Journal of Natural Disaster Science, Volume 23, Number 1, 2001, pp1-11

Development of a New Type Snow Fence with Airfoil Snow
Plates to Prevent Blowing-Snow Disasters:
Part 1, Evaluation of Performance by Blowing-Snow Simulation in a Wind Tunnel
Hiroshi SAKAMOTO
Professor, Kitami Institute of Technology
Masaru MORIYA
Associate Professor, Kitami Institute of Technology
Kazunori TAKAI
Research Scientist, Kitami Institute of Technology
Yoshihiro OBATA
Research Scientist, Kitami Institute of Technology(Received for 12 Jul., 2000 and in revised from 9 May., 2001)

ABSTRACTA new snow fence with airfoil snow plates to prevent snowdrift formation and improve visibility on roadways
was developed. It was designed in accordance with aerodynamic principles, and its performance evaluated in awind tunnel test in which natural snow particles were used to simulate blowing snow. Snowdrifts and visibility
blockage behind the snow fence were found to be caused by the alternating rolling-up of the bottom gap flow andshear layer separatsion from the top of the fence. Use of airfoil snow plates prevented the alternating rolling-up of
the bottom gap flow and shear layer separatsion from the top of the snow fence. On the basis of this finding, airfoil snow plates of optimum configuration were designed to prevent the alternating rolling-up of the flow behindthe snow fence. As compared to the conventional one, this newly developed snow fence with the airfoil snow
plates performed well in preventing the formation of snowdrifts and in improving visibility.

1. INTRODUCTION
Safe travel on roadways in winter in cold regions is a very
serious problem that can affect the economic activities of theregions. Primary traffic difficulties experienced on roads in winterare the deterioration of visibility and snowdrift formation causedby blowing snow (Yamada et al. 1988). In cold regions, snowdrifts and visibility blockage due to blowing snow are the most frequent causes of traffic accidents on winter roads. In recent years,
with the increase in the number of vehicles on the road, blowingsnow disasters have caused traffic accidents that involve a considerable number of automobiles. Blow-off type snow fences commonly are used as a countermeasure to prevent such disasters, but
the blow-off performance of the conventional snow fence is limited, the fences only being effective for a downstream distance
1.5−2.0 times the height of the snow fence (3 m−3.3 m) (Sakamoto et al. 1992). On two-lane roadways with an adjacentsidewalk 2 m−3 m wide (road width; 13 m) or four-lane roadways(road width; 20 m), visibility blockage and snowdrifts may occur
in opposite traffic-lanes beyond the center-line of the roadway. A
snow fence which has high blow-off performance for a 20 m wide
road therefore is strongly desired. Because the snow fence used atpresent was developed about thirty years ago, its shape is outdated,and snow fence performance has changed very little from thirty
years ago (Ishimoto et al. 1984). Moreover, as they are based onfield observations, performance evaluations have been made only
for measurements of snowdrifts around a snow fence (Takeuchi
1989, 1996). Furthermore, evaluations of visibility, which are ofutmost importance have rarely been made.
The performance of blow-off type snow fences primarily
depends on four snow plates installed at regular intervals. In theconventional model, because hardly any flow passes through theseplates, a large-scale vortex forms behind the snow fence. As aresult, the rolling-up of blowing snow occurs at a distance downstream that is 1.5−2.0 times the snow fence height, due to thealternating rolling-up of the bottom gap flow and the shear layer
being separated from the top of the snow fence, which causes visibility blockage and snowdrifts. To improve its blowing-off performance, we replaced the flat snow plates of the conventional snow
fence with Joukowsky airfoil snow plates and circular arc airfoil
snow plates that have a wide angle of attack. The design of these
airfoil snow plates was based on aerodynamic principles, and the
optimum configuration of the plates was determined in wind tunnel
tests for various shapes, sizes, and set-up angles. In addition, theperformance of this newly developed snow fence with airfoil snow
plates was investigated in wind tunnel tests, in which natural snow
particles were used to simulate blowing snow and in field investigations using a prototype snow fence model.

