What purpose do helical strakes serve?
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.
What are VIV strakes?
Make An Enquiry. Current flow around a pipeline can result in vibration created by vortex shedding. The frequency of this vibration can become close to the natural frequency of the pipe, which can cause fatigue or damage the pipeline.
How do you make helical strakes?
Capacity to Produce Helical Strakes
- Use three-set of helical strakes 120 degree apart attached to the stack circumference;
- The pitch of the helix should be five times the stack diameter over a 360 degree rotation;
- The strake width should be one-tenth of the stack diameter.
How do helical strakes work?
While fairings consist of a structure having two sides that streamline the flow past the structure (such as an airplane wing), helical strakes consist of one or more fins that spiral along the structure’s length. This causes the vortices along the structure’s length to be broken up into shorter and weaker segments.
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 are the spirals on chimneys called?
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.
How do you stop Viv?
To prevent substantial fatigue damage, it is often prudent to install VIV suppression devices over at least part of the tubular span (to reduce the vibration amplitude and/or frequency). VIV can usually be minimized with the careful selection and design of VIV suppression devices such as helical strakes and fairings.
How do you reduce vortex induced vibration?
The main results show the following:(1)The vortex generators effectively suppress vortex-induced vibration. They shorten the lock-in region and reduce the amplitude of vortex-induced vibration. The vortex generators have the best result for = 70°, which significantly reduces the amplitude.
What causes vortex shedding?
Vortex shedding happens when wind hits a structure, causing alternating vorticies to form at a certain frequency. This in turn causes the system to excite and produce a vibrational load.
Is vortex shedding turbulent?
Vortex shedding can be grouped into four regions according to the Reynolds number: 1. Below subcritical region (Re<300): In this region, vortices start to develop, increase linearly, and become turbulence when break away from the pipeline as Reynolds number increases.
What makes a helical strake a Viv suppression device?
The most common VIV suppression devices in use today are helical strakes and fairings. While fairings consist of a structure having two sides that streamline the flow past the structure (such as an airplane wing), helical strakes consist of one or more fins that spiral along the structure’s length.
What is the pitch of a Viv Strak?
Lankhorst VIV Strakes are typically recognized for their perpendicular intermittent vanes, wound around the pipe in a triple helix. The pitch of these helices is equal to 16 times the pipe OD, however alternative pitches are possible.
What kind of structure is a Viv strake?
VIV Strakes. Cylindrical structures, such as free-standing riser pipes or flowlines in free spans, interact with a uniform fluid such as seawater and shed Karman vortex sheets.
What should I know about helical strakes manufacturing process?
Our engineers will work with you to determine the best geometric profile, manufacturing materials, and fastening mechanisms required for your application. Variables such as fin height, strake pitch, etc., all can be optimized prior to production.