Convection Regularization of High Wavenumbers in Turbulence ANS Shocks

2011 ◽  
Author(s):  
Kamran Mohseni
Keyword(s):  
High Wavenumbers

Dynamics of homogeneous bubbly flows Part 2. Velocity fluctuations

2002 ◽  
Vol 466 ◽  
pp. 53-84 ◽  
Author(s):  
BERNARD BUNNER ◽  
GRÉTAR TRYGGVASON
Keyword(s):  
Kinetic Energy ◽  
Reynolds Stress ◽  
Void Fraction ◽  
Three Dimensional ◽  
Bubbly Flows ◽  
Rise Velocity ◽  
Velocity Fluctuations ◽  
Kinetic Energy Spectrum ◽  
Average Rise ◽  
High Wavenumbers

Direct numerical simulations of the motion of up to 216 three-dimensional buoyant bubbles in periodic domains are presented. The bubbles are nearly spherical and have a rise Reynolds number of about 20. The void fraction ranges from 2% to 24%. Part 1 analysed the rise velocity and the microstructure of the bubbles. This paper examines the fluctuation velocities and the dispersion of the bubbles and the ‘pseudo-turbulence’ of the liquid phase induced by the motion of the bubbles. It is found that the turbulent kinetic energy increases with void fraction and scales with the void fraction multiplied by the square of the average rise velocity of the bubbles. The vertical Reynolds stress is greater than the horizontal Reynolds stress, but the anisotropy decreases when the void fraction increases. The kinetic energy spectrum follows a power law with a slope of approximately −3.6 at high wavenumbers.

scholarly journals The stability of a trailing-line vortex in compressible flow

1994 ◽  
Vol 269 ◽  
pp. 323-351 ◽  
Author(s):  
Jillian A. K. Stott ◽  
Peter W. Duck
Keyword(s):  
Mach Number ◽  
Compressible Flow ◽  
Numerical Results ◽  
Line Vortex ◽  
Mach Numbers ◽  
The Stability ◽  
Vortex Axis ◽  
Very High ◽  
High Wavenumbers

We consider the inviscid stability of the Batchelor (1964) vortex in a compressible flow. The problem is tackled numerically and also asymptotically, in the limit of large (azimuthal and streamwise) wavenumbers, together with large Mach numbers. The nature of the solution passes through different regimes as the Mach number increases, relative to the wavenumbers. At very high wavenumbers and Mach numbers, the mode which is present in the incompressible case ceases to be unstable, whilst a new ‘centre mode’ forms, whose stability characteristics are determined primarily by conditions close to the vortex axis. We find that generally the flow becomes less unstable as the Mach number increases, and that the regime of instability appears generally confined to disturbances in a direction counter to the direction of the rotation of the swirl of the vortex.Throughout the paper comparison is made between our numerical results and results obtained from the various asymptotic theories.

scholarly journals Observation of Anderson localization beyond the spectrum of the disorder

2021 ◽  
Author(s):  
Alex Dikopoltsev ◽  
Sebastian Weidermann ◽  
Mark Kremer ◽  
Andrea Steinfurth ◽  
Hanan Herzig Sheinfux ◽  
...  
Keyword(s):  
Disordered Systems ◽  
Anderson Localization ◽  
Localization Length ◽  
Fundamental Wave ◽  
Disordered System ◽  
Finite Spectrum ◽  
Photonic Lattices ◽  
The Mean ◽  
Shed Light ◽  
High Wavenumbers

Abstract Anderson localization is a fundamental wave phenomenon predicting that transport in a 1D uncorrelated disordered system comes to a complete halt, experiencing no transport whatsoever. However, in reality, a disordered physical system is always correlated, because it must have a finite spectrum. Common wisdom in the field states that localization is dominant only for wavepackets whose spectral extent resides within the region of the wavenumber span of the disorder. Here, we experimentally observe that Anderson localization can occur and even be dominant for wavepackets residing entirely outside the spectral extent of the disorder. We study the evolution of waves in synthetic photonic lattices containing bandwidth-limited (correlated) disorder, and observe Anderson localization for wavepackets of high wavenumbers centered around twice the mean wavenumber of the disorder spectrum. Likewise, we predict and observe Anderson localization at low wavenumbers, also outside the spectral extent of the disorder, and find that localization there can be as strong as for first-order transitions. This feature is universal, common to all Hermitian wave systems, implying that low-wavenumber wavepackets localize with a short localization length even when the disorder is strictly at high wavenumbers. This understanding suggests that disordered media should be opaque for long-wavelengths even when the disorder is strictly at much shorter length scales. Our results shed light on fundamental aspects of physical disordered systems and offer avenues for employing spectrally-shaped disorder for controlling transport in systems containing disorder.

scholarly journals Distinguishing physical mechanisms using GISAXS experiments and linear theory: the importance of high wavenumbers

