Volumetric reconstruction of the mean flow around circular cylinders fitted with strakes |
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Authors: | Ivan Korkischko and Julio Romano Meneghini |
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Institution: | (1) NDF, Department of Mechanical Engineering, POLI, University of S?o Paulo, Av. Prof. Mello Moraes, 2231, CEP 05508-900, S?o Paulo, SP, Brazil; |
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Abstract: | The volumetric reconstruction technique presented in this paper employs a two-camera stereoscopic particle image velocimetry
(SPIV) system in order to reconstruct the mean flow behind a fixed cylinder fitted with helical strakes, which are commonly
used to suppress vortex-induced vibrations (VIV). The technique is based on the measurement of velocity fields at equivalent
adjacent planes that results in pseudo volumetric fields. The main advantage over proper volumetric techniques is the avoidance
of additional equipment and complexity. The averaged velocity fields behind the straked cylinders and the geometrical periodicity
of the three-start configuration are used to further simplify the reconstruction process. Two straked cylindrical models with
the same pitch (p = 10d) and two different heights (h = 0.1 and 0.2d) are tested. The reconstructed flow shows that the strakes introduce in the wake flow a well-defined wavelength of one-third
of the pitch. Measurements of hydrodynamic forces, fluctuating velocity, vortex formation length, and vortex shedding frequency
show the interdependence of the wake parameters. The vortex formation length is increased by the strakes, which is an important
effect for the suppression of vortex-induced vibrations. The results presented complement previous investigations concerning
the effectiveness of strakes as VIV suppressors and provide a basis of comparison to numerical simulations. |
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