scholarly journals Impact of height heterogeneity on canopy turbulence

2017 ◽  
Vol 813 ◽  
pp. 1176-1196 ◽  
Author(s):  
A. M. Hamed ◽  
M. J. Sadowski ◽  
H. M. Nepf ◽  
L. P. Chamorro
Keyword(s):  
Reynolds Shear Stress ◽  
Turbulent Transport ◽  
Homogeneous Model ◽  
Mixing Layer ◽  
Quadrant Analysis ◽  
Base Case ◽  
Model Base ◽  
Index Matching ◽  
Refractive Index Matching ◽  
Heterogeneous Canopies

The flow development above and within homogeneous and heterogeneous canopies was experimentally studied using particle image velocimetry in a refractive-index-matching channel. The experiments were designed to gain insight into the effect of height heterogeneity on the structure and spatial distribution of the turbulence. The homogeneous model (base case) is constituted of elements of height $h$ arranged in a staggered configuration; whereas the heterogeneous canopy resembled a row canopy and consisted of elements of two heights $h_{1}=h+(1/3)h$ and $h_{2}=h-(1/3)h$ alternated every two rows. Both canopies had the same density, element geometry and mean height. The flow was studied under three submergences $H/h=2$, 3 and 4, where $H$ denotes the flow depth. The experiments were performed at Reynolds number $Re_{H}\simeq 6500$, 11 300 and 12 300 and nearly constant Froude number $Fr\simeq 0.1$. Turbulence statistics complemented with quadrant analysis and proper orthogonal decomposition reveal richer flow dynamics induced by height heterogeneity. Topography-induced spatially periodic mean flows are observed for the heterogeneous canopy. Furthermore, and in contrast to the homogeneous case, non-vanishing vertical velocity is maintained across the entire length of the heterogeneous canopy with increased levels at lower submergence depths. Further alternations were induced in the magnitude and distribution of the turbulent kinetic energy, Reynolds shear stress and characteristics of the canopy mixing layer, evidencing enhanced mixing and turbulent transport for the heterogeneous canopy especially at lower submergence depths. Overall, the results indicate that heterogeneous canopies exhibit greater vertical turbulent exchange at the canopy interface, suggesting a potential for greater scalar exchange and a greater impact on channel hydraulic resistance than a homogeneous canopy of similar roughness density.

Experimental Characterization of Slug Flow Velocity Distribution in Two Phase Pipe Flow

2009 ◽  
Author(s):  
Afshin Goharzadeh ◽  
Peter Rodgers
Keyword(s):  
Velocity Distribution ◽  
Slug Flow ◽  
Two Phase ◽  
Significant Drop ◽  
Horizontal Pipe ◽  
Measured Velocity ◽  
Air Bubble ◽  
Velocity Magnitude ◽  
Index Matching ◽  
Refractive Index Matching

This paper presents an experimental study of gas-liquid slug flow inside a horizontal pipe. The influence of air bubble passage on liquid flow is characterized using Particle Image Velocimetry (PIV) combined with Refractive Index Matching (RIM) and fluorescent tracers. A physical insight into the velocity distribution within slug flow is presented. It was observed that the slug flow significantly influences the velocity profile in the liquid film. Measured velocity distributions also revealed a significant drop in the velocity magnitude immediately upstream of the slug nose. These findings aim to aid an understanding of the mechanism of solid transportation in slug flows.

Turbulence structure of a reattaching mixing layer

1981 ◽  
Vol 110 ◽  
pp. 171-194 ◽  
Author(s):  
C. Chandrsuda ◽  
P. Bradshaw
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Reynolds Shear Stress ◽  
Mixing Layer ◽  
Three Dimensional ◽  
Flow Region ◽  
Turbulent Energy ◽  
Turbulence Structure ◽  
Hot Wire ◽  
Recirculating Flow

Hot-wire measurements of second- and third-order mean products of velocity fluctuations have been made in the flow behind a backward-facing step with a thin, laminar boundary layer at the top of the step. Measurements extend to a distance of about 12 step heights downstream of the step, and include parts of the recirculating-flow region: approximate limits of validity of hot-wire results are given. The Reynolds number based on step height is about 105, the mixing layer being fully turbulent (fully three-dimensional eddies) well before reattachment, and fairly close to self-preservation in contrast to the results of some previous workers. Rapid changes in turbulence quantities occur in the reattachment region: Reynolds shear stress and triple products decrease spectacularly, mainly because of the confinement of the large eddies by the solid surface. The terms in the turbulent energy and shear stress balances also change rapidly but are still far from the self-preserving boundary-layer state even at the end of the measurement region.

