Journal of Natural Disaster Science, Volume 23, Number 1, 2001, pp13-22

Development of a New Type Snow Fence with Airfoil Snow
Plates to Prevent Blowing-Snow Disasters:
Part 2, Characteristics of the Aerodynamic Fluid Forces of Airfoil Snow Plates
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 was developed to prevent blowing-snow disasters. In a previous
report, we showed that in comparison with the conventional snow fence, this snow fence with airfoil snow plates
performed very well in preventing snowdrifts and in improving visibility. The characteristics of the aerodynamic
fluid forces on and flow-induced vibrations of the airfoil snow plates now have been investigated. The important
findings are (i) fluctuating fluid forces acting on the airfoil snow plate set at the topmost part of the snow fence
are the most serious, (ii) flow-induced vibrations generated in the airfoil snow plate attached to the topmost partof the snow fence are rapidly amplified by an increase in wind velocity, (iii) the fluctuating fluid forces on andflow-induced vibrations in the airfoil snow plates could be completely suppressed when a perforated plate was
attached to the topmost part of the snow fence.

1. INTRODUCTION
Most traffic difficulties on winter roads are caused by the formation of snowdrifts and visibility blockage generated by blowing
snow. Blow-off type snow fences are commonly used as a countermeasure of road transportation disasters being caused by blowing snow. In a previous report (Sakamoto et al. 2001), a snow
fence was developed that has airfoil snow plates, whose shape differs completely from that of the flat snow plates used for conventional snow fences. Examinations based on results of blowingsnow simulation tests in a wind tunnel showed that the newly
developed snow fence had high performance and was sufficient foruse on a road 20 m wide. The aerodynamic characteristics of the
newly developed snow fence with airfoil snow plates were investigated and the findings our discussed here. Little research on the
aerodynamic characteristic of snow fence has been studied, onlythat which examined time-averaged fluid forces (Sakamoto et al.
1992). Because lightening of the weight of snow plates whichconstitute a snow fence is desirable, it is necessary to understandthe unsteady aerodynamic forces acting on and characteristics ofthe flow-induced vibration of these snow plates. We therefore
have studied in detail the unsteady aerodynamic fluid forces thatcause fatigue breakdown in airfoil snow plates. The response characteristics of airfoil snow plates generated by flow-induced vibration also were investigated by the use of a free vibration model test

in a wind tunnel. A method for the suppression of unsteady aerodynamic fluid forces and flow-induced vibrations by means of aperforated plate attached to the topmost part of the snow fence ispresented, and its effectiveness verified.
2. EXPERIMENTAL ARRANGEMENT AND PROCEDURES
The aerodynamic fluid forces acting on the snow fence andthe airfoil snow plates were measured in a low-speed, closed-circuit wind tunnel. The test section of the wind tunnel was 0.3 ×1.2
m in cross section and 2.5 m in long. Time-averaged fluid forces(steady fluid forces) and fluctuating fluid forces (unsteady fluid
forces) were measured in box-type load cells. The time-averaged
fluid forces acting on the snow fence, necessary for evaluating therequired strength of the support and installed base size of the snow
fence, were measured for a single load cell, (Fig.1 (a)). These
fluid forces that act on airfoil snow plates also were measured for
two load cells that had identical characteristics. The two load cells
attached to double sides of the snow plate were used (Fig.1 (b)), toraise the natural frequency of the snow plate as much as possible.
The natural frequency, fc, of the airfoil snow plate supported by thetwo load cells was 400 Hz, about 20 times the prevailing frequency(19.9 Hz) of the fluctuating fluid forces. Fluctuating fluid forces
therefore could be measured with sufficient accuracy (So et al.
1981). A snow fence with Joukowsky airfoil snow plates also was

KEY WORDS: snow fence development, blowing-snow simulation, wind tunnel test, airfoil snow plate, aerodynamic fluid forces, flow-induced vibration,
perforated plate

