scholarly journals Higher-Order Velocity Moments, Turbulence Scales and Energy Dissipation Rate around a Boulder in a Rock-Ramp Fish Passage

2020 ◽  
Vol 12 (13) ◽  
pp. 5385
Author(s):  
Amir Golpira ◽  
Abul BM Baki ◽  
David Z. Zhu
Keyword(s):  
Energy Dissipation ◽  
Experimental Model ◽  
Swimming Performance ◽  
Vertical Mixing ◽  
Fish Passage ◽  
Energy Dissipation Rate ◽  
Higher Order ◽  
Length Scales ◽  
Dissipation Rates ◽  
Velocity Moments

This experimental study investigated the higher-order velocity moments, turbulence time and length scales, and energy dissipation rates around an intermediately submerged boulder within a wake-interference flow regime in a rock-ramp fish passage. The results show a noticeable variation in the studied parameters in the wake of the boulder, as well as near the bed and boulder crest. The higher-order velocity moments show the presence of infrequent strong ejections downstream of the boulder, which may lead to higher sediment deposition and vertical mixing. The eddy length scales and the volumetric energy dissipation in this experimental model were discussed in relation to fish behavior for both the experimental model and a prototype. Relationships were proposed to roughly estimate integral length scales and energy dissipation rates around the boulder over the flow depth. The findings of this study may improve the design of rock-ramp fish passages considering the effects of turbulence on fish swimming performance and sediment transport.

Modelling Multiphase Jet Flows for High Velocity Emulsification

2011 ◽  
Author(s):  
David Ryan ◽  
Mark Simmons ◽  
Mike Baker
Keyword(s):  
Energy Dissipation ◽  
Turbulent Energy ◽  
Energy Dissipation Rate ◽  
Jet Flows ◽  
Nozzle Orifice ◽  
Multiphase Mixture ◽  
Dissipation Rates ◽  
Mass Flow Rates ◽  
Recirculation Zones ◽  
Drop Size Distributions

Single phase steady-state Computational Fluid Dynamics (CFD) simulations are presented for turbulent flow inside a Sonolator (an industrial static mixer). Methodology is given for obtaining high quality, converged, mesh-independent results. Pressures, velocities and local specific turbulent energy dissipation rates throughout the fluid domain are obtained for three industrially-relevant mass flow rates at a fixed nozzle orifice size. Discharge coefficients calculated at the orifice are compared to literature values and to pilot plant experiments for initial validation. Streamlines in the flow are used to illustrate the presence of recirculation zones after the nozzle. Thus, residence time and peak local specific turbulent energy dissipation rates are calculated from streamline data as a function of inlet position. Values of local specific turbulent energy dissipation rate obtained are used to infer drop sizes for emulsification of a multiphase mixture under dilute, homogeneous flow conditions. The results show that different drop size distributions may be produced depending on the inlet condition of the multiphase mixture.

scholarly journals Observations of turbulent kinetic energy dissipation at the Labrador Sea surface layer

2017 ◽  
Vol 8 (3) ◽  
pp. 161-172
Author(s):  
Silvia Gremes-Cordero
Keyword(s):  
Energy Dissipation ◽  
Kinetic Energy ◽  
Turbulent Kinetic Energy ◽  
Phytoplankton Bloom ◽  
Global Climate ◽  
Energy Dissipation Rate ◽  
Labrador Sea ◽  
Wave Phase ◽  
Dissipation Rates ◽  
First Time

We present an analysis of turbulent kinetic energy dissipation rates in the upper ocean using in situ measurements collected by a coherent Doppler sonar in the Labrador Sea during summer 2004. The sonar recorded horizontal velocity fluctuations of the upper 2 m with an uncommonly small spatial resolution of 0.8 cm, allowing direct calculations of wavenumber spectra and the application of Kolmogorov theory to obtain turbulent kinetic energy dissipation rates for the first time in this area. The project presented a unique opportunity for the study of air–sea exchange during a phytoplankton bloom, being the first time a specialized air–sea interaction spar buoy was deployed during such particular event. An additional uniqueness of this experiment resulted from being the first turbulent kinetic energy dissipation rate observations obtained at higher latitudes, coincidentally in a well-known region of dense water formation, with a fundamental role in both global circulation and forecasting studies of global climate change. Focusing on the relationship between turbulent kinetic energy dissipation rates and wave phase in the upper 2 m, we estimated O[Formula: see text] turbulent kinetic energy dissipation rates, consistent with previous estimates obtained through similar devices and methods. A T-test between dissipation rates calculated at the crest and at the trough of waves showed no dependency of turbulent kinetic energy dissipation rates on the wave phase at 2 m depth, coinciding with many of the earlier findings available. a comparison with previous research showing conflicting results with our values is also discussed here linking them to the relative roles of experimental design variations, diverse dynamical frames, and particular environmental conditions.

