scholarly journals On the Evolution of the Integral Time Scale within Wind Farms

Energies ◽  
2018 ◽  
Vol 11 (1) ◽  
pp. 93 ◽  
Author(s):  
Huiwen Liu ◽  
Imran Hayat ◽  
Yaqing Jin ◽  
Leonardo Chamorro
Keyword(s):  
Time Scale ◽  
Wind Farms ◽  
Integral Time Scale ◽  
Integral Time

scholarly journals Turbulent dispersion properties from a model simulation of the western Mediterranean

2013 ◽  
Vol 10 (4) ◽  
pp. 1099-1125
Author(s):  
H. Nefzi ◽  
D. Elhmaidi ◽  
X. Carton
Keyword(s):  
Time Scale ◽  
Model Simulation ◽  
Western Mediterranean ◽  
Turbulent Dispersion ◽  
Chaotic Advection ◽  
Relative Dispersion ◽  
Integral Time Scale ◽  
Dispersion Properties ◽  
Integral Time ◽  
Relative Diffusivity

Abstract. Using a high resolution primitive equation model of the western Mediterranean Sea, we analyzed the dispersion properties of a set of homogeneously distributed, passive particle pairs. These particles were initially separated by different distances D0 (D0 = 5.55, 11.1 and 16.5 km), and were seeded in the model at initial depths of 44 and 500 m. This realistic ocean model, which reproduces the main features of the regional circulation, puts in evidence the three well-known regimes of relative dispersion. The first regime due to the chaotic advection at small scales, lasts only a few days (3 days at 44 m depth, a duration comparable with the integral time scale) and the relative dispersion is then exponential. In the second regime, extending from 3 to 20 days, the relative dispersion has a power law tα where α tends to 3 as D0 becomes small. In the third regime, a linear growth of the relative dispersion is observed starting from the twentieth day. For the relative diffusivity, the D2 growth is followed by the Richardson regime D4/3. At large scales, where particle velocities are decorrelated, the relative diffusivity is constant. At 500 m depth, the integral time scale increases (> 4 days) and the intermediate regime becomes narrower than that at 44 m depth due to weaker effect of vortices (this effect decreases with depth). The turbulent properties become less intermittent and more homogeneous and the Richardson law takes place.

Influence of the Lagrangian Integral Time Scale Estimation in the Near Wall Region on Particle Deposition

2012 ◽  
Vol 134 (7) ◽  
Author(s):  
Grégory Lecrivain ◽  
Uwe Hampel
Keyword(s):  
High Temperature ◽  
Particle Tracking ◽  
Time Scale ◽  
Particle Deposition ◽  
Normal Component ◽  
Turbulent Dispersion ◽  
Primary Circuit ◽  
Wall Region ◽  
Integral Time Scale ◽  
Integral Time

In a high temperature pebble-bed reactor core where thousands of pebbles are amassed, the friction between the outer graphite layer of the fuel elements triggers the formation of carbonaceous dust. This dust is eventually conveyed by the cooling carrier phase and deposits in the primary circuit of the high temperature reactor. The numerical prediction of carbonaceous dust transport and deposition in turbulent flows is a key safety issue. Most particle tracking procedures make use of the Lagrangian integral time scale to reproduce the turbulent dispersion of the discrete phase. In the present Lagrangian particle tracking procedure, the effect of the Lagrangian integral time scale near the wall is thoroughly investigated. It is found that, in the linear sublayer, a value of the normalized wall normal component of the Lagrangian integral time scale lower that 4 delivers accurate particle deposition velocities. The value worked out here near the wall region is in accordance with Lagrangian integral time scales derived from recent direct numerical simulations.

scholarly journals A Standard Criterion for Measuring Turbulence Quantities Using the Four-Receiver Acoustic Doppler Velocimetry

