scholarly journals Wave–Turbulence Interactions in a Breaking Mountain Wave

2008 ◽  
Vol 65 (10) ◽  
pp. 3139-3158 ◽  
Author(s):  
Craig C. Epifanio ◽  
Tingting Qian
Keyword(s):  
Breaking Wave ◽  
Turbulent Heat ◽  
Grid Spacing ◽  
Mean Flow ◽  
Mountain Wave ◽  
Turbulent Structures ◽  
Turbulent Dissipation ◽  
Flow Vorticity ◽  
Momentum Fluxes ◽  
The Mean

The mean and turbulent structures in a breaking mountain wave are considered through an ensemble of high-resolution (essentially large-eddy simulation) wave-breaking calculations. Of particular interest are the turbulent heat and momentum fluxes in the breaking wave and their roles in shaping the wave-scale and larger-scale flows. The evolution of the breaking wave in the ensemble mean is found to be broadly consistent with prior low-resolution calculations. A turbulent kinetic energy budget for the wave shows that the turbulence production is almost entirely due to the mean shear. Most of the production is at the top of the leeside shooting flow, where the mean-flow Richardson number is persistently less than 0.25. The turbulent dissipation of mean-flow wave energy is shown to result mainly from the turbulent momentum fluxes—specifically, from the tendency of these fluxes to act counter to the mean-flow disturbance wind. Of particular importance is the eddy deceleration of the leeside shooting flow. The resulting momentum dissipation leads to a mean-flow Bernoulli loss, a cross-stream mean-flow PV flux, and a permanent upward mean-flow vorticity transfer. The dependence of the turbulent fluxes on grid spacing is considered by computing a series of ensembles with grid spacings ranging from L/56 to L/3.7 (where L is the mountain half-width). At the highest resolution, the eddy fluxes are mostly resolved, but with increasing grid spacing, the resolved-scale fluxes decline and the parameterized fluxes become larger. It is shown that for the chosen parameter values, the parameterized fluxes overestimate the mean-flow PV flux: at L/3.7 the PV flux is nearly twice that computed at L/56.

Experimental and Numerical Investigations of the 3-D Turbulent Flow Characteristics Around Submerged Permeable Breakwaters

2017 ◽  
Author(s):  
Caleb Stanley ◽  
Georgios Etsias ◽  
Steven Dabelow ◽  
Dimitrios Dermisis ◽  
Ning Zhang
Keyword(s):  
Turbulent Flow ◽  
Laboratory Experiments ◽  
Flow Characteristics ◽  
Mean Flow ◽  
Turbulent Structures ◽  
3 Dimensional ◽  
The Mean ◽  
Design Simplicity ◽  
Study Laboratory ◽  
Geometric Designs

Submerged breakwaters are favored for their design simplicity in projects intended to dissipate wave energy and reduce erosion on coastlines. Despite their popularity, the effects that submerged breakwaters exhibit on the surrounding hydrodynamics are not clearly understood, mainly due to the flow complexity generated from 3-dimensional turbulent structures in the vicinity of the breakwaters that affect the mean flow characteristics and the transport of sediment. The objective of this study was to evaluate the effects that various geometric designs of submerged permeable breakwaters have on the turbulent flow characteristics. To meet the objective of this study, laboratory experiments were performed in a water-recirculating flume, in which the 3-dimensional velocity field was recorded in the vicinity of scaled breakwater models. Breakwaters that were tested include non-permeable, three-hole, and ten-hole models. The experimental data obtained was compared to results obtained from numerical simulations. Results demonstrated that permeable breakwaters exhibit more vertical turbulent strength than their non-permeable counterparts. It was also discovered that three-hole breakwater models produce higher turbulent fluctuations than that of the ten-hole breakwaters. The results from this study will be used eventually to enhance the performance of restoration projects in coastal areas in Louisiana.

