Plane Channel Research Articles

An Eddy-Viscosity Model Sensitized to Curvature and Wall-Roughness Effects for Reynolds-Averaged Closure

Abstract This paper presents a new extension of the realizable K−ε model that accounts for streamline curvature, system rotation, and surface roughness. The model is a type of realizable K−ε model, but the transport equations and the eddy-viscosity damping functions are modified, based on the Richardson number and roughness height; the roughness correction covers both the transitional and fully rough regimes. Flows in a rotating channel and a U-bend duct are used to validate the response of the new model to the system rotation and streamline curvature. The flow in a plane channel and the flow over a dune are used to validate the roughness extension. Finally, a rotating channel with rough walls is studied, to test the new model when both rotation and roughness are present.

Turbulent flows in square ducts: physical insight and suggestions for turbulence modellers

ABSTRACTWe carry out Direct Numerical Simulation (DNS) of flows in a straight duct with square cross-section. At high-friction Reynolds numbers, the Reynolds number dependence is similar to turbulent plane channels, hence flows in a square duct allows to investigate the Reynolds number dependency through a reduced number of simulations. Secondary motion play a minor role in this regime. At low Re, the profiles of the statistics differ from those in the two-dimensional channel due to the interaction of flow structures with different size. Large flow scales due to the mean motion are responsible for creating turbulence anisotropy in wall-bounded flows, causing serious difficulties for RANS turbulence closures. Projection of velocity vectors and of the Reynolds stress tensor along the eigenvectors of the mean strain-rate tensor yields reduced Reynolds stress anisotropy, and simple turbulence kinetic energy budgets. We show that the isotropic rate of dissipation is more difficult to model than the full dissipation rate, whose distribution does not largely differ from that of turbulence kinetic energy production. We expect that this information may be exploited for the development of advanced RANS models for complex flows.

Incoherent ultrarelativistic particle scattering by nuclei at planar channeling

The problem of high-energy charged particle motion in the field of atomic planes of oriented crystals, essential for particle beam manipulation, intensive gamma-radiation generation and prepared measurements of short-living elementary particle properties, such as magnetic and electric dipole momenta, is considered. A rigorously evaluated instant change of transverse channeling motion energy under the scattering by an atomic core is applied to deduce an expression for the average transverse energy growth rate, which takes into consideration both the quantum effects and sharp particle density variation inside an inter-plane channel. The latter makes it possible for the first time to describe numerically the key limitations of multiple applications of the channeling effects in high-energy physics, not involving the parameters, introduces earlier through the arbitrary qualitative considerations. Also, the expressions of both the large angle scattering cross section and average square of small scattering angles are obtained, making possible to formulate a consistent simulation method of both positively and negatively charged particles propagation both in and out of the channeling conditions, taking into consideration both quantum nature of incoherent and classical one of the coherent scattering of ultra-relativistic particles by crystal plane atoms.

Slip And Hall Effects On The Flow Of A Hyperbolic Tangent Fluid Through Porous Medium In A Planar Channel With Peristalsis

In this paper, the effect of Slip and Hall effects on the flow of Hyperbolic tangent fluid through a porous medium in a planar channel with peristalsis under the assumption of long wavelength is investigated. A Closed form solutions are obtained for axial velocity and pressure gradient by employing perturbation technique. The effects of various emerging parameters on the pressure gradient, time averaged volume flow rate and frictional force are discussed with the aid of graphs.

A new non-linear RANS model with enhanced near-wall treatment of turbulence anisotropy

A new ω-based non-linear eddy-viscosity model is proposed. It was developed based on the original k−ω model and formulated using a quadratic stress-strain relation for the Reynolds stress tensor, with an added realisability condition. For enhanced treatment of near-wall turbulence anisotropy, a formulation that scales only with the turbulent Reynolds number is proposed for the first time. The new model has been implemented in the open-source Computational Fluid Dynamics (CFD) package OpenFOAM and validated against plane channel flow, a zero-pressure-gradient flat plate, and a U-bend curved channel configuration. To further assess the performance of the model for more complex geometries, it has been tested on configurations relevant to automotive applications. Overall, the new model outperforms the standard k−ω model. For example, on a curved channel, improved predictions for the minimum pressure and maximum skin friction of approximately 50% are obtained. Improved predictions are also obtained for quantities of practical engineering relevance, such as the pressure distribution along the wall of a sudden expansion diffuser, a configuration used to inform the design of automotive exhaust systems. This demonstrates that the proposed model has important practical applications for internal flows where anisotropic turbulence effects dominate.

