The effect of blade pitch on the flow dynamics inside the rotor of a three-straight-bladed cross-flow turbine

Abstract

This study analyses the variations in flow dynamics inside the rotor of a three-straight-bladed cross-flow turbine for different blade pitches. A water towing tank facility has been used with a turbine model based on symmetric NACA-0015 profiles with a chord-to-diameter ratio of 0.16. The set-up was especially designed to measure the flow field inside and around the rotor, using planar digital particle image velocimetry. The experiments were made at a constant turbine diameter Reynolds number, [Formula: see text], of 6.1 × 104. The forced rotation of the cross-flow turbine using a direct current motor allowed changes in the ratio of the blade tangential speed to the freestream velocity (tip speed ratio), covering the range of 0.7–2.3. Toe-in and excessive toe-out angles have been associated in the past to low performances in this type of turbines. Pitch angle cases with expected low performances have been chosen, namely, [Formula: see text] of 8° toe-in and 16° toe-out, as well as a case with a high expected efficiency of 8° toe-out and another with [Formula: see text] as the reference case. The the goal is to better understand the flow dynamics and the blade–wake interactions inside the rotor of this type of machines, by studying cases with very different expected performances.