Spinning wind turbines in various configurations – horizontal or vertical axis, massive or micro, even flying – dominate the environmentally friendly electricity generation scene. However, what if you wanted an electricity source to power a small light? Spinning wind turbines are too costly. A second option is batteries (recharged by solar panels maybe). But now there is a third – the Wind Belt can convert wind energy into electricity, without spinning components, suitable for low-power appliances such as small lights.

Shawn Frayne, the Wind Belt inventor and Popular Mechanics 2007 Breakthrough Award winner, came up with the concept while working in Haiti. He identified the need for a cheap, simple, lower-power electricity source for lighting. His aim was to offer an alternative to the smoky and dangerous kerosene that is currently burnt in lamps.

The Wind Belt consists of a belt that vibrates (like a guitar string) in the presence of the wind. Attached to the belt is a magnet that moves perpendicular to a coil of wire. The magnet's movement causes electricity to flow through the coil. The same principle is used to generate electricity in a shake torch or Faraday flashlight.

Flutter

The Wind Belt relies on an aerodynamic phenomenon known as flutter (or mechanical resonance) to excite the motion of the belt. The air passing over the belt causes vortex shedding that induces alternate low and then high pressures on the belt, forcing it to move in a periodic manner. Resonance occurs when the vortex shedding frequency matches the natural frequency of the belt, and the motion will be amplified as long as the wind speed is within a required range.

The Wind Belt's use of flutter turns conventional thinking on its head. Usually flutter is viewed as a nuisance and, in extreme circumstances, dangerous. Washington's Tacoma Narrows suspension bridge (Galloping Gertie) demonstrated the hazards of vortex shedding corresponding to the natural frequency of a suspended roadway, resulting in the bridge's spectacular collapse in 1940. Flutter is also a concern to airplane designers, who have to ensure that the structure of a wing does not possess a natural frequency likely to be excited by air flow over the wing.

Improvements

Ideally the Wind Belt needs a means to tune its natural frequency to the different wind speeds it is likely to encounter. The headstock (tuners) and fretboard of a guitar may offer ideas on how to adjust the tension and length of the belt.

Fluid-Structure Interaction

To analyze a Wind Belt using a Computer-Aided Engineering (CAE) tool, you need to couple a fluid solver and a structural solver to perform a Fluid-Structure Interaction (FSI) simulation. FSI typically combines a Computational Fluid Dynamics (CFD) solver and a finite-element method (FEM) for structural mechanics. FSI proceeds by calculating the pressures over a shape due to the passage of the fluid. Next the pressures are used to calculate the structural deformation. The pressures are then re-calculated for the new deformed shape and so the cycle continues.

Caedium does not currently support FSI, but it will one day. In the meantime our prescribed rigid-body motion for transient fluid flow in our Professional add-on can simulate vortex shedding behind a pitching airfoil.