Development of a testing rig for vibration and wind based energy harvesters

Abstract

This article describes the fabrication and characterization of a medium scale vibration shaker and a wind tunnel for testing of micro and meso scale vibration based, wind based and hybrid (using combined vibration and wind) energy harvesters. The mechanical shakers used for vibration and shock testing are the most versatile, inexpensive and easy to operate, however, due to their fixed displacement, single frequency and sinusoidal behavior, usage of these shakers is limited. The less known electro-hydraulic shakers are more robust, but due to their high forces and high velocities, these are usually utilized to characterize heavy samples. Electromagnetic shakers are the most reliable and accurate and are increasingly used for accelerometers calibration and aerospace applications. Unlike mechanical shakers, electromagnetic shakers can produce random vibrations and can also be used for shock tests. The reported vibration shaker is electrodynamic type. Different parts of the vibration shaker and wind tunnel are fabricated by conventional machining. For vibration shaker, a 1000 W speaker is fitted in a wooden box. The wooden box is made adjustable and through the railing mechanism it can move vertically as well as horizontally. Moreover, a wooden block containing a fixture for a device is glued to the center of the speaker. A power amplifier and a function generator are utilized to provide the desired signal for the operation of the shaker. The wind generating portion of the testing rig comprised of a variable speed fan, a duct pipe and an anemometer. The vibration and wind producing units of the testing rig are assembled on the same base, such that, these can operate separately as well as simultaneously. In the testing rig the vibration shaker is characterized for sinusoidal input signals from the function generator. With the vibration shaker base acceleration levels from 0.01 g to 2.0 g are produce during a frequency sweep from 1 to 200 Hz. Beyond, 200 Hz, the excitation levels obtained from the shaker are constant. Moreover, the shaker is also characterized by placing different weights on the shaker’s table. The excitation levels for bare table test decreases down from 0.54 g to 0.30 g and 0.22 g by adding a weight of 500 grams and 1000 grams respectively. In the developed testing rig, the wind tunnel is capable of producing an air velocity from 0.4 to 11 m/s at the corresponding fan speed of 1000 rpm to 10000 rpm respectively. Furthermore, the reported wind tunnel is quite able to producing a maximum mass flow rate of 0.170 kg/s.