Vortex Induced Vibrations

Contents:

Vortices and Induced Vibrations.

Phenomena and Reduction of Vortex Induced Vibrations.

Latest Research Papers.

Summary.

Vortices:

A vortex is defined as the motion ofmultitude of fluid particles around acommon center.

Types of vortices:- Forced Vortex - Free Vortex

Vortices in the Real World:

Vortices in the real world like Tornados, Whirlpool in rivers are often a combination of free and forced vortices.

Forced vortex flow occurs at and near the center of the vortex while free vortex conditions are approximated outside this region.

Fig.(1) Velocity Distribution

Flow-Induced Vibration:

The vibration caused by a fluid flowing around a body is known as flow-induced vibration.

In the following examples, the vibration of the system continuously extracts energy from the source, leading to larger and larger amplitudes of vibration.

Phenomena of Induced Vibration:

- Tall chimneys, Submarine periscopes, Electric transmission lines and

Nuclear fuel rods are found to vibrate violently under certain conditions of fluid flow around them.

- Similarly, water and oil pipe lines and tubes in air compressors undergo sever vibrations under certain conditions of fluid flow through them.

In ice-covered electric transmission lines and the unstable vibration, known as flutter, of air foil sections.

High frequency vibration known as singing of transmission lines occurs due to the phenomena of vortex shedding.

Why Vortex Shedding Phenomena:

Vortex shedding was the primary cause of failure of the Tacoma Narrows suspension bridge in the state of Washington in 1940.

If the frequency of the vortex shedding is in resonance with the natural frequency of the member that produces it, large amplitudes of vibrations with resulting large stresses can develop.

Experimental data show that regular vortex shedding occurs strongly in the range of Reynolds number (Re) from about 60 to 5000.

Experiments shows also that the frequency of shedding is given in terms of Strouhal number (St), and this in turn is a function of the Reynolds number.

Other cylindrical and two dimensional bodies can also shed vortices.

Reduction of Flow-Induced Vibration: