Antiparallel Motion Research Articles

Numerical modeling of the heat and mass transfer of rarefied gas flows in a double-sided oscillatory lid-driven cavity

In micro/nano research and engineering applications, internal flows of rarefied gas in confined geometries with moving parts are of great interest. The rarefied gaseous flows in an oscillating lid-driven cavity are investigated numerically in this work, taking into account both the parallel and antiparallel motion of the driving walls. The discrete unified gas kinetic scheme (DUGKS) is applied to the evolution of the flow and temperature fields. The Shakhov collision model is incorporated into DUGKS to account for flows of non-unit Prandtl numbers. The validity of the Shakhov-DUGKS is confirmed in both single-sided oscillating and steady lid-driven cavity flows. The effects of gas compressibility, rarefaction, and lid oscillation frequency on the mass and heat transport are then thoroughly examined. The corresponding parameter spaces of the Mach, Knudsen and Stokes numbers are 0.16 ≤ Ma ≤ 1.2, 0.075 ≤ Kn ≤ 10 and 0.5 ≤ St ≤ 5, respectively. The shear force and Nusselt number Nu on the cavity walls, as well as the velocity, temperature, and heat flux lines in the cavity, are measured and analyzed. The results suggest that the anti-Fourier heat transfer phenomenon might also occur in the rarefied double-sided oscillating cavity flow. Nu is prone to non-simple harmonic oscillation in its evolution. Furthermore, in the parallel motion as opposed to the anti-parallel motion, the left wall experiences a greater intensity of heat transmission. Compressibility, expansion cooling, and viscous heating compete to provide the complicated flow and heat transfer characteristics found in cavities.

Constructing an entangled Unruh Otto engine and its efficiency

Uniformly accelerated frame mimics a thermal bath whose temperature is proportional to the proper acceleration. Using this phenomenon we give a detailed construction of an Otto cycle between two energy eigenstates of a system, consists of two entangled qubits. In the isochoric stages the thermal bath is being provided via the vacuum fluctuations of the background field for a monopole interaction by accelerating them. We find that making of Otto cycle is possible when one qubit is accelerating in the right Rindler wedge and other one is moving in the left Rindler wedge; i.e. in anti-parallel motion, with the initial composite state is a non-maximally entangled one. However, the efficiency greater than that of the usual single qubit quantum Otto engine is not possible. We provide values of the available parameters which make Otto cycle possible. On the other hand, Otto cycle is not possible if one considers the non-maximally entangled state for parallel motion. Moreover, for both initial symmetric and anti-symmetric Bell states we do not find any possibility of the cycle for qubits’ parallel and anti-parallel motion.

Role of thermal field in entanglement harvesting between two accelerated Unruh-DeWitt detectors

We investigate the effects of field temperature T(f) on the entanglement harvesting between two uniformly accelerated detectors. For their parallel motion, the thermal nature of fields does not produce any entanglement, and therefore, the outcome is the same as the non-thermal situation. On the contrary, T(f) affects entanglement harvesting when the detectors are in anti-parallel motion, i.e., when detectors A and B are in the right and left Rindler wedges, respectively. While for T(f) = 0 entanglement harvesting is possible for all values of A’s acceleration aA, in the presence of temperature, it is possible only within a narrow range of aA. In (1 + 1) dimensions, the range starts from specific values and extends to infinity, and as we increase T(f), the minimum required value of aA for entanglement harvesting increases. Moreover, above a critical value aA = ac harvesting increases as we increase T(f), which is just opposite to the accelerations below it. There are several critical values in (1 + 3) dimensions when they are in different accelerations. Contrary to the single range in (1 + 1) dimensions, here harvesting is possible within several discrete ranges of aA. Interestingly, for equal accelerations, one has a single critical point, with nature quite similar to (1 + 1) dimensional results. We also discuss the dependence of mutual information among these detectors on aA and T(f).

