In this letter, we show via numerical simulations that the typical flow structures appearing in transitional channel flows at moderate Reynolds numbers are not spots but isolated turbulent bands, which have much longer lifetimes than spots. Localized perturbations can evolve into bands by continuously growing obliquely when number is larger 660. However, interactions with other and local cause band breaking decay. The competition between extension does lead to a sustained turbulence until Re...

In this letter, the concentration of particles with size less than 10 μm (PM10) and flow velocities are measured synchronously at different heights in a sand storm, high-Reynolds number multi-phase turbulent boundary layer. It is revealed that low-speed very large scale motions (VLSMs) recurrent frequency dominating streamwise velocity power spectra modulate distribution PM10 concentration. logarithmic layer, VLSMs correspond to weak shear stress on bottom surface hence decrease upward flux....

The linear stability and energy of the plane Poiseuille flow with isotropic anisotropic slip boundary conditions are theoretically analyzed numerically calculated in this paper. asymptotic expansions critical parameters for derived from eigenvalue equations characterizing least stable modes. Reynolds number based on 1.5 times bulk mean streamwise velocity is found to be Rl2D≈(1+2741l2)R02D when non-dimensional length l ≪ 1, where R02D≈5772 under no-slip condition. numbers a wide range...

In this paper, the Rayleigh–Taylor instability (RTI) subjected to a dual-frequency vibration in normal direction of viscous interface is studied theoretically. comparison case with single frequency vibration, an enhanced suppression effect on RTI achieved due coupling between low-frequency vibrations. When frequencies are high, however, amplitude required stabilize or neutral becomes nearly independent phase lag vibrations, and diminishes. This phenomenon explained by asymptotic analytical...

In this Letter, we report on the induction of aluminum combustion within supercritical water, facilitated by an underwater explosion bubble. This bubble, initiated using aluminum-wire electrical discharge in a water-filled tank, typically spans tens centimeters and undergoes oscillatory dynamics characterized expansions compression. When significantly compressed, bubble reaches conditions elevated temperature pressure, sufficient to induce phase transition water from its normal state, which...

It is demonstrated theoretically that the nonlinear stage of Rayleigh-Taylor instability can be retarded at arbitrary Atwood numbers in a rotating system with axis rotation normal to acceleration interface between two uniform inviscid fluids. The Coriolis force provides an effective restoring on perturbed interface, and will always decrease saturation amplitude any disturbance wavelength.

In this letter, it is shown numerically that in plane Poiseuille flow and before the threshold of equilibrium turbulence defined by directed-percolation universality class, a sparse turbulent state form localized band can sustain either continuous increase fraction due to extension when domain large enough, or dynamic balance between breaking decay caused interaction finite domain. The width tilt angle keep statistically invariant during its oblique extension, process which not sensitive...

In this paper, the effect of vertical vibration on Rayleigh–Taylor instability at lower interface a sedimenting suspension layer sandwiched between viscous fluids is studied numerically and theoretically. It shown that suppresses amplitudes perturbations enlarges widths granular fingers, postponing nonlinear growth stage. By modeling as fluid with its effective density viscosity, stability analyses are carried out, dominant rate wave number predicted by dispersion relation agree numerical...

This paper investigates the evolution of asymmetric patterns for oscillatory flow in a baffled tube. A numerical simulation three-dimensional flows an axisymmetric geometry was developed and compared with experimental results obtained using particle image velocimetry (PIV). Sharp edged baffles were used both simulations experiments. From simulation, stability map symmetry as function Reynold-Strouhal numbers. The show that all Strouhal numbers, at Reynolds numbers less than 100 larger 225....

It has been shown experimentally over nearly 80 years that surface fine roughness of circular pipes a crucial effect on the natural transition to turbulence. In this Letter, theoretical explanation is suggested for roughness-induced instability. Once nonlinear introduced (through pipe with corrugation surface), mean velocity profile becomes unstable three-dimensional, asymmetric, and helical traveling waves at moderate Reynolds numbers. The threshold aspect ratio or shape factor element...

