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Gusty wind effects on driving safety of road vehicles
Journal o f Wind Engineering and Industrial Aerodynamics, 9 (1981) 181--191
181
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
GUSTY WIND EFFECTS ON DRIVING SAFETY OF ROAD VEHICLES*
NOBUYUKI NARITA
Structure Division, Structure and Bridge Department, Public Works Research Institute, Tsukuba Science City (Japan) MASATAKA KATSURAGI
Structure Division, Structure and Bridge Department, Public Works Research Institute, Tsukuba Science City (Japan)
Summary In this paper gusty wind characteristics produced by the effect of a local topographical feature are discussed in connection with the driving safety of road vehicles. The characteristics are derived from both field observations and wind-tunnel experiments. The field observations were carried out to clarify the wind flow pattern under the present full-scale topographical conditions and to allow comparison with the results of wind-tunnel experiments. The main purpose of the wind-tunnel experiments was to determine effective measures to improve the driving safety with respect to wind by modifying the topographical features. From the study it was found that a slight modification of the topographical features could improve the wind flow pattern in terms of the driving safety of road vehicles for particular wind conditions.
1. Introduction A driver has no problem in controlling a car under uniform wind conditions. In gusty wind, however, he or she m a y often lose control of the car due to the effects o f irreg~llarity in the wind flow conditions, and sudden changes in windspeed and/or wind direction m a y cause serious traffic accidents. On 29th October 1976, a small-sized unloaded truck with a h o o d travelling on National Highway R o u t e 8 toward Niigata City overturned near the Yoneyama Bridge in Niigata Prefecture, Japan. The m a x i m u m windspeed was estimated to be in excess of 30 m s -1 and the wind direction at the time was from between north-west and south-west. The strong, turbulent wind produced by the local topographical features in this area is considered to have played an important role in the matter.
*Paper presented at the 4th Colloquium on Industrial Aerodynamics (Vehicle Aerodynamics), Aachen, June 18, 1980.
0304-3908/0000--0000/$02.50 © 1981 Elsevier Scientific Publishing Company
182
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183
2. Topographical features near the Yoneyama Bridge The overturning accident occurred at a distance of ~ 2 0 0 m from the abutment of the Y o n e y a m a Bridge. The c o n t o u r map around this point is shown in Fig. 1. National Highway R o u t e 8 runs from south-west to north-east along the cliff configuration at a height of ~ 5 0 m. A small swelling ~ 4 m in height is located on the north-west side of the road and ~ 1 0 0 m away from the abutment. On the opposite side of the swelling, there is a cut-off slope of maximum height 20 m and length 180 m, with an inclination angle of ~ 4 0 °. Another road comes up from below the Yoney~ma Bridge and joins R o u t e 8 on the north~east side of the small hump. Figure 2 shows these topographical features.
Fig. 2. Topographical features near Yoneyama Bridge.
3. Field observations Field observations were c o n d u c t e d in order to clarify the wind flow pattern around the site with the present topographical features. This work was carried o u t b y the Nagaoka Works Office, Hokuriku Regional Construction Bureau, Ministry of Construction, under the technical guidance of PWRI, in 1978. An observation rack equipped with three Makino-type three-cup anemometers at heights of 1, 2, and 3 m above ground level was used. The o u t p u t for a given 2-min period was recorded on a pen oscillograph. After the measurements had been completed at one point, the rack was moved to the next Fig. 1. Contour map for region near Yoneyama Bridge.
184
position. The reference wind conditions were obtained continuously at a position 2.6 m above the t o p of the small hump, using another anemometer of the same type. The wind roses giving the distribution of wind directions recorded on 15th February 1978 are shown in Fig. 3. The dominant wind directions at each observation point on the road are greatly different from that at the reference point. Judging from these results, the wind transverse to the road axis is reflected from the surface of the cut-off slope and blows back near the road surface counter to the prevailing direction. Under these conditions, a car travelling on Y o n e y a m a Bridge is subjected to a north-west wind, while near the overturning point it is subjected to wind from the opposite side. This wind flow pattern, in which the wind direction changes suddenly at the critical point, is n o t desirable from the viewpoint of driving safety of road vehicles.