KEY WORDS: snow fence development, airfoil snow plates, blowing-snow disasters, snowdrifts and visibility, blowing-snow simulation, wind tunnel test

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H. SAKAMOTO, M. MORIYA, K. TAKAI & Y. OBATA

2. EXPERIMENTAL ARRANGEMENTS AND PROCEDURES
2.1 Blowing-snow simulation in a wind tunnel
Snow fence performance can be evaluated from the blowingoff effect (prevention of snowdrifts) and density distributions ofblowing snow (visibility blockage). These criteria were examinedin a blowing-snow wind tunnel, in which natural snow particles
were used (Sakamoto et al. 1998). The test section of the windtunnel had a 1.3×1.3 m cross section and was 10m long. To produce blowing snow, natural snow particles were uniformly distributed over a mobile sheet on a floor to a depth of 6 cm− 7 cm
within approximately 4 m of the entrance of the test section(Fig.1). The distributed particles were blown by wind generated
by four fans installed at the entrance of the wind tunnel. The
blowing of the particles usually was obtained at the near upstreamside of the distributed snow by slowly winding up the snow-covered mobile sheet at a velocity of 0.5 cm/s and rotating a brushinstalled at the near upstream end of the sheet at n=150 rpm. In
addition, because the blowing of the snow particles was based on
the rotational frequency of the brush, a considerable amount of
blowing snow would be generated intermittently. A 1/8−1/6
model of the prototype snow fence was installed 4.8 m downTable 1.

Classification of light and shade distribution of
256 graded digital images.

Fig. 1stream from the entrance of the test section. The wind velocity
was varied in the range of 6 m/s−8 m/s. The behavior of theblowing snow around the snow fence model was observed by irradiation with a uniform light sheet from a slit light apparatus
attached to the ceiling of the test section and recorded with a CCD
camera through transparent Plexiglas set in the side of the test section. Because the intensity of the light scattered from snow particles is considered to increase with the particle concentration, thelight intensity distribution in the blowing-snow image recordedwith the CCD camera is thought to indicate the spatial concentration distribution of the snow particles. The recorded images therefore were replaced frame by frame, the image of each frame being
digitized and stored in a computer by means of a video digitizer at
256 grades per pixel for 400 pixels in the vertical and 512 pixels in
the horizontal direction. The digitized images were classified into
six grade ranges (Table 1), and the contour line of each range wasdrawn on the computer screen. The corresponding Reynolds number RH (=UH/ν) based on the height of the snow fence model, H,
in the blowing-snow wind tunnel was (1.68−3.0)×105.
2.2 Water channel and wind tunnel experiment
Flow-visualized observations were made in a water channel inwhich the test section was 0.33 m deep, 0.25 m wide and 1.5 mlong (Fig.2). The hydrogen bubble method was used for flow visualization. Hydrogen bubbles were generated by tungsten wire 20
μm in diameter. A 1/22-scale model of the prototype snow fence
was used, and the experiment done at the constant velocity of 6
cm/s. The corresponding Reynolds number, RH was 6.8×103. In
addition, velocity distributions behind the snow fence were investigated in a low-speed, closed-circuit wind tunnel (Fig.3). The test
section of this wind tunnel was rectangular; height 1.2 m, width
0.3 m and length 2.5 m. The velocity distribution was measured
with a yaw-type pitot tube that had four holes which allowed the
direction and velocity of flow to be measured simultaneously. The
free-stream velocity was constant at 10 m/s. The size of the snow
fence model used was 1/10 that of the prototype snow fence. The
corresponding Reynolds number, RH, was 1.85×105.

Schematic view of the blowing-snow wind tunnel

DEVELOPMENT OF A NEW TYPE SNOW FENCE WITH AIRFOIL SNOW PLATES TO PREVENT BLOWING-SNOW DISASTERS:PART 1, EVALUATION OF PERFORMANCE BY BLOWING-SNOW SIMULATION IN A WIND TUNNEL

3

Fig. 2 Water channel used for flow visualization

Fig. 3

Wind tunnel used for velocity measurements

2.3 The developed snow fence model
The models are shown in Fig.4 (a) and (b), and a conventionalsnow fence with a snow plate size of W=600 mm and setup angleof β=23.5°is shown in Fig 4(c). The newly developed snow
fence has airfoil snow plates that differ completely from the flat
type snow plates used in the conventional snow fence. These airfoil snow plates are of two types; a Joukowsky airfoil snow plate

and a circular arc airfoil snow plate (Fig.5). Each of these airfoil
snow plates consists of two subtypes (Types A and B). The circular arc airfoil snow plates differ in the shape of the circular arc of
the leading edge, and the Joukowsky airfoil snow plates differ inthe camber line. Furthermore, each of these airfoil snow platetypes was produced in three sizes, all of which were geometricallysimilar (Fig.5).

