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Technical Brief

Trapped Cylindrical Flow with Multiple Inlets for Savonius Vertical Axis Wind Turbines

[+] Author and Article Information
Aaron S. Alexander

Department of Engineering Technology Oklahoma State University 378 Cordell South Stillwater, OK 74074
aaron.s.alexander@okstate.edu

Arvind Santhanakrishnan

Department of Mechanical and Aerospace Engineering Oklahoma State University 218 Engineering North Stillwater, OK 74074
askrish@okstate.edu

1Corresponding author.

ASME doi:10.1115/1.4038166 History: Received February 25, 2017; Revised September 22, 2017

Abstract

Savonius VAWTs typically suffer from low efficiency due to detrimental drag production during one half of the rotational cycle. The present study examines a stator assembly created with the objective of trapping cylindrical flow for application in a Savonius vertical axis wind turbine (VAWT). While stator assemblies have been studied in situ around Savonius rotors in the past, they have never been isolated from the rotor to determine the physics of the flow field, raising the likelihood that a moving rotor could cover up deficiencies attributable to the stator design. The flow field created by a stator assembly, sans rotor, is studied computationally using 3D numerical simulations in the commercial computational fluid dynamics (CFD) package Star-CCM+. Examination of the velocity and pressure contours at the central stator plane show that the maximum induced velocity exceeded the free stream velocity by 65%. However, flow is not sufficiently trapped in the stator assembly, with excess leakage occurring between the stator blades due to adverse pressure gradients and momentum loss from induced vorticity. A parametric study was conducted on the effect of the number of stator blades with simulations conducted with 6, 12, and 24 blades. Reducing the blade number resulted in a reduction in the cohesiveness of the internal swirling flow structure and increased the leakage of flow through the stator. Two unique energy loss mechanisms have been identified with both caused by adverse pressure gradients induced by the stator.

Copyright (c) 2017 by ASME
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