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A comparison of wake measurements in motor-driven and flow-driven turbine experiments

Araya, Daniel B. and Dabiri, John O. (2015) A comparison of wake measurements in motor-driven and flow-driven turbine experiments. Experiments in Fluids, 56 (7). Art. No. 150. ISSN 0723-4864. doi:10.1007/s00348-015-2022-7.

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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.

Item Type:Article
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Dabiri, John O.0000-0002-6722-9008
Additional Information:© 2015 Springer-Verlag Berlin Heidelberg. Received: 17 February 2015; Revised: 9 June 2015; Accepted: 25 June 2015. This work was funded by an NSF Graduate Research Fellowship as well as the Caltech Resnick Institute Graduate Fellowship to D.B.A. Funding to J.O.D. from the Gordon and Betty Moore Foundation through Grant No. GBMF2645 and the Office of Naval Research through Grant N000141211047 are also gratefully acknowledged.
Group:Resnick Sustainability Institute, GALCIT
Funding AgencyGrant Number
NSF Graduate Research FellowshipUNSPECIFIED
Resnick Sustainability InstituteUNSPECIFIED
Gordon and Betty Moore FoundationGBMF2645
Office of Naval Research (ONR)N000141211047
Issue or Number:7
Record Number:CaltechAUTHORS:20150720-130414126
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:58947
Deposited By: Tony Diaz
Deposited On:21 Jul 2015 21:04
Last Modified:10 Nov 2021 22:12

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