What are "Strakes"?
Those helical fins seen on certain industrial exhaust stacks do have a purpose.
I have on occasion seen smokestacks/chimneys with helical "fins" on the sides near the top, and have long been curious as to their purpose. The first instance was as a child on the Drake Incinerator - a portable incinerator which was used to treat contaminated soil at the Drake Chemical Superfund site in Lock Haven, PA.
Helical fin “strakes” on Fredriksburg, Norway's waste-to-energy plant. (Courtesy FREVAR)
STACK USED AT DRAKE SITE (from EPA)
While doing some work for my fluid mechanics course (analyzing the airflow over a cylinder), I stumbled upon an answer: It turns out that these are known as Helical Strakes for aerodynamic stabilization, to prevent wind vortex shedding from vibrating and tearing the thin metal stack apart.
They do not appear to be common. The Drake site is the only real-life instance I have seen one. I have seen them in pictures on oil refineries, and some waste-to-energy plants (mostly smaller ones) use them.
The strakes are cheap and easy to build but will increase the wind loading on the stack, meaning it and its foundation must be made stronger.
CREATED/WRITTEN: 2011-12-22 00:00