2021 ◽  
Vol 8 ◽  
Author(s):  
Hyoungchul Park ◽  
Jin Hwan Hwang
Keyword(s):  
Time Scale ◽  
Transverse Velocity ◽  
Sampling Period ◽  
Optimal Sampling ◽  
Doppler Velocimetry ◽  
Reynolds Stresses ◽  
Bootstrap Sampling ◽  
Integral Time Scale ◽  
Integral Time ◽  
Acoustic Doppler Velocimetry

Acoustic Doppler velocimetry (ADV) enables three-dimensional turbulent flow fields to be obtained with high spatial and temporal resolutions in the laboratory, rivers, and oceans. Although such advantages have led ADV to become a typical approach for analyzing various fluid dynamics mechanisms, the vagueness of ADV system operation methods has reduced its accuracy and efficiency. Accordingly, the present work suggests a proper measurement strategy for a four-receiver ADV system to obtain reliable turbulence quantities by performing laboratory experiments under two flow conditions. Firstly, in still water, the magnitude of noises was evaluated and a proper operation method was developed to obtain the Reynolds stress with lower noises. Secondly, in channel flows, an optimal sampling period was determined based on the integral time scale by applying the bootstrap sampling method and reverse arrangement test. The results reveal that the noises of the streamwise and transverse velocity components are an order of magnitude larger than those of the vertical velocity components. The orthogonally paired receivers enable the estimation of almost-error-free Reynolds stresses and the optimal sampling period is 150–200 times the integral time scale, regardless of the measurement conditions.

Inhomogeneous Structure in High-Speed and High-Number-Density Sprays

2011 ◽  
Author(s):  
Noritsune Kawaharada ◽  
Daisaku Sakaguchi ◽  
Keisuke Komada ◽  
Hironobu Ueki ◽  
Masahiro Ishida
Keyword(s):  
Diesel Fuel ◽  
Time Scale ◽  
High Speed ◽  
Sampling Rate ◽  
Data Sampling ◽  
Integral Time Scale ◽  
Fuel Sprays ◽  
Integral Time ◽  
Data Sampling Rate ◽  
Almost All

A L2F (Laser 2-Focus velocimeter) was applied for the measurements of the velocity and size of droplets in diesel fuel sprays. The micro-scale probe of the L2F has an advantage in avoiding the multiple scattering from droplets in a dense region of fuel sprays. A data sampling rate of 15MHz has been achieved in the L2F system for detecting almost all of the droplets which passed through the measurement probe. Diesel fuel was injected into the atmosphere by using a common rail injector. Measurement positions were located in the planes 15, 20, and 25 mm apart from the injector nozzle exit. Measurement result showed that the integral time scale of turbulence in size was nearly the same as the one in frequency. And the integral time scale of turbulence in velocity was about two times larger than the time scale of size and frequency.

An Analytical Study of Turbulent Dispersion of Bubbles

2001 ◽  
Author(s):  
Anthony L. Lawson ◽  
Ramkumar N. Parthasarathy
Keyword(s):  
Root Mean Square ◽  
Time Scale ◽  
Liquid Velocity ◽  
Added Mass ◽  
Mean Square ◽  
Rise Velocity ◽  
Velocity Fluctuations ◽  
Bubble Rise ◽  
Integral Time Scale ◽  
Bubble Rise Velocity

Abstract An analysis of the dispersion of bubbles in homogenous and isotropic turbulent liquid flows was performed to study the effects of bubble and flow characteristics on their dispersion. Bubbles were assumed to be spherical and to follow the fluid motion in the mean. No mass transfer occurred between the bubble and liquid; also, there was no interaction between individual bubbles. It was found that for accurate prediction of bubble dispersion requires a simultaneous consideration of the inertia of the added mass of liquid (because the inertia of the bubble itself is small) and the bubble rise velocity. Normalized bubble diffusivity, root-mean-square fluctuating velocity, and Lagrangian integral time scale were related to two non-dimensional parameters: ratio of the added mass response time to the liquid flow integral time scale, and the ratio of the bubble rise velocity to the root-mean-square liquid velocity fluctuation. In general, the bubble Lagrangian velocity auto-correlations decreased as the rise velocity ratio increased. The dependence of the autocorrelations on the time-scale ratio was complex. A surprising result was that the bubble velocity fluctuations could exceed the liquid velocity fluctuations for certain conditions because of their low inertia.