@
®
®
®
@
s~''°'° o,
Run-2 H = I.Om 13.32-13.48, 15 Fob. 1978
Fig. 3. R e m i t s of field observations.
4. Wind-tunnel experiments 4.1 Aims o f the wind-tunnel experiments The aims of the wind-tunnel experiments may be summarized as follows: (1) to grasp the wind flow characteristics for the present topographical features; and
185
the driving
(2) to determine effective measures to improve safety by changing the topographical features. The counter-measures considered were the removal of the small h u m p and/or the change of the inclination angle of the cut-off slope.
4.2 Topographical model The topographical model was constructed at a scale of 1/200 to simulate the topography within a circulararea I k m in di_ameteraround the overturning point. The small h u m p can be partiallyremoved and the inclinationangle of the cut~)ffslope can also be changed using replacement parts.Table I indicates the types of counter-measures examined for changing the wind flow pattern. TABLE 1 T y p e s o f c o u n t e r - m e a s u r e s a d o p t e d in t h e m o d e l t e s t s Model
Counter-measures
A
no counter-measures (present topographical features) r e m o v a l o f t h e small h u m p slope angle c h a n g e d t o ~ 63 ° slope angle c h a n g e d t o ~ 34 ° r e m o v a l o f t h e small h u m p , a n d ~ 6 3 ° slope angle (B + C) r e m o v a l o f t h e small h u m p , a n d ~ 3 4 ° slope angle (B + D)
B
C D E F
4.3 Wind tunnel The experiments were carried o u t in the open-ended wind tunnel at PWRI (Fig. 4) which has a working section 6 m in width, 3 m in height and 24 m in length. Figure 5 shows an inside view of the working section with the topographical model installed. 7.9S0
/ / ~ k,e.~/BY-PA'II"I ~\ //-~-~'°"V AIRSPEED CONTRACTION CARTDUCT~ \ ~, !1111i,.'." k
" ~ ' ~
.fCOmROL DAMPER
ST SECTION
I
~
-]11
~..-'t-~, ",, 'JIt
o
l!lli,'
IRECTIsILENcERMESH ROOM/[liP? AIR FILTER Fig. 4. W i n d t u n n e l a t PWRI.
I
186
Fig. 5. W i n d t u n n e l a n d t o p o g r a p h i c a l m o d e l .
A series of wind-tunnel experiments were performed under various conditions of model type, wind direction, and wind-tunnel air velocity, as shown in Table 2. TABLE 2 Conditions for the experiments Model
Wind-tunnel air v e l o c i t y
Wind direction
(ms -1)
NW
N
W
SW
1.5 3.5 5.0
1 2 26
8 31
14
--
B
3.5
3
9
15
--
C
3.5
4
10
16
--
D
3.5 5.0
5 27
11 30
17 20
23 22
E
3.5
6
12
18
--
F
3.5 5.0
7 28
13 29
19 21
25 24
A
187
4.4 Measurement equipment Mini-arrows and one-component hot-wire anemometers were used for the measurements of wind velocity and direction. The mini-arrows, made of piano-wire and paper (Fig. 6), gave an approximate indication of the wind flow pattern. Although hot-wire anemometers are well adapted for measuring gusty wind, close attention must be paid in using them, because of their strong directivity. Accordingly, a one-component hot-wire anemometer supported vertically was rotated on its axis with reference to the wind direction measured by the use of mini-arrows. Measurements were taken when the output showed a maximum, namely when the hot wire made a right-angle with the wind flow, at twenty specific points at intervals of 10 m along the centerline of the road and at heights of 1, 3, 5, and 10 m above the road surface. The reference point was the same as that in the field observations.
V--V
Fig. 6. Example of mini-arrows used to determine flow direction.