2017 ◽  
Vol 7 (1) ◽  
Author(s):  
Scott A. Norris ◽  
Joy C. Perkinson ◽  
Mahsa Mokhtarzadeh ◽  
Eitan Anzenberg ◽  
Michael J. Aziz ◽  
...  
Keyword(s):  
Linear Theory ◽  
Physical Mechanisms ◽  
High Wavenumbers

scholarly journals Anisotropy in MHD turbulence due to a mean magnetic field

1983 ◽  
Vol 29 (3) ◽  
pp. 525-547 ◽  
Author(s):  
John V. Shebalin ◽  
William H. Matthaeus ◽  
David Montgomery
Keyword(s):  
Magnetic Field ◽  
Reynolds Numbers ◽  
Combined Effects ◽  
Two Dimensional ◽  
Mhd Turbulence ◽  
Magnetohydrodynamic Turbulence ◽  
High Wavenumbers

The development of anisotropy in an initially isotropie spectrum is studied numerically for two-dimensional magnetohydrodynamic turbulence. The anisotropy develops through the combined effects of an externally imposed d.c. magnetic field and viscous and resistive dissipation at high wavenumbers. The effect is most pronounced at high mechanical and magnetic Reynolds numbers. The anisotropy is greater at the higher wavenumbers.

Do attractive scattering potentials concentrate particles at the origin in one, two and three dimensions? I. Potentials finite at the origin

1983 ◽  
Vol 388 (1795) ◽  
pp. 401-418 ◽  
Keyword(s):  
Quantum Mechanics ◽  
Classical Mechanics ◽  
Three Dimensions ◽  
Simple Extension ◽  
Final State ◽  
Central Potential ◽  
Scattering State ◽  
Square Well ◽  
Semiclassical Regime ◽  
High Wavenumbers

Paradoxically, in beta decay, for instance, the final-state Coulomb forces pulling the electron inwards accelerate the emission. Quantum mechanics (q. m. ) makes the rate proportional to α ≡ ρ 0 / ρ ∞ ; ρ 0, ∞ (and v 0, ∞ ) are the particle densities (and speeds) at r = 0 and far upstream in the scattering state which describes the electron. Hence, as regards the effects of finalstate interactions, one must base one’s physical intuition on this ratio α . It is shown that according to (non-relativistic) classical mechanics, if the origin is accessible, then any central potential U(r) where v 0 < ∞ (i. e. where U (0) > -∞) gives in 1, 2 and 3 dimensions, α 1 = v ∞ / v 0 , α 2 = 1, α 3 = v 0 / v ∞ ; the remaining course of U(r) is irrelevant to α . The same results hold also in q. m. in the semiclassical regime, i. e. in the W. K. B. approximation which for such potentials becomes valid at high wavenumbers; in 2D it needs rather careful formulation, and in 3D one must avoid the Langer modification. (The W. K. B. results apply even if d U / d r diverges at r = 0, provided U (0) remains finite; these cases are covered by a simple extension of the argument. ) The square-well and exponential potentials are discussed as examples. Potentials which diverge at the origin are treated in the following paper.

A new mechanism of small-scale transition in a plane mixing layer: core dynamics of spanwise vortices

1995 ◽  
Vol 298 ◽  
pp. 23-80 ◽  
Author(s):  
W. Schoppa ◽  
F. Hussain ◽  
R. W. Metcalfe
Keyword(s):  
Large Diameter ◽  
Mixing Layer ◽  
Meridional Flow ◽  
Transition To Turbulence ◽  
Small Scale ◽  
Plane Mixing Layer ◽  
Scale Transition ◽  
Vortex Lines ◽  
Core Dynamics ◽  
High Wavenumbers

We present a new mechanism of small-scale transition via core dynamics instability (CDI) in an incompressible plane mixing layer, a transition which is not reliant on the presence of longitudinal vortices (‘ribs’) and which can originate much earlier than ribinduced transition. Both linear stability analysis and direct numerical simulation are used to describe CDI growth and subsequent transition in terms of vortex dynamics and vortex line topology. CDI is characterized by amplifying oscillations of core size non-uniformity and meridional flow within spanwise vortices (‘rolls’), produced by a coupling of roll swirl and meridional flow that is manifested by helical twisting and untwisting of roll vortex lines. We find that energetic CDI is excited by subharmonic oblique modes of shear layer instability after roll pairing, when adjacent rolls with out-of-phase undulations merge. Starting from moderate initial disturbance amplitudes, twisting of roll vortex lines generates within the paired roll opposing spanwise flows which even exceed the free-stream velocity. These flows collide to form a nearly irrotational bubble surrounded by a thin vorticity sheath of a large diameter, accompanied by folding and reconnection of roll vortex lines and local transition. We find that accelerated energy transfer to high wavenumbers precedes the development of roll internal intermittency; this transfer, inferred from increased energy at high wavenumbers and an intensification of roll vorticity, occurs prior to the development of strong opposite-signed (to the mean) spanwise vorticity and granularity of the roll vorticity distribution. We demonstrate that these core dynamics are not reliant upon special symmetries and also occur in the presence of moderate-strength ribs, despite entrapment of ribs within pairing rolls. In fact, the roll vorticity dynamics are dominated by CDI if ribs are not sufficiently strong to first initiate transition; thus CDI may govern small-scale transition for moderate initial 3D disturbances, typical of practical situations. Results suggest that CDI constitutes a new generic mechanism for transition to turbulence in shear flows.

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