scholarly journals Refractive index matching applied to fecal smear clearing

2005 ◽  
Vol 47 (6) ◽  
pp. 347-350 ◽  
Author(s):  
Cláudio S. Ferreira
Keyword(s):  
Refractive Index ◽  
Sucrose Solution ◽  
Glycerol Solution ◽  
Human Feces ◽  
Microscope Slide ◽  
Helminth Eggs ◽  
Index Matching ◽  
Refractive Index Matching ◽  
Fecal Smear ◽  
Effect Of Light

Thick smears of human feces can be made adequate for identification of helminth eggs by means of refractive index matching. Although this effect can be obtained by simply spreading a fleck of feces on a microscope slide, a glycerol solution has been routinely used to this end. Aiming at practicability, a new quantitative technique has been developed. To enhance both sharpness and contrast of the images, a sucrose solution (refractive index = 1.49) is used, which reduces the effect of light-scattering particulates. To each slide a template-measured (38.5 mm³) fecal sample is transferred. Thus, egg counts and sensitivity evaluations are easily made.

scholarly journals Biological glass: structural determinants of eye lens transparency

2011 ◽  
Vol 366 (1568) ◽  
pp. 1250-1264 ◽  
Author(s):  
Steven Bassnett ◽  
Yanrong Shi ◽  
Gijs F. J. M. Vrensen
Keyword(s):  
Refractive Index ◽  
Cellular Level ◽  
Structural Determinants ◽  
Lens Transparency ◽  
Index Matching ◽  
Lens Fibre ◽  
Refractive Index Matching ◽  
Lens Membranes ◽  
Adhesive Proteins ◽  
Structural Adaptations

The purpose of the lens is to project a sharply focused, undistorted image of the visual surround onto the neural retina. The first pre-requisite, therefore, is that the tissue should be transparent. Despite the presence of remarkably high levels of protein, the lens cytosol remains transparent as a result of short-range-order interactions between the proteins. At a cellular level, the programmed elimination of nuclei and other light-scattering organelles from cells located within the pupillary space contributes directly to tissue transparency. Scattering at the cell borders is minimized by the close apposition of lens fibre cells facilitated by a plethora of adhesive proteins, some expressed only in the lens. Similarly, refractive index matching between lens membranes and cytosol is believed to minimize scatter. Refractive index matching between the cytoplasm of adjacent cells is achieved through the formation of cellular fusions that allow the intermingling of proteins. Together, these structural adaptations serve to minimize light scatter and enable this living, cellular structure to function as ‘biological glass’.

scholarly journals Kilowatt-level direct-‘refractive index matching liquid’-cooled Nd:YLF thin disk laser resonator

2016 ◽  
Vol 24 (2) ◽  
pp. 1758 ◽  
Author(s):  
Zhibin Ye ◽  
Chong Liu ◽  
Bo Tu ◽  
Ke Wang ◽  
Qingsong Gao ◽  
...  
Keyword(s):  
Refractive Index ◽  
Thin Disk ◽  
Laser Resonator ◽  
Disk Laser ◽  
Index Matching ◽  
Refractive Index Matching ◽  
Thin Disk Laser

scholarly journals Experimental study into the Rayleigh–Taylor turbulent mixing zone heterogeneous structure

2003 ◽  
Vol 21 (3) ◽  
pp. 375-379 ◽  
Author(s):  
Yu.A. KUCHERENKO ◽  
A.P. PYLAEV ◽  
V.D. MURZAKOV ◽  
A.V. BELOMESTNIH ◽  
V.N. POPOV ◽  
...  
Keyword(s):  
Turbulent Mixing ◽  
Measurement Errors ◽  
Density Ratio ◽  
Mixing Layer ◽  
Light Sheet ◽  
Immiscible Fluids ◽  
Heterogeneous Structure ◽  
Layer System ◽  
Glycerin Solution ◽  
Refractive Index Matching

Experiments conducted on the SOM facility at the Russian Federal Nuclear Center–VNIITF, concerning the turbulent mixing induced by the Rayleigh–Taylor instability in a three-layer system of immiscible liquids are described. The fluids are contained in a small tank 6.4 cm × 5.4 cm × 12 cm, which is accelerated vertically downward by a gas gun. The mixing layer evolution was imaged by seeding one of the fluids with particles and using a bidirectional light sheet method (refractive index matching was used to minimize measurement errors). Experiments were performed for two different accelerations (g = 350 g0 and g = 100 g0, where g0 = 980 cm/s2, and the acceleration decreases with distance traveled), and with aqueous solutions of glycerin and benzene (with density ratio 1.6). The lower, middle, and upper layers were a sodium hyposulfite–glycerin solution, a water–glycerin solution, and benzene, respectively. The glycerin solution was seeded with particles. The principal objective of the experiments was to obtain the distribution of fluid particle sizes arising from the mixing of the immiscible fluids.

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