Numerical analysis and explore of asymmetrical fluid flow in a two-sided lid-driven cavity

The two-dimensional asymmetrical flow in a two-sided lid-driven square cavity is numerically analyzed by the finite volume method (FVM). The top and bottom walls slide in parallel and antiparallel motions with various velocity ratio (UT/Ub=λ) where |λ|=2, 4, 8, and 10. In this study, the Reynolds number Re1 = 200, 400, 800 and 1000 is applied for the upper side and Re2 = 100 constant on the lower side. The numerical results are presented in terms of streamlines, vorticity contours and velocity profiles. These results reveal the effect of varying the velocity ratio and consequently the Reynolds ratio on the flow behaviour and fluid characteristics inside the cavity. Unlike conventional symmetrical driven flows, asymmetrical flow patterns and velocity distributions distinct the bulk of the cavity with the rising Reynolds ratio. For λ>2, in addition to the main vortex, the parallel motion of the walls induces two secondary vortices near the bottom cavity corners. however, the antiparallel motion generates two secondary vortices on the bottom right corner. The parallel flow proves affected considerably compared to the antiparallel flow.

Global 2D stability analysis of the cross lid-driven cavity flow with a streamfunction-vorticity approach

ABSTRACTWe have recently analyzed the global two-dimensional (2D) stability of the staggered lid-driven cavity (LDC) flow with a higher order compact (HOC) approach. In the analysis, critical parameters are determined for both the parallel and anti-parallel motion of the lids and a detailed analysis has been carried out on either side of the critical values.In this article, we carry out an investigation of flow stabilities inside a two-sided cross lid-driven cavity with a pair of opposite lids moving in both parallel and anti-parallel directions. On discretization, the governing 2D Navier–Stokes (N–S) equations describing the steady flow and flow perturbations results in a generalized eigenvalue problem which is solved for determining the critical parameters on four different grids. Elaborate computation is performed for a wide range of Reynolds numbers (Re) on either side of the critical values in the range 200 ⩽ Re ⩽ 10000. For flows below the critical Reynolds number Rec, our numerical results are compared with established steady-state results and excellent agreement is obtained in all the cases. For Reynolds numbers above Rec, phase plane and spectral density analysis confirmed the existence of periodic, quasi-periodic, and stable flow patterns.

Computation of Lattice Kinetic Scheme for Double-Sided Parallel and Antiparallel Wall Motion

This paper is concerned with the double-sided lid-driven cavity simulation of two-dimensional lattice kinetic scheme on the uniform lattice arrangement based on the standard lattice Boltzmann method. The double-sided lid-driven cavity problem has multiple steady solutions for some aspect ratios. However, for the double-sided square cavity no multiplicity of solutions has been observed for both the parallel and antiparallel motion of the walls. To validate this new lattice kinetic scheme, the numerical simulations of the double-sided square driven cavity flow at Reynolds numbers from 10 to 1000 are carried out. The Reynolds number effect on the flow structure is clearly manifested by the streamline patterns and velocity profiles. It is concluded that the present study in double-sided lid-driven cavity produces results that are in excellent conformity with earlier conventional numerical observations.

Global two-dimensional stability of the staggered cavity flow with an HOC approach

In this paper, we have carried out a global stability analysis of the flow inside a two sided staggered lid-driven cavity for both the parallel and anti-parallel motions of the lids. A fourth order spatially accurate and second order temporally accurate compact scheme is used to discretize the two-dimensional Navier–Stokes equations governing the flow as well as the perturbed equations leading to the generalized eigenvalue problem. Estimates of the critical parameters are found for several grids and extensive grid convergence study is performed to accurately identify them. Computation is performed for a wide range of Reynolds numbers (Re) on either side of the critical values in the range 50≤Re≤12,000. For flows below the critical Reynolds number Rec, our numerical results are compared with established steady-state results and an excellent agreement is obtained in all the cases. For Reynolds numbers above Rec, phase plane and spectral density analysis confirmed the existence of periodic and chaotic flow patterns.

