darboux transformation. Each bell-shaped asymptotic soliton of the bell-to-anti-bell-shaped soliton evolves into the anti-bell-shaped one.

Steady flow and heat transfer of the power-law fluid between two stretchable rotating disks with non-uniform heat source/sink

This study aims to analyze the heat transfer phenomenon of power-law fluid with the occurrence of non-uniform heat source/sink within two stretchable disks which are parted with the constant distance and are co-axially rotating. The thermal conductivity is obeying the similar properties of power-law as that of viscosity. Von Karman’s generalized similarity transformation has been used firstly to reduce the physically modeled partial differential equations to nonlinear coupled ordinary differential equations and then tackled numerically with shooting method by finding missing initial conditions with the help of Newton–Raphson method and then system of equations are handled by means of RK-method. The influence of physical parameters for instance rotation as well as stretching, power-law index, Prandtl number, heat sink/source parameters upon non-dimensional velocity and temperature profiles are studied profoundly, later on, comprehensive analysis is expressed in discussion and results segment. The results which are computed numerically illustrate that the emerging parameters have substantial influences on velocity and temperature fields. In addition, rotation enhances the velocity components but temperature is predicting two diverse behaviors for shear-thinning and shear-thickening fluids, whenever upper and lower disk stretching it leads to an upsurge in radial and axial velocities but causes a decline in tangential velocity and temperature. Moreover, velocity and temperature distributions are in increasing trend except for the tangential component of the velocity which is decreasing by boosting the index of power-law. Furthermore, temperature decreases along with the similarity variable with the increasing Prandtl number but enhances with the enhancement in heat source/sink parameters. Finally, the skin friction in radial direction and local Nusselt number are escalating along the stretching parameters and Prandtl number but skin friction in tangential direction plummeting.

Nonexistence of two-dimensional sessile drops in the diffuse-interface model

The diffuse-interface model (DIM) is a widely used tool for modeling fluid phenomena involving interfaces, such as sessile drops (liquid drops on a solid substrate, surrounded by saturated vapor) and liquid ridges (two-dimensional sessile drops). In this work, it is proved that, surprisingly, the DIM does not admit solutions describing static liquid ridges. If, however, the vapor-to-liquid density ratio is small-for example, for water at room temperature-the ridges can still be observed as quasistatic states, as their evolution is too slow to be distinguishable from evaporation. Interestingly, the nonexistence theorem cannot be extended to axisymmetric sessile drops and ridges near a vertical wall, which are not ruled out.

Separation scaling for viscous vortex reconnection

Abstract

Work-Life Synchronicity: An Ethnographic Study of Workers Who Live in Vans

After 50 years of studying how work and life interact, research continues to consider each of these domains as relatively rigid or static, with some seeing the two in conflict with the other (Greenhaus & Beutell, 1985) and others seen each enriching the other (Greenhaus & Powell, 2006). However, both work and life may not be static but instead be fluid and changing (Greenhaus & Kossek, 2014; Mark & Su, 2010; Spreitzer, Cameron, & Garrett, 2017), each with the potential to be adapted to better align with the other domain. To investigate the notion of the alignment of work and life as fluid phenomenon, we studied workers who live in vans, people maintain mobility in both work and non-work domains. In this ethnographic study, the principle investigator lived in a van while meeting and interviewing 18 workers who live in vans. Through thematic analysis, a variety of themes related to the extent to which work and home are aligned or in conflict were identified, including (1) the identification of the van as home, (2) sense of identity, (3) career and financial freedom and (4) work-life synchronicity. We consider how these findings contribute to theory on work-life synchronicity for all workers.

A mathematical framework for peristaltic mechanism of non-Newtonian fluid in an elastic heated channel with Hall effect

