Hydrodynamic Fluid Research Articles

Propagation of shock wave of nitrogen gas in Titan stratosphere

Nitrogen gas is considered one of the significant standard gases in stratosphere of Titan, Saturn's largest moon, which represents almost 98.4% of Titan atmosphere chemical composites. Hydrodynamics fluid model has been constructed to describe the Nitrogen gas flows in the inner part of the Titan stratosphere. Using Fourier analysis, the linear dispersion relation of the fluid equations has been derived. Exploration of the resultant dispersion relation elucidated that two independent phenomena occurred simultaneously. Moreover, the reductive perturbation method has been utilized, yielding Burgers equation. A shock wave enveloped solution has been obtained using the computational F-expansion method. The different effects of thermal conductivity and kinematic viscosity on propagating wave have been studied. They have found to cause dissipation of envelope wave but don't affect the amplitude of envelope wave. Our investigations showed that the dissipation in the enveloped waves caused by thermal conductivity and kinematic viscosity.

Semi‐analytical treatment of spherical solids in smoothed‐particle hydrodynamics fluid simulations

AbstractA method for modeling mobile spherical solids in Smoothed Particle Hydrodynamics simulations utilizing the semi‐analytical boundary formulation is given. The technique relies on evaluating individual contributions from ideally spherical bodies to the normalization factor and its gradient. A derivation is provided in both two and three dimensions (3D) and a close‐form solution is given for an arbitrary polynomial kernel function in 3D. The method is validated and implemented in an Smoothed‐Particle Hydrodynamics‐Discrete Element Method code to evaluate the solid fraction and results are compared to the previous standard.

Influence of the gravitational field variability on convective heat and mass transfer and on the free surface

The article is devoted to the influence of non-constancy of the earth’s gravitational field on fluid hydrodynamics and heat-mass transfer. The structure of convective fluid flow in a square cavity with lateral heated under constant and a variable on space gravity field. The changing diagonal symmetry of structure of convective flow and its effect on the distributions of temperature and concentration are considered. The results of modeling a problem of non-stationary flow of water with a free surface in a horizontal two-phase layer with an instantaneous change the acceleration of gravity from a constant g 0 to variable g(x) = g 0 x are presented. The nature of the wave change of the free surface of water with overturning, bursts of waves during intensive non-stationary flow in the horizontal layer caused by the changing of gravity from constant to variable is shown.

Experimental investigations on the effect of rod surface roughness on lubrication characteristics of a hydraulic O-ring seal

The surface roughness of friction pairs plays a significant role in the formation of hydrodynamic fluid film between rod-seal interface. To investigate the influence of rod surface roughness on lubrication characteristics of hydraulic reciprocating seal, the friction force and the net leakage of seal under quasi-constant speed conditions and variable speed conditions are compared and analyzed, by using a self-designed experimental device. The results show that the rod surface roughness has an important influence on seal behavior and cannot be ignored. The rougher the rod surface is, the greater the friction force and the net leakage are, and the seal is more prone to meet with the rolling torsion or fatigue failures under the conditions of frequent start-up and shut-down.

Development and Testing of a Block Hydrocyclone

The study aimed to theoretically substantiate the efficiency of liquid purification and obtain corroborating experimental data for a hydrocyclone, consisting of several blocks. Mathematical models of the process of hydrodynamic fluid filtration were developed with the use of screw swirlers. The obtained mathematical models characterize all the main processes of fluid movement in various zones of the functioning of the hydrocyclone. Formulas for calculating the structures of hydrocyclone blocks are included. A block for swirling the flow of the liquid to be cleaned has been made in the form of a three-way screw. For the first time, wear-resistant and high-strength plastic ZEDEX ZX-324 has been used as a material. An experimental study was conducted and the change in the Reynolds number and the coefficient of fluid consumption was shown, using different constructions of the three-way screw. The research results confirmed the correctness and sufficiency of mathematical models for the development and production of block hydrocyclones.