Molecular Mechanical Differences between Isoforms of Contractile Actin in the Presence of Isoforms of Smooth Muscle Tropomyosin

The proteins involved in smooth muscle's molecular contractile mechanism – the anti-parallel motion of actin and myosin filaments driven by myosin heads interacting with actin – are found as different isoforms. While their expression levels are altered in disease states, their relevance to the mechanical interaction of myosin with actin is not sufficiently understood. Here, we analyzed in vitro actin filament propulsion by smooth muscle myosin for -actin (A), -actin-tropomyosin- (A-Tm), -actin-tropomyosin- (A-Tm), -actin (A), -actin-tropomyosin- (A-Tm), and -actin-tropomoysin- (A-Tm). Actin sliding analysis with our specifically developed video analysis software followed by statistical assessment (Bootstrapped Principal Component Analysis) indicated that the in vitro motility of A, A, and A-Tm is not distinguishable. Compared to these three ‘baseline conditions’, statistically significant differences () were: A-Tm – actin sliding velocity increased 1.12-fold, A-Tm – motile fraction decreased to 0.96-fold, stop time elevated 1.6-fold, A-Tm – run time elevated 1.7-fold. We constructed a mathematical model, simulated actin sliding data, and adjusted the kinetic parameters so as to mimic the experimentally observed differences: A-Tm – myosin binding to actin, the main, and the secondary myosin power stroke are accelerated, A-Tm – mechanical coupling between myosins is stronger, A-Tm – the secondary power stroke is decelerated and mechanical coupling between myosins is weaker. In summary, our results explain the different regulatory effects that specific combinations of actin and smooth muscle tropomyosin have on smooth muscle actin-myosin interaction kinetics.

Multiplicity of steady solutions in a two-sided lid-driven cavity with different aspect ratios

This study presents a continuation method to calculate flow bifurcation in a two-sided lid-driven cavity with different aspect ratios for anti-parallel motion. In anti-parallel motion, the top and bottom walls of the cavity move in opposite directions simultaneously, while the two walls both moving to the right give parallel motion at the same speed. Comprehensive bifurcation diagrams of the cavity flows with different aspect ratios of the cavities are derived via Keller’s continuation method, and linear- stability analysis is used to identify the nature of the various flow solutions. The Reynolds number (1 ≤ Re ≤ 1,200) is used as the continuation parameter to trace the solution curves. In anti-parallel motion, the evolution of the bifurcation diagrams in cases with different aspect ratios (1 ≤ AR ≤ 2.5) is illustrated. Two stable symmetric flows and one stable asymmetric flow are identified, and the existent regions of the stable flows in the aspect ratios and Reynolds numbers are distinguished. The newly found asymmetric flow state can be obtained at a high aspect ratio and a low Reynolds number.

Applications of the CE/SE Scheme to Incompressible Viscous Flows in Two-Sided Lid-Driven Square Cavities

The spacetime conservation element-solution element (CE/SE) method is extended to two-dimensional incompressible viscous flow in a two-sided lid-driven square cavity. Based on the SIMPLE method concept, the preconditioned dual-time scheme is introduced for unsteady computations. The CE/SE-based code is validated by simulating one-sided lid-driven cavity flows. The two-sided lid-driven square cavity problem involves several interesting characteristics being successfully predicted, including development of a pair of off-corner vortices and a free shear layer in the case of parallel wall motion, as well as the appearance of corner vortices for lower Reynolds numbers in the case of anti-parallel motion of the walls. It is found that both the Reynolds number and the direction of the moving walls affect the fluid flow in the cavity.

