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Vortex Shedding
Flow around circular cylinders



MSc student: Bryce Sharman
lada@chalmers.se
Supervisor: Lars Davidson
lada@chalmers.se
Co-supervisor 1: Christoffer Norberg*
chris@ms.vok.lth.se
Co-supervisor 2: Fu-Sang Lien**
fslien@sunwise.uwaterloo.ca
Cooperation: Lund University*
Cooperation: Waterloo University**
Sponsors: -
Publications: [1]
Start of project: September 2000
End of project: December 2001


BACKGROUND
The subject of the periodic vortex shedding behind cylinders, which exhibits oscillatory behaviour, is of direct relevant to many practical applications, e.g. chimneys, offshore pipeline, heat exchangers, masts and wires.
 
When these structures are exposed to cross flow components, the separated flow usually develops vortices which are "shed" first from one side and then from the other side in a more or less regular manner. This phenomenon is referred to as vortex shedding.
 
THE PROJECT
Flows over multiple cylinders are extremely complicated and bear little resemblance to flows over a single cylinder. Flows over two tandem circular cylinders were analysed here. A Reynolds number of 100 was used to ensure that the flow remained laminar.

The CUCFD program was written to solve the Navier-Stokes and the continuity equations on unstructured meshes using a colocated variable arrangement. The Mesh2D and EasyMesh programs were used to generate the unstructured meshes. This program was extensively tested against benchmark tests. It was found to be accurate, especially for low-Reynolds number flows. The mean and fluctuating lift and drag coefficients were recorded for centre-to-centre cylinder spacings between 2 and 10 diameters. A critical cylinder spacing was found between 3.75 and 4 diameters. The fluctuating forces jumped appreciably at the critical spacing. It was found that there exists only one reattachment and one separation point on the downstream cylinder for spacings greater than the critical spacing.

The mean and the fluctuating surface pressure distributions were compared as a function of the cylinder spacing. The surface pressure distributions were also compared against experimental results at different Reynolds numbers for cylinder spacings of two and four diameters. The Reynolds number was found to have a large extect on the surface pressure, but no clear trends were found.

REFERENCES

  1. B. Sharman, "Numerical Predictions of Low Reynolds Number Flows Over Two Tandem Circular Cylinders", MSc Thesis, Mechanical Engineering, Waterloo, Ontarioo, Canada.

 

 


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