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H. SAKAMOTO, M. MORIYA, K. TAKAI & Y. OBATA

Fig. 4

Snow fence configurations

3. SIMILARITY LAW OF BLOWING-SNOW SIMULATION IN A WIND TUNNEL USING SNOW PARTICLES
Six parameters govern the flow of blowing snow around asnow fence: the approaching velocity, U; the height of the snow
fence, H; the diameter of the snow particle, d; the gravity, g; andthe viscosity,μ, and density of the fluid,ρ. When the three repeat
variables U, H, andρare adopted, three non-dimensional parameters are produced based on the BuckinghamΠtheorem:(1) The Reynolds number based on the height of the snow fence,
RH (=UH/ν)(2) The Froude number based on the height of the snow fence, FH(=U/√gH )(3)
The ratio between the diameter of the snow particles andheight of the snow fence, d/H
Moreover, by adopting the three repeat variables U, d, andρ, three
non-dimensional parameters are produced:(1) The Reynolds number based on the diameter of the snow particles, Rd (=Ud/ν)(2) The Froude number based on the diameter of the snow particles, Fd (=U/√gd )(3)
The ratio between the diameter of the snow particles andheight of the snow fence, d/HFirst, consider the Reynolds numbers RH and Rd. Rd does notneed to be taken into account because it becomes identity between
the real and the model case when natural snow particles are used as
the snow model. Moreover, there is hardly any effect of the
Reynolds number on flow together with separation, such as occurs
around the snow fence when the Reynolds number exceeds 104.
The RH of our snow fence model is (1.68−3.0)×105, and the RH of

the prototype snow fence 1.8×106. Consequently, it is not necessary to consider the Reynolds number RH, because for the modeland prototype snow fence it exceeds 10 4 . On the basis of thedimensionless parameter d/H, a snow particle size of 1/n must be
adopted when the dimension of the snow fence model is 1/n thescale of the prototype. Because snow particle motion is greatly
dependent on Rd at a low Reynolds number (Rd based on a snow
particle diameter of d =0.1 mm−0.2 mm is 50−100), snow particle motion in the test model differs considerably from the actuality
when the size of the snow particle model is 1/n. A method inwhich Rd is made to agree with the dimensionless parameters of Rd
and d/H therefore should be adopted.
Next, consider the Froude numbers FH and Fd. In nature, snow
particles usually begin to blow at a wind velocity of U=6 m−7m/s. If the Froude number, FH, based on the height H of the snow
fence governs the similarity law, the snow particles in the test
model begin to blow at U=1.9 m/s−2.2 m/s when scale of thesnow fence model is 1/10 that of the prototype. The wind velocity
at which the snow particles blow in the wind tunnel using snow
particles is U=6 m/s−7 m/s, as in nature. As a result, FH can not
be a parameter that governs the similarity law. Fd, which is basedon the diameter d of the snow particle therefore governs the similarity law. Consequently, the parameters that govern the flow of
blowing snow around a snow fence are the Reynolds number, Rd,
and the Froude number, Fd. In our experiment, Rd and Fd both in
the test model and in reality are identical because actual snow particles were used in the particle model. Results obtained with thetest model therefore can be regarded as reproducing the actual
result for an equivalent wind velocity. Figure 6 gives a comparison of snowdrift shape for the wind tunnel test model and a fieldDEVELOPMENT OF A NEW TYPE SNOW FENCE WITH AIRFOIL SNOW PLATES TO PREVENT BLOWING-SNOW DISASTERS:PART 1, EVALUATION OF PERFORMANCE BY BLOWING-SNOW SIMULATION IN A WIND TUNNEL

Fig. 5

5

Airfoil snow plate configuration

observation experiment made with the prototype snow fence.
Because these snowdrift shapes are very similar, the wind tunnel
test model that uses actual snow particles reproduces the results forreality in proportion to wind velocity with considerable accuracy.
4. RESULTS AND DISCUSSIONS
4.1 Method of evaluating snow fence performance
In the blowing-off type snow fence, blowing snow which
passes through the snow plates and the bottom gap must be transferred along the road surface without forming snowdrifts. To
improve the blowing-off performance, any decrease in flow velocity along the roads surface and any rolling-up must be suppressed
as much as possible. Snow fence performance can therefore be
evaluated by two methods: One is to examine the characteristics offlow behind the snow fence, particularly bottom gap flow. The
other is to examine the density of the blowing snow behind thefence (Haniu et al. 1995). We used these two methods to evaluate
the performance of the snow fence.