Using the Ansys Fluent for simulation of two-sided lid-driven flow in a staggered cavity

This paper is concerned with numerical study of the two-sided lid-driven fluid flow in a staggered cavity. The ANSYS FLUENT commercial software was used for the simulation, In one of the simulated cases the lids are moving in opposite directions (antiparallel motion) and in the other they move in the same direction (parallel motion). Calculation results for various Re numbers are presented in the form of flow patterns and velocity profiles along the central lines of the cavity. The results are compared with the existing data from the literature. In general, a good agreement is found, especially in the antiparallel motion, while in the parallel motion the same flow pattern is found, but the velocity profiles are slightly different.

Lattice Boltzmann simulation of two-sided lid-driven flow in a staggered cavity

In this article, the lattice Boltzmann method is employed in order to explore incompressible fluid flow inside a two-sided lid-driven staggered cavity. Results of the lattice Boltzmann simulation for antiparallel motion of lids are compared with the data from existing literature. For parallel motion of lids, the characteristics of flow pattern for a variety of Re numbers (50–3200) are presented. An asymmetric steady-state flow pattern for parallel motion of lids is obtained.

Experiments on the transition to three‐dimensional flow structures in two‐sided lid‐driven cavities

AbstractFlow instabilities in two‐sided lid‐driven cavities are studied experimentally. The transition of the nearly two‐dimensional flow to steady or time‐dependent three‐dimensional flow structures is investigated for one‐sided, for parallel, and for antiparallel motion of the driving walls and for two aspect ratios, Γ = 0.76 and Γ = 1. Stability diagrams are obtained by flow visualization. Six different three‐dimensional flow patterns have been characterized, each corresponding to a particular critical mode of a linear‐stability analysis. The structures of the near‐critical flows and the critical curves are in good agreement with the corresponding numerical predictions. In a few cases, however, the critical Reynolds numbers deviate form the numerical results. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Stability balloon for the double-lid-driven cavity flow

The linear stability of the two-dimensional, steady, incompressible flow in a rectangular cavity is investigated numerically. The flow is driven by the parallel or antiparallel motion of two facing walls. When the cavity is infinitely extended in the spanwise direction a variety of different, three-dimensional flow instabilities can arise. We provide an overview on the global structure of the critical hypersurface in the three-dimensional parameter space spanned by the cross-sectional aspect ratio and the two side-wall Reynolds numbers. It turns out that the critical hypersurface is made up of six major segments belonging to different modes of instability. The interrelation and connectivity of these critical modes is elucidated.

Linear stability of rectangular cavity flows driven by anti-parallel motion of two facing walls

The flow in an infinite slab of rectangular cross-section is investigated numerically by a finite volume method. Two facing walls which move parallel to each other with the same velocity, but in opposite directions, drive a plane flow in the cross-section of the slab. A linear stability analysis shows that the two-dimensional flow becomes unstable to different modes, depending on the cross-sectional aspect ratio, when the Reynolds number is increased. The critical mode is found to be stationary for all aspect ratios. When the separation of the moving walls is larger than approximately twice the height of the cavity, the basic flow forms two vortices, each close to one of the moving walls. The instability of this flow is of centrifugal type and similar to that in the classical lid-driven cavity problem with a single moving wall. When the moving walls are sufficiently close to each other (aspect ratio less than 2) the two vortices merge and form an elliptically strained vortex. Owing to the dipolar strain this flow becomes unstable through the elliptic instability. When both moving walls are very close, the finite-length plane-Couette flow becomes unstable by a similar elliptic mechanism near both turning zones. The critical mode produces wide streaks reaching far into the cavity. For a small range of aspect ratios near unity the flow consists of a single vortex. Here, the strain field is dominated by a four-fold symmetry. As a result the instability process is analogous to the instability of a Rankine vortex in an quadripolar strain field, resulting from vortex stretching into the four corners of the cavity.

