poster presentation in china 2011

Yokohama National University ： soulachack SOUKSIVONGXAY

Simulation of aerodynamic characteristics on rectangular cylindersby 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 flowSmooth 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 resultsTurbulent 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

Turbulence Partial Simulation?

Smooth flow: 2D(RANS) Turbulent flow: 3D(LES)

Reynolds number 2.21E+04Breadth/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+04Breadth/depth 1.0

Time step （ Δt ） 0.005(s)Number of time step 1000Number 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

2DB

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

Slip （ U≠0,V=0 ）

Symmetry plane

（ U≠0,V=0 ）

No-slip (u=v=0)

5D

20D

10D

Figure-3:wind speed fluctuation power spectral density distribution

Figure-4:pressure coefficient distribution on the object’s surface

： Hino ： ESDU74031 ：Ｉ u=5%,Lu/D=1.0 ：Ｉ u=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=1.00.00.5 1.5

2.0

Xp風

● ： Iu=7.5%,Lu/D=3.375 ● ： Iu=10%,Lu/D=1.0

Xp

CpE(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( Ｉ u) “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 ) Ｉ u: 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-sectionB/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/DX/D

U/U0

Out

let (

P=0)