4.5 Results of wind.tunnel experiments Some examples of the wind-tunnel experimental results are presented in Figs. 7--14, where the wind speed and direction I m above the road surface are expressed by vector arrows. 5. D i s c u s s i o n
5.1 Flow under present topographical conditions (Model A) Figures 7 and 8 show the wind flow patterns at a height of 1 m above the road surface under the present topographical conditions for wind directions of north-west and west. Figure 7 may be compared with the results of field observations (Fig. 3). Although complete agreement between them in wind direction cannot be seen, the wind flow reflected from the c u t o f f slope is apparent in the model tests. For a north-westerly wind (Fig. 7), there are three points where the wind direction changes suddenly. This may cause mishandling of vehicles, resulting in traffic accidents. V and Vma x (respectively the mean and maximum windspeeds at twenty points above the road) are respectively 48% and 83% of V (the wind-tunnel air velocity).
188
WIND~ AIRVELOCITY 5,0 M/S ,." ,/ ~ • WI~ DI~CTION NW / .." ~
I
,.-.-'"
-._..~__I- .
/ ~.,,,~"~
5,0 MIS
Fig. 7. Results of wind-tunnel experiments: Model A, wind direction north-west.
WIND~ AIRVE].OCIY 3,5 ~S ,'" ,'" ~ Will} DI~dL'I'ION W / ./' ~
/ ~"-
Fig. 8. Results of wind-tunnel experiments: Model A, wind direction west.
fl]tt.L ~IE B WIND~ AIRVELOCIY 3,5 M/S / / WI~ DIRECTIC~ NW ' /
s~~ "sI q .'" ..-
/
,I
~
~
J
Fig. 9. Results of wind-tunnel experiments: Model B, wind direction north-west.
189
The wind directions above the road for a westerly wind are more stable (Fig. 8), but V is much larger (63% of V) than for the north-westerly wind by which the overturning accident might have been caused. Judging from the wind direction on the day of the accident (NW--SW), it is not clear whether the accident was caused by the sudden changes in wind direction developed under north-westerly wind, or by the strong following wind under a westerly wind. For northerly wind, wind flow patterns dangerous fur running cars were not recognized. 5. 2 Model B For the case of north-westerly wind (Fig. 9), the reflected flow behind the hump observed in Model A is absent, due to the removal of the hump. V and Vmax are respectively 44% and 92% of V; the former value is smaller and the latter is larger than those in Model A. Accordingly, removal of the hump is considered to be effective in the sense of changing the wind direction characteristics into more stable ones. No desirable changes in the wind flow pattern are expected to result for westerly wind. 5.3 Model C The wind flow characteristics under north-westerly (Fig. 10) and westerly winds are similar to those in Model B.
~"-~ "-..--, ;"
)
"'"
-~'~
'~
"
~"
~~'~11
-"!1
v --~---~----~ " 3.5 M/S Fig. I0. Results of wind-tunnel experiments: Model C, wind direction north-west.
5.4 Model D For north-westerly wind (Fig. 11), the wind directions above the road show similar tendencies to those in Model A. On the other hand, the windspeeds are greatly reduced; V and Vmax are respectively 32% and 47% of V. Therefore, making the slope angle more gentle is estimated to be an effective measure in the sense of reducing the windspeeds. No desirable effects are expected to result for westerly wind.
190
f/ ~ ~ ~
~
I/
wI~v~ AIR~_OCI:Y , WI~DI~CTI~ NW
3.5 ~S ,'"
/'
/
,'" /'> // ~ _..,~"~-
3,5 MIS
Fig. 11. Results of wind-tunnel experiments: Model D, wind direction north-west.
WINDII//IIAIR~IOCI~Y 3,5 ~S /" ,'" //'> / DI~CTI~ NW / ./' ~ _..,,,a"~-
~
/
"""L",...-,..--"
~ ~ ~ 7 ~ - ~ ~
: ~-~-~
"~"
=
,,
3,5 ~ S
Fig. 12. Results of wind-tunnel experiments: Model E, wind direction north-west.
