scholarly journals Wind-Tunnel Experiments on Blowing Snow

1985 ◽  
Vol 6 ◽  
pp. 63-67 ◽  
Author(s):  
N. Maeno ◽  
R. Naruse ◽  
K. Nishimura ◽  
I. Takei ◽  
T. Ebinuma ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Pressure Gradient ◽  
Blowing Snow ◽  
Wind Tunnel Experiments ◽  
Complex Dynamic ◽  
Turbulent Diffusion Coefficient ◽  
Wide Range ◽  
The Mean ◽  
Cold Wind ◽  
Snow Drifting

Blowing snow was produced artificially in a cold wind-tunnel, and various measurements were conducted including particle diameters, concentrations, saltation lengths heat transport and electric charge. The mean diameter of blowing snow particles decreased only slightly with increasing height; in the saltation layer, standard deviation was large and velocities were scattered in a wide range, suggesting the complex dynamic process on taking-off. The mean saltation length ranged from a few cm to 40 cm increasing with wind velocity.When wind blew without snow drifting, the static air pressure on the snow surface was smaller at higher levels, the vertical pressure gradient being negative. The pressure gradient became positive when blowing snow was initiated eg +9.6 Pa/m at 11.2 m/s and -8.3 °C. The magnitude of à downward force acting on a saltating snow partice caused by the pressure gradient was not large enough to explain the downward acceleration found from photographic analyses of particle trajectories.Blowing snow particles were charged negatively the magnitude of charge increased with lowering temperature. Increase in vertical heat transfer was found in blowing snow by measuring the temperature of the air at various levels; the increase is reflected on that in the apparent turbulent diffusion coefficient.

scholarly journals Wind-Tunnel Experiments on Blowing Snow

1985 ◽  
Vol 6 ◽  
pp. 63-67 ◽  
Author(s):  
N. Maeno ◽  
R. Naruse ◽  
K. Nishimura ◽  
I. Takei ◽  
T. Ebinuma ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Pressure Gradient ◽  
Blowing Snow ◽  
Wind Tunnel Experiments ◽  
Complex Dynamic ◽  
Turbulent Diffusion Coefficient ◽  
Wide Range ◽  
The Mean ◽  
Cold Wind ◽  
Snow Drifting

Blowing snow was produced artificially in a cold wind-tunnel, and various measurements were conducted including particle diameters, concentrations, saltation lengths heat transport and electric charge. The mean diameter of blowing snow particles decreased only slightly with increasing height; in the saltation layer, standard deviation was large and velocities were scattered in a wide range, suggesting the complex dynamic process on taking-off. The mean saltation length ranged from a few cm to 40 cm increasing with wind velocity.When wind blew without snow drifting, the static air pressure on the snow surface was smaller at higher levels, the vertical pressure gradient being negative. The pressure gradient became positive when blowing snow was initiated eg +9.6 Pa/m at 11.2 m/s and -8.3 °C. The magnitude of à downward force acting on a saltating snow partice caused by the pressure gradient was not large enough to explain the downward acceleration found from photographic analyses of particle trajectories.Blowing snow particles were charged negatively the magnitude of charge increased with lowering temperature. Increase in vertical heat transfer was found in blowing snow by measuring the temperature of the air at various levels; the increase is reflected on that in the apparent turbulent diffusion coefficient.

Wingbeat frequency of barn swallows and house martins: a comparison between free flight and wind tunnel experiments

2002 ◽  
Vol 205 (16) ◽  
pp. 2461-2467 ◽  
Author(s):  
Felix Liechti ◽  
Lukas Bruderer
Keyword(s):  
Wind Tunnel ◽  
Single Pulse ◽  
Free Flight ◽  
Wind Tunnel Experiments ◽  
Wingbeat Frequency ◽  
Flight Costs ◽  
Radar Echo ◽  
The Mean ◽  
Barn Swallows ◽  
Air Speed

SUMMARYThe flight paths and wingbeat patterns of 39 barn swallows (Hirundo rustica) and 26 house martins (Delichon urbica) were recorded by tracking radar during the spring migration. Depending mostly on flight angle,hirundines performed anything from continuous flapping flight during climbing to single pulse-like wing beats during descent. Unlike most other passerines,hirundines rarely showed regular flapping and rest phases, allowing them to be distinguished from other bird migrants by radar echo signatures. Effective wingbeat frequency (Feff) was calculated as the mean number of wing beats per second, including non-flapping phases. Under comparable flight conditions, Feff was higher in house martins than in barn swallows. Within species, Feff values were higher during climbing and slow flying than during descent. Of the variance in Feff, 71 % could be explained by climb rate,air speed and species; similar results were obtained in the wind tunnel. Under comparable flight conditions, barn swallows and house martins in free flight had significantly lower values of Feff than individuals in wind tunnel experiments (by 40 % and 32 %, respectively). This difference may at least partly be due to the shorter wings of the juveniles tested in the wind tunnel during autumn. However, it seems unlikely that this can account for all of the large difference. It is suggested that wind tunnel experiments might overestimate birds' flight costs compared with free flight.

