scholarly journals Boundary streaming by internal waves

2018 ◽  
Vol 858 ◽  
pp. 71-90 ◽  
Author(s):  
A. Renaud ◽  
A. Venaille
Keyword(s):  
Boundary Layers ◽  
Internal Waves ◽  
Acoustic Streaming ◽  
Early Time ◽  
Mean Flow ◽  
Viscous Boundary Layer ◽  
Quasi Biennial Oscillation ◽  
Flow Interactions ◽  
Viscous Boundary ◽  
Boussinesq Fluid

Damped internal wave beams in stratified fluids have long been known to generate strong mean flows through a mechanism analogous to acoustic streaming. While the role of viscous boundary layers in acoustic streaming has been thoroughly addressed, it remains largely unexplored in the case of internal waves. Here we compute the mean flow generated close to an undulating wall that emits internal waves in a viscous, linearly stratified two-dimensional Boussinesq fluid. Using a quasi-linear approach, we demonstrate that the form of the boundary conditions dramatically impacts the generated boundary streaming. In the no-slip scenario, the early-time Reynolds stress divergence within the viscous boundary layer is much stronger than within the bulk while also driving flow in the opposite direction. Whatever the boundary condition, boundary streaming is however dominated by bulk streaming at larger time. Using a Wentzel–Kramers–Brillouin approach, we investigate the consequences of adding boundary streaming effects to an idealised model of wave–mean flow interactions known to reproduce the salient features of the quasi-biennial oscillation. The presence of wave boundary layers has a quantitative impact on the flow reversals.

Large-amplitude acoustic streaming

2014 ◽  
Vol 744 ◽  
pp. 329-351 ◽  
Author(s):  
G. P. Chini ◽  
Z. Malecha ◽  
T. D. Dreeben
Keyword(s):  
Boundary Layers ◽  
High Frequency ◽  
Large Amplitude ◽  
Acoustic Streaming ◽  
Ideal Gas ◽  
Mean Flow ◽  
Viscous Effects ◽  
Viscous Boundary ◽  
Streaming Flows ◽  
Hid Lamps

AbstractA mechanism is proposed for the generation of large-amplitude acoustically-driven streaming flows in which time-mean flow speeds are comparable to the instantaneous speed of fluid particles in a high-frequency sound-wave field. Motivated by streaming observed in high-intensity discharge (HID) lamps, two-dimensional flow of a density-stratified ideal gas in a channel geometry is analysed in the asymptotic limit of high-frequency acoustic-wave forcing. Predictions of streaming flow magnitudes based on classical arguments invoking Reynolds stress divergences originating in viscous boundary layers are orders of magnitude too small to account for the observed mean flows. Moreover, classical ‘Rayleigh streaming’ theory cannot account for the direction of the cellular mean flows often observed in HID lamps. In contrast, the mechanism proposed here, which invokes fluctuating baroclinic torques away from viscous boundary layers and thus is largely independent of viscous effects, can account both for the magnitude and the orientation of the observed streaming flows.

The Reflection of a Stationary Gravity Wave by a Viscous Boundary Layer

2007 ◽  
Vol 64 (9) ◽  
pp. 3363-3371 ◽  
Author(s):  
François Lott
Keyword(s):  
Boundary Layer ◽  
Gravity Wave ◽  
Richardson Number ◽  
Critical Level ◽  
Inviscid Limit ◽  
Mean Flow ◽  
Viscous Boundary Layer ◽  
Lee Waves ◽  
The Mean ◽  
Viscous Boundary

Abstract The backward reflection of a stationary gravity wave (GW) propagating toward the ground is examined in the linear viscous case and for large Reynolds numbers (Re). In this case, the stationary GW presents a critical level at the ground because the mean wind is null there. When the mean flow Richardson number at the surface (J) is below 0.25, the GW reflection by the viscous boundary layer is total in the inviscid limit Re → ∞. The GW is a little absorbed when Re is finite, and the reflection decreases when both the dissipation and J increase. When J > 0.25, the GW is absorbed for all values of the Reynolds number, with a general tendency for the GW reflection to decrease when J increases. As a large ground reflection favors the downstream development of a trapped lee wave, the fact that it decreases when J increases explains why the more unstable boundary layers favor the onset of mountain lee waves. It is also shown that the GW reflection when J > 0.25 is substantially larger than that predicted by the conventional inviscid critical level theory and larger than that predicted when the dissipations are represented by Rayleigh friction and Newtonian cooling. The fact that the GW reflection depends strongly on the Richardson number indicates that there is some correspondence between the dynamics of trapped lee waves and the dynamics of Kelvin–Helmholtz instabilities. Accordingly, and in one classical example, it is shown that some among the neutral modes for Kelvin–Helmholtz instabilities that exist in an unbounded flow when J < 0.25 can also be stationary trapped-wave solutions when there is a ground and in the inviscid limit Re → ∞. When Re is finite, these solutions are affected by the dissipation in the boundary layer and decay in the downstream direction. Interestingly, their decay rate increases when both the dissipation and J increase, as does the GW absorption by the viscous boundary layer.

