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Use of large eddy simulation to measure fluctuating pressure fields around buildings with wall openings
Journal of Wind Engineering and IndustrialAerodynamics, 46 & 47 (1993) 239-244 Elsevier
239
Use of large eddy simulation to measure fluctuating pressure fields around buildings with wall openings Kazuki Hibi Hiroshi Ueda Toshihiko Wakahara Kenji Shimada I n s t i t u t e of T e c h n o l o g y , S h i m i z u C o r p .
1
Introduction
Assessing the relation between a building's shape and wind-induced vibration has become increasingly important. The present study used large eddy simulation(LES) to perform three-dimensional numerical analysis of fluctuating pressure fields around cubic shaped building models. The cubic models were arrayed uniformly at a distance of 3Hb(Hb denotes building height). In particular, the experiment focuced on the relationship between fluctuating pressure fields around buildings with wall openings(Hb/5 x Hb/5 openings were set in the center of the building surface) and those without openings. Three types of wall opening were examined: facing the direction of the wind; spanwise; and in both directions. This paper analyzes the distribution of mean and fluctuating pressure fields around buildings. Result of these analyses were compared with those from wind tunnel experiments using simultaneous multi-channel pressure measurement techniques. These comparisons provide a number of findings concerning the relation between pressure fields around building and the drag, side and other forces acting on buildings.
2
Outline of LES
Computations were performed on uniform urban blocks composed of cubes, as shown in Fig. 1. The building interval was 3Hb, where Hb denotes the building height. The grid partition used in the computation is shown in Fig. 2. The number of grid points was 64(x) x 56(y) x 53(z), giving a total of 189,952. Cyclic boundary conditions were adopted in streamwise and spanwise directions. Power law boundary conditions were adopted on ground and building surfaces. Numerical analysis was performed using LES and the following basic equations: 0167-6105/93/$06.00 © 1993 - ElsevierSciencePublishers B.V. All fights reserved.
240 Oui Oxi
0
+ Or Oxj
(1)
--0
P
2 .
Ox, (7 +
0
)+
+
(2)
Here, (eii ~ 1/2 ~'scs
=
( C , A ) ~. ~ T
k" = , ~ / ( c ~ , )
Oui
Ouj
eiJ : ~Xj "~ ~'Oxi
J
'
~
. . z,3 = 1,2,3
Cs = 0.1, Ck = 0.094 Top hat filtering was also used. The computations were carried out on three types of buildings with a various of openings: 1. An H b / 5 width opening in the center of the building surface in both streamwise direction and spanwise directions. 2. A streamwise opening.
3. A spanwise opening.
3 3.1
R e s u l t s of N u m e r i c a l A n a l y s e s T i m e series and p o w e r s p e c t r u m for f l u c t u a t i n g p r e s s u r e
Figure 3 shows a time series for differential streamwise and spanwise pressure on building surfaces. Figure 4 shows a power spectrum in both directions. Here, 'pressure difference' denotes a pressure difference between the integrated pressure value of each opposite surface. The streamwise pressure difference shows lower frequency components than the spanwise pressure difference. The spectrum bandwidth of the streamwise pressure difference is therefore broader than the spanwise pressure difference. The spanwise pressure difference spectrum shows a narrow-band frequency component because of vortex shedding behind the building.
3.2
M e a n p r e s s u r e coefficient o f a b u i l d i n g s u r f a c e
Figure 5 shows the mean pressure coefficient of a building surface. The positive pressures near the opening on the windward surface were reduced in the analysis of cubes with streamwise and spanwise openings, but the leeward negative pressure was not changed. In analysis of cubes with a spanwise opening only, side face negative pressure was relatively large. In all cases, roof surface pressure remained at almost the same value.
241 3.3
Mean
pressure
coefficient
distribution
in the
flowfield
Figure 6 shows flowfield pressure distribution around a building in the Hb/2 horizontal plane. A streamwise opening shows a similar tendency but the maximum negative pressure value in the side plane was larger when there was no spanwise opening. A spanwise opening shows a large negative pressure value for the building side and leeward area. 3.4
Fluctuating
pressure
distribution
in the
flowfield
Figure 7 shows a fluctuating pressure field when the maximum streamwise pressure difference value and the spanwise pressure difference value appear in the time series of the Fig. 3. With a spanwise opening, the positive pressure value in the area of -4-0.6 is the largest for in all cases for the windward area of the building, and -0.6 pressure appears in the leeward area of the building. The negative pressure area on the side surface of the building with a spanwise opening is larger than with a streamwise opening.