Hydrodynamic instability of premixed flame propagating in narrow planar channel in the presence of gas flow

The paper analyses the hydrodynamic instability of a flame propagating in the space between two parallel plates in the presence of gas flow. The linear analysis was performed in the framework of a two-dimensional model that describes the averaged gas flow in the space between the plates and the perturbations development of two-dimensional combustion wave. The model includes the parametric dependences of the flame front propagation velocity on its local curvature and on the combustible gas velocity averaged along the height of the channel. It is assumed that the viscous gas flow changes the surface area of the flame front and thereby affects the propagation velocity of the two-dimensional combustion wave. In the absence of the influence of the channel walls on the gas flow, the model transforms into the Darrieus–Landau model of flame hydrodynamic instability. The dependences of the instability growth rate on the wave vector of disturbances, the velocity of the unperturbed gas flow, the viscous friction coefficients and other parameters of the problem are obtained. It is shown that the viscous gas flow in the channel can lead, in some cases, to a significant increase in instability compared with a flame propagating in free space. In particular, the instability increment depends on the direction of the gas flow with respect direction of the flame propagation. In the case when the gas flow moves in the opposite direction to the direction of the flame propagation, the pulsating instability can appear.

Mathematical model of oil displacement by water in a plane channel

Unstable displacement of immiscible liquids in a plane channel is a topical research in both theoretical and practical applications. In this paper, we consider a plane channel filled with an incompressible fluid. Over time, another fluid is injected into the channel. The fluids are immiscible. The paper builds a mathematical model of the process of oil displacement by water in a plane channel, which allows further numerical studies and comparison of the results with the obtained experimental data using the example of the Hele-Show cell. The mathematical model for a multiphase, multicomponent flow consists of the Navier-Stokes equations, the equations of conservation of mass, momentum and energy. Modern methods for modeling the dynamics of "viscous fingers“ are based mainly on numerical methods for solving systems of differential equations using the pressure gradient, viscosity and capillary forces as parameters. The influence of these parameters must be determined experimentally. To solve the problem, a quasi-hydrodynamic approach is used, based on the addition of a certain small parameter and allowing one to describe stable schemes with central differences. The complexity of solving such problems lies in the size of the considered models, which in practice have a wide range of applications from micro-scale to orders of one centimeter. A comprehensive study will allow us to evaluate and analyze the entire process as a whole, as well as to establish flow parameters to improve the efficiency of displacement and increase oil recovery, since in the numerical modeling of the process it is easier to create many independent experiments with the same initial data, in contrast to the experimental study.

Flow behavior of Cellulose Nano Fiber Suspension in Planar Channels with an Abrupt Contraction

Flow behavior of Cellulose Nano Fiber Suspension in Planar Channels with an Abrupt Contraction

Angular asymmetry of the nuclear interaction probability of high energy particles in short bent crystals

The rate of inelastic nuclear interactions in a short bent silicon crystal was precisely measured for the first time using a 180 GeV/c positive hadron beam produced in the North Experimental Area of the CERN SPS. An angular asymmetry dependence on the crystal orientation in the vicinity of the planar channeling minimum has been observed. For the inspected crystal, this probability is about sim 20% larger than in the amorphous case because of the atomic density increase along the particle trajectories in the angular range of volume reflection, whose dimension is determined by the crystal bending angle. Instead, for the opposite angular orientation with respect to the planar channeling, there is a smaller probability excess of sim 4%.