scholarly journals Relating Eulerian and Lagrangian Statistics for the Turbulent Dispersion in the Atmospheric Convective Boundary Layer

2005 ◽  
Vol 62 (4) ◽  
pp. 1175-1191 ◽  
Author(s):  
Alessandro Dosio ◽  
Jordi Vilá Guerau de Arellano ◽  
Albert A. M. Holtslag ◽  
Peter J. H. Builtjes
Keyword(s):  
Boundary Layer ◽  
Time Scales ◽  
Convective Boundary Layer ◽  
Time Scale ◽  
Vertical Motion ◽  
Horizontal Motion ◽  
Convective Boundary ◽  
Lagrangian Statistics ◽  
Integral Time ◽  
Capping Inversion

Abstract Eulerian and Lagrangian statistics in the atmospheric convective boundary layer (CBL) are studied by means of large eddy simulation (LES). Spectra analysis is performed in both the Eulerian and Lagrangian frameworks, autocorrelations are calculated, and the integral length and time scales are derived. Eulerian statistics are calculated by means of spatial and temporal analysis in order to derive characteristic length and time scales. Taylor’s hypothesis of frozen turbulence is investigated, and it is found to be satisfied in the simulated flow. Lagrangian statistics are derived by tracking the trajectories of numerous particles released at different heights in the turbulent flow. The relationship between Lagrangian properties (autocorrelation functions) and dispersion characteristics (particles’ displacement) is studied through Taylor’s diffusion relationship, with special emphasis on the difference between horizontal and vertical motion. Results show that for the horizontal motion, Taylor’s relationship is satisfied. The vertical motion, however, is influenced by the inhomogeneity of the flow and limited by the ground and the capping inversion at the top of the CBL. The Lagrangian autocorrelation function, therefore, does not have an exponential shape, and consequently, the integral time scale is zero. If distinction is made between free and bounded motion, a better agreement between Taylor’s relationship and the particles’ vertical displacement is found. Relationships between Eulerian and Lagrangian frameworks are analyzed by calculating the ratio β between Lagrangian and Eulerian time scales. Results show that the integral time scales are mainly constant with height for z/zi < 0.7. In the upper part of the CBL, the capping inversion transforms vertical motion into horizontal motion. As a result, the horizontal time scale increases with height, whereas the vertical one is reduced. Current parameterizations for the ratio between the Eulerian and Lagrangian time scales have been tested against the LES results showing satisfactory agreement at heights z/zi < 0.7.

scholarly journals Multi-time scale energy management of wind farms based on comprehensive evaluation technology

2017 ◽  
Vol 93 ◽  
pp. 012066
Author(s):  
Y P Xu ◽  
Y H Huang ◽  
Z J Liu ◽  
Y F Wang ◽  
Z Y Li ◽  
...  
Keyword(s):  
Energy Management ◽  
Time Scale ◽  
Comprehensive Evaluation ◽  
Wind Farms

Large-scale Motion of Solar Filaments

2000 ◽  
Vol 179 ◽  
pp. 205-208
Author(s):  
Pavel Ambrož ◽  
Alfred Schroll
Keyword(s):  
Magnetic Flux ◽  
Proper Motion ◽  
Time Scale ◽  
Large Scale ◽  
Accuracy Of Measurements ◽  
Solar Filaments ◽  
General Movement ◽  
Scale Motion ◽  
Velocity Scatter

AbstractPrecise measurements of heliographic position of solar filaments were used for determination of the proper motion of solar filaments on the time-scale of days. The filaments have a tendency to make a shaking or waving of the external structure and to make a general movement of whole filament body, coinciding with the transport of the magnetic flux in the photosphere. The velocity scatter of individual measured points is about one order higher than the accuracy of measurements.

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