Experiments on the stability and transition of wind-driven water surfaces

2001 ◽  
Vol 446 ◽  
pp. 25-65 ◽  
Author(s):  
FABRICE VERON ◽  
W. KENDALL MELVILLE
Keyword(s):  
Surface Current ◽  
Field Measurements ◽  
Surface Flow ◽  
Transition To Turbulence ◽  
Surface Velocity ◽  
Small Scale ◽  
Gas Transfer ◽  
Water Surfaces ◽  
Langmuir Circulations ◽  
The Stability

We present the results of laboratory and field measurements on the stability of wind-driven water surfaces. The laboratory measurements show that when exposed to an increasing wind starting from rest, surface current and wave generation is accompanied by a variety of phenomena that occur over comparable space and time scales. Of particular interest is the generation of small-scale, streamwise vortices, or Langmuir circulations, the clear influence of the circulations on the structure of the growing wave field, and the subsequent transition to turbulence of the surface flow. Following recent work by Melville, Shear & Veron (1998) and Veron & Melville (1999b), we show that the waves that are initially generated by the wind are then strongly modulated by the Langmuir circulations that follow. Direct measurements of the modulated wave variables are qualitatively consistent with geometrical optics and wave action conservation, but quantitative comparison remains elusive. Within the range of parameters of the experiments, both the surface waves and the Langmuir circulations first appear at constant Reynolds numbers of 370 ± 10 and 530 ± 20, respectively, based on the surface velocity and the depth of the laminar shear layer. The onset of the Langmuir circulations leads to a significant increase in the heat transfer across the surface. The field measurements in a boat basin display the same phenomena that are observed in the laboratory. The implications of the measurements for air–sea fluxes, especially heat and gas transfer, and sea-surface temperature, are discussed.

scholarly journals Photogrammetry for Free Surface Flow Velocity Measurement: From Laboratory to Field Measurements

Water ◽  
2021 ◽  
Vol 13 (12) ◽  
pp. 1675
Author(s):  
Hang Trieu ◽  
Per Bergström ◽  
Mikael Sjödahl ◽  
J. Gunnar I. Hellström ◽  
Patrik Andreasson ◽  
...  
Keyword(s):  
Free Surface ◽  
Particle Tracking ◽  
Field Measurements ◽  
Free Surface Flow ◽  
Surface Flow ◽  
Hydropower Plant ◽  
Surface Velocity ◽  
Camera System ◽  
Particle Tracking Method ◽  
Calibration Methods

This study describes a multi-camera photogrammetric approach to measure the 3D velocity of free surface flow. The properties of the camera system and particle tracking velocimetry (PTV) algorithm were first investigated in a measurement of a laboratory open channel flow to prepare for field measurements. The in situ camera calibration methods corresponding to the two measurement situations were applied to mitigate the instability of the camera mechanism and camera geometry. There are two photogrammetry-based PTV algorithms presented in this study regarding different types of surface particles employed on the water flow. While the first algorithm uses the particle tracking method applied for individual particles, the second algorithm is based on correlation-based particle clustering tracking applied for clusters of small size particles. In the laboratory, reference data are provided by particle image velocimetry (PIV) and laser Doppler velocimetry (LDV). The differences in velocities measured by photogrammetry and PIV, photogrammetry and LDV are 0.1% and 3.6%, respectively. At a natural river, the change of discharges between two measurement times is found to be 15%, and the corresponding value reported regarding mass flow through a nearby hydropower plant is 20%. The outcomes reveal that the method can provide a reliable estimation of 3D surface velocity with sufficient accuracy.

scholarly journals Measurement of turbulence in the oceanic mixed layer using Synthetic Aperture Radar (SAR)

2012 ◽  
Vol 9 (5) ◽  
pp. 2851-2883 ◽  
Author(s):  
S. G. George ◽  
A. R. L. Tatnall
Keyword(s):  
Surface Layer ◽  
Synthetic Aperture Radar ◽  
Wave Interaction ◽  
Surface Current ◽  
Surface Flow ◽  
Synthetic Aperture ◽  
Small Scale ◽  
Radar Images ◽  
The Impact ◽  
Aperture Radar