Acoustic streaming about a cylinder in orthogonal beams

1992 ◽  
Vol 242 ◽  
pp. 387-394 ◽  
Author(s):  
N. Riley
Keyword(s):  
Boundary Layer ◽  
Acoustic Streaming ◽  
Sound Waves ◽  
Viscous Boundary Layer ◽  
Single Beam ◽  
Plane Sound ◽  
Orthogonal Beams ◽  
Viscous Boundary ◽  
The Waves ◽  
Potential Vortex

When orthogonal, plane sound waves of the same frequency, wavelength and amplitude, but with phase difference ½π, are incident upon a circular cylinder there is a time-independent streaming about the cylinder which is in the form of a potential vortex separated from the cylinder by a thin, viscous Stokes layer. As the amplitude of the waves in one of the beams decreases, an additional viscous boundary layer is involved until, when the amplitude is sufficiently small, this flow structure is destroyed as fluid erupts from the boundary layer. In the limit of a single beam it is known that this eruption results in opposing jets perpendicular to the wavefronts of the oncoming wave.

scholarly journals The Impact of GCM Dynamical Cores on Idealized Sudden Stratospheric Warmings and Their QBO Interactions

2016 ◽  
Vol 73 (9) ◽  
pp. 3397-3421 ◽  
Author(s):  
Weiye Yao ◽  
Christiane Jablonowski
Keyword(s):  
General Circulation ◽  
Flow Characteristics ◽  
Circulation Model ◽  
Mean Flow ◽  
Single Vortex ◽  
Tem Analysis ◽  
Quasi Biennial Oscillation ◽  
Spectral Transform ◽  
Flow Interactions ◽  
The Impact

Abstract The paper demonstrates that sudden stratospheric warmings (SSWs) can be simulated in an ensemble of dry dynamical cores that miss the typical SSW forcing mechanisms like moist processes, land–sea contrasts, or topography. These idealized general circulation model (GCM) simulations are driven by a simple Held–Suarez–Williamson (HSW) temperature relaxation and low-level Rayleigh friction. In particular, the four dynamical cores of NCAR’s Community Atmosphere Model, version 5 (CAM5), are used, which are the semi-Lagrangian (SLD) and Eulerian (EUL) spectral-transform models and the finite-volume (FV) and the spectral element (SE) models. Three research themes are discussed. First, it is shown that SSW events in such idealized simulations have very realistic flow characteristics that are analyzed via the SLD model. A single vortex-split event is highlighted that is driven by wavenumber-1 and -2 wave–mean flow interactions. Second, the SLD simulations are compared to the EUL, FV, and SE dynamical cores, which sheds light on the impact of the numerical schemes on the circulation. Only SLD produces major SSWs, while others only exhibit minor stratospheric warmings. These differences are caused by SLD’s more vigorous wave–mean flow interactions in addition to a warm pole bias, which leads to relatively weak polar jets in SLD. Third, it is shown that tropical quasi-biennial oscillation (QBO)–like oscillations and SSWs can coexist in such idealized HSW simulations. They are present in the SLD dynamical core that is used to analyze the QBO–SSW interactions via a transformed Eulerian-mean (TEM) analysis. The TEM results provide support for the Holton–Tan effect.

scholarly journals Acoustic Streaming Generated by Sharp Edges: The Coupled Influences of Liquid Viscosity and Acoustic Frequency

Micromachines ◽  
2020 ◽  
Vol 11 (6) ◽  
pp. 607 ◽  
Author(s):  
Chuanyu Zhang ◽  
Xiaofeng Guo ◽  
Laurent Royon ◽  
Philippe Brunet
Keyword(s):  
Boundary Layer ◽  
Scaling Laws ◽  
Acoustic Streaming ◽  
Maximal Velocity ◽  
Liquid Viscosity ◽  
Viscous Boundary Layer ◽  
Acoustic Frequency ◽  
Streaming Velocity ◽  
Viscous Boundary ◽  
Streaming Flow

Acoustic streaming can be generated around sharp structures, even when the acoustic wavelength is much larger than the vessel size. This sharp-edge streaming can be relatively intense, owing to the strongly focused inertial effect experienced by the acoustic flow near the tip. We conducted experiments with particle image velocimetry to quantify this streaming flow through the influence of liquid viscosity ν , from 1 mm 2 /s to 30 mm 2 /s, and acoustic frequency f from 500 Hz to 3500 Hz. Both quantities supposedly influence the thickness of the viscous boundary layer δ = ν π f 1 / 2 . For all situations, the streaming flow appears as a main central jet from the tip, generating two lateral vortices beside the tip and outside the boundary layer. As a characteristic streaming velocity, the maximal velocity is located at a distance of δ from the tip, and it increases as the square of the acoustic velocity. We then provide empirical scaling laws to quantify the influence of ν and f on the streaming velocity. Globally, the streaming velocity is dramatically weakened by a higher viscosity, whereas the flow pattern and the disturbance distance remain similar regardless of viscosity. Besides viscosity, the frequency also strongly influences the maximal streaming velocity.

