Flow-induced oscillations of prisms with two degrees of freedom

Flow-induced oscillations of triangular and square prisms, placed in water are studied for a system with both inline and cross-flow degrees of freedom. The experimental apparatus permits low mass-damping and low structural coupling between the two degrees of freedom. A combination of displacement and force measurements together with flow visualization is used to investigate the prism’s response as the flow velocity is increased. Direct force measurements indicate the formation of higher harmonics in the lift and drag forces. Wake visualization relates the vortex shedding angle to the phase angle shift between lift and velocity and the normal angles of the faces. For the triangular case, alignment between the surface normal and the shedding angle results in a widening of the VIV lock-in region.