STUDY OF VON KÁRMÁN INSTABILITY RESULTING FROM A BINARY CYLINDER SYSTEM

Abstract

Experimental results are presented of the temporal evolution of the wake associated with von Kármán, instability produced by a system of two vertical cylinders of different diameters (binary cylindrical system) facing a uniform airflow. The goal is to study the influence of the binary system on the linear stability of the wake at moderate Reynolds numbers, as well as the vortex emission. From the measurements of the velocity profiles we were able to analyse the wake’s dynamic behaviour in both the subcritical and critical ranges. Furthermore, it was possible to determine the frequency content of the vortex emission of the system, finding a coupling (lock-in) in the wake of both cylinders at the onset of the von Kármán instability. This coupling is developed, even, in the condition of greatest distance between the wakes (α = 90◦ ). The non-linear condition of the wake is reflected in the power spectrum (PSD) of the velocity time series, presenting additional frequency modes to the fundamental vortex shedding frequency of each cylinder.