Abstract. Turbulence in the surface layer of the ocean contributes to the transfer of heat, gas and momentum across the air-sea boundary. As such, study of turbulence in the ocean surface layer is becoming increasingly important for understanding its effects on climate change. Direct Numerical Simulation (DNS) techniques were implemented to examine the interaction of small-scale wake turbulence in the upper ocean layer with incident electromagnetic radar waves. Hydrodynamic-electromagnetic wave interaction models were invoked to demonstrate the ability of Synthetic Aperture Radar (SAR) to observe and characterise surface turbulent wake flows. A range of simulated radar images are presented for a turbulent surface current field behind a moving surface vessel, and compared with the surface flow fields to investigate the impact of turbulent currents on simulated radar backscatter. This has yielded insights into the feasibility of resolving small-scale turbulence with remote-sensing radar and highlights the potential for extracting details of the flow structure and characteristics of turbulence using SAR.

The behaviour of naturally oscillating three-dimensional flow around a cylinder

1978 ◽  
Vol 85 (1) ◽  
pp. 161-186 ◽  
Author(s):  
Claude Tournier ◽  
Bernard Py
Keyword(s):  
Cross Section ◽  
Velocity Gradient ◽  
Three Dimensional ◽  
Surface Flow ◽  
Surface Velocity ◽  
Small Scale ◽  
Spanwise Direction ◽  
Wave System ◽  
Natural Oscillations ◽  
Stagnation Region

Split-film electrochemical transducer theory is briefly outlined so as to show its ability to separate statistical properties of each component of the surface velocity gradient in regions as different as a boundary layer, a separated zone and a three-dimensional separation line. A lot of measurements of the flow field near a cylinder which are not yet available elsewhere are carried out everywhere on the cross-section of a yawed cylinder. A direct verification of the independence principle and Wild's thermal analogy in separated zones is executed. The periodic and random parts of each component of the surface velocity gradient are separated. Cross-spectral analysis between any pair of points shows that the periodic surface flow is coherent upon any cross-section and in a large region in the spanwise direction. The stationary wave system is investigated in space and time. The reconstitution, instant by instant, of the averaged integral wall streamlines leads to an understanding of the synchronization of the natural oscillations. The four main stagnation or separation lines quickly move from one extreme position to the other, and at certain times contrary vortices stretching in the direction of the generators can appear. In the rearward stagnation region random small-scale fluctuations are probably turbulent, but in the intermediate region high-level random fluctuations in the spanwise direction are much more coherent and probably contribute to keeping the flow in phase at large distances.

scholarly journals STUDI STABILITAS SISTEM SUB SURFACE FLOW CONSTRUCTED WETLAND (SSF-CW) MENGGUNAKAN TANAMAN MELATI AIR DAN MEDIA TANAM ZEOLIT DALAM MENURUNKAN LOGAM Hg

2019 ◽  
Vol 1 (01) ◽  
pp. 17-27
Author(s):  
Angge Dhevi Warisaura ◽  
Ilma Fadlilah ◽  
Agus Prasetya ◽  
Moh. Fahrurrozi
Keyword(s):  
Constructed Wetland ◽  
Mine Waste ◽  
Surface Flow ◽  
Small Scale ◽  
Growth Media ◽  
Direct Mercury Analyzer ◽  
The Stability ◽  
Inlet Zone ◽  
Simple Technology ◽  
Two Stages

