Computer controlled test bench for axial turbines and propellers

The authors describe the experimental facility, measurement instrumentation, and preliminary tests carried out with a small-scale model of a wind turbine. The reported work is mainly concerned with the experimental details associated with the measurement technique, developed to cope with the small dimensions of the model turbine and correspondingly low torque and power. The test made use of a low-speed closed-circuit tunnel, with a variable air speed of up to 13 m/s. A new test bench has been built in which a microcomputer is used to set and monitor the turbine speed and to measure and record instantaneous torque and power, as well as the main working parameters of the wind tunnel. Regulation of braking torque was achieved with a simple yet flexible generator load circuit, in which current is controlled by transistors in linear operation and power is dissipated directly in the transistors. Braking torque adjustment and recording of experimental data were performed by the microcomputer based system, which allowed the measurement of complete torque vs. speed curves with little human intervention. Preliminary results are presented and the accuracy of the collected data is examined. It is shown that the facility described provides a versatile tool for the investigation of small-scale axial turbines