Flow over a Circular Cylinder- Practical Significance and Simulation

Flow over a circular cylinder is one of the basic benchmark conventional problems over a range of bluff body problems because of its importance application in aerodynamic and hydrodynamic problems. The study gives important views on flow separation and wake around the cylinder and also formation of vortex shedding is studied as a function of Reynolds number.   

One of the majorly focused results from the study is the Drag force. Practically, in external flow applications the resulted Drag force becomes a major challenge for design engineers in Automotive, Aerospace etc. applications, as built structures in reality are complex and understanding those streamline interfaces and variations in body curvature is a real challenge. One of the ways to solve this problem is to simplify the complex body structure to simple shapes and solve using analytical, experimental (Video shown below) and computational methods. Hence, flow over a circular cylinder problem finds application as one of the simple shapes.

    

Experimental Setup: Flow over a circular cylinder

The problem is studied opting computational technique using Computation Fluid Dynamics (CFD) software and the general steps involved in solving any CFD problem are:

1. Pre-processing: Modeling, Meshing, defining boundaries and Application of physics and Boundary conditions

2. Solver setup: Residual monitoring, Selection of Solving Schemes/Algorithms and iteration setup

3. Post-processing: Display of geometry, grid (mesh) display, Vector and Contour plots, Particle tracking and Graph plots

Initially, problem was defined for steady state and laminar flow application. Simple two dimensional circular cylinder geometry with circular fluid domain was created. Later, the problem was set for meshing.

Fig (a): Meshing

Fig (a), shows the meshing of circular fluid domain over the cylinder. The mesh is finer at the interface of fluid and cylinder surface and gradually becomes coarser as moved away from the cylinder. Why  meshing is made finer at the interface ? is what to be understood by good meshing professional. Meshing technique is always meant as an art.

Fig (b) Velocity contour

Fig (c) Vorticity

Fig (d) Stream function

Fig (b), (c) and (d) shows the simulation results highlighting the Maximum and Average Pressure and Velocity zones, flow separation regions and wake vortex around the cylinder. Also results on Total Drag Force, Drag Coefficients, Vorticity magnitude and Velocity stream function can be plotted/tabulated.

Similarly, the simulation can be carried for varied Reynolds number to understand the vortex shedding also known as Von Karman Vortex street as simulated and experimentally demonstrated in below shown videos and also steady state results can be compared with transient state study.

    

Simulation and Experimental video- Vortex shedding at varied Reynolds number

Likewise the above problem, square cylinder shaped object is studied. It's important application in Tall building, Skyscrapers, offshore structures etc. those are exposed to continuous wind loads.  

Conclusion:

Continuous and rapid increasing innovative design market demands clear understanding of basic problems. Hence, before getting involved in any complex problem solving, it is necessary to start from basics. Flow over a cylinder is one such benchmark problem which helps us to understand various phenomenon and influencing parameters which is still important and applicable in designing many complex models. Theoretical, Conceptual and Physics understanding is must before proceeding to any software tools. This article gives general overview on a problem and application of CFD software for Beginners. 

Finally to mention, this was the first problem solved during my UG program and presented here. 

More theoretical videos can be found for understanding flow over a cylinder, few are below.

   

Thank you for reading and have great learning............... Cheers..!☺