Role of the shear layer instability in the near wake behavior of two side-by-side circular cylinders |
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Authors: | Email author" target="_blank">C?BrunEmail author D?Tenchine E?J?Hopfinger |
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Institution: | (1) DRN/DTP/SETEX/LETS, Comissariat à lÉnergie Atomique, 38054 Grenoble, France;(2) LEGI, CNRS, Université Joseph Fourier, INPG, B.P. 53, 38041 Grenoble, France;(3) Polytech Orléans/LME, 8, rue Léonard de Vinci, 45072 Orleans CEDEX 2, France |
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Abstract: | Wakes, and their interaction behind two parallel cylinders lying in a plane perpendicular to the flow, have been investigated experimentally in the sub-critical Reynolds number regime. The experiments were performed in a water channel using laser Doppler velocimetry. The gap between the two cylinders was less than the cylinder diameter, a geometry referred to as strong interaction configuration. In this case the blockage is strong and a gap-jet appears between the cylinders. Two flow regimes of the near wake region have been identified: one below a critical Reynolds number Re
c ]1000;1700, where the gap jet is stably deflected to one side and the double near-wake becomes asymmetric; the other, above Re
c, where the gap-jet deflection is unstable and a random flopping phenomenon takes place. When Re<Re
c, two different Strouhal numbers are identified, related to the Kármán vortex shedding behind each cylinder. When Re>Re
c, a third frequency appears in the near wake, related to the development of Kelvin-Helmholtz vortices in the separated shear layer of the cylinders Prasad A, Williamson CHK (1997) J Fluid Mech 333:375]. The observed flopping behavior is attributed to the birth of these Kelvin-Helmholtz instabilities and their intermittent nature. Further downstream, beyond about five cylinder diameters, the random flopping flow phenomena disappear while a slightly asymmetric single wake persists. It is characterized by a Strouhal number St=0.13, a value that one would normally measure behind a single cylinder of twice its diameter. |
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