Characterization of Turbulent Heat Transfer in Ribbed Pipe Flow

2016 ◽  
Vol 138 (4) ◽  
Author(s):  
Changwoo Kang ◽  
Kyung-Soo Yang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Pipe Flow ◽  
Temperature Fields ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Mean Flow ◽  
Transfer Enhancement ◽  
Pitch Ratio ◽  
The Mean

In the current investigation, we performed large eddy simulation (LES) of turbulent heat transfer in circular ribbed-pipe flow in order to study the effects of periodically mounted square ribs on heat transfer characteristics. The ribs were implemented on a cylindrical coordinate system by using an immersed boundary method, and dynamic subgrid-scale models were used to model Reynolds stresses and turbulent heat flux terms. A constant and uniform wall heat flux was imposed on all the solid boundaries. The Reynolds number (Re) based on the bulk velocity and pipe diameter is 24,000, and Prandtl number is fixed at Pr = 0.71. The blockage ratio (BR) based on the pipe diameter and rib height is fixed with 0.0625, while the pitch ratio based on the rib interval and rib height is varied with 2, 4, 6, 8, 10, and 18. Since the pitch ratio is the key parameter that can change flow topology, we focus on its effects on the characteristics of turbulent heat transfer. Mean flow and temperature fields are presented in the form of streamlines and contours. How the surface roughness, manifested by the wall-mounted ribs, affects the mean streamwise-velocity profile was investigated by comparing the roughness function. Local heat transfer distributions between two neighboring ribs were obtained for the pitch ratios under consideration. The flow structures related to heat transfer enhancement were identified. Friction factors and mean heat transfer enhancement factors were calculated from the mean flow and temperature fields, respectively. Furthermore, the friction and heat-transfer correlations currently available in the literature for turbulent pipe flow with surface roughness were revisited and evaluated with the LES data. A simple Nusselt number correlation is also proposed for turbulent heat transfer in ribbed pipe flow.

The Response of an Idealized Atmosphere to Localized Tropical Heating: Superrotation and the Breakdown of Linear Theory

2018 ◽  
Vol 75 (1) ◽  
pp. 3-20 ◽  
Author(s):  
Nicholas J. Lutsko
Keyword(s):  
Temperature Gradient ◽  
General Circulation ◽  
Circulation Model ◽  
Mean Flow ◽  
Heating Rates ◽  
Momentum Fluxes ◽  
The Mean ◽  
The Stability ◽  
The Waves ◽  
Large Heating

An equatorial heat source mimicking the strong diabatic heating above the west Pacific is added to an idealized, dry general circulation model. For small (<0.5 K day−1) heating rates the responses closely match the expectations from linear Matsuno–Gill theory, though the amplitudes of the responses increase sublinearly. This “linear” regime breaks down for larger heating rates and it is found that this is because the stability of the tropical atmosphere increases. At the same time, the equatorial winds increasingly superrotate. This superrotation is driven by stationary eddy momentum fluxes by the waves excited by the heating and is damped by the vertical advection of low-momentum air by the mean flow and, at large heating rates, by the divergence of momentum by transient eddies. These dynamics are explored in additional experiments in which the equator-to-pole temperature gradient is varied. Very strong superrotation is produced when a large heating rate is applied to a setup with a relatively weak equator-to-pole temperature gradient, though there is no evidence that this is a case of “runaway” superrotation.

Orientation and rotation of inertial disk particles in wall turbulence

2015 ◽  
Vol 766 ◽  
Author(s):  
Niranjan Reddy Challabotla ◽  
Lihao Zhao ◽  
Helge I. Andersson
Keyword(s):  
Translational Motion ◽  
Turbulent Channel Flow ◽  
Stokes Number ◽  
Wall Turbulence ◽  
Rotational Inertia ◽  
Inertial Particles ◽  
Mean Flow ◽  
Flow Vorticity ◽  
Oblate Spheroids ◽  
The Mean

AbstractThe translational and rotational dynamics of oblate spheroidal particles suspended in a directly simulated turbulent channel flow have been examined. Inertial disk-like particles exhibited a significant preferential orientation in the plane of the mean shear. The rotational inertia about the symmetry axis of the disk-like particles hampered the spin-up of the flattest particles to match the mean flow vorticity. The influence of the particle shape on the orientation and rotation diminished as the translational inertia increased from Stokes number 1 to 30. An isotropization of both orientation and rotation could be observed in the core region of the channel. The translational motion of the oblate spheroids had a weak dependence on the aspect ratio. We therefore concluded that inertial particles sample nearly the same flow field irrespective of shape. Nevertheless, the orientation and rotation of disk-like particles turned out to be qualitatively different from the dynamics of fibre-like particles.