An exact theoretical analysis is presented, mainly concerning linearly elastic Rayleigh–Taylor (RT) and Richtmyer–Meshkov (RM) instabilities at spherical interfaces by using the decomposition method. A stability performed to investigate growth rates of instability with degree harmonics n, dimensionless radius Br, Atwood number At, ratio T. Generally, RT RM resemble their planar counterparts when Br or n large. However, low mode perturbations behave quite differently from ones, which also...

In this paper, we present a linear analysis of the Rayleigh–Taylor instability (RTI) in cylindrical geometry to investigate effects viscosity and elasticity on growth rates using decomposition method. This method decomposes fourth-order differential equations into two coupled second-order easily obtain dispersion relations. The motions interfaces are analyzed for at liquid/liquid, solid/liquid, solid/solid interfaces, results retrieve those previously obtained inviscid fluids. Generally,...

The interaction of Co with Si and SiO2 during rapid thermal annealing has been investigated. Phase sequence, layer morphology, reaction kinetics were studied by sheet resistance, x-ray diffraction, Auger electron spectroscopy, photoelectron scanning microscopy. With increasing temperature, film on Si(100) is transformed sequentially into Co2Si, CoSi, finally CoSi2 which corresponds to the minimum resistance. No evidence silicide formation was observed for Co/SiO2 annealed even at high...

In the previous studies of Rayleigh-Taylor instability, different methods were used to consider effects elasticity, viscosity, and magnetic fields. this paper, a unified method, which was first for fluids, is validated physical models, where unstable mode decomposed into an irrotational part rotational part, latter one includes nonconservative forces constitutive relations. Previous results solid liquid with or without fields finite thickness can be easily recovered after applying...

In this paper, the rotational part of disturbance flow field caused by viscous Rayleigh-Taylor instability (RTI) at cylindrical interface is considered, and most unstable mode revealed to be three-dimensional for interfaces small radii R. With an increase in R, azimuthal wave number increases step step, corresponding axial as well each number. When amplitude wave-number vector much larger or smaller than 1/R, RTI close semi-infinite planar limit finite-thickness creeping-flow limit,...

This paper investigates the spatio-temporal instability of natural-convection boundary-layer flow adjacent to a vertical heated flat plate immersed in thermally stratified ambient medium. The temperature on surface is distributed linearly. By introducing gradient radio and Prandtl number global frequency are discussed as well.

The Rayleigh-Taylor (RT) mixing induced by random interface disturbances between two incompressible viscous fluids is simulated numerically. ensemble averaged spike velocity found to be remarkably retarded when the are superimposed with an optimized additional mode. mode's wavenumber selected large enough avoid enhancing dominance of long-wavelength modes, but not so that its saturated and bubble velocities too small stimulate a growing effective density-gradient layer suppressing modes....

The spatiotemporal instability of the buoyancy-driven flow adjacent to a vertically heated wall, which is immersed in thermally stratified medium, studied theoretically and numerically. temperature gradients ratio between wall ambient fluid shown lead rich scenario absolute-convective transitions. direct numerical simulations consistent with theoretical prediction are presented. supercritical steady state, found previous natural convection square cavity, explained terms convective...

A theoretical study is presented of convection in a horizontal fluid layer heated from below or above which periodically accelerated its plane. The analysis based on Galerkin methods as well direct numerical simulations the underlying Boussinesq equations. Shaking fixed direction breaks original isotropy layer. At onset and at small acceleration, we find longitudinal rolls, where roll axis aligns parallel to acceleration direction. With increasing amplitude, shear instability takes over...

Transition from a Taylor-Couette turbulent flow to completely two-dimensional axisymmetric state is realized numerically by increasing gradually the strength of azimuthal magnetic field produced electric current flowing through axial rod. With increase Hartmann number, Taylor-vortex-like structures shrink, move closer inner cylinder, and turn into unsteady but perfect tori at sufficiently high numbers.