4.2 Parameters governing snow fence performanceSix parameters govern the performance of the snow fence: (1)snow plate shape, (2) snow plate size W, (3) snow plate setup
angle β, (4) number of snow plates n, (5) height of the bottom gap
K, and (6) snow fence height H. In our study, the number of thesnow plates was limited to n=4 because the standard snow fence iscomposed of four snow plates. In addition, the height of the snow
fence, H, was kept constant at 2.8 m because standard snow fence
height usually is approximately 3 m. The remaining four parameters were examined in detail to evaluate the performance of our
newly developed snow fence.
4.3 Performance evaluation based on blowing-snow density
4.3.1 Airfoil snow plate shape
Figure 7 shows spatial density distributions of blowing snow
around a snow fence constructed different snow plate shapes. Twotypes of Joukowsky airfoil snow plates and circular arc airfoil
snow plates were used (Fig.5). Density distributions of the blowing snow were measured by the image-processing method. This

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H. SAKAMOTO, M. MORIYA, K. TAKAI & Y. OBATA

method is based on the fact that the strength of scattered light froma slit light source changes with the spatial concentration of snow
particles. A computer was used to divide the recorded images into
an intensity distribution of 256 grades, and blowing-snow density
was evaluated by classifying the grades in the six ranges shown in
Table 1. As the gradation number increases, the blowing snow
gradually reaches a high density. Snow fence performance basedon the density distribution of blowing snow also can be evaluatedas follows: (1) blowing snow passes over a region lower than theFig. 6driver’s eye level of 1.35 m, (2) blowing snow passes as near theroad surface as possible.
First, consider a snow fence constructed with Joukowsky airfoil snow plates: More blowing snow of high density passes in thevicinity of the road surface with Type A which has a large camberline than with Type B which has a small one. This seems to becaused by a difference in the deflection of blowing snow that passes through the snow plates toward the road due to the difference inthe camber lines. The blowing-off performance of a snow fence

Comparison of snowdrifts formed with the wind tunnel model and full-scale fence

Fig. 7

Density distributions of blowing snow for different snow plates shapes

DEVELOPMENT OF A NEW TYPE SNOW FENCE WITH AIRFOIL SNOW PLATES TO PREVENT BLOWING-SNOW DISASTERS:PART 1, EVALUATION OF PERFORMANCE BY BLOWING-SNOW SIMULATION IN A WIND TUNNEL

with Type A snow plates therefore is higher than that of one withType B snow plates. Now consider a snow fence with circular arc
airfoil snow plates. The blowing-off performance of Type A snow
plate is slightly better than that of Type B snow plates which havea smaller circular arc. For comparison, the blowing-snow density
distribution around a conventional snow fence with the flat snow
plates is shown in Fig.7(c). The rolling-up of blowing snow occurs
from the position x/H=1.5−2.0 behind the snow fence, then highdensity, blowing snow passes over the spatial region higher thanthe driver’s eye level (1.35 m). The performance of a snow fencewith airfoil snow plates is markedly improved in comparison tothat of a conventional snow fence. Most high density blowing
snow that passes the snow fence with the airfoil snow plates moves
along the roads surface with no rolling-up, even at distances from

Fig. 8Fig. 97

the fence that exceed x/H=5.0. A snow fence with the airfoil snow
plates therefore would be sufficient for a wide road with a width
exceeding 20 m.
4.3.2 Snow plate size
Figure 8 shows the spatial density distribution of blowing
snow around snow fences that have the snow plates of various
sizes. Figure 8(a) shows results when the size of Joukowsky airfoil snow plate (Type A) is W=600, 650, and 700 mm, and Figure8(b) when the size of the circular arc airfoil snow plate (Type A) is
L=520, 620, and 950 mm. The snow fence height and the bottom
gap are constant at H=2.8 m and K=1.2 m. The setup angles are β=60°for the Joukowsky airfoil snow plate and β=35°for the circular arc airfoil snow plate. In the case of a snow fence with
Joukowsky airfoil snow plates, performance improves as theDensity distributions of blowing snow for different snow plate sizes

