Revisiting the wake-triggered secondary vortices over a circular-cylinder/flat-plate configuration

The wake-vortex/boundary-layer interaction is significant for both fundamental and practical aspects of fluid mechanics. The wake vortex triggered the well-known single-secondary vortex over a canonical circular-cylinder/flat-plate configuration. However, recent investigations reported wake-triggered double-secondary vortices over a multi-element airfoil or a simplified circular-cylinder/airfoil configuration. Motivated by this contrast, this paper revisits this topic with a circular-cylinder/flat-plate configuration and finally observes the double-secondary vortices in the boundary layer. The disturbances related to the shedding frequency of the wake vortex and its second harmonic are found to penetrate the boundary layer and be further amplified to form the double-secondary vortices.