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.

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.

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.

Publisher’s Note: “Tensorial time scale in turbulent gradient transport of Reynolds stresses” [Phys. Fluids 17, 071701 (2005)]

2005 ◽  
Vol 17 (9) ◽  
pp. 099901
Author(s):  
Choong Won Cho ◽  
Myung Kyoon Chung ◽  
Kyoungyoun Kim ◽  
Hyung Jin Sung
Keyword(s):  
Time Scale ◽  
Reynolds Stresses

A novel photonic Doppler velocimetry for transverse velocity measurement

2013 ◽  
Vol 84 (1) ◽  
pp. 013101 ◽  
Author(s):  
Guanghua Chen ◽  
Detian Wang ◽  
Jun Liu ◽  
Jianhua Meng ◽  
Shouxian Liu ◽  
...  
Keyword(s):  
Velocity Measurement ◽  
Transverse Velocity ◽  
Doppler Velocimetry ◽  
Photonic Doppler Velocimetry

Experimental Study of the Type VI Stilling Basin Performance

2015 ◽  
Vol 137 (3) ◽  
Author(s):  
Seyed Sobhan Aleyasin ◽  
Nima Fathi ◽  
Peter Vorobieff
Keyword(s):  
Experimental Study ◽  
Kinetic Energy ◽  
River Flow ◽  
Doppler Velocimetry ◽  
Huge Amount ◽  
Stilling Basin ◽  
Stilling Basins ◽  
Turbulence Data ◽  
Flow Turbulence ◽  
Acoustic Doppler Velocimetry

Understanding the estuarine turbulent flow from dams, channels, and pipes, as well as the river flow are very important due to the potential to cause damage to the bed of the river or channel and cause scouring of structures such as the saddles of bridges, because of the huge amount of the kinetic energy carried by the flow. One of the most efficient yet simple ways to dissipate this energy is to install a stilling basin at the discharge point to calm the flow. Turbulence data were recorded using acoustic Doppler velocimetry (ADV) for type VI2 of stilling basins for pipe outlets. During the study, various splitters and a cellular baffle were placed in the stilling basin, and the baffle locations were changed to assess the effect on the energy dissipation. Velocity at several locations in the basin was measured for different Froude numbers to investigate the effect of flow rate. Based on the findings of the experiments, several suggestions regarding the efficiency and geometry of stilling basins were made.

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