CAE Software【Femtet】Murata Software Co., Ltd.
The flow around the cylinder is analyzed.
The flow velocity distribution, the fluid velocity vectors, the streamlines, the vorticity, and the force on the wall face are solved.
Unless specified in the list below, the default conditions are applied.
Item 
Setting 
Analysis Space 
2D 
Model Unit 
mm 
Item 
Tab 
Setting 

Solver 
Solver Selection 
Fluid Analysis [Bernoulli] 

Analysis Type 
Fluid Analysis 
Transient analysis 

Laminar Flow/Turbulent Flow 
Fluid Analysis 
Select Laminar flow 

Layer Mesh Setting for Wall Surface (General Settings) 
Fluid Analysis 
Specify mesh height of 1st layer Height of 1st layer mesh: 0.5 [mm] 

Timestep 
Transient Analysis 
Timestep: Specify


Meshing Setup 
Mesh 
General mesh size: 3[mm] 
The material of Air (000_Air) is set to a rectangular sheet body. The boundary conditions of inlet and outlet are set on the left edge and the right edge respectively.
The slip wall outer boundary condition is applied to the top and bottom edges where the boundary condition is not set.
The model is a circle sheet body and the material is iron (007_Fe).
The edges surrounding a circle is a boundary of solid and fluid. Solid wall is automatically set to them.
Body Number/Type 
Body Attribute Name 
Material Name 
0/Solid 
air 
000_Air(*) 
1/Solid 
column 
007_Fe * 
* Available from the material DB
Boundary Condition Name/Topology 
Tab 
Boundary Condition Type 
Setting 
Inlet/Edge 
Fluid 
Inlet 
Forced Inflow 
Outlet/Face 
Fluid 
Outlet 
Natural Outflow 
Outer Boundary Condition 
Fluid 
Slip Wall 
– 
If Reynolds number exceeds 100, the time dependency of the turbulence occurs. It makes calculation difficult in the steadystate analysis.
The Reynolds number calculated with this model form, material property, and flow velocity is about 126.0. Use transient analysis instead.
Viscosity μ=1.816e5[Pa s]
Density ρ=1.144[kg/m3]
Kinematic viscosity v=μ/ρ=1.816e5/1.144=1.587e5[m2/s]
Flow velocity V=0.05[m/s]
Diameter of cylinder D=0.04[m]
Reynolds number Re = V*L/ν=0.05*0.04/1.587e5 = 126.0
The vectors of the flow velocity distribution around the cylinder at time 48[s] and 50[s] are shown below.
The vectors are adjusted to the same length in the graphics setup.
It is known that at a Reynolds number of 126, the Karman vortices are shed from the alternating sides of the cylinder.
In the diagram below, a vortex appears on the upper side of the cylinder at 48[s] and the lower side at 50[s].
48[s]  
50[s] 
The figure below is the contour of Y component of the vortex at 50[s]. The scale is minimum: 2[/s] and maximum: 2[/s].
The vortex strength in the Y direction is shown. The clockwise vortices are shown in the positive value, and the counterclockwise vortices in the negative value.
You can observe the vortices are shed downstream from the cylinder.
The force on the wall face is shown by the table.
[column] represents the force which the cylinder receives from the fluid.
The result below shows only column/X component (drag F: force in the flowing direction).
(Double click the graph to show the plot option. Deselect [Display Yaxis (primary axis)] except column/X component. Change the color of column/X component to red.)
The range of the scale for the vertical axis is changed to 0.9 x 10^7 ～1.0 x 10^7.
The drag force near time 50[s] fluctuates centering around 9.8 x 10^8[N] at a cycle of about 2[s].
The result below shows only column/Z component (lift: force in the direction perpendicular to the flow).
(Double click the graph to show the plot option. Deselect [Display Yaxis (primary axis)] except column/X component. Change the color of column/X component to blue.)
You can see that the lift is fluctuating at a constant cycle of about 4 [s].
The drag coefficient CD can be calculated from the drag F.
Thickness in depth direction t = 1[mm]
Cross sectional area S = D * t = 0.04 * 0.001 = 4e5 [m2]
Dynamic pressure Pk = 0.5 * ρ*V^2 = 0.5 * 1.144 * 0.05 * 0.05 = 1.430e3 [Pa]
Drag coefficient (CD) = F / Pk / S = 9.8e8 / 1.430e5 /4e5 = 1.71