Vortex shedding lock-on in a periodic freestream flow past a circular cylinder

Vortex lock-on phenomena in flow past a circular cylinder with a periodic component superimposed on the mean free stream flow is investigated using concepts from dynamical systems (chaos) theory. Numerical results show that in addition to classical lock-on phenomenon (where the wake and forcing frequencies coincide or lock-on in a subharmonic multiple) regions are observed in which the wake frequency locks-on to a fractional ratio of the freestream oscillation frequency. The observed phenomena are compared to qualitative predictions of circle map theory. A possible general framework for understanding lock-on phenomena using circle map theory is discussed. 157 183 188 183-188