Amalgamation to gold in artisanal small scale generally uses mercury (Hg) that decrease the quality of environment especially water. A study of mercury artisanal small scale gold mine waste water was conducted by utilizing simple technology using Sub Surface Flow - Constructed Wetland (SSF-CW) system.   This system is a combination of phytoremediation methods using Echinodorus palaefolius plant with zeolite as growth media. The purpose of this study was to determine the stability of SSF-CW in reducing Hg concentration in water. This SSF-CW system model has dimensions of 820 mm x 320 mm x 585 mm consisting of 3 zones, namely the inlet zone, the reaction zone and the outlet zone. The study was conducted with an initial HgCl2 waste concentration of 14.94 mg / L which was carried out in two stages, continuous and batch for 12 hours and lasted for 3 days for each stage. Effluent samples were taken every 0 hours, 4 hours, 8 hours, and 12 hours for mercury concentration analysis using Direct Mercury Analyzer (DMA). The result showed that SSF-CW could support the process of reducing Hg concentration n wastewater with removal efficiency of 98.99%. Echinodorus had the ability to accumulate metals with a BCF value of 9,117.  and the accumulation of Hg in the zeolite (as growth media) was still far from the saturated capacity to absorb mercury

scholarly journals Transition to turbulence through steep global-modes cascade in an open rotating cavity

2011 ◽  
Vol 688 ◽  
pp. 493-506 ◽  
Author(s):  
Bertrand Viaud ◽  
Eric Serre ◽  
Jean-Marc Chomaz
Keyword(s):  
Threshold Value ◽  
Secondary Instability ◽  
Base Flow ◽  
Transition To Turbulence ◽  
Small Scale ◽  
Global Mode ◽  
Rotating Boundary ◽  
The Stability ◽  
Real Flow ◽  
Secondary Instabilities

AbstractThe transition to turbulence in a rotating boundary layer is analysed via direct numerical simulation (DNS) in an annular cavity made of two parallel corotating discs of finite radial extent, with a forced inflow at the hub and free outflow at the rim. In a former numerical investigation (Viaud, Serre & Chomaz J. Fluid Mech., vol. 598, 2008, pp. 451–464) realized in a sectorial cavity of azimuthal extent $2\lrm{\pi} / 68$, we have established the existence of a primary bifurcation to nonlinear global mode with angular phase velocity and radial envelope coherent with the so-called elephant mode theory. The former study has demonstrated the subcritical nature of this primary bifurcation with a base flow that keeps being linearly stable for all Reynolds numbers studied. The present work investigates the stability of this elephant mode by extending the cavity both in the radial and azimuthal direction. When the Reynolds number based on the forced throughflow is increased above a threshold value for the existence of the nonlinear global mode, a large-amplitude impulsive perturbation gives rise to a self-sustained saturated wave with characteristics identical to the 68-fold global elephant mode obtained in the smaller cavity. This saturated wave is itself globally unstable and a second front appears in the lee of the primary where small-scale instability develops. These secondary instabilities are identical for the $2\lrm{\pi} / 68$ and the $2\lrm{\pi} / 4$ long sectorial cavities, indicating that transition involves a Floquet mode of zero azimuthal wavenumber. This secondary instability leads to a very disorganized state, defining the transition to turbulence. The observed transition to turbulence linked to the secondary instability of a global mode confirms, for the first time on a real flow, the possibility of a direct transition to turbulence through an elephant mode cascade, a scenario that was up to now only observed on the Ginzburg–Landau model.

PIV field measurements of surface flow on a river by using a helicopter

2001 ◽  
Vol 21 (2Supplement) ◽  
pp. 61-62
Author(s):  
Ichiro FUJITA ◽  
Shiro AYA ◽  
Masahiro TAMAI ◽  
Kohsei TAKEHARA ◽  
Hitoshi MIYAMOTO ◽  
...  
Keyword(s):  
Field Measurements ◽  
Surface Flow

scholarly journals Experimental and theoretical progress in pipe flow transition

2008 ◽  
Vol 366 (1876) ◽  
pp. 2671-2684 ◽  
Author(s):  
A.P Willis ◽  
J Peixinho ◽  
R.R Kerswell ◽  
T Mullin
Keyword(s):  
Pipe Flow ◽  
Quantitative Agreement ◽  
Travelling Wave ◽  
Turbulent Pipe Flow ◽  
Transition To Turbulence ◽  
Reynolds Number Flow ◽  
Threshold Amplitude ◽  
Number Flow ◽  
The Stability ◽  
Laminar State