Richtmyer-Meshkov instability of an imploding flow with a two-fluid plasma model

The two-fluid (ions and electrons) plasma Richtmyer-Meshkov instability of a cylindrical light/heavy density interface is numerically investigated without an initial magnetic field. Varying the Debye length scale, we examine the effects of the coupling between the electron and ion fluids. When the coupling becomes strong, the electrons are restricted to co-move with the ions and the resulting evolution is similar to the hydrodynamic neutral fluid case. The charge separation that occurs between the electrons and ions results in self-generated electromagnetic fields. We show that the Biermann battery effect dominates the generation of magnetic field when the coupling between the electrons and ions is weak. In addition to the Rayleigh-Tayler stabilization effect during flow deceleration, the interfaces are accelerated by the induced spatio-temporally varying Lorentz force. As a consequence, the perturbations develop into the Rayleigh-Taylor instability, leading to an enhancement of the perturbation amplitude compared with the hydrodynamic case.

Hydrodynamic Fluid Film and Tribofilm Formation—Combining the Friction Signals with Contact Resistance

Abstract Under unidirectional sliding, the Stribeck-type curve traverses different lubrication regimes. Under mixed/boundary conditions, tribofilms formed by additives in lubricants represent a key mechanism for preventing wear but are difficult to investigate because of the complex composition of lubricants, their small thickness, and their amorphous nature. The formation of a hydrodynamic fluid film depends on the topography and the viscometric fluid properties. Low coefficients of friction do not consequently indicate that hydrodynamic fluid films were formed. The electric contact resistance serves here as a complementary indicator to identify the hydrodynamic fluid film and tribofilm formation under transient or static sliding conditions. The frictional work (WR) is a useful quantity to assess the contribution to the frictional losses of all lubrication regimes in a Stribeck-type curve.

The Roles of Fluid Hydrodynamics, Mass Transfer, Rust Layer and Macro-Cell Current on Flow Accelerated Corrosion of Carbon Steel in Oxygen Containing Electrolyte

The flow accelerated corrosion (FAC) of EH 36 carbon steel in the oxygen containing flowing electrolyte is studied using multi-electrode array arranged in a jet rig system. The FAC of the working electrodes (WEs) under both uncoupled and coupled conditions are investigated in conjunction with computational fluid dynamics (CFD) simulation. Results show that a higher mass transfer rate would lead to a higher FAC rate when the WEs are uncoupled. The rust layer could retard the oxygen diffusion, resulting in the FAC rate decreasing. The mass transfer process and the distribution of the rust layer are significantly influenced by the fluid hydrodynamics. However, when the WEs are coupled together, serious FAC damage would occur on the WEs where lower mass transfer rates are registered. The macro-cell currents would become the main lead of FAC propagation at coupled conditions.

New approaches for modelling vortex flow meters

The paper proposes a new model of a vortex flow meter, which is developed on the basis of modification of the basic equations of incompressible fluid hydrodynamics. The article deals with the modification of the Euler equation and the continuity equation of the flow. In this paper, dependencies are obtained for estimating the final standard uncertainty of flow rate using a vortex transducer. A detailed analysis of the influence of incompressible fluid flow parameters and the geometric dimensions of the vortex transducer on the final uncertainty of flow rate is performed. Recommendations are given for improving the method of flow rate using vortex transducers.

Rotating vortices in two-dimensional inhomogeneous strongly coupled dusty plasmas: Shear and spiral density waves.

