1) The document describes computational fluid dynamics (CFD) simulations of aerodynamic characteristics on rectangular cylinders in both smooth and turbulent flows. 2) For smooth flow, 2D and 3D analyses were conducted using RANS and LES models. Results matched well with previous experimental and computational studies. 3) For turbulent flow, a 3D LES analysis using a "turbulence partial simulation" method was used to model effects on a bridge deck structure. The validity of this method was confirmed by the pressure coefficient distribution matching effects of higher turbulence intensities.

1. Yokohama National University ：soulachack SOUKSIVONGXAY
Simulation of aerodynamic characteristics on rectangular cylinders
by computational fluid dynamics
Email :souksivongxay-soulachack-wk@ynu.ac.jp Yokohama National University soulachack SOUKSIVONGXAY
Wind tunnel testing :
Experimental investigation used in aerodynamic
research to study the effects of air moving past
the objects, but there are some problems: modeling
natural wind, using a lot of times and cost in some cases
Computational Fluid Dynamics Analysis(CFD):
to solve the Navier-Stoke function numerically by large computer capacity,
flow patterns and flow-induced phenomena can be simulated, easy to model
various shapes, using times and cost can be reduced in some cases.
Using CFD together with Wind tunnel testing :
To Investigate the aerodynamic characteristic
for the structural design Will be more efficiency !
Investigation of aerodynamic mechanism around structures
Take a rectangular cylinder as the object of modeling in smooth flow and turbulence flow
Smooth flow: conducted two dimensional analysis (RANS) and Three dimensional analysis(LES)
to calculate the three component static force coefficient(Drag coefficient , Lift
coefficient and moment coefficient) , wind pressure coefficient and flow pattern
around the body…..etc.
compare the present analysis results with the previous studies ' s experimental and
computational results
Turbulent flow: conducted three dimensional analysis(LES)
“the turbulence partial simulation” was investigated on a rectangular cylinder
covering a bridge deck structure
Purpose of the study
Difficult to simulate the entire frequency region of the Wind
velocity fluctuation’s power spectral density distribution
⇒ partial similarity is necessary
the aerodynamic characteristic between The created two
turbulent flows based on Irwin’s equation can be similarity
Smooth flow: 2D(RANS) Turbulent flow: 3D(LES)
Reynolds number 2.21E+04
Breadth/depth 0.3～3.0
Time step（Δt） 0.005(s)
Number of time step 1000
Number of elements 21360～21786
Reynolds number 2.21E+04
Breadth/depth 1.0
Time step（Δt） 0.005(s)
Number of time step 1000
Number of elements 120532
Analysis modeling and technique
CD=2.73 CD=2.20CD=3.43
Analysis result (Turbulent flow)
Analysis result (Smooth flow)
Present analysis result Experimental and analysis result of
previous studies
Figure-2:Distribution of time-averaged horizontal wind velocity
on the central axis (B/D=1.0)
Figure-1:rerationship between drag coefficient and
Cross-sectional breadth/depth ratio
★the CD was evaluated higher than the previous results. But
the whole tendency and critical cross-section was matched
★the separated flow pattern around the critical cross section
was verified (most approached to the rear side)
B/D=0.3 B/D≒0.6 B/D=1.0
B
No-slip条件(u=v=0)
D=10cm
5D5D
5D 20D
Slip （U≠0,V=0）
Slip （U≠0,V=0）
inlet U0=4.1m/s
Figure-3:wind speed fluctuation power spectral
density distribution
Figure-4:pressure coefficient distribution on the
object’s surface
：Hino
：ESDU74031
：Ｉu=5%,Lu/D=1.0
：Ｉu=7.5%,Lu/D=3.375
⇒自然風
★ Irwin’s equation(similarity requirement for small-scale Vortex region)
High-frequency Sub-inertia range power
spectral density distribution can be simulated
★ the turbulence partial simulation method’s validity(● ●) is confirmed
by the pressure coefficient distribution on the object’s surface(Fig-4),
due to the effects of larger turbulence intensity(●) the greater negative
pressure is appeared
●：Iu=5%,Lu/D=1.0
0.0
0.5 1.5
2.0
Xp
風
●：Iu=7.5%,Lu/D=3.375
●：Iu=10%,Lu/D=1.0
Xp
Cp
E(f)
f(Hz)
Conclusion:
1) Aerodynamic characteristics around the object placed in the smooth flow：
Flow pattern properties around the object and the averaged aerodynamic
force coefficients are in good agreement with experimental and analysis results
of the previous studies
2) Aerodynamic characteristics around the object placed in the turbulent flow:
the turbulence partial simulation methods validity is confirmed. But, need to
consider in various cases and methods
rather than the simulation of turbulence intensity(Ｉu) “the turbulence partial
simulation” will be an alternative and reasonable method to simulate
the turbulence effects on a bridge deck structures
Karman vortex shedding
(Turbulence similarity requirement )
Ｉu: turbulence intensity
Lu: turbulence scale
Irwin’s equation:
◊ ：Nakaguchi et al.
Δ ：Ohtsuki et al.
○：Tamura&Ito(3D cal.)
●：Shimada&Ishihara(2D cal.)
Main analysis parameters:Main analysis parameters:
Critical cross-section
B/D≒0.6 Critical cross-section
B/D≒0.6
CD
B/D
Present analysis result Experimental and analysis result of
previous studied
the whole tendency and cavity region was corresponded well
with the previous studies
：Shimada&Ishihara
：Franke&Rodi
：Kato&Launder
：Experiment by I.yn
Cavity region
U/U0
X/D
X/D
U/U0
Outlet(P=0)