4
Conclusion Three conclusions were reached. 1. The existence of a streamwise opening reduces the peak value of streamwise and spanwise pressure differences. 2. The spectrum peak value of the spanwise pressure difference falls with the presence of both streamwise and spanwise openings. . Utilization of computational visualization techniques such as flowfield pressure distribution is a powerful way to analyze the mechanism for reducing streamwise and spanwise pressure difference.
References [1]
Dutton, R., and Isyumov, N., 6th U.S. National Conference on Wind Eng. Mar. 1989.
[2]
Murakami,S., A.Mochida, K.Hibi, Numerical Simulation of Velocity and Pressure Fields around Building Models, 7th International Conference on Wind Eng. Vol.2, 1987.
242
--~
3.b
~ /
3Hb
--
Area of computation
Cubic-shap.ed building with ~ openings /
~:
I
4Hb Z
Hb: Building Height
-x
L__~x
4Hb
t
(2)Horizontal plane (with streamwise and spanwise openings)
(1)Vertical plane
Fig. 1 Cubic-shaped Buildings
Fig. 2 Finite difference grid system 0.80 0.60
A
0.30 0,2O I 0.10
0.40
"0.20"0"°V
0.20 0.00 0
20
40
60
80
t*
0
(1) Openings in streamwise and spanwise direction
20
40
80
60
t*
(1) Openings in streamwise
and spanwise direction
0.80
n~ 0.60
A
I~ 040
.~.
0.30 O.2O
0.20 ~/~ A
I~
I~ "0.2o"0"°'~]~N ~..
0.00
.0.30 0
20
40
6O
80
0
(2) Opening in streamwise direction
2o
40
6o
8o t *
(2) Opening in streamwise direction 0.30
0.80
^
~ 0.60 [~
w v ,,-.,
"0.20
v/
0.40
020
M
0.00 0
20
40
fK
A
olo M ~ I~. I~lt I .fL~ , o.oo ,_. ~IV I Vl.t" ~I V "'v ~,~ J~ "0.10 60
80
t*
0
20
40
60
(3) Opening in spanwise direction
(3) Opening in spanwise direction (a) Streamwise pressure difference
Fig. 3 Time R
41.20
(b) Spanwise pressure difference
of fluctuating pressure
t* 80
243 ~0~
__
Openings in streamwise
--
Opening in
....
Opening in spanwise direction
1#
,~61
......
:,
1~2
and spanwise direction streamwise direction
161
~
103 10.2
10.1 100 nHb/<~b>
1~3I 10.2
101
,',~ 10"1 100 nl-~<~b>
(b) Power spectrum in spanwise direction
(a) Power spectrum in streamwise direction
Fi~ 4 Power spectrum of fluctuating pressure l~
101
/ (a) O p e n i n g s In streamwise and spanwlse direction
Openings in streamwise and spanwise direction
.. .......... Opening in 1.0 i~:~ ' sveamwise direction I "~"~. "............. Opening in -..,.
...............ij';::::~....
1,0
..
0,0
~
...
0.0
1,0
(b) Opening in streamwise direction
(a) Vertical plane (center line of building) l.
Openings in atreamwise and spanwise direction
.......... Opening in
1.0 ~-~,. streamwise direction J ",.,~.,.: ............. Opening in I -",...~se direcUon
o ol
......
(c) Opening in spanwise direction
(b) Horizontal plane (height=Hb/2) Fig. $ Mean p r e l m r e ¢oefr~eat
on the building surface
Fig. 6 Distribution of mean pressure field around building
244
(I) Openings In streamwlse and spanwlsedirection
(2) Opening in streamwise direction
(3) Opening in spanwisedirection (a) Moment of maximum streamwise pressure difference
(1) Openings in =treamwise and spanwisedirection
(2) Opening in streamwise direction
(3) Opening in spanwisedirection (b) Moment of maximum spanwise pressure difference
Fig. 7 Distribution of fluctuating pressure field around buildings
239
Use of large eddy simulation to measure fluctuating pressure fields around buildings with wall openings Kazuki Hibi Hiroshi Ueda Toshihiko Wakahara Kenji Shimada I n s t i t u t e of T e c h n o l o g y , S h i m i z u C o r p .