MEASURING ENERGY DISSIPATION RATES IN A WAVE TANK

2005 ◽  
Vol 2005 (1) ◽  
pp. 183-186 ◽  
Author(s):  
Albert D. Venosa ◽  
Vikram J. Kaku ◽  
Michel C. Boufadel ◽  
Kenneth Lee
Keyword(s):  
Energy Dissipation ◽  
Open Water ◽  
Breaking Waves ◽  
Pilot Scale ◽  
Energy Dissipation Rate ◽  
Breaking Wave ◽  
Field Scale ◽  
Wave Tank ◽  
Dissipation Rates ◽  
Wave Maker

ABSTRACT The effectiveness of dispersants is typically evaluated at various scales ranging from the smallest (10 cm, typical of flask tests in the laboratory) to the largest (10's to 100's of meters, typical of field scale open water dispersion tests). This study aims at evaluating dispersant effectiveness at intermediate or pilot scale. The hypothesis is that the energy dissipation rate per unit mass, ɛ, plays a major role in the effectiveness of a dispersant. Therefore, it is stipulated that in fairly general conditions, conservation of ɛ between the wave tank scale and that of the field scale is sufficient to accurately evaluate the effectiveness of a dispersant to disperse oil droplets. A wave tank measuring 16 m long x 0.6 m wide x 2 m deep was constructed on the premises of the Bedford Institute of Oceanography, Halifax, Nova Scotia. Waves were generated using a flap-type wave maker. Conditions of the breaking waves were created using a dispersive focusing technique in which the wave maker is started at high frequency and then the frequency decreased to create breaking waves. Experiments defining the velocity profile and energy dissipation rates in the wave tank were conducted at 2 different induced breaking-wave energies. Energy in the wave tank was measured with an Acoustic Doppler Velocimeter (ADV) coupled to a data acquisition system. Energy in the lab flasks was measured with a Hot Wire Anemometer.

MINIMUM ENERGY DISSIPATION AND FRACTAL STRUCTURES OF VASCULAR SYSTEMS

Fractals ◽  
1995 ◽  
Vol 03 (01) ◽  
pp. 123-153 ◽  
Author(s):  
TAO SUN ◽  
PAUL MEAKIN ◽  
TORSTEIN JØSSANG
Keyword(s):  
Fractal Dimension ◽  
Energy Dissipation ◽  
Dissipation Rate ◽  
Vascular System ◽  
Minimum Energy ◽  
Energy Dissipation Rate ◽  
Power Law Distribution ◽  
Fractal Structures ◽  
Length Scales ◽  
Minimum Energy Dissipation

A two dimensional minimum energy dissipation rate model has been used to study the structure of vascular networks. The geometry of the resulting minimum energy dissipation rate vascular system (MEDVS) has been studied. The structures of MEDVS networks are self-similar and have a fractal dimension of 2 on long length scales with a crossover to a fractal dimension of 1 on short length scales. A power-law distribution of link energy dissipation rates was found. The MEDVS networks have also been studied in terms of their transport properties.

scholarly journals Estimating the population mean for a vertical profile of energy dissipation rate

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Nozomi Sugiura ◽  
Shinya Kouketsu ◽  
Shuhei Masuda ◽  
Satoshi Osafune ◽  
Ichiro Yasuda
Keyword(s):  
Energy Dissipation ◽  
Energy Dissipation Rate ◽  
Observational Constraints ◽  
Observation Data ◽  
Ocean Energy ◽  
Population Mean ◽  
Oceanic Turbulence ◽  
Statistical Property ◽  
Dissipation Rates ◽  
Vertical Evolution

AbstractEnergy dissipation rates are an important characteristic of turbulence; however, their magnitude in observational profiles can be incorrectly determined owing to their irregular appearance during vertical evolution. By analysing the data obtained from oceanic turbulence measurements, we demonstrate that the vertical sequences of energy dissipation rates exhibit a scaling property. Utilising this property, we propose a method to estimate the population mean for a profile. For scaling in the observed profiles, we demonstrate that our data exhibit a statistical property consistent with that exhibited by the universal multifractal model. Meanwhile, the population mean and its uncertainty can be estimated by inverting the probability distribution obtained by Monte Carlo simulations of a cascade model; to this end, observational constraints from several moments are imposed over each vertical sequence. This approach enables us to determine, to some extent, whether a profile shows an occasionally large mean or whether the population mean itself is large. Thus, it will contribute to the refinement of the regional estimation of the ocean energy budget, where only a small amount of turbulence observation data is available.