Dusty plasma experiments can be performed quite easily in a strong coupling regime. In our previous work [V.S. Dharodi, S.K. Tiwari, and A. Das, Physics of Plasmas 21, 073705 (2014)]PHPAEN1070-664X10.1063/1.4888882, we numerically explored such plasmas with constant density and observed the transverse shear (TS) waves from the rotating vortex. Laboratory dusty plasmas are good examples of homogeneous plasmas; however, heterogeneity (e.g., density, temperature, and charge) may be due to the existence of voids, different domains with different orientations, presence of external forces like magnetic and/or electric, size or charge imbalance, etc. Here, we examine how the density heterogeneity in dusty plasmas responds to the circularly rotating vortex monopoles, specifically, smooth and sharp cutoff. For this purpose, we have carried out a series of two-dimensional fluid simulations in the framework of the incompressible generalized hydrodynamics fluid model. The rotating vortices are placed at the interface of two incompressible fluids with different densities. The smooth rotating vortex causes two effects: First, the regions are stretched to form the spiral density waves; second, there is a shear in flows which consequently induces the TS waves. The TS waves move slower in the denser side than in the lighter side. The difference in speeds of the waves induces the net flow of the medium towards the lower density side. We notice that the spiral density arms are distinguishable in the early time while later they get smeared out. In sharp flows, the interplay between the TS waves and the vortices of Kelvin-Helmholtz instability distorts the formation of the regular spiral density arms around the rotor.

Numerical Simulation of Scour Depth and Scour Patterns in Front of Vertical-Wall Breakwaters Using OpenFOAM

An advanced coupled numerical model was developed and implemented in the present work, describing the scour patterns and predicting the scour depth in front of vertical-wall breakwaters. It consists of two independent models, a hydrodynamic Computational Fluid Dynamics (CFD) Reynolds Averaged Navier–Stokes (RANS) model developed on the OpenFOAM (version 2.4.0) toolbox (CFD), describing the wave propagation and the associated hydrodynamic field, and a morphodynamic one (sediment transport model), which was developed in FORTRAN by the authors and yields the updated seabed morphology. The method used here is iterative. The hydrodynamic model is applied for any given initial seabed geometry and wave conditions, resulting in the hydrodynamic field of the flow, which is used as input by the second sediment transport model for the seabed morphology evolution. This process is repeated until the equilibrium profile is achieved. Model results are compared satisfactorily with experimental data for both scour patterns and prediction of scour depth.

Hydrodynamics of two-dimensional compressible fluid with broken parity: Variational principle and free surface dynamics in the absence of dissipation

We consider an isotropic compressible non-dissipative fluid with broken parity subject to free surface boundary conditions in two spatial dimensions. The hydrodynamic equations describing the bulk dynamics of the fluid as well as the free surface boundary conditions depend explicitly on the parity breaking non-dissipative odd viscosity term. We construct a variational principle in the form of an effective action which gives both bulk hydrodynamic equations and free surface boundary conditions. The free surface boundary conditions require an additional boundary term in the action which resembles a $1+1D$ chiral boson field coupled to the background geometry. We solve the linearized hydrodynamic equations for the deep water case and derive the dispersion of chiral surface waves. We show that in the long wavelength limit the flow profile exhibits an oscillating vortical boundary layer near the free surface. The thickness of the layer is controlled by the length scale given by the ratio of odd viscosity to the sound velocity $\delta \sim \nu_o/c_s$. In the incompressible limit, $c_s\to \infty$ the vortical boundary layer becomes singular with the vorticity within the layer diverging as $\omega \sim c_s$. The boundary layer is formed by odd viscosity coupling the divergence of velocity $\boldsymbol\nabla \cdot \boldsymbol{v}$ to vorticity $\boldsymbol\nabla \times \boldsymbol{v}$. It results in non-trivial chiral free surface dynamics even in the absence of external forces. The structure of the odd viscosity induced boundary layer is very different from the conventional free surface boundary layer associated with dissipative shear viscosity.

