Have you ever wondered… why spiral ‘wings’ are affixed to tall chimneys?
Tall, metallic tubular structures, like smokestacks, chimneys, antenna masts, and tethered cables are usually found to have corkscrew shaped spirals wrapped around them. These metallic strips that wind like coil springs around the top of tall towers are called helical strakes. Helical strakes are aerodynamic stabilizers that help reduce the impact of vortex shedding. During a windy day, a regular, uncoiled cylindrical structure will vibrate, not owing to the gusting of wind, but due to swirls of air that are created as the wind hits the round structure.
These swirls of air (called vortices) are alternatively shed behind either side of the tubular structure in a phenomenon called vortex shedding, pulling the cylinder one way and then the other due to consequent pressure difference created between the two sides. The structure, hence, vibrates. Continuous vibrations of the structure for an extended amount of time can cause the metal to fatigue, which can be fatal. The helical strakes, however, keeps these structures safe from the powers of vortex shedding. As winds hit a helically straked structure, instead of vortex forming along the length of the cylinder (rolling around and shedding behind one after the other), the coiled fins break vortices up and change the time around which they come. This action evens out the whole process, preventing vibrations and ultimately potential failure of the structure.