WINDDIRECTION NW
"',%'-,.
/
._: /
-
5.0
./
,"
x / ~,,~a.t
~'~'-'~o~v,~_ ~
j.
~S
Fig. 13. Results of wind-tunnel experiments: Model F, wind direction north-west.
'I~
191
5. 5 Model E In the case o f north-westerly wind (Fig. 12), the sudden changes in wind direction are controlled, and moreover V is reduced to 38% of V, in comparison with Model A. However, Vmax is rather large, 79% of V. 5.6 Model F The windspeeds and directions above the road are greatly improved under north-westerly wind (Fig. 13), due to the fact that this model combines the counter-measures in Model B with those in Model D; namely, V is 38% and Vmax is only 51% of V. Significant changes in the wind flow pattern are not apparent for westerly wind (Fig. 14); V is 64% of V, as in other models.
WI~PJ~ELAIR~..OCI~ 5,0 M/S /'" WI~ DIllON
W
._..
I
..." !
/'" <,~
J~_ _ ~
J
Fig. 14. Results of wind-tunnel experiments: Model F, wind direction west.
6. Conclusions Field observations on wind flow characteristics in a region near the Yoneyama Bridge (refer to Fig. 1) indicate the presence of wind flow reflected from a c u t o f f slope, which is undesirable for the driving safety of road vehicles. A comparison between the results of the field observations and windtunnel experiments shows fairly good agreement. It is not clear whether an overturning accident which occurred near the bridge was caused by the reflected wind flow developed under north-westerly wind or by the strong following wind under westerly wind. The removal of a h u m p on the no~h-west side of the road is shown to reduce the reflected wind flow. The use of a more gentle slope to the northeast results in a lowering of the windspeeds in the area only in the case of north-westerly wind. In the case of north-westerly wind, a combination of the removal of the hump and the more gentle slope is the most effective measure to ensure the driving safety o f road vehicles. None of the counter-measures seemed to have any effects for westerly wind.
181
Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands
GUSTY WIND EFFECTS ON DRIVING SAFETY OF ROAD VEHICLES*
NOBUYUKI NARITA
Structure Division, Structure and Bridge Department, Public Works Research Institute, Tsukuba Science City (Japan) MASATAKA KATSURAGI
Structure Division, Structure and Bridge Department, Public Works Research Institute, Tsukuba Science City (Japan)
Summary In this paper gusty wind characteristics produced by the effect of a local topographical feature are discussed in connection with the driving safety of road vehicles. The characteristics are derived from both field observations and wind-tunnel experiments. The field observations were carried out to clarify the wind flow pattern under the present full-scale topographical conditions and to allow comparison with the results of wind-tunnel experiments. The main purpose of the wind-tunnel experiments was to determine effective measures to improve the driving safety with respect to wind by modifying the topographical features. From the study it was found that a slight modification of the topographical features could improve the wind flow pattern in terms of the driving safety of road vehicles for particular wind conditions.
1. Introduction A driver has no problem in controlling a car under uniform wind conditions. In gusty wind, however, he or she m a y often lose control of the car due to the effects o f irreg~llarity in the wind flow conditions, and sudden changes in windspeed and/or wind direction m a y cause serious traffic accidents. On 29th October 1976, a small-sized unloaded truck with a h o o d travelling on National Highway R o u t e 8 toward Niigata City overturned near the Yoneyama Bridge in Niigata Prefecture, Japan. The m a x i m u m windspeed was estimated to be in excess of 30 m s -1 and the wind direction at the time was from between north-west and south-west. The strong, turbulent wind produced by the local topographical features in this area is considered to have played an important role in the matter.
*Paper presented at the 4th Colloquium on Industrial Aerodynamics (Vehicle Aerodynamics), Aachen, June 18, 1980.
0304-3908/0000--0000/$02.50 © 1981 Elsevier Scientific Publishing Company
182
!
