Flow characterization in an axial micro-hydroturbine model

The flow characteristics behind the runner of an air model of a propeller-type micro-hydroturbine were studied in detail by varying the operation conditions from part-load to high overload. The Reynolds number was varied from 3×10⁴ to 9×10⁴, and the swirl number from 0.7 to -0.4. An automated laser-Doppler anemometer (LDA) system for non-contact optical diagnostics was used to perform detailed measurements of the flow field distribution, including the profiles of two components of averaged velocities and pulsations and LDA signal spectra. Based on the results, a correlation was found between the identified features of the development of the flow structure under changing operating conditions of the hydroturbine and the nature of the evolution of the integral swirl number, which determines the state of the swirling flow. This can be used to develop recommendations for expanding the range of regulation of hydroturbine operation while maintaining high efficiency.