Density distributions of blowing snow for different snow plate setup angles β8

H. SAKAMOTO, M. MORIYA, K. TAKAI & Y. OBATA

width, W, increase, and similarly for a snow fence with circular arc
airfoil snow plates. In contrast, for a Joukowsky airfoil snow plateof W=600 mm and a circular arc airfoil snow plate of L=520 mm,
blowing snow passes in the spatial region beyond the driver’s eye

Fig. 10Density distributions of blowing snow for different bottom gaps

Fig. 11level (1.35 m), and the snow fence performance decreases. A
Joukowsky airfoil snow plate of W=650 mm and a circular arc airfoil snow plate of L=620 mm therefore are judged to be the minimum acceptable sizes.
4.3.3 Snow plate setup angles
Figure 9 shows the density distributions of blowing snow forvarious setup angles, β, of the snow plate. The height of the snow
fence is constant at H=2.8 m. For Joukowsky airfoil snow plate(Type A), shown in Fig.9(a), the selected height of the bottom gap
is K=1.2 m, and the selected snow plate size W=650 mm. For thecircular arc airfoil snow plate (Type A), K=1.2 m and L=620 mm
are the values. With a snow fence that has Joukowsky airfoil snow
plates, because the vortex region formed behind the snow fence islarge at the setup angle of β=55°, the flow passing through thebottom gap is rolled up lowering the blowing-off performance.
Moreover, at β=65°, because there is little deflection of the blowing snow passing through the snow plates, the blowing-off performance also is lowered. The optimum value of the setup angle, β,therefore is approximately 60°. As is clear from Fig.9(b), the optimum value of the setup angle is approximately β=35°for a snow
fence with the circular arc airfoil snow plates.
4.3.4 Height of the bottom gap
Figure 10 shows the density distributions of blowing snow
around a snow fence with Joukowsky airfoil snow plates for different bottom gap heights. The fence had a height of H=2.8 m, snow
plate size of W=650 mm, and setup angle of β=60°. For K=0.8 m
and 1.0 m, because the interval between snow plates installed atregular intervals is large, blowing snow that passes through theplates traverses the road at a level higher than the driver’s eye(1.35 m). For K=1.2 m, most of the blowing snow that passes
through the snow plates traverses the spatial region lower than thedriver’s eye level. For K=1.4 m, rolling-up of the blowing snow

Visualization of flow patterns around snow fenceDEVELOPMENT OF A NEW TYPE SNOW FENCE WITH AIRFOIL SNOW PLATES TO PREVENT BLOWING-SNOW DISASTERS:PART 1, EVALUATION OF PERFORMANCE BY BLOWING-SNOW SIMULATION IN A WIND TUNNEL

behind the snow fence occurs, producing a lower blowing-off performance for the snow fence. Optimum height of the bottom gap,
K, therefore is approximately 1.2 m when snow fence height is
H=2.8 m. Moreover, the optimum height of the bottom gap, K, isapproximately 1.2 m for a snow fence with circular arc airfoil
snow plates.
4.4 Performance evaluation based on the flow pattern
The performance of a snow fence can be evaluated by observing the flow pattern. The flow pattern around a snow fence with
Joukowsky airfoil snow plates was determined. The snow fence
height was H=2.8 m, bottom gap height K=1.2 m, and snow platesize W=650 mm. Figure 11 shows the flow patterns around a snow
fence when the setup angle, β, of the snow plates is changed. At
β=50°, the flow which passes over the topmost part of the snow
fence and that which passes through the bottom gap roll up alternately behind the snow fence, causing a large-scale vortex. Thisphenomenon leads to high-density blowing snow being spreadover the entire area behind the snow fence. At β=60°, the flow
passes through the snow plates is deflected toward the roads surface, then moves along that surface together with the bottom gap
flow, but with no rolling-up of the flow downstream. This flow
pattern produces a large blowing-off effect. At β=70°, there is norolling-up of the flow behind the snow fence. Because deflectionof the flow that passes through the snow plates is small, a considerable amount of blowing snow with high-density passes over thefence in the high spatial region such that visibility blockage may
occur. The flow pattern around a conventional snow fence isshown in Fig.11 (d). The flow approaching the snow fence isdivided into top and bottom gap flows, which alternately roll up
behind the snow fence. Due to the rolling-up of the bottom gap
flow, snowdrifts and visibility blockage occur at the position
x/H=1.5~2.0. To improve the blowing-off performance of thesnow fence, the vortex region formed behind the fence should bedecreased as much as possible, thereby preventing the rolling-upof the bottom gap flow.
4.5 Performance evaluation based on flow characteristics
4.5.1 Time-averaged velocity distributions
The time-averaged velocity distributions behind the snow
fence were measured to evaluate the characteristics of bottom gap
flow and the vortex region formed behind the fence, both of whichgovern snow fence performance. For the time averaged-velocity

