scholarly journals Anatomy of subcritical submarine flows with a lutocline and an intermediate destruction layer

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jorge S. Salinas ◽  
S. Balachandar ◽  
M. Shringarpure ◽  
J. Fedele ◽  
D. Hoyal ◽  
...  
Keyword(s):  
Layer Structure ◽  
Interface Layer ◽  
The Body ◽  
Turbidity Currents ◽  
Mean Flow ◽  
Ambient Fluid ◽  
Turbulent Structures ◽  
The Mean ◽  
Turbulence Production ◽  
Interface Layers

AbstractTurbidity currents are sediment-laden flows that travel over a sloping bed under a stagnant ambient fluid, driven by the density difference between the current and the ambient. Turbidity currents transport large amounts of carbon, nutrients and fresh water through oceans and play an important role in global geochemical cycling and seafloor ecosystems. Supercritical currents are observed in steeper slopes. Subcritical currents are observed in milder slopes, where the near-bed and interface layers are prevented from interacting across the velocity maximum. Past works show the existence of such a barrier to vertical momentum transfer is essential for the body of the subcritical current to extend over hundreds of kilometers in length without much increase in height. Here we observe the body of subcritical currents to have a three layer structure, where the turbulent near-bed layer and the non-turbulent interface layer are separated by an intermediate layer of negative turbulence production. We explain the mechanism by which this layer prevents the near-bed turbulent structures from penetrating into the interface layer by transferring energy back from turbulence to the mean flow.

Analysis of Turbulence in the Tip Region of a Waterjet Pump Rotor

2010 ◽  
Author(s):  
Huixuan Wu ◽  
Rinaldo L. Miorini ◽  
Joseph Katz
Keyword(s):  
Energy Flux ◽  
Large Scale ◽  
Multiple Scales ◽  
Tip Clearance ◽  
Mean Flow ◽  
Production Characteristic ◽  
Pump Rotor ◽  
The Mean ◽  
Turbulence Production ◽  
Waterjet Pump

A series of high resolution planar particle image velocimetry measurements performed in a waterjet pump rotor reveal the inner structure of the tip leakage vortex (TLV) which dominates the entire flow field in the tip region. Turbulence generated by interactions among the TLV, the shear layer that develops as the backward leakage flow emerges from the tip clearance as a “wall jet”, the passage flow, and the endwall is highly inhomogeneous and anisotropic. We examine this turbulence in both RANS and LES modelling contexts. Spatially non-uniform distributions of Reynolds stress components are explained in terms of the local mean strain field and associated turbulence production. Characteristic length scales are also inferred from spectral analysis. Spatial filtering of instantaneous data enables the calculation of subgrid scale (SGS) stresses, along with the SGS energy flux (dissipation). The data show that the SGS energy flux differs from the turbulence production rate both in trends and magnitude. The latter is dominated by energy flux from the mean flow to the large scale turbulence, which is resolved in LES, whereas the former is dominated by energy flux from the mean flow to the SGS turbulence. The SGS dissipation rate is also used for calculating the static and dynamic Smagorinsky coefficients, the latter involving filtering at multiple scales; both vary substantially in the tip region, and neither is equal to values obtained in isotropic turbulence.

Unsteady disturbances of streaming motions around bodies

1989 ◽  
Vol 209 ◽  
pp. 385-403 ◽  
Author(s):  
H. M. Atassi ◽  
J. Grzedzinski
Keyword(s):  
Wave Equation ◽  
Body Surface ◽  
Source Term ◽  
The Body ◽  
Entire Body ◽  
Two Dimensional ◽  
Mean Flow ◽  
Inhomogeneous Wave ◽  
Inhomogeneous Wave Equation ◽  
The Mean

For small-amplitude vortical and entropic unsteady disturbances of potential flows, Goldstein proposed a partial splitting of the velocity field into a vortical part u(I) that is a known function of the imposed upstream disturbance and a potential part ∇ϕ satisfying a linear inhomogeneous wave equation with a dipole-type source term. The present paper deals with flows around bodies with a stagnation point. It is shown that for such flows u(I) becomes singular along the entire body surface and its wake and as a result ∇ϕ will also be singular along the entire body surface. The paper proposes a modified splitting of the velocity field into a vortical part u(R) that has zero streamwise and normal components along the body surface, an entropy-dependent part and a regular part ∇ϕ* that satisfies a linear inhomogeneous wave equation with a modified source term.For periodic disturbances, explicit expressions for u(R) are given for three-dimensional flows past a single obstacle and for two-dimensional mean flows past a linear cascade. For weakly sheared flows, it is shown that if the mean flow has only a finite number of isolated stagnation points, u(R) will be finite along the body surface. On the other hand, if the mean flow has a stagnation line along the body surface such as in two-dimensional flows then the component of u(R) in this direction will have a logarithmic singularity.For incompressible flows, the boundary-value problem for ϕ* is formulated in terms of an integral equation of the Fredholm type. The theory is applied to a typical bluff body. Detailed calculations are carried out to show the velocity and pressure fields in response to incident harmonic disturbances.

scholarly journals Unsteady low Reynolds number flow in a heated tube of slowly varying section

1988 ◽  
Vol 30 (2) ◽  
pp. 179-202 ◽  
Author(s):  
A. R. Bestman
Keyword(s):  
Fluid Motion ◽  
The Body ◽  
Axial Component ◽  
Axial Distance ◽  
Mean Flow ◽  
Steady Streaming ◽  
Reynolds Number Flow ◽  
Number Flow ◽  
The Mean ◽  
Oscillatory Pressure

AbstractFluid motion established by an oscillatory pressure gradient superimposed on a mean, in a tube of slowly varying section, is studied when the temperature of the tube wall varies with axial distance. Particular attention is focussed on the mean flow and steady streaming components of the oscillatory flow of higher approximation. For the velocity components, the axial component takes the pride of place, since this component is responsible for convection of nutrients to various parts of the body of a mammal in systematic circulation. A salient point in the paper concerns consequences of free convection currents at a constriction (stenosis).