1
Introduction
Assessing the relation between a building's shape and wind-induced vibration has become increasingly important. The present study used large eddy simulation(LES) to perform three-dimensional numerical analysis of fluctuating pressure fields around cubic shaped building models. The cubic models were arrayed uniformly at a distance of 3Hb(Hb denotes building height). In particular, the experiment focuced on the relationship between fluctuating pressure fields around buildings with wall openings(Hb/5 x Hb/5 openings were set in the center of the building surface) and those without openings. Three types of wall opening were examined: facing the direction of the wind; spanwise; and in both directions. This paper analyzes the distribution of mean and fluctuating pressure fields around buildings. Result of these analyses were compared with those from wind tunnel experiments using simultaneous multi-channel pressure measurement techniques. These comparisons provide a number of findings concerning the relation between pressure fields around building and the drag, side and other forces acting on buildings.
2
Outline of LES
Computations were performed on uniform urban blocks composed of cubes, as shown in Fig. 1. The building interval was 3Hb, where Hb denotes the building height. The grid partition used in the computation is shown in Fig. 2. The number of grid points was 64(x) x 56(y) x 53(z), giving a total of 189,952. Cyclic boundary conditions were adopted in streamwise and spanwise directions. Power law boundary conditions were adopted on ground and building surfaces. Numerical analysis was performed using LES and the following basic equations: 0167-6105/93/$06.00 © 1993 - ElsevierSciencePublishers B.V. All fights reserved.
240 Oui Oxi
0
+ Or Oxj
(1)
--0
P
2 .
Ox, (7 +
0
)+
+
(2)
Here, (eii ~ 1/2 ~'scs
=
( C , A ) ~. ~ T
k" = , ~ / ( c ~ , )
Oui
Ouj
eiJ : ~Xj "~ ~'Oxi
J
'
~
. . z,3 = 1,2,3
Cs = 0.1, Ck = 0.094 Top hat filtering was also used. The computations were carried out on three types of buildings with a various of openings: 1. An H b / 5 width opening in the center of the building surface in both streamwise direction and spanwise directions. 2. A streamwise opening.
3. A spanwise opening.
3 3.1
R e s u l t s of N u m e r i c a l A n a l y s e s T i m e series and p o w e r s p e c t r u m for f l u c t u a t i n g p r e s s u r e
Figure 3 shows a time series for differential streamwise and spanwise pressure on building surfaces. Figure 4 shows a power spectrum in both directions. Here, 'pressure difference' denotes a pressure difference between the integrated pressure value of each opposite surface. The streamwise pressure difference shows lower frequency components than the spanwise pressure difference. The spectrum bandwidth of the streamwise pressure difference is therefore broader than the spanwise pressure difference. The spanwise pressure difference spectrum shows a narrow-band frequency component because of vortex shedding behind the building.
3.2
M e a n p r e s s u r e coefficient o f a b u i l d i n g s u r f a c e
Figure 5 shows the mean pressure coefficient of a building surface. The positive pressures near the opening on the windward surface were reduced in the analysis of cubes with streamwise and spanwise openings, but the leeward negative pressure was not changed. In analysis of cubes with a spanwise opening only, side face negative pressure was relatively large. In all cases, roof surface pressure remained at almost the same value.
241 3.3
Mean
pressure
coefficient
distribution
in the
flowfield
Figure 6 shows flowfield pressure distribution around a building in the Hb/2 horizontal plane. A streamwise opening shows a similar tendency but the maximum negative pressure value in the side plane was larger when there was no spanwise opening. A spanwise opening shows a large negative pressure value for the building side and leeward area. 3.4
Fluctuating
pressure
distribution
in the
flowfield
Figure 7 shows a fluctuating pressure field when the maximum streamwise pressure difference value and the spanwise pressure difference value appear in the time series of the Fig. 3. With a spanwise opening, the positive pressure value in the area of -4-0.6 is the largest for in all cases for the windward area of the building, and -0.6 pressure appears in the leeward area of the building. The negative pressure area on the side surface of the building with a spanwise opening is larger than with a streamwise opening.