Fig. 129

distribution measurements, a snow fence with Joukowsky airfoil
snow plates, whose blowing-off performance was highest in theblowing-snow simulation test, was used. Specifically, this snow
fence had a height of H=2.8 m and bottom gap height of K=1.2 m.
The size of its snow plates was W=650 mm and the setup angle β=60°. The time-averaged velocity distributions for a conventionalsnow fence also were measured for comparison. Figure 12 showsthe equi-velocity lines for the velocity u in the x flow direction.
For the conventional snow fence, bottom gap flow accelerates considerably after passage through the snow fence, whereas bottom
gap flow along the road surface decelerates quickly and flows
upward from the approximate position of x/H=2.0. High-density
blowing snow that passes through the bottom gap therefore getsrolled up due to its upward flow, lowering the blowing-off performance of the snow fence. A acceleration of bottom gap flow is
low with the newly developed snow fence. Moreover, decelerationof the bottom gap flow at downstream is small, and the bottom gap
flow moves along the road surface without rolling-up, therefore,
the newly developed snow fence produces a high blowing-off .
Consider the vortex region formed behind the snow fence.
For a conventional snow fence it is a large-scale vortex that covers
the entire snow fence. With the newly developed snow fence, thevortex region forms only at the rear of the snow plate at the topmost part of the snow fence. This reduction in the vortex region of
the snow fence with the airfoil snow plate produces so little
rolling-up of the bottom gap flow that blowing-off performance ismarkedly improved as compared to that of the conventional snow
fence.
4.5.2 Momentum of bottom gap flow
Momentum along the road surface governs the transportationof blowing snow. Figure 13 shows the momentum of bottom gap
flow calculated from the time-averaged velocity distributions.
Here, the M/M0 of the ordinate axis is the momentum calculated byequation (1), and the abscissa axis is the distance, x/H, from thesnow fence.

k

∫

k

2

∫ρ(vcosθ) dy

M= ρOvcosθ=
0

0

(1)
k

∫ρkU

M0=

0

Equi-velocity line behind snow fence models

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H. SAKAMOTO, M. MORIYA, K. TAKAI & Y. OBATA

Here, v is the absolute velocity, θ the angle between the
direction of absolute velocity and the x-axis, U the approachingflow velocity, and K the height of the bottom gap. M 0 is themomentum when the flow velocity passing through the bottom gap
is the approaching velocity U. For the conventional snow fence,
the momentum of the bottom gap flow immediately after passage
through the snow fence is considerably large, whereas the decreasein momentum is large in the downstream, approximately 25% of
the momentum immediately after passage through the snow fence
at x/H=5.0. For the newly developed snow fence, the momentum
immediately after passage through the snow fence is less than thatof the conventional snow fence, but the decrease in momentum inthe downstream direction is small, significant momentum being
retained; 75% of the momentum immediately after passage
through the snow fence at x/H=5.0. The increase in momentum atapproximately x/H=1.7 is due to the addition of the momentum of
the flow that passes through the snow plate. The blowing-off per-formance of the newly developed snow fence therefore is
improved because the decrease in momentum in the downstream isconsiderably less than that for the conventional snow fence.
4.6 Performance evaluated by a field observation experiment
A snow fence model with the circular arc airfoil snow platesof L=950 mm was used in the field observations. This model,
overall length of 30.4 m, was installed contiguous to a conventional snow fence to allow comparison. For snowdrift evaluation,
three poles were installed windward of the snow fence and ten
poles leeward in the direction of the road.
Figure 14 shows the snowdrift formation findings from
December 27, 1997 to February 6, 1998. There was no blockageof the bottom gap generated by snowdrifts upstream of the newly
developed snow fence, whereas there was for the conventionalsnow fence, because the snowdrift volume was extremely large.
Blowing-off performance is always retained with the newly developed snow fence because there is no blockage of the bottom gap
by snowdrifts. Leeward of the road, the maximum snowdrift
height is approximately 50 cm for the newly developed snow
fence, whereas for the conventional one it is approximately 200
cm. With the newly developed snow fence, there are almost no
snowdrifts for a distance of 30 m on the leeward side. The newly
developed snow fence therefore appears to retain the blowing-off
effect over a considerable distance.
2. CONCLUSIONS

