Abstract
Laser Doppler Velocimetry (LDV) measurements, flow visualizations and unsteady Reynolds-Averaged Navier-Stokes (RANS) Computational Fluid Dynamics (CFD) simulations have been carried out to study the turbulent wake that is formed behind a semi-circular step cylinder at a constant flow rate. The semi-circular cylinder has two diameters, a so-called step cylinder. The results from the LDV measurements indicate that wake length and vortex shedding frequency varies with the cylinder diameter. This implies that a step cylinder can be used to attract fish of different size. By visualizations of the formation of a recirculation region and the well-known von Kármán vortex street behind the cylinder are disclosed. The simulation results predict the wake length and shedding frequency well for the flow behind the large cylinder but fail to capture the dynamics of the flow near the step in diameter to some extent and the flow behind the small cylinder to a larger extent when compared with measurements.
Highlights
Hydro and nuclear power are the major sources of electricity in Sweden
These vortices are influenced by wake and shedding frequency, but these wake and vortex shedding frequencies are greatly dependent on the cylinder diameter [8]
A cylinder with different diameters, such as a step cylinder, could generate an interesting flow behind it and variable wake and shedding frequencies. This warrants this study of wake and vortex shedding behind a semicircular step cylinder with Laser Doppler Velocimetry (LDV)
Summary
Hydro and nuclear power are the major sources of electricity in Sweden. Swedish Energy [1]. Another study from Dunn et al [10] found significant effects of free-stream shearing on vortex-shedding characteristics from a step-cylinder. Detailed studies of the wake vortex dynamics behind step-cylinder are provided He [17] has recently used tomographic-PIV (3D-PIV) behind a step cylinder for three-dimensional (3D) information of vortex shedding. The flow dynamics of the step and diameter change is interesting from a fluid mechanics point of view but as the half cylinders have shown to be interesting for fish migration, the difference in wake formation and shedding of vortices behind the different cylinder diameters could be designed to fit different sizes and species of fish
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