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Research Papers: Alternative Energy Sources

A New Approach Toward Power Output Enhancement Using Multirotor Systems With Shrouded Wind Turbines

[+] Author and Article Information
Ohya Yuji

Professor
Research Institute for Applied Mechanics,
Kyushu University,
6-1 Kasuga-Koen,
Kasuga, 816-8580, Japan
e-mail: ohya@riam.kyushu-u.ac.jp

Watanabe Koichi

Kyushu University Platform of Inter/
Transdisciplinary Energy Research,
6-1 Kasuga-Koen,
Kasuga, 816-8580, Japan
e-mail: koichi-watanabe@riam.kyushu-u.ac.jp

Contributed by the Advanced Energy Systems Division of ASME for publication in the JOURNAL OF ENERGY RESOURCES TECHNOLOGY. Manuscript received July 17, 2018; final manuscript received October 20, 2018; published online January 9, 2019. Assoc. Editor: Ryo Amano.

J. Energy Resour. Technol 141(5), 051203 (Jan 09, 2019) (10 pages) Paper No: JERT-18-1541; doi: 10.1115/1.4042235 History: Received July 17, 2018; Revised October 20, 2018

A multirotor system (MRS) is defined as containing more than one rotor in a single structure. MRSs have a great potential as a wind turbine system, saving mass and cost, and showing scale ability. The shrouded wind turbine with brimmed diffuser-augmented wind turbines (B-DAWT) has demonstrated power augmentation for a given turbine diameter and wind speed by a factor of about 2–5 compared with a bare wind turbine. In the present research, B-DAWTs are used in a multirotor system. The power output performance of MRSs using two and three B-DAWTs in a variety of configurations has been investigated in the previous works. In the present study, the aerodynamics of an MRS with five B-DAWTs, spaced in close vicinity in the same vertical plane normal to a uniform flow, has been analyzed. Power output increases of up to 21% in average for a five-rotor MRS configuration are achieved in comparison to that for the stand-alone configuration. Thus, when B-DAWTs are employed as the unit of a MRS, the total power output is remarkably increased. As the number of units for an MRS is increased from two to five, the increase in power output becomes larger and larger. This is because that the gap flows between B-DAWTs in a MRS are accelerated and cause lowered pressure regions due to vortex interaction behind the brimmed diffusers. Thus, a MRS with more B-DAWTs can draw more wind into turbines showing higher power output.

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References

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Figures

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Fig. 1

Schematics of three WLTs in a SBS arrangement SBS) (left) and its photo in the wind tunnel (right)

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Fig. 2

Present MRS with five WLTs with equal gap width s in a vertical plane

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Fig. 3

Procedure of measuring Cp and Cd in each setup (right) and schematic of the measurement system for the power output and the drag force (left)

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Fig. 4

Measurement systems for wind velocity and static pressure distributions

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Fig. 5

Variations in Cpi for the present MRS configuration with five WLTs in the two-row arrangement compared to those for the stand-alone configuration. “AVE” means the averaged power output increase of five WLTs.

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Fig. 6

Variations in Cd for the present MRS configuration of five WLTs in the two-row arrangement compared to those for the stand-alone configuration. “AVE” means the averaged drag increase of five WLTs.

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Fig. 7

Pressure and u-velocity distributions are evaluated along the line A-A behind a WLT with 0.4Drotor separation

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Fig. 8

Pressure and u-velocity distributions behind a single WLT in a stand-alone configuration at 0.4Drotor downstream behind the rotor

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Fig. 9

Lines A and B for static pressure and u-velocity distribution measurements located 0.4Drotor behind rotor in the downstream of a five-WLT MRS arrangement

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Fig. 10

(a) Pressure and u-velocity distributions along line A behind two WLTs in the upper row in the present five-WLT arrangement at a gap ratio of s/Dbrim = 0.2 and 0.4Drotor behind rotor in the downstream and (b) pressure and u-velocity distributions along line B behind three WLTs in the lower row in the present five-WLT arrangement at a gap ratio of s/Dbrim = 0.2 and 0.4Drotor behind rotor in the downstream

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Fig. 11

Comparisons of u-velocity distributions between a two-WLT MRS in SBS (open symbols) and the two WLTs (closed symbols) in the upper row of the present five-WLT arrangement (top figure), and between a three-WLT MRS in SBS (open symbols) and the three WLTs (closed symbols) in the lower row of the present five-WLT MRS configuration (bottom figure), at the same gap ratio of s/Dbrim = 0.2 and 0.4Drotor behind rotor in the downstream

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Fig. 12

Comparisons of pressure distributions between a two-WLT MRS in SBS (open symbols) and the two WLTs (closed symbols) in the upper row of the present five-WLT arrangement (top figure), and between a three-WLT MRS in SBS (open symbols) and the three WLTs (closed symbols) in the lower row of the present five-WLT MRS configuration (bottom figure), at the same gap ratio of s/Dbrim = 0.2 and 0.4Drotor behind rotor in the downstream

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Fig. 13

Computational domain for a MRS with five WLTs in the present arrangement

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Fig. 14

Comparison of power output increases of each turbine in the five-WLT MRS between CFD and wind tunnel experiments at s/Dbrim = 0.2

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Fig. 15

Comparisons of pressure (P) and u-velocity (Ux) distributions in the five-WLT MRS between CFD and wind tunnel experiments at s/Dbrim = 0.2, evaluated at 0.4Drotor behind rotor in the downstream. The top figure shows the results of the upper row (two WLTs) and the bottom figure shows those of the lower row (three WLTs) of the present five-WLT arrangement.

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Fig. 16

Time averaged u-velocity field (left) and static pressure field (right) for five-WLT MRS configuration at s/Dbrim = 0.2, evaluated at 0.4Drotor behind rotor in the downstream of the MRS with five WLTs

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Fig. 17

Instantaneous u- velocity field (left) and static pressure field (right) for the upper and lower rows for the present five-WLT configuration in the two horizontal planes of A and B (Fig. 16), at s/Dbrim = 0.2

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Fig. 18

Comparisons of static pressure p and u-velocity distributions between a two-WLT MRS in SBS (broken lines) and the two WLTs (solid lines) in the upper row of the present five-WLT arrangement (top figure), and comparisons of those between a three-WLT MRS in SBS (broken lines) and the three WLTs (solid lines) in the lower row of the present five-WLT MRS configuration (bottom figure), at the same gap ratio s/Dbrim = 0.2, evaluated from CFD results at 0.4Drotor behind rotor in the downstream

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