Purposeobjective of the present investigation is to examine the influence of Hall on the peristaltic mechanism of Johnson-Segalman fluid in a heated channel with elastic walls. The transmission of heat is carried out. Relevant equations are computed for heat transfer coefficient, temperature and velocity. Low Reynolds number assumptions and long wavelength are employed. The interpretation of various parameters is analyzed. The results indicate that the heat transfer coefficient, temperature and velocity are larger for viscous material in comparison with Johnson-Segalman material.Design/methodology/approachThe transmission of heat is carried out. Relevant equations are computed for heat transfer coefficient, temperature and velocity. Low Reynolds number assumptions and long wavelength are employed. The interpretation of various parameters is analyzed. The results indicate that the heat transfer coefficient, temperature and velocity are larger for viscous material in comparison with Johnson-Segalman material.FindingsThe formulation of paper is executed as follows. Section 2 comprises problem summary and mathematical design. Solution methodology is discussed, and expressions for temperature, velocity and coefficient of heat transfer are derived in Section 3. Graphical outcomes for the parameters are reported in Section 4. Conclusions are outlined in Section 5.Practical implicationsPeristaltic phenomenon of fluids has a definite role in many physiological, industrial and engineering processes. The mechanical devices for instance finger and roller pumps operate via this process, and it is quite significant for vasomotion of blood vessels, consumption of food via esophagus, chyme flow in gastrointestinal zone, toxic liquid flow in nuclear industry and transport of corrosive fluids.Originality/valueLiterature review witnesses that information about peristalsis of conducting fluid in a heated channel with flexible walls and Hall effect is scarce. So, our goal is to discuss the peristaltic activity of non-Newtonian fluids in flexible channel. Johnson-Segalman fluid is taken into account. This model is used to allow non-affine deformations. Experimentalists relate “spurt” with wall slip. That is why the work presented is original.

Numerical platform for the interface analysis of magnetic fluids by use of the Boundary Element Method

For the stability analysis or dynamic analysis of the interface phenomena of magnetic fluids as the Rosensweig instability, this paper presents mainly a magnetic analysis with reduced loads, since magnetic fields must be re-calculated every time step the interface changes. This method adopts the indirect boundary element method (IBEM), since the behavior of the surface can be explained mainly by the magnetic stress difference obtained from the interface magnetic field. Starting with Green’s theorem applied for harmonic fields, the magnetic potential and the normal magnetic induction are obtained separately through the density of singular sources on boundaries. The problems of sharp-pointed peaks on the interface, or edges and corners where boundaries cross are avoided easily. The magnetic field, the interface stresses and the fluid velocity are calculated on the largely-deformed interface in a two-layered system of fluid and vacuum domain under a homogeneous vertical magnetic field. In consideration of the nonlinear equation of motion of the pattern amplitude (Gollwitzer et al., 2010), the sum of interface stresses and the normal fluid velocity are shown in the phase space of the height of the solitary-wave interface profile and the intensity of the applied magnetic induction. This IBEM is compared with another method called Magnetic Analysis for General Use (MAGU, Mizuta, 2011) on the formulation basis, and their extension to the nonlinear magnetization is discussed.

Effect of the fluidic injection on the flow of a converging-diverging conical nozzle

The flow in an Over-Expanded Nozzle is subjected to shock waves leading to the unsteady separation of the boundary layer. Free detachment may be followed by a restricted detachment. During the expansion regime in propellant nozzles, several physical phenomena are encountered: supersonic jet, jet separation, adverse pressure gradient, shock wave, turbulent boundary layer, highly compressible mixture layer, return flow, large scale turbulence. These very complex phenomena can considerably affect the performance of the nozzle.The numerical investigation was performed by the CFD-FASTRAN search code, using the k-w SST model as the turbulence model. The calculation is performed by solving the Navier-Stokes equations of two-dimensional compressible turbulent flow. It is based on the study of the fluidic vectorization phenomenon of the thrust of a double-injection convergent-divergent supersonic conical nozzle. The study is based on the effect of the ratio of NPR pressures with SPR = 1 on the overall structure of shock waves. The calculation is highlighting the behavior of a flow that has not neglected. In particular, the appearance of the separation zone formed by the fluid jet and the deflection of the main jet cause separation shocks.

On heat and mass transfer using evaporating self-rewetting mixtures in microchannels

Evaporation heat and mass transfer in open microchannels was investigated using pure liquids (ethanol, deionized water and butanol), an ordinary (non-self-rewetting) mixture (5% v/v ethanol/water mixture) and a self-rewetting fluid (5% v/v butanol/water mixture). The applied heating power ranged from 0 mW to 282.76 mW (giving heat fluxes from 0 W/m2 to 4501 W/m2) with wall temperatures ranging from 24 °C to 95 °C. When the microchannel had no external heating, diffusion was found to be the main mechanism of mass transfer. With external heating, the diffusion model underestimated the experiment results, and buoyancy-driven convection may account for this. Evaporation rates remain high for the self-rewetting fluid even when the meniscus recedes significantly (by 6 times the inner diameter) in the microchannel under heating conditions. Additionally, the self-rewetting fluid showed the highest conduction rate in the axial direction in high heating power conditions. Meniscus-wall contact angles and flow visualizations were obtained for various heating rates. The “contact angle shift” phenomenon of the self-rewetting fluid was observed. Marangoni-induced convection in the microchannel accounts for the mechanism of better heat and mass transfer as well as the “contact angle shift” phenomenon for the self-rewetting fluid.