Quasinormal modes in charged fluids at complex momentum

We investigate the convergence of relativistic hydrodynamics in charged fluids, within the framework of holography. On the one hand, we consider the analyticity properties of the dispersion relations of the hydrodynamic modes on the complex frequency and momentum plane and on the other hand, we perform a perturbative expansion of the dispersion relations in small momenta to a very high order. We see that the locations of the branch points extracted using the first approach are in good quantitative agreement with the radius of convergence extracted perturbatively. We see that for different values of the charge, different types of pole collisions set the radius of convergence. The latter turns out to be finite in the neutral case for all hydrodynamic modes, while it goes to zero at extremality for the shear and sound modes. Furthermore, we also establish the phenomenon of pole-skipping for the Reissner-Nordström black hole, and we find that the value of the momentum for which this phenomenon occurs need not be within the radius of convergence of hydrodynamics.

Удосконалення процесу обробки тіл обертання електричною дугою

In modern mechanical engineering, electrical discharge machining (EDM) methods are widely used for machining bodies of rotation from difficult-to-machine materials. Those methods ensure sparing cutting and make it possible to machine any electrically conductive material irrespective of its physical and chemical properties, in particular hardness. There is a known method for dimensional machining of bodies of rotation with electric arc using a wire electrode tool that is pulled along in the machining area thus "compensating" for that tool's EDM wear and tear. The machining accuracy is therefore significantly heightened. However, when implementing this method, an effect of splashing the working fluid outside the working area of the machine and a pronounced luminous effect from the burning of the electric arc in the machining area are observed. That worsens the working conditions. In addition, when pulling the wire electrode tool along the convex surface of the electrode holder, the sliding friction arises, which eventually leads to mechanical destruction of the contact point. As a result, a deep kerf is formed on the electrode holder. When the depth of the kerf reaches the diameter of the wire electrode tool, the destruction of the electrode holder by the electric arc begins. Consequently, the durability of the electrode holder in the known method is unsatisfactory. A method of dimensional machining of bodies of rotation with electric arc using a wire electrode tool with the immersion of the machining area in the working fluid has been proposed, which makes it possible to improve the working conditions of the operator by eliminating the effect of fluid splashing and removing the luminous effect of arc burning in the machining area. In addition, it has been proposed to make the electrode holder in the form of a roller that rotates with a guide groove for the wire electrode tool, while the nozzle for creating the transverse hydrodynamic fluid flow has been proposed to be mounted in a separate fixed housing that is adjacent to the electrode holder. This technical solution replaces the sliding friction with the rolling one thus enhancing the durability of the electrode holder. Mathematical models of the process characteristics of the DMA-process (dimensional machining with electric arc) for bodies of rotation using a wire electrode tool with the immersion of the machining area in the working fluid have been obtained that make it possible to control the machining productivity, the specific machining productivity, the specific electric power consumption, and the roughness of the surface machined.

Dust-acoustic envelope solitons in strongly coupled dusty plasmas

The propagation nature and the modulational instability (MI) criteria of low frequency amplitude modulated dust-acoustic envelope solitons are analyzed theoretically and numerically in an unmagnetized dusty plasma consisting of strongly coupled micron-sized inertial dust grains, Boltzmann distributed non-inertial electrons and ions. A hydrodynamical fluid model approach is used, based on [V. V. Yaroshenko, F. Verheest, H. M. Thomas and G.E. Morfill, New J. Phys. 11, 073013 (2009); V. V. Yaroshenko, V. Nosenko, and G. E. Morfill, Phys. Plasmas, 17, 103709 (2010)], where the strong coupling between dust grains for by an effective electrostatic pressure is accounted, which is in fact a dynamical function of the dust-density and the electrostatic potential. It is seen that the strong coupling between dust particles due to the effective electrostatic ``pressure” modifies the wavepacket stability and affects the occurrence of MI. A cubic nonlinear Schrodinger-type equation, which describes the evolution of the wavepacket’s envelope, is derived by adopting a multiscale technique for the amplitude dynamics. It is shown that long-wavelength dust-acoustic wavepackets are stable, while MI sets in beyond a carrier wavenumber threshold, which is evaluated in terms of intrinsic plasma parameters of relevance. On the other hand, the MI window is larger for higher ion density. The effect of the ion number density on MI is twofold, in that a higher ion density leads to a higher threshold (thus, the wave will be modulationally unstable for the larger values of the carrier wavenumber) but it also entails a wider instability window (hence, external perturbations must be of specific wavenumbers to trigger the instability). Numerical simulation confirms that the bright-type envelope soliton solution is stable beyond the carrier wavenumber threshold, i.e., in the modulationally unstable region, while the dark type envelope soliton is stable for wavenumbers below the threshold.

