Flow over Cylinder-ANSYS
OBJECTIVE-For Re = 100, simulate the flow over a cylinder using steady and transient mode.
Steps involved in the simulation
- Geometry
- Mesh
- Setup
- Solution
- Results
Flow over cylinder-Steady state
Geometry-A 2d geometry was created for cylinder and a domain for analysis.
Mesh-
Element size-0.25
No of elements in Mesh-40502
Inflation layers were generated to capture detailed physics near wall surface
No of inflation layers-6
Growth rate-1.2
The figure below shows the inflation layers.
Setup-
Solver Type-Pressure Based Solver
Steady state
Model-Viscous laminar
Boundary conditions- Inlet-Velocity inlet=1 m/s
Outlet=pressure outlet=0 pa
Symmetry-Symmetry
Cylinder wall-Wall
Material properties- Density=1 kg/m3 , Dynamic viscosity=0.02 kg-m/s
Reynolds no.-`(rhovd)/mu`=`(1*1*2)/0.02`=100
Method- SIMPLE
Initialization- Hybrid initialization
Solution-
The solution converged at around 400 iterations.This can be seen from the below graph that the residuals have become constant after 400 iterations.
Results-
Velocity Contour
Vortex Shedding can be seen in the velocity contour
Pressure Contour
Flow over cylinder-Transient State
Geometry-Same as in case of Steady state
Mesh-Same as in case of Steady state
Setup-
Solver Type-Pressure Based Solver
-Transient
Model-Viscous laminar
Boundary conditions- Inlet-Velocity inlet=1 m/s
Outlet=pressure outlet=0 pa
Symmetry-Symmetry
Cylinder wall-Wall
Material properties- Density=1 kg/m3 , Dynamic viscosity=0.02 kg-m/s
Reynolds no.-`(rhovd)/mu`=`(1*1*2)/0.02`=100
Method- SIMPLE
Initialization- Hybrid initialization
Calculations-Time step size-0.1 s
No. of time steps-1000
Solution-
From the residual plot it can be seen that the residuals are repeating itself after 17500 iterations.So we can conclude that the solution is converged.
Vertex average of velocity magnitude
Strouhal number calculation can be only be calculated in case of transient simulation as oscillations cannot be captured wrt time in steady state analysis
Strouhal number calculations
Cylinder diameter=2m
inlet Velocity=1m/s
frequency=No of oscillations per time=7.5/50=0.15
Strouhal Number =(Frequency*Diameter)/velocity=(0.15*2)/1
=0.3
Results-
Velocity Contour
Pressure Contour
CONCLUSION
1. Vortex sheding can be seen in both steady state as well as transient state simulations.But Transient state simulation should be prefered for more realistic results.
2. Strouhal number calculation can only be calculated in case of transient simulation as oscillations cannot be captured wrt time in steady state analysis.