•
p..4 ~ - ,
rn
ii
Q
-Jrr
183
2. Topographical features near the Yoneyama Bridge The overturning accident occurred at a distance of ~ 2 0 0 m from the abutment of the Y o n e y a m a Bridge. The c o n t o u r map around this point is shown in Fig. 1. National Highway R o u t e 8 runs from south-west to north-east along the cliff configuration at a height of ~ 5 0 m. A small swelling ~ 4 m in height is located on the north-west side of the road and ~ 1 0 0 m away from the abutment. On the opposite side of the swelling, there is a cut-off slope of maximum height 20 m and length 180 m, with an inclination angle of ~ 4 0 °. Another road comes up from below the Yoney~ma Bridge and joins R o u t e 8 on the north~east side of the small hump. Figure 2 shows these topographical features.
Fig. 2. Topographical features near Yoneyama Bridge.
3. Field observations Field observations were c o n d u c t e d in order to clarify the wind flow pattern around the site with the present topographical features. This work was carried o u t b y the Nagaoka Works Office, Hokuriku Regional Construction Bureau, Ministry of Construction, under the technical guidance of PWRI, in 1978. An observation rack equipped with three Makino-type three-cup anemometers at heights of 1, 2, and 3 m above ground level was used. The o u t p u t for a given 2-min period was recorded on a pen oscillograph. After the measurements had been completed at one point, the rack was moved to the next Fig. 1. Contour map for region near Yoneyama Bridge.
184
position. The reference wind conditions were obtained continuously at a position 2.6 m above the t o p of the small hump, using another anemometer of the same type. The wind roses giving the distribution of wind directions recorded on 15th February 1978 are shown in Fig. 3. The dominant wind directions at each observation point on the road are greatly different from that at the reference point. Judging from these results, the wind transverse to the road axis is reflected from the surface of the cut-off slope and blows back near the road surface counter to the prevailing direction. Under these conditions, a car travelling on Y o n e y a m a Bridge is subjected to a north-west wind, while near the overturning point it is subjected to wind from the opposite side. This wind flow pattern, in which the wind direction changes suddenly at the critical point, is n o t desirable from the viewpoint of driving safety of road vehicles.
@
®
®
®
@
s~''°'° o,
Run-2 H = I.Om 13.32-13.48, 15 Fob. 1978
Fig. 3. R e m i t s of field observations.
4. Wind-tunnel experiments 4.1 Aims o f the wind-tunnel experiments The aims of the wind-tunnel experiments may be summarized as follows: (1) to grasp the wind flow characteristics for the present topographical features; and
185
the driving
(2) to determine effective measures to improve safety by changing the topographical features. The counter-measures considered were the removal of the small h u m p and/or the change of the inclination angle of the cut-off slope.
4.2 Topographical model The topographical model was constructed at a scale of 1/200 to simulate the topography within a circulararea I k m in di_ameteraround the overturning point. The small h u m p can be partiallyremoved and the inclinationangle of the cut~)ffslope can also be changed using replacement parts.Table I indicates the types of counter-measures examined for changing the wind flow pattern. TABLE 1 T y p e s o f c o u n t e r - m e a s u r e s a d o p t e d in t h e m o d e l t e s t s Model
Counter-measures
A
no counter-measures (present topographical features) r e m o v a l o f t h e small h u m p slope angle c h a n g e d t o ~ 63 ° slope angle c h a n g e d t o ~ 34 ° r e m o v a l o f t h e small h u m p , a n d ~ 6 3 ° slope angle (B + C) r e m o v a l o f t h e small h u m p , a n d ~ 3 4 ° slope angle (B + D)
B
C D E F
4.3 Wind tunnel The experiments were carried o u t in the open-ended wind tunnel at PWRI (Fig. 4) which has a working section 6 m in width, 3 m in height and 24 m in length. Figure 5 shows an inside view of the working section with the topographical model installed. 7.9S0
/ / ~ k,e.~/BY-PA'II"I ~\ //-~-~'°"V AIRSPEED CONTRACTION CARTDUCT~ \ ~, !1111i,.'." k
" ~ ' ~
.fCOmROL DAMPER
ST SECTION
I
~
-]11
~..-'t-~, ",, 'JIt
o
l!lli,'
IRECTIsILENcERMESH ROOM/[liP? AIR FILTER Fig. 4. W i n d t u n n e l a t PWRI.