STEADY STATE HEAT TRANSFER TO FULLY DEVELOPED TURBULENT FLOW IN A CURVED CHANNEL

1957 ◽  
Vol 35 (4) ◽  
pp. 410-434
Author(s):  
A. W. Marris
Keyword(s):  
Heat Transfer ◽  
Turbulent Flow ◽  
Turbulent Heat Transfer ◽  
Turbulent Heat ◽  
Mean Flow ◽  
Curved Channel ◽  
Mean Velocity ◽  
Fully Developed Turbulent Flow ◽  
Angular Velocities ◽  
The Mean

A vorticity transfer analogy theory of turbulent heat transfer is developed first for the case of fully developed turbulent flow under zero transverse pressure and temperature gradients such as that in the annulus between concentric cylinders rotating with different angular velocities or in a "free vortex". The mean flow is assumed to be two-dimensional. The theory, which requires that the turbulence be statistically isotropic, yields a temperature distribution in agreement with experiment except in narrow regions immediately adjacent to the boundaries. An argument is given to show that the boundary layer thickness should be of the order of the reciprocal of the square root of the mean velocity, these boundaries are introduced, and Nusselt moduli are defined and their dependence on Reynolds and Prandtl numbers is investigated.The temperature distributions for the case of non-zero transverse temperature and pressure gradients, i.e. for the case of flow in a curved channel in which the fluid does not flow back into itself, are then obtained and the applicability of the simpler equations for zero transverse gradients to this case is investigated.

scholarly journals Seasonal Variations of High-Frequency Gravity Wave Momentum Fluxes and Their Forcing toward Zonal Winds in the Mesosphere and Lower Thermosphere over Langfang, China (39.4° N, 116.7° E)

Atmosphere ◽  
2020 ◽  
Vol 11 (11) ◽  
pp. 1253
Author(s):  
Caixia Tian ◽  
Xiong Hu ◽  
Yurong Liu ◽  
Xuan Cheng ◽  
Zhaoai Yan ◽  
...  
Keyword(s):  
Seasonal Variations ◽  
High Frequency ◽  
Momentum Flux ◽  
Lower Thermosphere ◽  
Mean Flow ◽  
Zonal Winds ◽  
Short Period ◽  
Momentum Fluxes ◽  
The Mean ◽  
Mesosphere And Lower Thermosphere

Meteor radar data collected over Langfang, China (39.4° N, 116.7° E) were used to estimate the momentum flux of short-period (less than 2 h) gravity waves (GWs) in the mesosphere and lower thermosphere (MLT), using the Hocking (2005) analysis technique. Seasonal variations in GW momentum flux exhibited annual oscillation (AO), semiannual oscillation (SAO), and quasi-4-month oscillation. Quantitative estimations of GW forcing toward the mean zonal flow were provided using the determined GW momentum flux. The mean flow acceleration estimated from the divergence of this flux was compared with the observed acceleration of zonal winds displaying SAO and quasi-4-month oscillations. These comparisons were used to analyze the contribution of zonal momentum fluxes of SAO and quasi-4-month oscillations to zonal winds. The estimated acceleration from high-frequency GWs was in the same direction as the observed acceleration of zonal winds for quasi-4-month oscillation winds, with GWs contributing more than 69%. The estimated acceleration due to Coriolis forces to the zonal wind was studied; the findings were opposite to the estimated acceleration of high-frequency GWs for quasi-4-month oscillation winds. The significance of this study lies in estimating and quantifying the contribution of the GW momentum fluxes to zonal winds with quasi-4-month periods over mid-latitude regions for the first time.

scholarly journals Effect of Fluid Viscoelasticity on Turbulence and Large-Scale Vortices behind Wall-Mounted Plates

2014 ◽  
Vol 6 ◽  
pp. 823138
Author(s):  
Takahiro Tsukahara ◽  
Masaaki Tanabe ◽  
Yasuo Kawaguchi
Keyword(s):  
Viscoelastic Fluid ◽  
Large Scale ◽  
Vortex Pair ◽  
Mean Flow ◽  
Turbulent Structures ◽  
Frictional Drag ◽  
Local Skin ◽  
Smooth Channel ◽  
The Mean ◽  
Free Area

Direct numerical simulations of turbulent viscoelastic fluid flows in a channel with wall-mounted plates were performed to investigate the influence of viscoelasticity on turbulent structures and the mean flow around the plate. The constitutive equation follows the Giesekus model, valid for polymer or surfactant solutions, which are generally capable of reducing the turbulent frictional drag in a smooth channel. We found that turbulent eddies just behind the plates in viscoelastic fluid decreased in number and in magnitude, but their size increased. Three pairs of organized longitudinal vortices were observed downstream of the plates in both Newtonian and viscoelastic fluids: two vortex pairs were behind the plates and the other one with the longest length was in a plate-free area. In the viscoelastic fluid, the latter vortex pair in the plate-free area was maintained and reached the downstream rib, but its swirling strength was weakened and the local skin-friction drag near the vortex was much weaker than those in the Newtonian flow. The mean flow and small spanwise eddies were influenced by the additional fluid force due to the viscoelasticity and, moreover, the spanwise component of the fluid elastic force may also play a role in the suppression of fluid vortical motions behind the plates.

