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We investigate the effects of active wake-jets (characterized by a dimensionless jet momentum coefficient C µ) on the suppression of aerodynamic forces and the manipulation of wake flow topology behind a cylindrical model through wind tunnel tests. The active jets are positioned at the rear stagnation points of the cylindrical test model. The experimental campaign is conducted at a subcritical Reynolds number of Re= 3.33 × 10 4. The surface pressure distributions around the bare and controlled cylinders are obtained by using a pressure measurement system. Apart from pressure measurements, we also obtain the streamwise and spanwise flow structures around the circular cylinder with different C µ (including C µ = 0) by employing the particle image velocimetry (PIV) technique. Pressure measurement results demonstrate that the lift force acting on the cylindrical test model is greatly reduced and drag decreased with the implementation of active wake-jets. Besides, it is found that a higher C µ contributes to a better control effectiveness in unsteady lift forces but not necessarily a better drag reduction. PIV measurement results indicate that the mechanism of the active jet control scheme is to impose steady and symmetric perturbations into the unsteady and asymmetric flows in the cylinder wake. Owing to the dynamic competition of the wake-jet flow and shear layer flows, the vortex shedding pattern behind the controlled cylinder is greatly modified, vortex formation length significantly elongated and the fluctuations of aerodynamic forces conceivably suppressed.

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We reproduce multi-modal vortex-induced vibrations (VIVs) and multi-modal rainwind-induced vibrations (RWIVs) of an inclined and yawed cable in wind tunnel tests. The flexible cable model has low mass and low damping. First, the cable model is kept dry and exposed to uniform airflow; it experiences first-, second-and third-mode VIVs with the increase of wind speed. The structural responses of VIVs are analysed and the frequency lock-in phenomenon is observed for different modes of VIVs of the flexible cable. In addition to VIVs of the dry cable, RWIVs are excited by guiding water rivulets on the cable surface from a water tube. The first-, second-and third-mode RWIVs of the flexible cable are observed and identified at a much higher range of incoming wind speeds than that of the VIVs. To further explore the origin of the multi-modal behaviours of RWIVs, the upper rivulet is guided and restricted to forming locally along the cable. Experimental results reveal that the higher-and multiple-mode RWIVs can be excited by a local rivulet, even under a lower wind speed. Finally, RWIVs are compared to VIVs to uncover their underlying similarities and relationships.