Where does strake collide?

In offshore and wind engineering a strake is a helical fin wrapped around a slender cylindrical structure such as a riser, mooring line, chimney, or cable to suppress vortex-induced vibration. By breaking the spanwise coherence of the vortices shed in a cross-flow, the helical strakes stop the regular, resonant shedding that would otherwise drive large oscillations and fatigue, trading a modest rise in steady drag for far smaller vibration. Korkischko and Meneghini's 2010 study measured how strakes reduce flow-induced vibration on circular cylinders. Here the construct is an add-on aerodynamic or hydrodynamic device defined by its effect on vortex shedding, distinct from a plank of a hull or a wing surface.[1]

Unit

The reduction in vortex-induced vibration amplitude a helical fin produces on a bluff cylinder

Recovery means

Not applicable

Measured by

Quantified by vibration amplitude and drag with and without strakes across a range of reduced velocity

In aircraft design a strake, or leading-edge extension, is a slender, highly swept surface added at the root of a wing ahead of its main leading edge, which at high angles of attack sheds a strong, stable vortex over the wing's upper surface. That vortex re-energises the flow and adds vortex lift, delaying stall and improving manoeuvring, which is why strakes are a signature feature of agile combat aircraft. Raymer's Aircraft design: A conceptual approach describes strakes and the vortex lift they create. The referent is an aerodynamic lifting device defined by the vortex it controls, a different construct from a hull plank or an anti-vibration fin.[2]

Unit

The added vortex lift and stall delay a leading-edge extension provides

Recovery means

Not applicable

Measured by

Evaluated by the lift increment and the angle of attack at which the strake vortex forms and bursts