Biologically inspired transport of solid spherical nanoparticles in an electrically-conducting viscoelastic fluid with heat transfer

Bio-inspired pumping systems exploit a variety of mechanisms including peristalsis to achieve more efficient propulsion. Non-conducting, uniformly dispersed, spherical nanosized solid particles suspended in viscoelastic medium forms a complex working matrix. Electromagnetic pumping systems often employ complex working fluids. A simulation of combined electromagnetic bio-inspired propulsion is observed in the present article. Currents formation has increasingly more applications in mechanical and medical industry. A mathematical study is conducted for MHD pumping of a bi-phase nanofluid coupled with heat transfer in a planar channel. Two-phase model is employed to separately identity the effects of solid nanoparticles. Base fluid employs Jeffery?s model to address viscoelastic characteristics. The model is simplified using long wavelength and creeping flow approximations. The formulation is taken to wave frame and non-dimensionalise the equations. The resulting boundary value problem is solved analytically, and exact expressions are derived for the fluid velocity, particulate velocity, fluid-particle temperature, fluid and particulate volumetric flow rates, axial pressure gradient and pressure rise. The influence of volume fraction density, Prandtl number, Hartmann number, Eckert number, and relaxation time on flow and thermal characteristics is evaluated in detail. The axial flow is accelerated with increasing relaxation time and greater volume fraction whereas it is decelerated with greater Hartmann number. Both fluid and particulate temperature are increased with increment in Eckert and Prandtl numbers, whereas it is reduced when the volume fraction density increases. With increasing Hartmann number pressure rise is reduced

Flow behaviour of Fiber Suspention in Planar Channels with an abrupt Contraction

Flow behaviour of Fiber Suspention in Planar Channels with an abrupt Contraction

Electroosmosis as a probe for electrostatic correlations.

We study the role of ionic correlations on the electroosmotic flow in planar double-slit channels, without salt. We propose an analytical theory, based on recent advances in the understanding of correlated systems. We compare the theory with mean-field results and validate it by means of dissipative particle dynamics simulations. Interestingly, for some surface separations, correlated systems exhibit a larger flow than predicted by mean-field. We conclude that the electroosmotic properties of a charged system can be used, in general, to infer and weight the importance of electrostatic correlations therein.

ZnO Nanowire-Anchored Microfluidic Device With Herringbone Structure Fabricated by Maskless Photolithography.

The integration of nanomaterials in microfluidic devices has emerged as a new research paradigm. Microfluidic devices composed of ZnO nanowires have been developed for the collection of urine extracellular vesicles (EVs) at high efficiency and in situ extraction of various microRNAs (miRNAs). The devices can be used for diagnosing various diseases, including kidney diseases and cancers. A major research need for developing micro total analysis systems is to enhance extraction efficiency. This article presents a novel fabrication method for a herringbone-patterned microfluidic device anchored with ZnO nanowire arrays. The substrates with herringbone patterns were created by maskless photolithography. The ZnO nanowire arrays were grown on the substrates by chemical bathing. The patterned design was to introduce turbulent flows as opposed to laminar flow in traditional devices to increase the mixing and contact of the urine sample with ZnO nanowires. The device showed reduced flow rates compared with conventional planar microfluidic channels and successfully extracted urine EV-encapsulated miRNAs.

Stability of Detonation Waves Propagating in Plane and Rectangular Channels

Stability of detonation waves (DWs) propagating in a plane or rectangular channel with respect to two-dimensional and three-dimensional disturbances is considered. Accepting a simple hypothesis that the most unstable mode of the linear theory continues to dominate even in the nonlinear regime, one can derive a number of fairly definite predictions of the developed DW structure from the linear stability theory. In particular, the theory predicts the number of detonation cells formed in a channel of a specified size and the cell size, the minimum size of the channel in which the multifront DW structure can still exist, and the parameters at which the number of cells changes in a jump-like manner. All these predictions are qualitatively consistent with available experimental data and numerical results.

