Wake flow characteristics of small wind turbine models with single- and double-rotor arrangements: A wind tunnel study

In the multirotor system of a wind turbine, the overall power generation is greatly influenced by the placement and interaction of rotors in proximity. Thus, a great deal of study is needed to ascertain the integration strategy of small wind turbines. In this paper, the wake flow patterns have been investigated for two model wind turbines, viz., single-rotor and double-rotor arrangements operating at a low tip speed ratio. The model rotors composed of SG6043 airfoil have a similar configuration. In the single-rotor arrangement, the model rotor is placed at the center of the wind tunnel. While in the double-rotor arrangement, the model rotors are placed at an equal distance from the central line axis of the wind tunnel. To understand the wake propagation and interaction, experiments have been performed at various wind speed conditions such that the corresponding tip speed ratio is kept between 2.5 and 3. The study is, therefore, specifically focused on the wake characteristics of the rotors under low lambda, and the assessment has been made within the near wake region. The span-wise and stream-wise assessments of the wake for the double rotor suggest a minimal velocity deficit close to the rotor plane and a higher deficit downstream contrary to the single-rotor configuration.