Vortex Shedding 
PhD student: 
Ahmad Sohankar lada@chalmers.se 
Supervisor: 
Lars Davidson lada@chalmers.se 
Cooperation:  Dr. Christoffer Norberg 
Sponsors:  The Ministry of Culture and Higher Education of Iran 
Publications:  [18], see references below 
Start of project:  spring 1994 
End of project:  December 1998 
THE PROJECT The subject of flow past slender bluff bodies is of relevance to technical problems associated with energy conservation, structural design and acoustic emissions. In this work, calculations of unsteady 2D and 3Dflow around rectangular cylinders, which are a type of slender bluff bodies, are carried out. Some useful physical quantities such as the dominating wake frequency (Strouhal number), mean and RMS values of lift, drag and moment, various surface pressure were calculated for different Reynolds number. In 2Dcalculations, flow around rectangular cylinders were performed. An incompressible SIMPLEC code is used employing nonstaggered grid arrangement. The QUICK and Van Leer schemes are used for the convective terms. The time discretization is implicit and a secondorder CrankNicolson scheme is employed. The influence of Reynolds number(Re=45500), body side ratio (B/A=14) and angle of incidence (alpha=090) is investigated. Effect of the various numerical parameters such as time step, domain size, blockage, grid distribution and spatial resolution in both far and nearbody regions is investigated. At outlet of the computational domain, a convective Sommerfeld boundary condition is compared with a traditional Neumann condition. The onset of vortex shedding is investigated by using the StuartLandau equation, at various angles of incidence for a square cylinder. In 3Dcalculations, direct numerical simulation (DNS) of unsteady flow around a square cylinder at zero incidence for moderateReynolds numbers (Re=150  500) and large eddy simulation (LES) at Re=22000 are performed. A nonstaggered grid arrangement, incompressible, finitevolume code is used employing an implicit fractional step method with a multigrid pressure Poisson solver. A secondorder central scheme is used for the convective and diffusion terms. The influence of the aspect ratio, finer grid and time step on the results are investigated for DNS. By DNS simulations, the study of transition from 2D to 3Dflow, the wake structure, A and Bmode of secondary vortices and a comparison of 2D and 3D results with experimental results are carried out. Also some dissimilarities with the flow around a circular cylinder are investigated. In LES simulations, three different Subgridscale models, the Smagorinsky, dynamic and dynamic oneequation models for Re=22000, are applied and their results are compared with experimental results. REFERENCES  click to view postscript file

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