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.

scholarly journals Parametrization of momentum and energy depositions from gravity waves generated by tropospheric hydrodynamic sources

1997 ◽  
Vol 15 (12) ◽  
pp. 1570-1580 ◽  
Author(s):  
N. M. Gavrilov
Keyword(s):  
Gravity Waves ◽  
Wave Energy ◽  
Internal Gravity Waves ◽  
Mean Flow ◽  
Energy Fluxes ◽  
The Mean ◽  
Turbulence Production

Abstract. The mechanism of generation of internal gravity waves (IGW) by mesoscale turbulence in the troposphere is considered. The equations that describe the generation of waves by hydrodynamic sources of momentum, heat and mass are derived. Calculations of amplitudes, wave energy fluxes, turbulent viscosities, and accelerations of the mean flow caused by IGWs generated in the troposphere are made. A comparison of different mechanisms of turbulence production in the atmosphere by IGWs shows that the nonlinear destruction of a primary IGW into a spectrum of secondary waves may provide additional dissipation of nonsaturated stable waves. The mean wind increases both the effectiveness of generation and dissipation of IGWs propagating in the direction of the wind. Competition of both effects may lead to the dominance of IGWs propagating upstream at long distances from tropospheric wave sources, and to the formation of eastward wave accelerations in summer and westward accelerations in winter near the mesopause.

Numerical study of turbulent magnetohydrodynamic channel flow

2007 ◽  
Vol 572 ◽  
pp. 179-188 ◽  
Author(s):  
THOMAS BOECK ◽  
DMITRY KRASNOV ◽  
EGBERT ZIENICKE
Keyword(s):  
Channel Flow ◽  
Numerical Study ◽  
Layer Structure ◽  
Momentum Balance ◽  
Mean Flow ◽  
Mean Velocity ◽  
Static Approximation ◽  
The Mean ◽  
Magnetohydrodynamic Channel ◽  
Normal Magnetic Field

Mean flow properties of turbulent magnetohydrodynamic channel flow with electrically insulating channel walls are studied using high-resolution direct numerical simulations. The Lorentz force due to the homogeneous wall-normal magnetic field is computed in the quasi-static approximation. For strong magnetic fields, the mean velocity profile shows a clear three-layer structure consisting of a viscous region near each wall and a plateau in the middle connected by logarithmic layers. This structure reflects the significance of viscous, turbulent, and electromagnetic stresses in the streamwise momentum balance dominating the viscous, logarithmic, and plateau regions, respectively. The width of the logarithmic layers changes with the ratio of Reynolds- and Hartmann numbers. Turbulent stresses typically decay more rapidly away from the walls than predicted by mixing-length models.

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.

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.

scholarly journals Bluff bodies in deep turbulent boundary layers: Reynolds-number issues

2007 ◽  
Vol 571 ◽  
pp. 97-118 ◽  
Author(s):  
HEE CHANG LIM ◽  
IAN P. CASTRO ◽  
ROGER P. HOXEY
Keyword(s):  
Reynolds Number ◽  
Boundary Layers ◽  
Delta Wing ◽  
Body Height ◽  
Turbulent Boundary Layers ◽  
The Body ◽  
Bluff Bodies ◽  
Mean Flow ◽  
Order Of Magnitude ◽  
The Mean

It is generally assumed that flows around wall-mounted sharp-edged bluff bodies submerged in thick turbulent boundary layers are essentially independent of the Reynolds number Re, provided that this exceeds some (2–3) × 104. (Re is based on the body height and upstream velocity at that height.) This is a particularization of the general principle of Reynolds-number similarity and it has important implications, most notably that it allows model scale testing in wind tunnels of, for example, atmospheric flows around buildings. A significant part of the literature on wind engineering thus describes work which implicitly rests on the validity of this assumption. This paper presents new wind-tunnel data obtained in the ‘classical’ case of thick fully turbulent boundary-layer flow over a surface-mounted cube, covering an Re range of well over an order of magnitude (that is, a factor of 22). The results are also compared with new field data, providing a further order of magnitude increase in Re. It is demonstrated that if on the one hand the flow around the obstacle does not contain strong concentrated-vortex motions (like the delta-wing-type motions present for a cube oriented at 45° to the oncoming flow), Re effects only appear on fluctuating quantities such as the r.m.s. fluctuating surface pressures. If, on the other hand, the flow is characterized by the presence of such vortex motions, Re effects are significant even on mean-flow quantities such as the mean surface pressures or the mean velocities near the surfaces. It is thus concluded that although, in certain circumstances and for some quantities, the Reynolds-number-independency assumption is valid, there are other important quantities and circumstances for which it is not.

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.

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