The 3-D transition of the flow behind a circular cylinder has been investigated experimentally.Natural wake transition in the low Reynolds number regime is characterized by two modes ofshedding, Mode A and Mode B. Besides to the natural modes of shedding there are two additionalmodes which can be triggered by either placing a control wire in the near wake (ModeC) or by heating the cylinder (Mode E). Despite the different character of the disturbancesand Reynolds number ranges, both modes show 3-D structures with a spanwise wavelength ofapproximately 2 cylinder diameters. Detailed experiments are done to investigate the influenceof a control wire on various properties of the flow, such as primary vortex shedding patterns anddynamics of the spanwise structures, and to compare the results with earlier obtained resultsfor the heated cylinder case. Information about the flow physics is obtained from flow visualizationexperiments which are performed in a towing tank using electrochemical tin-precipitationmethod. Flow visualizations have been performed in both 2-D and 3-D configurations. Theexperiments showed that when a thin wire is placed in the wake of a cylinder, the natural vortexshedding is altered. For the Reynolds numbers where the flow is 2-D (Re = 110) this effectshows itself as the prevention of the vortex roll-up in the formation region. In the 3-D transitionregion (Re = 185, 215) the wire causes an unnatural mode of shedding, namely Mode C, tooccur. From these visualization experiments it can be concluded that the spanwise wavelengthof those Mode C structures is determined in the near wake of the cylinder and is approximately2 cylinder diameters. Top view visualizations also showed that period doubling is taking placein the 3-D transition region for the wired case. The flow visualization results obtained for ModeC transition are used to asses the similarities and the differences between Mode C and ModeE transition.
|Title of host publication||Proceedings of the 5th European Thermal-Sciences Conference (Eurotherm 2008), 18-22 May 2008 Eindhoven, the Netherlands|
|Editors||G.G.M. Stoffels, T.H. Meer, van der, A.A. Steenhoven, van|
|Place of Publication||Eindhoven|
|Publisher||Technische Universiteit Eindhoven|
|Number of pages||8|
|Publication status||Published - 2008|