CFD Analysis of Vertical Axis Wind Turbines in Close Proximity

Author: Marius Paraschivoiu, Chad X. Zhang, Selvanayagam Jeyatharsan, Norbert V. Dy, Farooq Saeed, Robert N. Thomas, Ion Paraschivoiu
Publication: IOPARA, Inc.
Year Published: 2011

This paper presents an analysis based on computational fluid dynamics of vertical axis wind turbines when placed in close proximity in a linear array. It has been noticed that VAWTs placed close to each other with counter rotation motions have a higher coefficient of power than a single turbine. This was termed the “coupled vortex effect”. Two mechanisms have been identified to cause this increase in efficiency: the stream tube contraction effect and the vortex effect. The first is due to the blockage effect from neighboring turbines while the later is related to the neighboring turbine acting as a vortex that induces an increased flow field. This paper analyzes each of these effects and studies the influence of the turbine size and the rotation speed. The change of torque on each blade due to these effects is investigated for two different sizes of wind turbines.

Letter of Support for WHI’s VAWT Wake Research Proposal

Author: Marius Parashivoiu
Publication: Concordia University
Year Published: 2019

As consultant for Iopara Inc., I collaborated with WHI on their prior project, Modeling Blade Pitch and Solidities in Straight Bladed VAWTs, funded through the CEC’s Energy Innovations Small Grant Program. For that research project, Iopara created an aerodynamic model of WHI’s vertical axis wind turbine using data collected from a 3-turbine array located in Palm Springs, CA. Iopara’s modeling validated the “coupled vortex effect” and predicted that the physics and wind effects the phenomenon generated by certain configurations of turbines would be able to significantly increase the energy output of lower solidity VAWTs such as WHI’s G168.
WHI’s proposed Applied Research and Development project will test these predictions, confirming the increase in Capacity Factor that can be realized by the strategic positioning of a VAWT near its neighbor. The project will further build on the findings of the previous study in order to develop a commercially viable strategy for deployment of VAWTs in the understories of existing horizontal axis wind turbines. Although our CEC funded study evaluated two dimensional wakes produced directly behind the VAWT array, our other work on VAWTs indicates that a region of turbulence will develop just above an array of closely spaced turbines. Above that, the increase in wind flowing over the top of the VAWT array will produce a region of wind moving faster than the incoming wind speed at that height. In order to take advantage of the speed-up effect, the VAWT arrays would need to be placed so that the HAWT rotors operate in the higher-speed wind zone without being impacted by the turbulent region.

Windstar 530G Prototype

Author: Kevin Wolf
Publication: Wind Harvest International
Year Published: 2001

The Windstar 530G was a three turbine array designed to test the coupled vortex effect, a phenomenon first hypothesized by Wind Harvest founder Bob Thomas in the early 1990’s. The array was placed in one of the highly energetic wind farms of San Gorgonio Pass Wind Resource Area in California.