4
Conclusion Three conclusions were reached. 1. The existence of a streamwise opening reduces the peak value of streamwise and spanwise pressure differences. 2. The spectrum peak value of the spanwise pressure difference falls with the presence of both streamwise and spanwise openings. . Utilization of computational visualization techniques such as flowfield pressure distribution is a powerful way to analyze the mechanism for reducing streamwise and spanwise pressure difference.
References [1]
Dutton, R., and Isyumov, N., 6th U.S. National Conference on Wind Eng. Mar. 1989.
[2]
Murakami,S., A.Mochida, K.Hibi, Numerical Simulation of Velocity and Pressure Fields around Building Models, 7th International Conference on Wind Eng. Vol.2, 1987.
242
--~
3.b
~ /
3Hb
--
Area of computation
Cubic-shap.ed building with ~ openings /
~:
I
4Hb Z
Hb: Building Height
-x
L__~x
4Hb
t
(2)Horizontal plane (with streamwise and spanwise openings)
(1)Vertical plane
Fig. 1 Cubic-shaped Buildings
Fig. 2 Finite difference grid system 0.80 0.60
A
0.30 0,2O I 0.10
0.40
"0.20"0"°V
0.20 0.00 0
20
40
60
80
t*
0
(1) Openings in streamwise and spanwise direction
20
40
80
60
t*
(1) Openings in streamwise
and spanwise direction
0.80
n~ 0.60
A
I~ 040
.~.
0.30 O.2O
0.20 ~/~ A
I~
I~ "0.2o"0"°'~]~N ~..
0.00
.0.30 0
20
40
6O
80
0
(2) Opening in streamwise direction
2o
40
6o
8o t *
(2) Opening in streamwise direction 0.30
0.80
^
~ 0.60 [~
w v ,,-.,
"0.20
v/
0.40
020
M
0.00 0
20
40
fK
A
olo M ~ I~. I~lt I .fL~ , o.oo ,_. ~IV I Vl.t" ~I V "'v ~,~ J~ "0.10 60
80
t*
0
20
40
60
(3) Opening in spanwise direction
(3) Opening in spanwise direction (a) Streamwise pressure difference
Fig. 3 Time R
41.20
(b) Spanwise pressure difference
of fluctuating pressure
t* 80
243 ~0~
__
Openings in streamwise
--
Opening in
....
Opening in spanwise direction
1#
,~61
......
:,
1~2
and spanwise direction streamwise direction
161
~
103 10.2
10.1 100 nHb/<~b>
1~3I 10.2
101
,',~ 10"1 100 nl-~<~b>
(b) Power spectrum in spanwise direction
(a) Power spectrum in streamwise direction
Fi~ 4 Power spectrum of fluctuating pressure l~
101
/ (a) O p e n i n g s In streamwise and spanwlse direction
Openings in streamwise and spanwise direction
.. .......... Opening in 1.0 i~:~ ' sveamwise direction I "~"~. "............. Opening in -..,.
...............ij';::::~....
1,0
..
0,0
~
...
0.0
1,0
(b) Opening in streamwise direction
(a) Vertical plane (center line of building) l.
Openings in atreamwise and spanwise direction
.......... Opening in
1.0 ~-~,. streamwise direction J ",.,~.,.: ............. Opening in I -",...~se direcUon
o ol
......
(c) Opening in spanwise direction
(b) Horizontal plane (height=Hb/2) Fig. $ Mean p r e l m r e ¢oefr~eat
on the building surface
Fig. 6 Distribution of mean pressure field around building
244
(I) Openings In streamwlse and spanwlsedirection
(2) Opening in streamwise direction
(3) Opening in spanwisedirection (a) Moment of maximum streamwise pressure difference
(1) Openings in =treamwise and spanwisedirection
(2) Opening in streamwise direction
(3) Opening in spanwisedirection (b) Moment of maximum spanwise pressure difference
Fig. 7 Distribution of fluctuating pressure field around buildings