Energy dissipation rate in a baffled vessel with pitched blade turbine impeller

1991 ◽  
Vol 56 (9) ◽  
pp. 1856-1867 ◽  
Author(s):  
Zdzisław Jaworski ◽  
Ivan Fořt
Keyword(s):  
Energy Dissipation ◽  
Cross Sections ◽  
Mechanical Energy ◽  
Vessel Diameter ◽  
Energy Dissipation Rate ◽  
Mean Velocity ◽  
Agitated Vessel ◽  
Radial Profiles ◽  
Pitched Blade Turbine ◽  
Turbine Impeller

Mechanical energy dissipation was investigated in a cylindrical, flat bottomed vessel with four radial baffles and the pitched blade turbine impeller of varied size. This study was based upon the experimental data on the hydrodynamics of the turbulent flow of water in an agitated vessel. They were gained by means of the three-holes Pitot tube technique for three impeller-to-vessel diameter ratio d/D = 1/3, 1/4 and 1/5. The experimental results obtained for two levels below and two levels above the impeller were used in the present study. Radial profiles of the mean velocity components, static and total pressures were presented for one of the levels. Local contribution to the axial transport of the agitated charge and energy was presented. Using the assumption of the axial symmetry of the flow field the volumetric flow rates were determined for the four horizontal cross-sections. Regions of positive and negative values of the total pressure of the liquid were indicated. Energy dissipation rates in various regions of the agitated vessel were estimated in the range from 0.2 to 6.0 of the average value for the whole vessel. Hydraulic impeller efficiency amounting to about 68% was obtained. The mechanical energy transferred by the impellers is dissipated in the following ways: 54% in the space below the impeller, 32% in the impeller region, 14% in the remaining part of the agitated liquid.

Observations of Small-Scale Turbulence and Energy Dissipation Rates in the Cloudy Boundary Layer

2006 ◽  
Vol 63 (5) ◽  
pp. 1451-1466 ◽  
Author(s):  
Holger Siebert ◽  
Katrin Lehmann ◽  
Manfred Wendisch
Keyword(s):  
Boundary Layer ◽  
Energy Dissipation ◽  
Wind Velocity ◽  
Turbulence Theory ◽  
Horizontal Wind ◽  
Inertial Subrange ◽  
Intermittent Flow ◽  
Small Scale ◽  
Dissipation Rates ◽  
Wide Range

Abstract Tethered balloon–borne measurements with a resolution in the order of 10 cm in a cloudy boundary layer are presented. Two examples sampled under different conditions concerning the clouds' stage of life are discussed. The hypothesis tested here is that basic ideas of classical turbulence theory in boundary layer clouds are valid even to the decimeter scale. Power spectral densities S( f ) of air temperature, liquid water content, and wind velocity components show an inertial subrange behavior down to ≈20 cm. The mean energy dissipation rates are ∼10−3 m2 s−3 for both datasets. Estimated Taylor Reynolds numbers (Reλ) are ∼104, which indicates the turbulence is fully developed. The ratios between longitudinal and transversal S( f ) converge to a value close to 4/3, which is predicted by classical turbulence theory for local isotropic conditions. Probability density functions (PDFs) of wind velocity increments Δu are derived. The PDFs show significant deviations from a Gaussian distribution with longer tails typical for an intermittent flow. Local energy dissipation rates ɛτ are derived from subsequences with a duration of τ = 1 s. With a mean horizontal wind velocity of 8 m s−1, τ corresponds to a spatial scale of 8 m. The PDFs of ɛτ can be well approximated with a lognormal distribution that agrees with classical theory. Maximum values of ɛτ ≈ 10−1 m2 s−3 are found in the analyzed clouds. The consequences of this wide range of ɛτ values for particle–turbulence interaction are discussed.

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