There have been many investigations of the stability of Hagen–Poiseuille flow in the 125 years since Osborne Reynolds' famous experiments on the transition to turbulence in a pipe, and yet the pipe problem remains the focus of attention of much research. Here, we discuss recent results from experimental and numerical investigations obtained in this new century. Progress has been made on three fundamental issues: the threshold amplitude of disturbances required to trigger a transition to turbulence from the laminar state; the threshold Reynolds number flow below which a disturbance decays from turbulence to the laminar state, with quantitative agreement between experimental and numerical results; and understanding the relevance of recently discovered families of unstable travelling wave solutions to transitional and turbulent pipe flow.

scholarly journals Monitoring Lakes Surface Water Velocity with SAR: A Feasibility Study on Lake Garda, Italy

2021 ◽  
Vol 13 (12) ◽  
pp. 2293
Author(s):  
Marina Amadori ◽  
Virginia Zamparelli ◽  
Giacomo De Carolis ◽  
Gianfranco Fornaro ◽  
Marco Toffolon ◽  
...  
Keyword(s):  
Surface Water ◽  
Wind Waves ◽  
Test Site ◽  
Water Velocity ◽  
Surface Velocity ◽  
Medium Size ◽  
Small Scale ◽  
Lake Garda ◽  
Marine Applications

The SAR Doppler frequencies are directly related to the motion of the scatterers in the illuminated area and have already been used in marine applications to monitor moving water surfaces. Here we investigate the possibility of retrieving surface water velocity from SAR Doppler analysis in medium-size lakes. ENVISAT images of the test site (Lake Garda) are processed and the Doppler Centroid Anomaly technique is adopted. The resulting surface velocity maps are compared with the outputs of a hydrodynamic model specifically validated for the case study. Thermal images from MODIS Terra are used in support of the modeling results. The surface velocity retrieved from SAR is found to overestimate the numerical results and the existence of a bias is investigated. In marine applications, such bias is traditionally removed through Geophysical Model Functions (GMFs) by ascribing it to a fully developed wind waves spectrum. We found that such an assumption is not supported in our case study, due to the small-scale variations of topography and wind. The role of wind intensity and duration on the results from SAR is evaluated, and the inclusion of lake bathymetry and the SAR backscatter gradient is recommended for the future development of GMFs suitable for lake environments.

scholarly journals Surface kinetic energy transfer in surface quasi-geostrophic flows

2008 ◽  
Vol 604 ◽  
pp. 165-174 ◽  
Author(s):  
XAVIER CAPET ◽  
PATRICE KLEIN ◽  
BACH LIEN HUA ◽  
GUILLAUME LAPEYRE ◽  
JAMES C. MCWILLIAMS
Keyword(s):  
Kinetic Energy ◽  
Surface Velocity ◽  
Small Scale ◽  
Surface Dynamics ◽  
Spectral Flux ◽  
Advection Term ◽  
Wide Range ◽  
Geostrophic Flows ◽  
Scale Range ◽  
Density Variance

The relevance of surface quasi-geostrophic dynamics (SQG) to the upper ocean and the atmospheric tropopause has been recently demonstrated in a wide range of conditions. Within this context, the properties of SQG in terms of kinetic energy (KE) transfers at the surface are revisited and further explored. Two well-known and important properties of SQG characterize the surface dynamics: (i) the identity between surface velocity and density spectra (when appropriately scaled) and (ii) the existence of a forward cascade for surface density variance. Here we show numerically and analytically that (i) and (ii) do not imply a forward cascade of surface KE (through the advection term in the KE budget). On the contrary, advection by the geostrophic flow primarily induces an inverse cascade of surface KE on a large range of scales. This spectral flux is locally compensated by a KE source that is related to surface frontogenesis. The subsequent spectral budget resembles those exhibited by more complex systems (primitive equations or Boussinesq models) and observations, which strengthens the relevance of SQG for the description of ocean/atmosphere dynamics near vertical boundaries. The main weakness of SQG however is in the small-scale range (scales smaller than 20–30 km in the ocean) where it poorly represents the forward KE cascade observed in non-QG numerical simulations.

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