I
186
Fig. 5. W i n d t u n n e l a n d t o p o g r a p h i c a l m o d e l .
A series of wind-tunnel experiments were performed under various conditions of model type, wind direction, and wind-tunnel air velocity, as shown in Table 2. TABLE 2 Conditions for the experiments Model
Wind-tunnel air v e l o c i t y
Wind direction
(ms -1)
NW
N
W
SW
1.5 3.5 5.0
1 2 26
8 31
14
--
B
3.5
3
9
15
--
C
3.5
4
10
16
--
D
3.5 5.0
5 27
11 30
17 20
23 22
E
3.5
6
12
18
--
F
3.5 5.0
7 28
13 29
19 21
25 24
A
187
4.4 Measurement equipment Mini-arrows and one-component hot-wire anemometers were used for the measurements of wind velocity and direction. The mini-arrows, made of piano-wire and paper (Fig. 6), gave an approximate indication of the wind flow pattern. Although hot-wire anemometers are well adapted for measuring gusty wind, close attention must be paid in using them, because of their strong directivity. Accordingly, a one-component hot-wire anemometer supported vertically was rotated on its axis with reference to the wind direction measured by the use of mini-arrows. Measurements were taken when the output showed a maximum, namely when the hot wire made a right-angle with the wind flow, at twenty specific points at intervals of 10 m along the centerline of the road and at heights of 1, 3, 5, and 10 m above the road surface. The reference point was the same as that in the field observations.
V--V
Fig. 6. Example of mini-arrows used to determine flow direction.
4.5 Results of wind.tunnel experiments Some examples of the wind-tunnel experimental results are presented in Figs. 7--14, where the wind speed and direction I m above the road surface are expressed by vector arrows. 5. D i s c u s s i o n
5.1 Flow under present topographical conditions (Model A) Figures 7 and 8 show the wind flow patterns at a height of 1 m above the road surface under the present topographical conditions for wind directions of north-west and west. Figure 7 may be compared with the results of field observations (Fig. 3). Although complete agreement between them in wind direction cannot be seen, the wind flow reflected from the c u t o f f slope is apparent in the model tests. For a north-westerly wind (Fig. 7), there are three points where the wind direction changes suddenly. This may cause mishandling of vehicles, resulting in traffic accidents. V and Vma x (respectively the mean and maximum windspeeds at twenty points above the road) are respectively 48% and 83% of V (the wind-tunnel air velocity).
188
WIND~ AIRVELOCITY 5,0 M/S ,." ,/ ~ • WI~ DI~CTION NW / .." ~
I
,.-.-'"
-._..~__I- .
/ ~.,,,~"~
5,0 MIS
Fig. 7. Results of wind-tunnel experiments: Model A, wind direction north-west.
WIND~ AIRVE].OCIY 3,5 ~S ,'" ,'" ~ Will} DI~dL'I'ION W / ./' ~
/ ~"-
Fig. 8. Results of wind-tunnel experiments: Model A, wind direction west.
fl]tt.L ~IE B WIND~ AIRVELOCIY 3,5 M/S / / WI~ DIRECTIC~ NW ' /
s~~ "sI q .'" ..-
/
,I
~
~
J
Fig. 9. Results of wind-tunnel experiments: Model B, wind direction north-west.