An advanced hybrid smoothed particle hydrodynamics–fluid implicit particle method on adaptive grid for condensation simulation

AbstractIn this article, we propose a novel hybrid framework by combining smoothed particle hydrodynamics and adaptive narrow band fluid implicit particle method (NB‐FLIP) to faithfully model the multiphysical processes involving heat transfer and phase transition, and to precisely simulate the dynamics of condensed droplets moving along intricate objects. We first formulate a governing physical model built upon an improved phase transition model and an augmented on‐surface drop analysis method to achieve realistic condensation effects over intricate hydrophilic/hydrophobic interface. To achieve both high‐fidelity interactions and high‐resolution visual effects, we further develop an adaptive NB‐FLIP solver with octree‐dictated background grid in order to further enhance the performance of our framework. Experimental results have shown that our approach can be used to efficiently and realistically simulate the small‐scale interaction details between condensed drops and complex objects with arbitrary geometry.

Physiologic blood flow is turbulent

Contemporary paradigm of peripheral and intracranial vascular hemodynamics considers physiologic blood flow to be laminar. Transition to turbulence is considered as a driving factor for numerous diseases such as atherosclerosis, stenosis and aneurysm. Recently, turbulent flow patterns were detected in intracranial aneurysm at Reynolds number below 400 both in vitro and in silico. Blood flow is multiharmonic with considerable frequency spectra and its transition to turbulence cannot be characterized by the current transition theory of monoharmonic pulsatile flow. Thus, we decided to explore the origins of such long-standing assumption of physiologic blood flow laminarity. Here, we hypothesize that the inherited dynamics of blood flow in main arteries dictate the existence of turbulence in physiologic conditions. To illustrate our hypothesis, we have used methods and tools from chaos theory, hydrodynamic stability theory and fluid dynamics to explore the existence of turbulence in physiologic blood flow. Our investigation shows that blood flow, both as described by the Navier–Stokes equation and in vivo, exhibits three major characteristics of turbulence. Womersley’s exact solution of the Navier–Stokes equation has been used with the flow waveforms from HaeMod database, to offer reproducible evidence for our findings, as well as evidence from Doppler ultrasound measurements from healthy volunteers who are some of the authors. We evidently show that physiologic blood flow is: (1) sensitive to initial conditions, (2) in global hydrodynamic instability and (3) undergoes kinetic energy cascade of non-Kolmogorov type. We propose a novel modification of the theory of vascular hemodynamics that calls for rethinking the hemodynamic–biologic links that govern physiologic and pathologic processes.

Buoyancy driven mixed convection flow of magnetized Maxell fluid with homogeneous-heterogeneous reactions with convective boundary conditions

This investigation explored the significances of heterogeneous and homogeneous reactions on magneto hydrodynamic Maxell fluid flow induced by radially stretching disks under influence of buoyancy driven force. The steady state system is examined for the specific case in which the coefficient of diffusion of the reactants and auto catalytic agent are identical. The mathematical formulation for present flow problem is developed by using flow assumptions. The analytical solution for formulated flow problem is determined analytically by using homotopy analysis method (HAM) by using MATHEMATICA software. It is noticed that presence of Deborah number and thermal Biot number enhances the temperature profile. The homogeneous and heterogeneous parameter and Deborah number decays the concentration profile effectively. Further, an improved concentration distribution is noted for Archimedes number.

