Abstract
The flow patterns over a finite square cylinder of aspect ratio of 3 were analyzed experimentally in a subsonic wind tunnel using the time-resolved particle image velocimetry (TR - PIV) techniques. The near wake flow structures and vortex shedding characteristics were investigated using mean flow analysis, spectral analysis and proper orthogonal decomposition (POD). The cylinders were fixed on a elliptical leading edge flat plate, creating a boundary layer which interacted with the cylinder wake. The 2D PIV measurements were conducted at a low horizontal plane, z/h = 0.3, to investigate possible boundary layer interactions. Due to the complexity of the phenomena, the flow was characterized both in terms of average behavior and time-resolved velocity fields. Both symmetrical and anti-symmetrical vortices structures occur in the cylinder wake, which can be identified based on the coefficients of the first four POD modes. The results indicated that the alternating Karman vortex structures are dominant, described by the first two POD modes.
Highlights
The flow around a cylinder has been a subject of investigation since the beginning of fluid mechanics as a science
The purpose of this paper is to investigate the combined use of time-resolved PIV data and the proper orthogonal decomposition (POD) technique to characterize the main organized flow structures but as a guide for instant-velocity map visualization and spectral analysis
The flow patterns over a square cylinder with aspect ratio AR = 3 were analyzed in a low horizontal plane, z/h = 0.3
Summary
The flow around a cylinder has been a subject of investigation since the beginning of fluid mechanics as a science. Starting from D’Alembert’s paradox, this type of flow eluded scientists due to its simple geometry and complex flow structure, which presents many patterns, depending on Reynolds number, ranging from quasi-potential flow for very low Reynolds, to complex vortexshedding mechanisms at higher Reynolds values. Turbulence associated instabilities will be more pronounced in the real-life wake, but parameters such as vortex shedding frequency and shedding type, as well as mean velocity fields, must match. Another possible application is in preventing flutter onset in all sorts of structures. Due to its simple format, a cylinder can be used as a model for structures ranging from a skyscraper to an antenna. Antenna flutter is hardly a problem for the vehicle structural integrity, but it may damage the antenna
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