Helical strakes are aerodynamic stabilizers that reduce forces and deflections experienced on the stack due to vortex shedding. Strakes consist of 3 vanes which can be wrapped in a helical pattern on the upper one-third part of the stack.
Who invented helical strakes?
The effectiveness of helical strakes for reducing vortex induced vibration was discovered in 1957 by Christopher Scruton and D. E. J. Walshe at the National Physics Laboratory in Great Britain. They are therefore often described as Scruton strakes.
How do I stop vortex shedding?
The entrainment of fluid into the inner side of the separated shear layers is obstructed by the downstream splitter plate. Our results suggest that by attaching in-line splitter plates both upstream and downstream of the cylinder, the vortex shedding can be suppressed, as well as a reduction in drag be obtained.
What is a Strake on a chimney?
Helical Strakes are aerodynamic stabilizers which are sometimes used to reduce the forces and deflections of the stack experienced due to vortex shedding. They have the appearance of a “Snake” which spirals around the stack. When strakes are added the drag coefficient of the stack is increased greatly.
What is vortex shedding effect?
Vortex shedding is a phenomenon, when the wind blows across a structural member, vortices are shed alternately from one side to the other, and where alternating low-pressure zones are generated on the downwind side of the structure giving rise to a fluctuating force acting at right angles to the wind direction (Fig.
Who invented vortex shedding?
Henri Bénard
We present in this article the work of Henri Bénard (1874–1939), a French physicist who began the systematic experimental study of two hydrodynamic systems: the thermal convection of fluids heated from below (the Rayleigh–Bénard convection and the Bénard–Marangoni convection) and the periodical vortex shedding behind a …
Is vortex shedding turbulent?
Turbulence-induced vibrations The cylinders will be subjected not only to the periodic vortex shedding induced forces but also to broad band turbulence. The latter excitation becomes relatively more important when the periodic shedding frequency is far from the structural frequency.
Why is vortex shedding bad?
For structures that are tall and uniform in size and shape, the vibrations can be damaging and ultimately lead to fatigue failure. Masts or towers are highly susceptible to vibrations induced by vortex shedding.
Why do smoke stacks have spirals?
The wind circles around the chimney upwards which pushes whatever gases being released even higher into the sky. The wind circles around the chimney downwards which prevent the chimney from going left or right and rather “push” it downwards to make it more steady.
What is bilge strake?
The strake at the turn of bilge extending outward to a point where the side rises vertically.
What are helical strakes?
Helical Strakes are aerodynamic stabilizers which are sometimes used to reduce the forces and deflections of the stack experienced due to vortex shedding. Strakes consist of three (3) vanes which can be wrapped in a helical pattern on the upper 1/3 of the stack.
How do I add helical strakes in mecastack?
Helical strakes can be added in MecaStack. Go to the “Design”, “Damping” menu, and there is a helical strake option. The button at the right, “Damping Device Menu”, lets you enter the parameters. Although MecaStack does let you simulate helical strakes, their use still requires some engineering judgment.
What is a strake in a stack?
Strakes consist of three (3) vanes which can be wrapped in a helical pattern on the upper 1/3 of the stack. They have the appearance of a “Snake” which spirals around the stack. When strakes are added the drag coefficient of the stack is increased greatly.
What is the difference between a smooth and a helical strakes chimney?
The side force (perpendicular to the flow direction and parallel to the ground) time history shows that the helical strakes chimney has a lower frequency of VIV than the smooth chimney. However, the average side-force magnitude for the helical strakes chimney is many times (~300%) higher than that of the smooth chimney.