Fig. 13

Momentum of bottom gap flow of snow fences

Fig. 14(1) In the wind tunnel experiment made with actual snow particles, the similarity law is prescribed by the Froude number, Fd,
based on the diameter, d, of the snow particles(2) The vortex region formed behind the snow fence induces
rolling-up of bottom gap flow. This vortex region therefore
must be reduced as much as possible to improve the blowing-off
performance of the snow fence.
(3) The vortex region formed behind the snow fence with the air-Field observations of a full-scale snow fence model for snowdrifts

DEVELOPMENT OF A NEW TYPE SNOW FENCE WITH AIRFOIL SNOW PLATES TO PREVENT BLOWING-SNOW DISASTERS:PART 1, EVALUATION OF PERFORMANCE BY BLOWING-SNOW SIMULATION IN A WIND TUNNEL

foil snow plates is considerably reduced, such that rolling-up of
bottom gap flow completely is suppressed.
(4) The size and setup angle of the airfoil snow plate and heightof the bottom gap are the parameters that govern snow fence
performance. We determined the optimum size and setup angleof the snow plate and the height of the bottom gap.
(5) Both the wind tunnel and field observation experiments
showed that the blowing-off performance of the snow fencewith airfoil snow plates is markedly improved as compared tothat of the conventional snow fence.
ACKNOWLEDGMENTS
This study was supported by a Grant-in-Aid for Scientific
Research [(B)(2) (No.09558048)] from the Ministry of Education,
Science, Sports and Culture of Japan.
REFERENCES
Ishimono, K., Takeuchi, M., Nohara, T. and Fukuzawa, Y., 1984. A study
on snow fences, Ice and Roads, 1, 96-100. (in Japanese).
Haniu, H. and Sakamoto, H., 1995. Improvement of blower type snow
fences by control of the shear layer, Journal of Natural Disaster
Science, 17-1, 53-64.
Sakamoto, H., Haniu, H, Kiyota, M. and Obata, Y., 1992. Development
and performance of snow fences for prevention of blowing-snow disasters, Transactions of the Japan Society of Mechanical Engineers(B), 58-550, 2017-2023. (in Japanese).
Sakamoto, H., 1999. Estimation of snow-fence performance by a wind tunnel simulation test, Bulletin of the Natural Disaster Science Data

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Center Hokkaido, 13, 53-65. (in Japanese).
Takeuchi, M., 1989. Snow-collection mechanism and the capacities ofsnow fences, Annuals of Glaciology, 13, 248-251.
Takeuchi, M., 1996. For the control of blowing snow, Journal of theJapanese Society of Snow and Ice, 58-2, 161-168. (in Japanese).
Yamada, T., Akitaya, A. and Tachibana, Y., 1988. Disasters created bysnow and ice in Hokkaido, Proceedings of the ’88 Cold Region
Technology Conference, 179-184. (in Japanese).

NOMENCLATURE
Fd : Froude number based on snow particle diameter
H : height of the snow fence
K : height of the bottom gap
L : size of the circular arc airfoil snow plate
M : momentum of the bottom gap flow
M0 : momentum of the bottom gap flow based on velocity U
RH : Reynolds number based on snow fence heightU : approaching flow velocity
u : velocity in the x directionv : absolute velocity
W : size of the Joukowsky airfoil snow platex , y : cartesian coordinate system
β : setup angle of the snow plateθ : angle between the direction of absolute velocity and xaxis
ν : kinematic viscosity of fluidρ : density of fluid
μ : viscosity of fluid.