Experimental investigation of the galloping instability of rectangular cylinders at Reynolds numbers between 1000 and 10,000*

Transverse galloping occurs when oscillation in the direction normal to the approach stream of an elastically mounted body causes the aerodynamic force in the same direction to become amplified and sustained. The motivation for this work derives from a recent study (Seifers et al., AIAA 2013-0064) suggesting that galloping could cause large-amplitude vibration of the suspension lines of precision airdrop systems. To first approximation, the cross-sections of these suspension lines resemble a rectangle with rounded corners, and they operate in the Reynolds number range less than 10⁴. This work represents a systematic experimental investigation of the effects of geometry on galloping of rectangular cylinders for Reynolds numbers between 1000 and 10,000.  The geometric parameters of interest are the ratio of the chord to thickness and the ratio of the corner radius to the thickness. These parameters are varied from 1 to 3 and 0 to 0.5, respectively. Direct measurements of lift and drag variation with angle-of-attack are used to compute the transverse force and assess the susceptibility to galloping. Surface pressure distributions are also measured for selected cases to connect the force behavior to the flow conditions.