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

Fig. 1

Fig. 2

Load cell apparatus for measuring of aerodynamic force acting on the snow fence and snow
platesSchematic diagram of the free-vibration apparatus

tested. The fence height was H=2.8 m, the bottom gap K=1.2 m,
snow plate size W=650 mm and setup angle of the snow plate β=60°the dimensions that gave the best performance in a previous
report. The airfoil snow plate was constructed of wood to reduce
its weight as much as possible. In the experiment, the free-stream
velocity was kept constant at 9 m/s. The model snow fence tested
was 1/15.5 the size of the prototype. The corresponding Reynolds
number, RH, was 1.04×105.
The flow-induced vibrations of the airfoil snow plate were
evaluated with the free-vibration equipment shown in Fig.2. There
are two modes of flow-induced vibration; cross-flow and rotational
vibration of the airfoil snow plate. In this study, we found rota-

tional vibration, and examined the response characteristics. The
airfoil snow plate was constructed of balsawood to make the model
as light as possible. A rotating shaft installed in two bearings
attached to each side wall of the wind tunnel was supported byfour coil springs installed in the arms to allow free rotational oscillation. Displacement of rotational oscillation was measured with alaser displacement meter. The reduced velocity, Ur [=U/(fc・W)
varied in the range of 0−16. The natural frequency, fc, of the airfoil snow plate installed on the free-vibration equipment was 9 Hz.
In addition, the reduced damping factor, C n [=Iδ/(ρW 4 ), in
which I is the inertia moment of the airfoil snow plate and δ thelogarithmic damping factor], was 0.0046.
Next, the fluctuating fluid forces and flow-induced vibrationsof the airfoil snow plates were suppressed by means of a perforated
plate attached to the topmost part of the snow fence (Fig.3). In thisexperiment, the width, w, of the perforated plate was kept constant,and the porosity, a, and interval between the topmost snow plate
and the perforated plate, G, were varied. The model snow fence
tested was 1/5.4 the size of the prototype.
3. RESULTS AND DISCUSSIONS
3.1

Time-averaged aerodynamic fluid forces acting on thesnow fence
Figures 4 and 5 respectively show the time-averaged dragcoefficient, CDH, and time-averaged lift coefficient, CLH, of the
newly developed snow fence for changes in the setup angle,β, ofthe airfoil snow plates in the range of 100−800. CDH and CLH are
defined by:(CDH ,CLH) = (DH ,LH) / (0.5ρU2A)(1)

DEVELOPMENT OF A NEW TYPE SNOW FENCE WITH AIRFOIL SNOW PLATES TO PREVENT BLOWING-SNOW DISASTERS:PART 2,
CHARACTERISTICS OF THE AERODYNAMIC FLUID FORCES OF AIRFOIL SNOW PLATES

Fig. 3Fig. 415

Perforated plate for snow flow control

Drag coefficient, CDH, of the snow fence versus the set up angle, βWhere DH and LH respectively are the time-averaged drag andthe time-averaged lift, and A is the projected area A=H'×l ( inwhich H' is the height of the snow fence, H, minus the bottom gap
height of K, and l the length of the span of the snow fence). CDH
and CLH for a conventional snow fence are shown in these figures
for comparison. CDH decreases as setup angleβof the airfoil snow
plate increases, because flow blockage through the snow plates
decreases as the setup angle increases. Also, CDH in the case ofβ=60°of the snow plate in the previous report for which the blow-

ing-off effect was highest is about 0.75. This value is considerably
smaller than CDH =1.30 for a conventional snow fence with flatsnow plates and an optimum setup angle ofβ=23.5°. The wakeformed behind the newly developed snow fence therefore is considerably reduced compared to that formed behind the conventional snow fence. The time-averaged lift coefficient, CLH, increases as
setup angleβof the airfoil snow plate increases, reaching a maximum at the optimum angleβ=60°because separation of the flow
passing through the snow plate is suppressed the most at that16

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

angle.
Figure 6 shows the time-averaged fluid forces acting on the
airfoil snow plates. The time-averaged drag coefficient, CD, lift
coefficient, CL, and resultant force coefficient, CR, are defined by :strongly influenced by the effect of the shear layer that rolls up
from the upper end of the snow fence. The CDf and CLf of the airfoil(CD , CL) = (D ,L ) / (0.5ρU 2Wl )(2)CR =√CD2+CL2
Where, D is the force in the flow direction, L the force in the
direction perpendicular to the flow, and CD and CL are the maximum values for the airfoil snow plate of ②. This is because thedeflection of the flow passing through the snow plate of ②
becomes large, as seen from the visualized observations shown in
Fig.10. It therefore is necessary to evaluate the required strengthof the airfoil snow plate of ② based on aerodynamic forces.
3.2 Fluctuating drag and lift acting on snow plates
Figure 7 shows the fluctuating drag, CDf and fluctuating lift
coefficient, CLf, for each airfoil snow plate. CDf and CLf are defined
by:

(

)

(CDf , CLf )= √Df 2 , √Lf2 / (0.5ρU 2Wl )(3)

Where, Df is the fluctuating fluid force in the flow direction,and Lf the fluctuating fluid force in direction perpendicular to flow.
The CLf of the snow plate of ①, located at the topmost part of thesnow fence has the maximum value because this snow plate isFig. 5

Fig. 6 CD, CL, and CR of each snow plate

Lift coefficient, CLH, of the snow fence versus the set up angle, βDEVELOPMENT OF A NEW TYPE SNOW FENCE WITH AIRFOIL SNOW PLATES TO PREVENT BLOWING-SNOW DISASTERS:PART 2,
CHARACTERISTICS OF THE AERODYNAMIC FLUID FORCES OF AIRFOIL SNOW PLATES

snow plates of ②, ③, and ④, however, are very small as compared to the airfoil snow plate of ① because the effect of the shear
layer rolled-up from the upper end of the snow fence is weakened.
To verify the generation mechanism of the fluctuating fluid forces,
the power spectrum distributions of the fluctuating drag and lift
acting on the airfoil snow plates and the fluctuating velocity at
x/H=2.0 (the y direction position is changed) behind the snow
fence were investigated. The respective findings are shown in figures 8 and 9. The fluctuating drag on and lift of the airfoil snow
plates vary with a prevailing frequency of fv =19.9 Hz, identical tothat of the fluctuating velocity behind the snow fence. Fluctuating
drag and lift therefore are generated by the rolling-up of the shear
layer with periodicity from the upper end of the snow fence. Theenergy level of the power spectrum of the fluctuating drag and thelift of the snow plate of ① also are considerably larger than theseof the other snow plates. Accordingly, generation of the fluctuating fluid forces on airfoil snow plates can be suppressed by controlling the shear layer because these forces occur as the result of

Fig. 7 CDf and CLf of each snow plate

Fig. 817

the rolling-up of the shear layer from the upper end of the snow
fence.
3.3

Control of fluctuating fluid forces acting on the snowplate
The fluctuating drag and lift acting on the airfoil snow plates
were suppressed by the use of a perforated plate attached to the
topmost part of the snow fence, as shown in Fig.3. A flow visualization experiment was made in a water channel to determine theoptimum value of porosity, a, of the perforated plate and interval,G, between the airfoil snow plate attached to the topmost part ofthe snow fence and the perforated plate. Figure 10 shows visualization of the flow pattern around the snow fence with a perforated
plate attached to its topmost pert. The Reynolds number, RH, basedon the height, H, of the snow fence and the approaching flow

Fig. 9Power spectrums of fluctuating velocity behind the snow fencePower spectrums of fluctuating drag and lift of the airfoil snow plates

18

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

Fig. 10Visualization of the flow pattern around the snow fence with a perforated plate attached to its topmost part

DEVELOPMENT OF A NEW TYPE SNOW FENCE WITH AIRFOIL SNOW PLATES TO PREVENT BLOWING-SNOW DISASTERS:PART 2,
CHARACTERISTICS OF THE AERODYNAMIC FLUID FORCES OF AIRFOIL SNOW PLATES

19

velocity, U, was 6.8×103 in this experiment, which value differsfrom RH=1.03×105 found in measuring the aerodynamic fluid
forces in a wind tunnel, but there does not appear to be a problem
in the case of a qualitative evaluation. The porosity of the perforated plate was changed (0%, 20%, 30%, 40%, and 50%), as was
the G/H interval between the airfoil snow plate and perforated
plate (0.029, 0.043, and 0.057). When the porosity of a=0%, 20%,and 30%, the rolling-up of the shear layer that is separated fromthe topmost part of the snow fence occurs, whereas for porositiesof 40% and 50% and an interval of G/H=0.057, almost no rollingup of the shear layer occurs. Also, the flow through the bottom
gap moves along the surface of road with no rolling-up for porosities of a=40% and 50% and on interval of G/H=0.057.
Accordingly, a perforated plate at position G/H=0.057, and which
has a porosity greater than 40% is judged to be the most effective

