Why vortex shedding occurs

However, the pitch-to-diameter ratio center-to-center distance divided by tube diameter is important. For two cylinders, placed in-line, vortex shedding occurs behind each cylinder separately if the pitch-to-diameter ratio exceeds a certain value while for smaller values, the two cylinders behave as a single body in terms of vortex shedding.

In closely spaced tube bundles, the frequency associated with vortex shedding is not so distinct but might appear as a broadbanded peak. Vortex shedding is one of the mechanisms producing flow-induced vibration in shell-and-tube heat exchangers.

Blevins, R. Chen, S. Login: Guest. References Blevins, R. Related content in other products Begell House Inc. About Editors Contact us Access. Vortex-induced vibrations are important in that they can have a strong influence in countless situations ranging from tethered structures in the ocean, pipes bringing oil from the ocean floor to the surface, aeolian harps, tall buildings, and chimneys, to name but a few.

For example, the tallest building in the world, the Burj Khalifa in Dubai, UAE, incorporates a variation in cross section with height to help ensure that vortices are not shed coherently along the entire height of the building. As with most fluid dynamics phenomena, the physics of vortex-induced vibrations is quite rich and very complicated. For example, various vortex wake modes are possible with fluid flow jumping from one mode to another.

Also, depending on the phase between object and fluid motion as well as their frequency difference, a lock-in or synchronization effect may or may not occur. Furthermore, the ratio of the object-to-fluid mass as well as damping forces have a significant effect, leading to parameters described in the literature as effective mass, critical mass, high-mass ratio, etc.

Reference [4] is an excellent resource for those that wish to go deeper into the subject matter—and it can be quite deep indeed! Strouhal, "Ueber eine besondere Art der Tonerregung," Ann. Chem Leipzig 5 10 , Fey, M. Williamson and R. Irwin, "Vortices and tall buildings: A recipe for resonance," Physics Today 63 9 , Billah and R. Scanlan, "Resonance, Tacoma Narrows bridge failure, and undergraduate physics textbooks," Am.

Complete key to listings. Skip to main content. The simplest is to address the fluid flow and create a disturbance on the structure so that the vortex street cannot form. This is commonly done by adding a spiral at the top of the structure but any change to the body that disrupts the vortex would work. Another method is to design the structure itself so the natural frequencies are outside the operating frequencies. This can be done by varying the cross-section along the length of the structure or by adding or changing supports.

There are also dynamic systems such as dampeners that can successfully be applied to absorb vibration. While vortex shedding is a common phenomenon that can lead to structural failure, it is one that is often overlooked because of the complexity of modeling the situation correctly.

Using the steps outlined above, vibrational problems can be easily identified and a few hypothesis can be tested. Design changes can be made before any real problem arises.

The key point to remember is if you are designing a tall slender mechanical system exposed to wind loading, make sure the engineer is considering vortex shedding vibrations and conducts the appropriate analysis. Spirals added to chimneys to prevent vortex shedding. Written by Sparta No Comments. Recent Blog Posts. Featured Designs.

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