Magnetoinertial Oscillations of Jupiter’s Inner Radiation Belt

Quasi-periodic 40 minute (QP-40) bursts of both relativistic electrons (energy E ~ 10 MeV) and radio emissions (frequency ν 700 kHz) from the south Jovian pole were detected by the instrument onboard the Ulysses spacecraft at high jovigraphic latitudes (~30-40 S°). We show here that Jupiter's inner radiation belt (IRB) may oscillate globally with a quasi-period of ~40 minutes or so and propose that, as results of asymmetries and small-scale circumpolar magnetic irregularities/anomalies, a fraction of relativistic electrons normally trapped within the IRB may go astray from a roughly circular zone surrounding the Jovian magnetic pole during certain phases of such IRB magnetoinertial oscillations. The escaped relativistic electrons rapidly convert their transverse motions to (anti)parallel motions along the magnetic field lines by the mirror force. The observed QP-40 radio bursts are closely associated with such QP-40 leaks of relativistic electrons in near-antiparallel motions. Our prediction for QP-40 magnetoinertial oscillations of the IRB can be tested by directly observing variations of IRB decimetric brightness using ground-based radio telescopes, especially upon the arrival of high-speed solar winds at Jupiter. Several relevant aspects of this scenario are also discussed.

Influence of dissipation on one- and two-dimensional quantum tunneling

The influence of low-frequency oscillations of the medium on the particle tunneling probability is investigated in a system with a selected tunneling coordinate, when the two-well tunnel potential takes the form of two parabolas of the same frequency. With parallel or antiparallel tunneling of two interacting particles, taking the interaction with the medium into account has no qualitative effect on the process. Quantitatively, however, the medium always influences the parallel motion of the tunneling particles and does not influence the action along the basic trajectory (R1=−R2) with antiparallel motion of the tunneling particles.

Striated jets due to nonlinear ponderomotive forces in laser produced plasmas at obliquely incident light

An analysis is made of one of the expected nonlinear and anomalous mechanisms and instabilities in the corona of a laser irradiated plasma. As is well known, nonlinear ponderomotive forces generate a net acceleration of the plasma toward lower densities. It is demonstrated that the same forces at oblique incidence of the radiation, can cause a net motion perpendicular to the well-known forces along the density gradient: The standing wave generated that is split into zones (slabs) of the thickness of a quarter of a wave length, where the plasma is moving in the plane of incidence parallel and antiparallel to the slabs. This striated motion can also occur in an underdense plasma, while for the net acceleration toward lower density the strong change of the refractive index near the cutoff density is necessary. The striated parallel and antiparallel motion of the slabs is limited by the mean free path, by the velocity toward lower density and is determined by the condition of laminar and turbulent motion. The time constants on the order of picoseconds and the nonlinear absorption due to the generation of this striated motion are evaluated. Laser intensities exceeding 1013 W/cm2 incident at angles of 25° should build up striated jets with ion energies of a few keV.

The Crystal Structure of dl-1,1,4aα-Trimethyl-2α-hydroxy-8β-methoxy-1,2,3,4,4a,5,6,7,8,9-decahydrophenanthrene

Abstract The crystal structure of the title compound has been determined from three-dimensional data collected on an automatic, four-circle diffractometer. The racemic crystals are triclinic, with two molecules in a unit cell of these dimensions; a=10.502, b=11.706, c=7.488 Å, α=71°33′, β=91°46′, and γ=116°22′. The space group is P\bar1. The structure was solved by the symbolic addition method and was then refined by the block-diagonalmatrix least-squares method, with isotropic temperature factors for the hydrogen atoms and with anisotropic ones for the others. The final R value was 6.7%. The length of the C–C single bond opposite to the double bond in the cyclohexene ring is only 1.34±0.01 Å. This apparent remarkable shortening can be well explained on the assumption that the two atoms concerned vibrate vigorously with parallel and antiparallel harmonic components perpendicular to the plane of the ring. It is shown that, if the root-mean-square amplitudes of the former components are taken to be equal to that of the thermal vibration of the carbon atom adjacent to one of the two atoms, the above C–C distance, corrected for these antiparallel motions, becomes quite reasonable: 1.60 Å.