Construction of subcritical isotherms for model and real gases on the basis of Mayer's cluster expansion.

Existing rigorous statistical approaches still cannot quantitatively describe condensation phenomena in real fluids and even model systems with some simplified interaction potential. Here, we present a method to evaluate the unlimited subcritical set of Mayer's reducible cluster integrals (the power coefficients of virial expansions) by using the information on several virial coefficients and empirical value of saturation activity. As to the requirements on the initial number of known virial coefficients, the calculations for the Lennard-Jones model indicate that only the second virial coefficient is sufficient to reproduce gas isotherms (including the flat phase-transition region) with high accuracy at low temperatures. This remarkable feature allows the simplification of the method for real fluids with an unknown interaction potential: In particular, the calculated isotherms of several real substances (including water) are in good agreement with experiments. Additionally, the obtained results indicate the existence of some important universality which needs serious future exploration.

Six degrees of freedom flight simulation of tilt-rotor aircraft with nacelle conversion

This paper presents six degrees of freedom flight simulation with mode conversion between airplane mode and helicopter mode as an application for realizing Digital Flight of the tiltrotor aircraft. The tiltrotor aircraft has the characteristics of both helicopters and propeller planes with changing the flight mode by tilting the engine nacelles. However, much less work with continuously changing these modes has been done so far. In this paper, the main components such as rotors, engine nacelles, fixed wings and a fuselage are considered. In order to perform large deformations of mesh geometry such as the rotation of the rotor and nacelle as well as the change of the position and attitude of the aircraft, the computational domain is decomposed into multiple domains corresponding to each component. Independently moving these domains makes possible to perform the characteristic behavior of a tiltrotor aircraft. To deal with rotations of multiple decomposed domains, the multi-axis sliding mesh approach is applied. As the solver for simulating unsteady flow driven by complicated moving boundaries, the unstructured Moving-Grid Finite-Volume method is adopted. Based on this solver, the Moving Computational Domain method enables the aircraft to fly in any size of region without restriction of mesh size. The airframe is treated as a rigid body, and the coupled simulations considering interaction with surrounding fluid of the aircraft are demonstrated. The result shows complicated fluid phenomena around the tiltrotor aircraft that occur when it flies with mode change.

Isochoric heat capacity of near- and supercritical benzene and derived thermodynamic properties

As part of a continuing study of the critical and supercritical phenomena in fluids and fluid mixtures, one- (CV1) and two-phase (CV2) isochoric heat capacities, densities (ρS) and phase-transition temperatures (TS) of benzene were measured in the critical and supercritical regions. Measurements were made in the immediate vicinity of the liquid-gas phase transition and the critical points in order to accurately determine of the phase transition properties (TS,ρS,CV1, and CV2). The measurements cover the temperature range from (347 to 616) K for 10 liquid and vapor isochores between (265 and 653) kg·m−3 at pressure up to 7.5 MPa. The measurements were performed using a high-temperature, high-pressure, nearly constant-volume adiabatic calorimeter. The standard uncertainties of the density, temperature, and isochoric heat capacity, CV, measurements are estimated to be 0.1%, 0.02 K, and 1.5%, respectively. The measured one- (CV1) and two-phase (CV2) isochoric heat capacities along the critical isochore and the saturated liquid (ρS') and vapor (ρS") densities near the critical point were used to accurately estimate the theoretically meaningful asymptotic critical amplitudes (A0±and B0) and related amplitudes for other properties (Γ0+, D0, ξ0), and their universal relations, A0+/A0−, A0+Γ0+B02, αA0+Γ0+B0−2, D0Γ0+B0δ−1, ξ0αA0+vC1/3. Saturated liquid and vapor densities (ρS′,ρS″) together with measured two-phase CV2 data were used to estimate the values of asymmetric parameters a3 (complete scaling parameter) and b2 of the coexistence curve singular diameter. Experimentally determined asymptotical critical amplitudes (A0±and B0 fluid-specific parameters) were used to check and confirm the predictive capability of the universal correlation in terms of their dependence on the acentric factor ω based on the generalized corresponding states principle. The measured values of two-phase CV2 as a function of the specific volume V along various isotherms were used to calculate second temperature derivatives of vapor pressure d2PSdT2 and chemical potential d2μdT2 and to estimate the value of Yang-Yang anomaly strength parameter Rμ = − 0.683 for benzene. The contributions of the vapor pressure, CVP=VCTd2PSdT2, and the chemical potential, CVμ=−Td2μdT2, to the measured total two-phase CV2 were derived from the measurements.

