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The present study is devoted to the flow peoperties of a vortex shedding system behind a bluff body that has a crescent cross-section, facing downstream of the flow. The investigation is conducted numerically using a lattice Boltzmann method. As a benchmark validation, the studied system was compared to the system of vortices formed behind the classical case of a circular cylinder for the same flow configuration and dynamic conditions, while varying the Reynolds number. The flow simulations have revealed that the crescent body affected substantially the shedding mechanism with remarkable differences when compared to the classical cylindrical case. There was a clear decrease in the shedding frequency with the crescent body that is beneficial when using this system as a metering tool.
The vortex shedding flow system had, and still has, a lot of interest from researchers in fluid dynamics due to its many applications for flow metering purposes, for studies of vortical flows or as a benchmark case for numerical methods (Tuann and Olson, 1978; Loc, 1980; Coutanceau & Defaye, 1991; Lakshmipathy, 2004; Reich et al., 2005). The Von-Karman vortex system, known as vortex shedding, occurs when a flow passes around a bluff body, classically cylindrical. To investigate different aspects of the vortex shedding, bluff bodies with different shapes were studied both experimentally and numerically.
The flow behind a circular cylinder is classicaly supposed symmetric at low Reynolds numbers in the range of 70 to 100. When Reynolds number increases, the flow begins separating just at the downstream edge of the cylinder and forms an alternating system of vortices with a constant shedding frequency. This phenomenon has been used as means to measure flow rates with a high accuracy due to its low cost and low maintenance, and being not sensitive to physical properties of the fluid flows measured. Therefore, this metering method has been used in several industries to measure flow rates of liquids, gases and steam flows over a large interval of Reynolds numbers. From the fundamental point of view, this flow system was investigated numerically by many authors. One of first authors was Payne (1958) who studied this flow system for Reynolds numbers below 100 and characterized in details the shedding system in this flow rates range.