Modelling of noise reduction in complex multistream jets

2017 ◽  
Vol 834 ◽  
pp. 555-599 ◽  
Author(s):  
Dimitri Papamoschou
Keyword(s):  
Noise Reduction ◽  
Reynolds Stress ◽  
Time Correlation ◽  
Nozzle Geometry ◽  
Navier Stokes ◽  
Acoustic Analogy ◽  
Mean Flow ◽  
Turbulent Structures ◽  
Prediction Scheme ◽  
The Mean

The paper presents a low-order prediction scheme for the noise change in multistream jets when the nozzle geometry is altered from a known baseline. The essence of the model is to predict the changes in acoustics due to the redistribution of the mean flow as computed by a Reynolds-averaged Navier–Stokes (RANS) solver. A RANS-based acoustic analogy framework is developed that addresses the noise in the polar direction of peak emission and uses the Reynolds stress as a time-averaged representation of the action of the coherent turbulent structures. The framework preserves the simplicity of the Lighthill acoustic analogy, using the free-space Green’s function, while accounting for azimuthal effects via special forms for the space–time correlation combined with source–observer relations based on the Reynolds stress distribution in the jet plume. Results are presented for three-stream jets with offset secondary and tertiary flows that reduce noise in specific azimuthal directions. The model reproduces well the experimental noise reduction trends. Principal mechanisms of noise reduction are elucidated.

Non-equilibrium scaling laws in axisymmetric turbulent wakes

2015 ◽  
Vol 781 ◽  
pp. 166-195 ◽  
Author(s):  
T. Dairay ◽  
M. Obligado ◽  
J. C. Vassilicos
Keyword(s):  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Scaling Laws ◽  
Reynolds Shear Stress ◽  
Mean Flow ◽  
Turbulent Dissipation ◽  
Turbulent Wakes ◽  
The Mean ◽  
Energy Equations ◽  
Non Equilibrium

We present a combined direct numerical simulation and hot-wire anemometry study of an axisymmetric turbulent wake. The data lead to a revised theory of axisymmetric turbulent wakes which relies on the mean streamwise momentum and turbulent kinetic energy equations, self-similarity of the mean flow, turbulent kinetic energy, Reynolds shear stress and turbulent dissipation profiles, non-equilibrium dissipation scalings and an assumption of constant anisotropy. This theory is supported by the present data up to a distance of 100 times the wake generator’s size, which is as far as these data extend.

scholarly journals Turbulence structure and interaction with steep breaking waves

2011 ◽  
Vol 674 ◽  
pp. 522-577 ◽  
Author(s):  
DJAMEL LAKEHAL ◽  
PETAR LIOVIC
Keyword(s):  
Fluid Flow ◽  
Water Waves ◽  
Three Dimensional ◽  
Breaking Waves ◽  
Small Scale ◽  
Breaking Wave ◽  
Turbulence Structure ◽  
Mean Flow ◽  
Scale Breaking ◽  
The Mean

Large-eddy and interface simulation using an interface tracking-based multi-fluid flow solver is conducted to investigate the breaking of steep water waves on a beach of constant bed slope. The present investigation focuses mainly on the ‘weak plunger’ breaking wave type and provides a detailed analysis of the two-way interaction between the mean fluid flow and the sub-modal motions, encompassing wave dynamics and turbulence. The flow is analysed from two points of views: mean to sub-modal exchange, and wave to turbulence interaction within the sub-modal range. Wave growth and propagation are due to energy transfer from the mean flow to the waves, and transport of mean momentum by these waves. The vigorous downwelling–upwelling patterns developing at the head and tail of each breaker are shown to generate both negative- and positive-signed energy exchange contributions in the thin sublayer underneath the water surface. The details of these exchange mechanisms are thoroughly discussed in this paper, together with the interplay between three-dimensional small-scale breaking associated with turbulence and the dominant two-dimensional wave motion. A conditional zonal analysis is proposed for the first time to understand the transient mechanisms of turbulent kinetic energy production, decay, diffusion and transport and their dependence and/or impact on surface wrinkling over the entire breaking process. The simulations provide a thorough picture of air–liquid coherent structures that develop over the breaking process, and link them to the transient mechanisms responsible for their local incidence.

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