Nanoscale Bubble Dynamics Induced by Damage of Graphene Liquid Cells.

Graphene liquid cells provide the highest possible spatial resolution for liquid-phase transmission electron microscopy. Here, in graphene liquid cells (GLCs), we studied the nanoscale dynamics of bubbles induced by controllable damage in graphene. The extent of damage depended on the electron dose rate and the presence of bubbles in the cell. After graphene was damaged, air leaked from the bubbles into the water. We also observed the unexpected directional nucleation of new bubbles, which is beyond the explanation of conventional diffusion theory. We attributed this to the effect of nanoscale confinement. These findings provide new insights into complex fluid phenomena under nanoscale confinement.

Sound generation by water drop impact on surfaces

In this work, we experimentally study the acoustic response of water drop impacts onto a variety of surfaces using both audio recording and high-speed imaging. Audio recordings of the airborne sound emitted by single drop impacts on deep pools, thin liquid films, and dry aluminum and masonry surfaces are captured in the laboratory. Longer audio recordings are also collected for natural rainfall on wet concrete surfaces. These airborne sound pressure versus time measurements are converted to power spectra using the fast Fourier transform. Each impact type results in unique features in the spectra from 1 to 20 kHz that can be related to the impact and subsequent fluid phenomena. For example, in the case of water drops impacting a deep pool of water, we observe two distinct sound events: one as the drop breaks through the free surface of the pool with frequency content centered around 10 kHz and then approximately 50 ms later at the time of air cavity collapse and Worthington jet formation with frequency content around 4 kHz. A Helmholtz resonator model for the collapse of an air cavity describes the observed acoustic signature well. The acoustic spectra of various natural rainfall events on wet surfaces are comparable to those of discrete drops recorded in the laboratory, but upshifted in frequency.

Fluidics in an emptying bottle during breaking and making of interacting interfaces

An experimental effort has been reported in the present study analyzing the fluidics during the emptying of a bottle. The viscosity of the containing liquid and the orientation of the bottle while emptying are varied to obtain different emptying modes. Stages during the emptying of a vertical upended and an inclined bottle have been demarcated based on prompt flow features. Fluidic phenomena such as formation and pinch-off of an encapsulated bubble, ejector jet, flooding, and stratification have been observed in a vertically upended bottle. The rise velocity, collapse dynamics, and growth rate of the bubble at the bottle mouth are affected by the angle of inclination and mainly viscosity of the emptying liquid. Two distinct bottle emptying modes have been identified in one of which the discharge rate is increased due to a high-frequency pinch-off of air bubbles inside the bottle and in another mode due to an increase in the volume of the pinched-off bubble at a comparatively lower frequency. The interaction of dominant forces during the emptying process has been established by quantifying Reynolds number, Weber number, and Bond number. For all emptying liquids, bottle emptying time reduces linearly up to a critical angle of inclination, θcrit ∼ 20°, and further follows an asymptote. We hypothesize that the transition between the linear regime and the asymptotic regime is due to the saturation of the voidage of the air at the cylindrical section of the bottle mouth. Furthermore, the geometry of the bottle also facilitates the growth rate of the bubble inside the bottle at θcrit.

Predictability, fast calculation and simulation for the interaction solutions to the cylindrical Kadomtsev-Petviashvili equation

The cylindrical Kadomtsev-Petviashvili (cKP) equation related to cylindrical geometry, as one type of the variable-coefficient KP equation, is widely used to describe nonlinear phenomena in fluid, plasma and other fields. With symbolic computation, we have derived the multi-soliton solutions, rational solutions, lump solutions and interaction solutions to the cKP equation based on its bilinear representation. The interaction solutions include two types: The interaction between lump and stripe, and the interaction between lump and soliton. Moreover, we have proposed a new approach to search for the interaction solutions, which can decrease the complexity of the associated nonlinear algebraic equations via reducing the number of the variables. The fast calculation approach provides the condition for the predictability of the interaction solution.

