Design, Fabrication, and Experimental Performance Analysis of a Prototype Archimedes Spiral Wind Turbine.

This paper covers the construction, testing and design for the Spiral Watt. This is a small Archimedes-type (drag based) turbine built with urban rooftops in mind and later a wind-solar hybrid device used to charge a battery and power an LED. Unlike lift-based turbines, which require high steady wind and a large rotor swept area, which most rooftops simply cannot provide, the spiral blade design acts based on drag so will still produce power in the poor quality wind typically experienced in urban settings. Four samples of the 3D printed (PLA) blade with radii ranging from 5 to 14cm and mass between 30g and 200g were built to provide comparative data on how radius and mass impact the rotation speed, electrical output and efficiency. Four blade samples were run for a total of 20 tests; each was subjected to five identical operating conditions: 3 speed settings on an AC hairdryer, 1 stationary control (indoors), and 1 outside condition, with readings taken using a handheld anemometer, alongside voltage readings taken with a digital multimeter and rotational speed taken with an application on a mobile phone. For the 16 out of 20 tests (4 were control tests), the power coefficient averaged around 0.180 and ranged between 0.1799 and 0.1802; the values fell within a tight bound, which represents 18% of available wind (30.4% of the optimal Betz limit of 0.593). Exact mass and radius measurement appeared to have a significant impact on efficiency. However, absolute output was very scale-dependent; the number 3 blade with a radius of 13 cm and mass of 150g achieved an output of 10.89W at 12.3m/s. An opposite trend compared to electrical current was noted for rotational speed; the smallest lightest blade rotated at its highest speed and produced the largest amount of voltage at low current, while the largest, heaviest blade spun slowest and utilised the highest amount of current. The best performing blade was fitted into the hybrid unit. Under test conditions of 9 m/s, it generated 2.4 V at 1.3 A with an associated output of 3.12 W attributed solely to the wind, Cp= 0.492 (82.9% Betz limit), which should also be considered to have had a solar contribution. Equipped with 2x 2.8V solar cells, the device generated 6.12 W, which was more than sufficient to simultaneously power the LED and charge the battery. Overall, these tests correlate with theoretical expectation for P ∝ v³, while also suggesting that turbine efficiency is generally independent across scale in the drag-based design. Fully 3D printable, low mass, low cost, Archimedes style wind-only turbine, then modified to become a hybrid wind-solar unit, was proven capable of producing the wattage required to power a LED and simultaneously charge a battery, operating off the low and turbulent wind provided in a residential urban setting under testing conditions.