for suppressing the rolling-up of the shear layer that is separated
from the topmost part of the snow fence.
Figure 11 shows the fluctuating drag, CDf and fluctuating lift,CLf, coefficients of the airfoil snow plates for a perforated plate
installation at the interval G/H=0.057 and with a porosity of 40%.
The C Lf and C Df of the airfoil snow plate of ① are markedly
reduced as compared to values without the perforated plate. The
CLf and CDf of the other airfoil snow plates also become small ascompared to values without the perforated plate. Figure 12 shows
the power spectrum of the fluctuating drag and fluctuating lift acting on the snow plates, and Figure 13 that of the fluctuating velocity behind the snow fence with a perforated plate having porosity of
40% and an interval G/H=0.057. No clear spectral peaks exist forfluctuating drag, fluctuating lift, and fluctuating velocity, evidence
that the perforated plate is very effective in suppressing fluctuating
fluid forces.
Figure 14 shows the time-averaged drag, CD, and lift, CL, coefficients of each airfoil snow plate for a perforated plate with aporosity of 40% and interval of G/H=0.057. Except for airfoil

Fig. 11 CDf and CLf of each snow plate when a perforated plate is attached
to topmost part of the snow plate

Fig. 13

Fig. 12Power spectrums of fluctuating velocity behind the snow fence(with perforated plate)Power spectrums of fluctuating drag and lift of the airfoil snow plates (with perforated plate)20

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

snow plate ①, CD and CL are decreased as compared with snow
plates without the perforated plate, the CD and CL of the airfoil
snow plate of ① being considerably increased as compared withsnow plates without the perforated plate. This is because the separation of the flow along the upper surface of the airfoil snow plateis suppressed as a result of deflection by the perforated plate, andnegative pressure on the upper surface is increased. Accordingly,
this situation must be taken into account when evaluating therequired strength of the airfoil snow plate of ①.

Fig. 14 CD and CL of each snow plate when a perforated plate is attached
to topmost part of the snow plate

Fig. 16

Rotary oscillation response of snow plate number ① when a perforated plate is attached to the topmost part of the snow fence

Fig. 15

Fig. 17

Response of each snow plate when a perforated plate is attachedto the topmost part of the snow fence

Rotary oscillation response of each snow plate in the absence ofa perforated plate

3.4

Vibration characteristics and suppression of the vibrationof a snow plate
The response of the airfoil snow plates was measured by theuse of the free-rotation vibration equipment shown in Fig.2.
Figure 15 shows the response characteristics of each airfoil snow
plate in the snow fence without a perforated plate. The ordinate

DEVELOPMENT OF A NEW TYPE SNOW FENCE WITH AIRFOIL SNOW PLATES TO PREVENT BLOWING-SNOW DISASTERS:PART 2,
CHARACTERISTICS OF THE AERODYNAMIC FLUID FORCES OF AIRFOIL SNOW PLATES

gives the rms value of the amplitude angle, a, of rotational oscillation. The abscissa gives the reduced velocity, Ur [=U/(fc・W)].
Negligible the flow-induced vibration occurs at the airfoil snow
plates ②, ③, and ④, whereas vibrations of the airfoil snow plate① occur from approximately Ur=4.0 and are quickly amplified
with the increase in the reduced velocity.
Figure 16 shows the response characteristics of the airfoil
snow plate of ① when the perforated plate is installed in the topmost part of the snow fence. The porosity of the perforated plate
was varied at 0%, 20%, 30%, and 40%, and the interval G/H at
0.029, 0.043, and 0.057. The rotational oscillation response
decreases with the porosity of the perforated plate. Notably, thegeneration of flow-induced vibration is completely suppressed at
the porosity of a=40% and interval of G/H=0.057. The generationof flow-induced vibration of the airfoil snow plate of ① therefore
can be completely prevented by installing a perforated plate.
Figure 17 shows the response characteristics of the airfoil snow
plates for installation of a perforated plate of a=40% and
G/H=0.057. No generation of flow-induced vibration wasobserved for either airfoil snow plate. These findings indicate that
installation of a perforated plate is very effective in suppressing thegeneration of flow-induced vibration of airfoil snow plates.

