1.Theory and Background:

We want to tackle a classical Fluid Dynamic Problem - Laminar flow of a 2D Cylinder

Critical Reynolds Number would be used to determine accuaracy of our implimentation as there is consensus on this value. Source : Fezia 2018

Choice of Software: Ansys Fluent vs OpenFoam:
Parameters to Consider -

• Automation
• Meshing
• Community Support and Code Ba

2.Simulation:

Inlet Velocity is maintained at 5 m/s while we change Kinematics Viscosity

Boundary Conditions - At Cylinder wall u = v = 0 m/s At inlet u = 5 m/s V = 0 m/s

Max Skewness 0.629 < 0.8

Cell count ~ 18,000

2. Simulation:

Using OpenFoam for ease of Automation / Solver - icoFoam / The solver uses the PISO algorithim to solver the continuity equation

$\nabla \cdot u = 0$

and momnentum equation

$\frac{\partial u}{\partial t} + \nabla \cdot (u \otimes u) - \nabla \cdot (\nu \nabla u) = - \nabla p$

where $u$ is Velocity and $p$ is Kinematic pressure

Integration Time: 0.001 Simulation Time: 5 sec

3. Implementation Challenges

• Boundary Conditions on Top and Bottom Walls and Outlet

  • Symmetry Plane vs No Slip

• Step Time and Simulation Time

  • Sampling Frequency to detect Strouhal Frequency

• Mesh Clarity for Boundary Layer

  • Balancing Mesh Thickness near Boundary layer and Skewness

• Post Processing

4. Results and Discussion

The middle circle is peak frequency where as the 2 cricles abovce and below it are to judge the interval size

Total Simulation Run Time: ~2 hours

Mean Error 8.977 %

Critical Reynold Number: 46 - 49

Click to watch Video for Reynolds number of 100

6. Project Takeaways

• Strouhal Number is highly sensitive parameter

• Computational Fluid Dynamics Require

  • Appropriate Meshing

• Appropriate Time Step

• Understanding Dynamics of the Problem

7. References

1. Fezai, Salwa & Oueslati, Fakher & Ben-Cheikh, Nader & Beya, Brahim. (2018). Sensitivity of wake parameters to diameter changes for a circular cylinder. International Journal of Modern Physics C. 29. 25. 10.1142/S0129183118500870.

2. https://www.openfoam.com/documentation/guides/latest/doc/guide-applications-solvers-incompressible-icoFoam.html

3. Williamson, C.H., & Brown, G.L. (1998). A SERIES IN 1/√Re TO REPRESENT THE STROUHAL–REYNOLDS NUMBER RELATIONSHIP OF THE CYLINDER WAKE. Journal of Fluids and Structures, 12, 1073-1085.

4. Griffith, Martin & Leontini, J. & Thompson, Mark & Hourigan, Kerry. (2011). Vortex shedding and three-dimensional behaviour of flow past a cylinder confined in a channel. Journal of Fluids and Structures - J FLUID STRUCTURE. 27. 855-860. 10.1016/j.jfluidstructs.2011.02.007.