189
The wind directions above the road for a westerly wind are more stable (Fig. 8), but V is much larger (63% of V) than for the north-westerly wind by which the overturning accident might have been caused. Judging from the wind direction on the day of the accident (NW--SW), it is not clear whether the accident was caused by the sudden changes in wind direction developed under north-westerly wind, or by the strong following wind under a westerly wind. For northerly wind, wind flow patterns dangerous fur running cars were not recognized. 5. 2 Model B For the case of north-westerly wind (Fig. 9), the reflected flow behind the hump observed in Model A is absent, due to the removal of the hump. V and Vmax are respectively 44% and 92% of V; the former value is smaller and the latter is larger than those in Model A. Accordingly, removal of the hump is considered to be effective in the sense of changing the wind direction characteristics into more stable ones. No desirable changes in the wind flow pattern are expected to result for westerly wind. 5.3 Model C The wind flow characteristics under north-westerly (Fig. 10) and westerly winds are similar to those in Model B.
~"-~ "-..--, ;"
)
"'"
-~'~
'~
"
~"
~~'~11
-"!1
v --~---~----~ " 3.5 M/S Fig. I0. Results of wind-tunnel experiments: Model C, wind direction north-west.
5.4 Model D For north-westerly wind (Fig. 11), the wind directions above the road show similar tendencies to those in Model A. On the other hand, the windspeeds are greatly reduced; V and Vmax are respectively 32% and 47% of V. Therefore, making the slope angle more gentle is estimated to be an effective measure in the sense of reducing the windspeeds. No desirable effects are expected to result for westerly wind.
190
f/ ~ ~ ~
~
I/
wI~v~ AIR~_OCI:Y , WI~DI~CTI~ NW
3.5 ~S ,'"
/'
/
,'" /'> // ~ _..,~"~-
3,5 MIS
Fig. 11. Results of wind-tunnel experiments: Model D, wind direction north-west.
WINDII//IIAIR~IOCI~Y 3,5 ~S /" ,'" //'> / DI~CTI~ NW / ./' ~ _..,,,a"~-
~
/
"""L",...-,..--"
~ ~ ~ 7 ~ - ~ ~
: ~-~-~
"~"
=
,,
3,5 ~ S
Fig. 12. Results of wind-tunnel experiments: Model E, wind direction north-west.
WINDDIRECTION NW
"',%'-,.
/
._: /
-
5.0
./
,"
x / ~,,~a.t
~'~'-'~o~v,~_ ~
j.
~S
Fig. 13. Results of wind-tunnel experiments: Model F, wind direction north-west.
'I~
191
5. 5 Model E In the case o f north-westerly wind (Fig. 12), the sudden changes in wind direction are controlled, and moreover V is reduced to 38% of V, in comparison with Model A. However, Vmax is rather large, 79% of V. 5.6 Model F The windspeeds and directions above the road are greatly improved under north-westerly wind (Fig. 13), due to the fact that this model combines the counter-measures in Model B with those in Model D; namely, V is 38% and Vmax is only 51% of V. Significant changes in the wind flow pattern are not apparent for westerly wind (Fig. 14); V is 64% of V, as in other models.
WI~PJ~ELAIR~..OCI~ 5,0 M/S /'" WI~ DIllON
W
._..
I
..." !
/'" <,~
J~_ _ ~
J
Fig. 14. Results of wind-tunnel experiments: Model F, wind direction west.
6. Conclusions Field observations on wind flow characteristics in a region near the Yoneyama Bridge (refer to Fig. 1) indicate the presence of wind flow reflected from a c u t o f f slope, which is undesirable for the driving safety of road vehicles. A comparison between the results of the field observations and windtunnel experiments shows fairly good agreement. It is not clear whether an overturning accident which occurred near the bridge was caused by the reflected wind flow developed under north-westerly wind or by the strong following wind under westerly wind. The removal of a h u m p on the no~h-west side of the road is shown to reduce the reflected wind flow. The use of a more gentle slope to the northeast results in a lowering of the windspeeds in the area only in the case of north-westerly wind. In the case of north-westerly wind, a combination of the removal of the hump and the more gentle slope is the most effective measure to ensure the driving safety o f road vehicles. None of the counter-measures seemed to have any effects for westerly wind.