caa a22 4500 606197664 CHVBK 20210128100930.0 cr unu---uuuuu 210128e20150701xx s 000 0 eng 10.1007/s00348-015-2022-7 doi (NATIONALLICENCE)springer-10.1007/s00348-015-2022-7 A comparison of wake measurements in motor-driven and flow-driven turbine experiments [Elektronische Daten] [Daniel Araya, John Dabiri] We present experimental data to compare and contrast the wake characteristics of a turbine whose rotation is either driven by the oncoming flow or prescribed by a motor. Velocity measurements are collected using two-dimensional particle image velocimetry in the near-wake region of a lift-based, vertical-axis turbine. The wake of this turbine is characterized by a spanwise asymmetric velocity profile which is found to be strongly dependent on the turbine tip speed ratio (TSR), while only weakly dependent on Reynolds number (Re). For a given Re, the TSR is controlled either passively by a mechanical brake or actively by a DC motor. We find that there exists a finite region in TSR versus Re space where the wakes of the motor-driven turbine and flow-driven turbine are indistinguishable to within experimental precision. Outside of this region, the sign of the net circulation in the wake changes as TSR is increased by the motor. Shaft torque measurements show a corresponding sign change above this TSR threshold set by circulation, indicating a transition from net torque due to lift to net torque due to drag produced by the turbine blades, the latter of which can give wake measurements that are inconsistent with a flow-driven turbine. The results support the claim that the turbine kinematics and aerodynamic properties are the sole factors that govern the dynamics of its wake, irrespective of the means to move the turbine blades. This has significance for both experimental and computational studies where it may be necessary, or perhaps more economical, to prescribe the turbine kinematics in order to analyze its aerodynamic characteristics. Springer-Verlag Berlin Heidelberg, 2015 Araya Daniel Graduate Aerospace Laboratories, California Institute of Technology, 91125, Pasadena, CA, USA aut Dabiri John Graduate Aerospace Laboratories and Bioengineering, California Institute of Technology, 91125, Pasadena, CA, USA aut Experiments in Fluids Springer Berlin Heidelberg 56/7(2015-07-01), 1-15 0723-4864 56:7<1 2015 56 348 https://doi.org/10.1007/s00348-015-2022-7 text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 research-article jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s00348-015-2022-7 text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Araya Daniel Graduate Aerospace Laboratories, California Institute of Technology, 91125, Pasadena, CA, USA aut NATIONALLICENCE 700 1- Dabiri John Graduate Aerospace Laboratories and Bioengineering, California Institute of Technology, 91125, Pasadena, CA, USA aut NATIONALLICENCE 773 0- Experiments in Fluids Springer Berlin Heidelberg 56/7(2015-07-01), 1-15 0723-4864 56:7<1 2015 56 348