Research Papers

Small Wind Turbines in the Built Environment: Influence of Flow Inclination on the Potential Energy Yield

[+] Author and Article Information
Serena Bianchi

e-mail: bianchi@vega.de.unifi.it

Alessandro Bianchini

e-mail: bianchini@vega.de.unifi.it

Giovanni Ferrara

e-mail: giovanni.ferrara@unifi.it
Department of Industrial Engineering,
University of Florence,
Via di Santa Marta,
3 Firenze 50139, Italy

Lorenzo Ferrari

National Research Council of Italy,
Via Madonna del Piano 10,
Sesto Fiorentino 50019, Italy
e-mail: lorenzo.ferrari@iccom.cnr.it

Contributed by the International Gas Turbine Institute (IGTI) of ASME for publication in the JOURNAL OF TURBOMACHINERY. Manuscript received June 18, 2013; final manuscript received July 22, 2013; published online September 26, 2013. Editor: Ronald Bunker.

J. Turbomach 136(4), 041013 (Sep 26, 2013) (8 pages) Paper No: TURBO-13-1101; doi: 10.1115/1.4025169 History: Received June 18, 2013; Revised July 22, 2013

Increasing interest is being paid by architects, project developers and local governments to understanding where small wind turbines can effectively be exploited to provide delocalized power in the built environment. The wind conditions in the rooftop area of buildings in urban locations are, however, very complex and the real adaptability of wind turbines to these environments is not yet tested both in terms of real producibility and of structural compatibility with the building themselves. In these installations, in particular, the flow that incomes on the rotor is often inclined with respect to the horizontal direction due to the interaction with the building façade and the roof. A correct estimation of the impact of an inclined flow on the performance of horizontal-axis wind turbines, therefore, becomes a very relevant issue to correctly predict the potential energy yield of a machine. To this purpose, a simulation code based on a blade element momentum (BEM) approach was developed and validated by means of experimental data found in the literature. The code was then used to evaluate the energetic suitability of a small-size wind turbine installation in the rooftop of a building in a conventional European city. A numerical computational fluid dynamics (CFD) analysis was carried out to characterize the flow field in the rooftop area of different buildings. The flow velocity modulus and direction were calculated for several oncoming wind profiles: The results were projected into an available wind power curve in the rooftop of the building. The effective energy-yield capabilities were then corrected using the model for the flow inclination as a function of the specific flow conditions in the rooftop area. The results were finally exploited to analyze the energy-oriented feasibility of an installation in a similar context.

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Fig. 1

Example of the flow behavior approaching the rooftop of a high building (ideal central section of the building, far from corners)

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Fig. 2

BEM modeling scheme of a horizontal-axis wind turbine

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Fig. 3

Code validation on literature data

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Fig. 4

Flow-rotor interaction in an inclined flow

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Fig. 5

Flow components acting on the blade

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Fig. 6

Code validation: power coefficient variation in inclined flow for NREL phase II (Hansen [36])

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Fig. 7

Code validation: normal force during revolution at 80% span of NREL phase VI (Schepers [37])

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Fig. 9

Investigated configuration (turbine not in scale)

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Fig. 10

Modified wind distribution in a-type cases

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Fig. 11

Energy potential variation: case 1a versus case 1c (short building-medium skew angle in the rooftop)

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Fig. 12

Energy potential variation: case 2a versus case 2b (high building with acceleration-high skew angle in the rooftop)

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Fig. 13

Energy potential variation: cases 2a, 2d, and 2e (high building but with different rooftop conditions due to the surrounding buildings)




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