scholarly journals Drop Shapes and Axis Ratio Distributions: Comparison between 2D Video Disdrometer and Wind-Tunnel Measurements

2009 ◽  
Vol 26 (7) ◽  
pp. 1427-1432 ◽  
Author(s):  
M. Thurai ◽  
V. N. Bringi ◽  
M. Szakáll ◽  
S. K. Mitra ◽  
K. V. Beard ◽  
...  
Keyword(s):  
Wind Tunnel ◽  
Close Agreement ◽  
Drop Diameter ◽  
Wind Tunnel Experiments ◽  
Axis Ratio ◽  
Wind Tunnel Measurements ◽  
Mean Shape ◽  
The Mean ◽  
Ratio Versus ◽  
Made In

Abstract Comparisons of drop shapes between measurements made using 2D video disdrometer (2DVD) and wind-tunnel experiments are presented. Comparisons are made in terms of the mean drop shapes and the axis ratio distributions. Very close agreement of the mean shapes is seen between the two sets of measurements; the same applies to the mean axis ratio versus drop diameter. Also, in both sets of measurements, an increase in the oscillation amplitudes with increasing drop diameter is observed. In the case of the 2DVD, a small increase in the skewness was also detected. Given that the two sets of measurements were conducted in very different conditions, the agreement between the two sets of data implies a certain “robustness” in the mean shape of oscillating drops that may be extended to natural raindrop oscillations, at least in steady rainfall and above the surface layer.

scholarly journals Snow Control Studies of Elevated Buildings in the Antarctic

1983 ◽  
Vol 4 ◽  
pp. 188-191
Author(s):  
Hiromi Mitsuhashi ◽  
Toshio Hannuki ◽  
Toshio Sato ◽  
Kou Kusunoki
Keyword(s):  
Wind Tunnel ◽  
Blowing Snow ◽  
Wind Tunnel Experiments ◽  
Syowa Station ◽  
Design Concepts ◽  
Drifting Snow ◽  
Scale Models ◽  
The Difference ◽  
Wind Profiles ◽  
The Antarctic

To elaborate design concepts of elevated buildings in an area of drifting snow, snow deposition and wind profiles around two buildings at Syowa station, Antarctica, were observed in 1978. To interpret the observed results in detail, wind-tunnel experiments on scale models were carried out. A wind-scooped snow deposit was formed behind the building and a sharp ridge was formed on the lee side. The highest point of the deposit was at a distance of 1 or 1.5 times the floor height (about 1.5 m) and the skirt of the snowdrift extended about 5 times the height of the roof. Wind profiles measured near one of the buildings (ionosphere hut) were expressed in terms of the logarithmic law. Two methods based on wind-tunnel experiments were used to estimate the development of snowdrifts around the building: one is to estimate the deposition from the difference in transport of blowing snow calculated from wind profiles and snowdrift flux profiles, the other is by deduction from the distribution of wind profiles. These experiments together with previous ones indicated that the optimum floor height was about 44Î of the height of the building.

Supplementary Boundary-Layer Approximations for Turbulent Flow

1989 ◽  
Vol 111 (4) ◽  
pp. 420-427 ◽  
Author(s):  
L. C. Thomas ◽  
S. M. F. Hasani
Keyword(s):  
Boundary Layer ◽  
Shear Stress ◽  
Wall Shear Stress ◽  
Pressure Gradient ◽  
Adverse Pressure Gradient ◽  
Boundary Layer Flows ◽  
Mean Velocity ◽  
Wide Range ◽  
The Mean ◽  
Wall Shear

Approximations for total stress τ and mean velocity u are developed in this paper for transpired turbulent boundary layer flows. These supplementary boundary-layer approximations are tested for a wide range of near equilibrium flows and are incorporated into an inner law method for evaluating the mean wall shear stress τ0. The testing of the proposed approximations for τ and u indicates good agreement with well-documented data for moderate rates of blowing and suction and pressure gradient. These evaluations also reveal limitations in the familiar logarithmic law that has traditionally been used in the determination of wall shear stress for non-transpired boundary-layer flows. The calculations for τ0 obtained by the inner law method developed in this paper are found to be consistent with results obtained by the modern Reynolds stress method for a broad range of near equilibrium conditions. However, the use of the proposed inner law method in evaluating the mean wall shear stress for early classic near equilibrium flow brings to question the reliability of the results for τ0 reported for adverse pressure gradient flows in the 1968 Stanford Conference Proceedings.

scholarly journals The splash function for snow from wind-tunnel measurements

2004 ◽  
Vol 38 ◽  
pp. 71-78 ◽  
Author(s):  
James N. McElwaine ◽  
Norikazu Maeno ◽  
Konosuke Sugiura
Keyword(s):  
Wind Tunnel ◽  
Mass Transport ◽  
Physical Properties ◽  
Wind Flow ◽  
Ejection Velocity ◽  
Wind Tunnel Experiments ◽  
Wind Tunnel Measurements ◽  
The Mean ◽  
Horizontal Momentum ◽  
Determining Factor

AbstractIn wind transport of snow, horizontal momentum is extracted from the mean wind flow and transferred to the snow grains. Upon colliding with the surface the grains can bounce and eject further grains in a process known as splashing. How efficiently the horizontal momentum is converted to vertical momentum in the splash process is the determining factor for mass-transport rates. This paper discusses wind-tunnel experiments performed to calculate the splash function for snow particles. The data are used to develop a new splash function. Particular care is taken to include correlations in the data such as between ejection velocity and ejection angle. The new splash function includes these correlations, and its parameters are related to physical properties of the bed and snow.