Hierarchical Mass Transfer Analysis of Drug Particle Dissolution, Highlighting the Hydrodynamics, pH, Particle Size, and Buffer Effects for the Dissolution of Ionizable and Nonionizable Drugs in a Compendial Dissolution Vessel.

Dissolution is a crucial process for the oral delivery of drug products. Before being absorbed through epithelial cell membranes to reach the systemic circulation, drugs must first dissolve in the human gastrointestinal (GI) tract. In vivo and in vitro dissolutions are complex because of their dependency upon the drug physicochemical properties, drug product, and GI physiological properties. However, an understanding of this process is critical for the development of robust drug products. To enhance our understanding of in vivo and in vitro dissolutions, a hierarchical mass transfer (HMT) model was developed that considers the drug properties, GI fluid properties, and fluid hydrodynamics. The key drug properties include intrinsic solubility, acid/base character, pKa, particle size, and particle polydispersity. The GI fluid properties include bulk pH, buffer species concentration, fluid shear rate, and fluid convection. To corroborate the model, in vitro dissolution experiments were conducted in the United States Pharmacopeia (USP) 2 dissolution apparatus. A weakly acidic (ibuprofen), a weakly basic (haloperidol), and a nonionizable (felodipine) drug were used to study the effects of the acid/base character, pKa, and intrinsic solubility on dissolution. 900 mL of 5 mM bicarbonate and phosphate buffers at pH 6.5 and 37 °C was used to study the impact of the buffer species on drug dissolution. To investigate the impacts of fluid shear rate and convection, the apparatus was operated at different impeller rotational speeds. Moreover, presieved ibuprofen particles with different average diameters were used to investigate the effect of particle size on drug dissolution. In vitro experiments demonstrate that the dissolution rates of both the ionizable compounds used in this study were slower in bicarbonate buffer than in phosphate buffer, with the same buffer concentration, because of the lower interfacial buffer capacity, a unique behavior of bicarbonate buffer. Therefore, using surrogates (i.e., 50 mM phosphate) for bicarbonate buffer for biorelevant in vitro dissolution testing may overestimate the in vivo dissolution rate for ionizable drugs. Model simulations demonstrated that, assuming a monodisperse particle size when modeling, dissolution may overestimate the dissolution rate for polydisperse particle size distributions. The hydrodynamic parameters (maximum shear rate and fluid velocity) under in vitro conditions in the USP 2 apparatus under different rotational speeds are orders of magnitude higher compared to the in vivo situation. The inconsistencies between the in vivo and in vitro drug dissolution hydrodynamic conditions may cause an overestimation of the dissolution rate under in vitro conditions. The in vitro dissolution data supported the accuracy of the HMT for drug dissolution. This is the first drug dissolution model that incorporates the effect of the bulk pH and buffer concentration on the interfacial drug particle solubility of ionizable compounds, combined with the medium hydrodynamics effect (diffusion, convection, shear, and confinement components), and drug particle size distribution.

THE ROLE OF SUPERTHERMAL ELECTRONS ON THE ESCAPING IONS FROM THE UPPER ATMOSPHERE OF TITAN AND VENUS

The observed escape of ions from the ionosphere of planets and moons is of interest during the last few years. Different mechanisms that can explain the escape of charged particles were assumed. One of the recent mechanisms to explain the ionospheric loss is the plasma expansion approach. In the present work, we investigate the ionic loss from the moon Titan and planet Venus, where their ionospheres suffer from a continuous loss reaches to several tons of ions per day. For this purpose, we use a suitable set of hydrodynamic fluid equations to describe the plasma system in either Titan or Venus. Interestingly, it is observed that superthermal electrons exist in both cases (i.e. Titan and Venus ionosphere). The self-similar transformation is used to reduce the basic equations to ordinary differential equations which can be solved numerically to obtain the profiles of the plasma ion density, velocity, and potential during the expansion interval. Furthermore, it is of interest to examine the role of the superthermal electrons on the expansion profile properties.