Progressive internal waves on slopes

1969 ◽  
Vol 35 (1) ◽  
pp. 131-144 ◽  
Author(s):  
Carl Wunsch
Keyword(s):  
Boundary Layers ◽  
Internal Waves ◽  
Three Dimensional ◽  
Two Dimensions ◽  
Inhomogeneous Waves ◽  
Usual Manner ◽  
Propagating Waves ◽  
Viscous Boundary ◽  
The Waves ◽  
Interior Solutions

The refraction of progressive internal waves on sloping bottoms is treated for the case of constant Brunt—Väisälä frequency. In two dimensions simple, explicit expressions for the changing wavelengths and amplitudes are found. For small slopes, the solutions reduce to simple propagating waves at infinity.The singularity along a characteristic is shown to be removable, though the solutions are now inhomogeneous waves. The viscous boundary layers of the wedge geometry are briefly considered with the inviscid solutions remaining as interior solutions.A theory valid for small slopes is obtained for three-dimensional waves. The waves are refracted in the usual manner, turning parallel to the beach in shallow water.

scholarly journals Suppressed Thermocline Mixing in the Center of Anticyclonic Eddy in the North South China Sea

2021 ◽  
Vol 9 (10) ◽  
pp. 1149
Author(s):  
Yongfeng Qi ◽  
Huabin Mao ◽  
Xia Wang ◽  
Linhui Yu ◽  
Shumin Lian ◽  
...  
Keyword(s):  
South China Sea ◽  
Internal Waves ◽  
South China ◽  
Northern South China Sea ◽  
Mesoscale Eddy ◽  
Fine Scale ◽  
Mean Flow ◽  
China Sea ◽  
Flow Interactions ◽  
Background Shear

Direct microstructure observations and fine-scale measurements of an anticyclonic mesoscale eddy were conducted in the northern South China Sea in July 2020. An important finding was that suppressed turbulent mixing in the thermocline existed at the center of the eddy, with an averaged diapycnal diffusivity at least threefold smaller than the peripheral diffusivity. Despite the strong background shear and significant wave–mean flow interactions, the results indicated that the lack of internal wave energy in the corresponding neap tide period during measurement of the eddy’s center was the main reason for the suppressed turbulent mixing in the thermocline. The applicability of the fine-scale parameterization method in the presence of significant wave–mean flow interactions in a mesoscale eddy was evaluated. Overprediction via fine-scale parameterization occurred in the center of the eddy, where the internal waves were inactive; however, the parameterization results were consistent with microstructure observations along the eddy’s periphery, where active internal waves existed. This indicates that the strong background shear and wave–mean flow interactions affected by the mesoscale eddy were not the main contributing factors that affected the applicability of fine-scale parameterization in the northern South China Sea. Instead, our results showed that the activity of internal waves is the most important consideration.

Periodicity disruption of a model quasi-biennial oscillation of equatorial winds

2020 ◽  
Author(s):  
Antoine Renaud ◽  
Louis-Philippe Nadeau ◽  
Antoine Venaille
Keyword(s):  
Large Scale ◽  
Physical Review ◽  
Stratified Fluids ◽  
Mean Flow ◽  
Quasi Biennial Oscillation ◽  
Flow Interactions ◽  
Quasiperiodic Route To Chaos ◽  
Secondary Bifurcation ◽  
Secondary Bifurcations ◽  
Biennial Oscillation

<p>In the Earth's atmosphere, fast propagating equatorial waves generate slow reversals of the large scale stratospheric winds with a  period of about 28 months. This quasi-biennial oscillation is a spectacular manifestation of wave-mean flow interactions in stratified fluids, with analogues in other planetary atmospheres and laboratory experiments. Recent observations of a disruption of this periodic behavior have been attributed to external perturbations, but the mechanism explaining the disrupted response has remained elusive. We show the existence of secondary bifurcations and a quasiperiodic route to chaos in simplified models of the equatorial atmosphere ranging from the classical Holton-Lindzen-Plumb model to fully nonlinear simulations of stratified fluids. Perturbations of the slow oscillations are widely amplified in the proximity of the secondary bifurcation point. This suggests that intrinsic dynamics may be equally influential as external variability in explaining disruptions of regular wind reversals  [1].</p><p>[1] Renaud, A., Nadeau, L. P., & Venaille, A. (2019). Periodicity Disruption of a Model Quasibiennial Oscillation of Equatorial Winds. Physical Review Letters, 122(21), 214504.<br> </p>

Sign in / Sign up

Export Citation Format

Share Document