Stability of Detonation Waves Propagating in Plane and Rectangular Channels

Stability of Detonation Waves Propagating in Plane and Rectangular Channels

Деканалирование высокоэнергетических частиц из плоскостных каналов кристалла. Упругие и неупругие процессы рассеяния

Based on the principles of nonequilibrium statistical thermodynamics, the kinetic theory of de-channeling of high-energy particles from planar channels of a crystal have been deduced. The de-channeling rate coefficient is considered from the point of view of the transition of a fast particle from the directional motion mode to the state of chaotic motion. The corresponding equation have been obtained that takes into account both the coherent nature of the diffraction of a particle beam in a regular single crystal and the inelastic scattering of channeled particles by electrons and phonons. An analytical solution of this equation have been obtained on the class of confluent hypergeometric function using which the de-channeling rate constant Re have been calculated. It have been shown that up to second-order terms in terms of the interaction potential the constant Re is inversely proportional to the relaxation time of the system tph. In calculating tph the polarization of space by a fast charged particle is not taken into account. The temperature and isotopic dependences of the de-channeling rate have been obtained.

On the Lattice Boltzmann Deviatoric Stress: Analysis, Boundary Conditions, and Optimal Relaxation Times

We analytically solve the two-dimensional, nine-velocity, lattice Boltzmann model in planar channel flow and determine its deviatoric stress tensor. The shear component of its stress takes the expe...

Modelling uncertainty using stochastic transport noise in a 2-layer quasi-geostrophic model

The stochastic variational approach for geophysical fluid dynamics was introduced by Holm (Proc Roy Soc A, 2015) as a framework for deriving stochastic parameterisations for unresolved scales. This paper applies the variational stochastic parameterisation in a two-layer quasi-geostrophic model for a $ \beta $-plane channel flow configuration. We present a new method for estimating the stochastic forcing (used in the parameterisation) to approximate unresolved components using data from the high resolution deterministic simulation, and describe a procedure for computing physically-consistent initial conditions for the stochastic model. We also quantify uncertainty of coarse grid simulations relative to the fine grid ones in homogeneous (teamed with small-scale vortices) and heterogeneous (featuring horizontally elongated large-scale jets) flows, and analyse how the spread of stochastic solutions depends on different parameters of the model. The parameterisation is tested by comparing it with the true eddy-resolving solution that has reached some statistical equilibrium and the deterministic solution modelled on a low-resolution grid. The results show that the proposed parameterisation significantly depends on the resolution of the stochastic model and gives good ensemble performance for both homogeneous and heterogeneous flows, and the parameterisation lays solid foundations for data assimilation.

Effects of Slip and Hall on the Peristaltic Transport of a Hyperbolic Tangent Fluid in a Planar Channel

Effects of Slip and Hall on the Peristaltic Transport of a Hyperbolic Tangent Fluid in a Planar Channel

Coupled reaction mechanism reduction for the hetero-/homogeneous combustion of syngas over platinum

Coupled reduced mechanisms were developed for the hetero-/homogeneous combustion of fuel-lean and fuel-rich H2/CO/O2/N2 mixtures in a Pt-coated planar channel, using a method based on the Directed Relation Graph (DRG) and for a wide range of operating conditions for which detailed measurements are available. It is demonstrated that catalytic and gas-phase reaction mechanisms can be reduced together for all the fuel-lean cases. On the other hand, when joint reduction is performed for low-pressure fuel-rich cases (using a strict threshold value to capture the relatively weak, yet still important coupling between the catalytic and gas-phase reaction pathways) the result is a less efficient reduction process. For the high-pressure fuel-rich cases the catalytic-gaseous chemical coupling is weak enough to be neglected such that the reduction can be conducted separately for higher reduction efficiency. The reduced mechanisms reproduced well the major gaseous species concentrations, gas temperatures and homogeneous ignition distances obtained with the detailed mechanisms, thus demonstrating the capacity of the applied method in reducing catalytic/gas-phase reaction mechanisms. In addition, it is shown that for fuel-lean stoichiometries the reduction could provide a rapid indication if gas-phase combustion is ignited, without the need of full simulations. The reduced mechanisms are expected to facilitate large-scale simulations, with fidelity, for the design and thermal management of practical catalytic combustion systems.