Confining Liquids inside Carbon Nanotubes: Accelerated Molecular Dynamics with Spliced, Soft-Core Potentials and Simulated Annealing.

Understanding emergent phenomena of fluids under physical confinement requires the development of advanced tools for rapid and accurate simulation of their physiochemical properties. Simulating liquid molecules commensurate in size with the nanoscale enclosures that confine them is a key challenge. We demonstrate an accelerated molecular dynamics simulation technique that combines soft-core potentials (SCP) and simulated annealing (SA) to analyze confined liquids. This integrated SCP/SA method relies on a new spliced soft-core potential (SSCP), which enables tunable accuracy with respect to the target hard-core potential (HCP). SCP/SA enables the packing of enclosures with bulk material in a controlled, thermodynamically consistent manner. The enhanced SSCP accuracy is a critical feature of SCP/SA, enabling a smooth transition between the SCP and the HCP at a desired SCP hardness. We applied SCP/SA to the problem of filling a carbon nanotube (CNT) in periodic boundary conditions with a popular ionic liquid (IL), 1-butyl-3-methylimidazolium hexafluorophosphate [BMIM+][PF6-]. We performed a series of triplicate simulations on systems with varying CNT diameter and charge to demonstrate SCP/SA's versatility. Beyond this IL/CNT system, the SCP/SA simulation framework has a broad range of potential applications, not limited to nanoscale enclosures and interfaces, including both solid-state and biological systems.

Embedded droplet printing in yield-stress fluids

Microfluidic tools and techniques for manipulating fluid droplets have become core to many scientific and technological fields. Despite the plethora of existing approaches to fluidic manipulation, non-Newtonian fluid phenomena are rarely taken advantage of. Here we introduce embedded droplet printing-a system and methods for the generation, trapping, and processing of fluid droplets within yield-stress fluids, materials that exhibit extreme shear thinning. This technique allows for the manipulation of droplets under conditions that are simply unattainable with conventional microfluidic methods, namely the elimination of exterior influences including convection and solid boundaries. Because of this, we believe embedded droplet printing approaches an ideal for the experimentation, processing, or observation of many samples in an "absolutely quiescent" state, while also removing some troublesome aspects of microfluidics including the use of surfactants and the complexity of device manufacturing. We characterize a model material system to understand the process of droplet generation inside yield-stress fluids and develop a nascent set of archetypal operations that can be performed with embedded droplet printing. With these principles and tools, we demonstrate the benefits and versatility of our method, applying it toward the diverse applications of pharmaceutical crystallization, microbatch chemical reactions, and biological assays.

A theoretical analysis of Biorheological fluid flowing through a complex wavy convergent channel under porosity and electro-magneto-hydrodynamics Effects

Background and ObjectiveFlow generated via peristaltic waves in naturally occurring physical phenomenon inside human body. Its combination with electric and magnetic forces makes it even more versatile in biomedical engineering applications. The results presented in this article are useful in designing artificial tubes, lab-on-a-chip devices for cell manipulation, drug design, flow amalgamation, micro-scale pumps and micro-bots which can be externally controlled by electric and magnetic sensors. Motivated by the aforesaid facts the current investigation is based on the transportation of a couple stress bio-fluid by peristalsis through a convergent channel under the postulates of creeping phenomena and long wavelength, respectively MethodsA closed form solution is acquired for the axial velocity profile, volumetric flow rate and streamlines, respectively. The physical influence of involved parameters on the rheological characteristics are argued analytically with the help of Mathematica software 12.0.1 in detail. Additionally, the flow system is considered to take place under the both porosity and electro-magneto-hydrodynamics effects, respectively. The amplitude of axial velocity across one wavelength is strongly affected at the larger values of numerous embedded parameters: Darcy number, Hartmann number, Electro-osmotic velocity parameter and non-Newtonian (couple stress) parameter. ResultsWe have observed remarkable effects of embedded parameters on velocity distribution, flow rate and trapping phenomena under porous and electro-osmotic (combination of both magnetic and electric) effects. The circulation of boluses and number of streamlines are reduced/enhanced for larger Hartmann number/Darcy number due strong magnetic/porosity effects. This research study additionally tells us how to control the transportation phenomena of biological fluids by appropriate adjusting the porosity effects (the effects of porous media) and electro-osmotic influences. Moreover, in order to enhance the performance of a peristaltic pump at the micro-scale level, we have used complex peristaltic wave scenario in the boundary walls of the convergent micro-channel.