21

3.5

Performance evaluation of the snow fence with a perforated plate
The snow fence that gave the best performance had a height of
H=2.8 m, bottom gap of K=1.2 m, size of W=650 mm and setup
angle of β=60°for Jowkowsky airfoil snow plate. Installation of
the perforated plate at the topmost part of the snow fence is very
effectively suppresses flow-induced vibration of the airfoil snow
plates. Therefore, when a perforated plate is installed at the topmost part of such a snow fence the effectiveness of the fence forpreventing blowing snow disasters was investigated. Figure 18
shows the spatial density distributions of blowing-snow around thesnow fence for differences in the porosity of the perforated plate
when the interval between the airfoil snow plate attached to the
topmost part of the snow fence and perforated plate was constant at
G/H=0.057. The density distribution of blowing-snow was measured in a blowing-snow wind tunnel. High-density, blowing snow
passed to the vicinity of the road surface increases as porosity
increases. For a porosity of a=40%, most of the blowing-snow
passes below half the driver's eye level of 1.35 m, and visibility ismore greatly improved as compared with visibility without the perforated plate, evidence that the installation of a perforated plate
therefore is a very effective method for improving visibility.
4. CONCLUSIONS(1) Time-averaged and fluctuating fluid forces acting on a snow
fence and airfoil snow plates examined could evalute of therequired design strength.
(2) Fluctuating fluid forces acting on airfoil snow plates, which
are induced by the rolling-up of the shear layer separated fromthe topmost part of the snow fence, are the greatest on an airfoil
snow plate installed at the topmost part of the snow fence.
(3) Flow-induced vibration of the airfoil snow plate at the topmost part of the snow fence is generated and amplified by anincrease in wind velocity.
(4) A perforated plate installed at the topmost part of the snow
fence is very effective for suppressing the fluctuating fluid
forces that act on airfoil snow plates.
(5)
Flow-induced vibration of airfoil snow plates can be completely suppressed by the use of a perforated plate with porosityof a=40% and setup interval of G/H=0.057.
(6) The blowing-off performance of a snow fence with the perforated plate is much better than that of a snow fence without sucha plate.
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

Fig. 18

Density distribution of blowing snow for the snow fence with aperforated plate

Sakamoto, H., Haniu, H., Kiyota, M. and Obata, Y., 1992. Development
and performance of snow fences for the prevention of blowing-snow
disasters, Transactions of the Japan Society of Mechanical Engineers(B), 58; 550: 2017-2023. (in Japanese).
Sakamoto, H., Moriya, M., Takai, K. and Obata, Y., 2000. Development of

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

a new type snow fence with airfoil snow plates to prevent blowingsnow disasters (Part 1 Evaluation of performance by blowing-snow
simulation in a wind tunnel), Journal of Natural Disaster Science.
So, R.M.C. and Savkar, S.D., 1981. Buffeting forces on rigid circular cylinders in cross flows, Journal of Fluid Mechanics, 105; 397-425.

NOMENCLATURE
A : projected area based on length of H'=( H−K )a : porosity of the perforated plate
CD : time-averaged drag coefficient of the airfoil snow plate
CDf : fluctuating drag coefficient of the airfoil snow plate
CDH: time-averaged drag coefficient of the snow fence
CL : time-averaged lift coefficient of the airfoil snow plate
CLf : fluctuating lift coefficient of the airfoil snow plate
CLH : time-averaged lift coefficient of the snow fence
CR : time-averaged resultant force coefficient of the airfoil
snow plate
D : time-averaged drag acting on the airfoil snow plate

Df : fluctuating drag acting on the airfoil snow plate
DH : time-averaged drag on the snow fenced : porous hole diameter of the perforated platefc : natural frequency of the airfoil snow plate
fv : frequency of vortex shedding from the airfoil snow plate
G : interval between the airfoil snow plate and perforatedplate
H : height of the snow plate
K : height of the bottom gap
L : time-averaged lift of the airfoil snow plate
Lf : fluctuating lift of the airfoil snow plate
LH : time-averaged lift of the snow fencel : span length of the airfoil snow plate
Ur : reduced velocity
Urc : reduced velocity for vortex resonancew : width of the perforated plate
α : rms value of amplitude angle