On the role of a centrifugal instability in the vortex-induced vibration of a two-degrees of freedom circular cylinder at moderate Reynolds numbers
Document typeConference report
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In this work, the formation and role of a centrifugal instability in the VIV phenomenon at moderate Reynolds numbers are investigated for the ¿rst time. Large eddy simulations of a low mass ratio (m = 2.6) two-degree-of-freedom circular cylinder at subcritical Reynolds (Re = 3900, 5300, 11000, 50000) numbers andatzerodamping(¿ = 0)havebeenperformed. Results for three different values of the reduced velocity U* = 4.3, 5.5 and 6.5 at Re = 5300 are shown. This valuesof thereduced velocitymark thebeginning, the middleandtheendofthestablepartofthesuper-upper (SU) branch. Results show that the xy oscillations trigger a centrifugal instability at the cylinder boundary layer. G¨ortler-like vortices appear at U* ˜ 4.5 with Ay/D ˜ 0.902 and Ax/D = 0.156 when there is an important change in the slope of the increment of the maximum amplitude trend as a function of the reduced velocity. The G¨ortler like vortices become irregular as the reduced velocity increases and cease at thesuper-upperlowertransition. Also,itisshownthat the formation of the counter-rotating pair of vortices is modulated by a frequency of twice the vortex shedding (the frequency of the cylinder oscillation in the in-linedirection)whenthecylinderstartstoaccelerate. Finally, some important characteristics of the Görtler like vortices and their interaction with the vortex formation are described.
CitationPastrana, D., Cajas, J., Lehmkuhl, O., Rodriguez, I., Vazquez, M., Houzeaux, G. On the role of a centrifugal instability in the vortex-induced vibration of a two-degrees of freedom circular cylinder at moderate Reynolds numbers. A: International ERCOFTAC Symposium on Engineering Turbulence Modelling and Measurements. "The 12th International ERCOFTAC Symposium on Engineering Turbulence Modelling and Measurements 26-28 September 2018, Montpellier, France : conference proceedings". 2018, p. 1-6.