Experimental Investigation of the Effect of Upstream Conditions on Smooth and Rough Zero Pressure Gradient Turbulent Boundary Layer Flows at Very High Reynolds Numbers

2002 ◽  
Author(s):  
Luciano Castillo ◽  
Junghwa Seo ◽  
T. Gunnar Johansson ◽  
Horia Hangan
Keyword(s):  
Boundary Layer ◽  
Reynolds Number ◽  
Wind Tunnel ◽  
Turbulent Boundary Layer ◽  
Pressure Gradient ◽  
Reynolds Stresses ◽  
Mean Velocity ◽  
The Mean ◽  
High Reynolds ◽  
Very High

A 2D turbulent boundary layer experiment in a zero pressure gradient (ZPG) has been carried out using two cross hot-wire probes. The mean velocity and all non-zero Reynolds stresses were measured in a number of positions, 14–28 m from the inlet of the wind tunnel over a rough and a smooth surface. Wind tunnel speeds of 10 m/s and 20 m/s were set up in order to test the effect of the upstream conditions on the downstream flow. The long test section allowed us to investigate the mean velocity and Reynolds stresses dependence on the local Reynolds number and the initial conditions at very high Reynolds number (i.e. Rθ ∼ 120,000). Furthermore, it will be shown that the mean velocity deficit profiles and some of the Reynolds stresses collapse when the upstream conditions are kept fixed for smooth and rough surface.

scholarly journals Effect of unsteady wind on drifting snow: first investigations

2002 ◽  
Vol 2 (3/4) ◽  
pp. 129-136 ◽  
Author(s):  
J.-L. Michaux ◽  
F. Naaim-Bouvet ◽  
M. Naaim ◽  
M. Lehning ◽  
G. Guyomarc’h
Keyword(s):  
Wind Tunnel ◽  
Numerical Models ◽  
Wind Gust ◽  
Strong Wind ◽  
Blowing Snow ◽  
Wind Tunnel Experiments ◽  
Drifting Snow ◽  
In Situ Experiments

Abstract. Wind is not always a steady flow. It can oscillate, producing blasts. However, most of the current numerical models of drifting snow are constrained by one major assumption: forcing winds are steady and uniform. Moreover, very few studies have been done to verify this hypothesis, because of the lack of available instrumentation and measurement difficulties. Therefore, too little is known about the possible role of wind gust in drifting snow. In order to better understand the effect of unsteady winds, we have performed both experiments at the climatic wind tunnel at the CSTB (Centre Scientifique et Technique des Bâtiments) in Nantes, France, and in situ experiments on our experimental high-altitude site, at the Lac Blanc Pass. These experiments were carried out collaboratively with Cemagref (France), Météo-France, and the IFENA (Switzerland). Through the wind tunnel experiments, we found that drifting snow is in a state of permanent disequilibrium in the presence of fluctuating airflows. In addition, the in situ experiments show that the largest drifting snow episodes appear during periods of roughly constant strong wind, whereas a short but strong blast does not produce significant drifting snow.  Key words. Drifting snow, blowing snow, gust, blast, acoustic sensor

Pressure-gradient-dependent logarithmic laws in sink flow turbulent boundary layers

2008 ◽  
Vol 615 ◽  
pp. 445-475 ◽  
Author(s):  
SHIVSAI AJIT DIXIT ◽  
O. N. RAMESH
Keyword(s):  
Differential Equations ◽  
Pressure Gradient ◽  
Boundary Layers ◽  
Turbulent Boundary Layers ◽  
Pressure Gradients ◽  
Mean Flow ◽  
Mean Velocity ◽  
Wide Range ◽  
Gradient Parameter ◽  
The Mean

Experiments were done on sink flow turbulent boundary layers over a wide range of streamwise pressure gradients in order to investigate the effects on the mean velocity profiles. Measurements revealed the existence of non-universal logarithmic laws, in both inner and defect coordinates, even when the mean velocity descriptions departed strongly from the universal logarithmic law (with universal values of the Kármán constant and the inner law intercept). Systematic dependences of slope and intercepts for inner and outer logarithmic laws on the strength of the pressure gradient were observed. A theory based on the method of matched asymptotic expansions was developed in order to explain the experimentally observed variations of log-law constants with the non-dimensional pressure gradient parameter (Δp=(ν/ρU3τ)dp/dx). Towards this end, the system of partial differential equations governing the mean flow was reduced to inner and outer ordinary differential equations in self-preserving form, valid for sink flow conditions. Asymptotic matching of the inner and outer mean velocity expansions, extended to higher orders, clearly revealed the dependence of slope and intercepts on pressure gradient in the logarithmic laws.

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