Kyushu University Academic Staff Educational and Research Activities Database
List of Papers
Koichi Watanabe Last modified dateļ¼š2023.11.28

Post-doctoral Fellow / Research and Education Center for Offshore Wind

1. Koichi Watanabe, Sho Fukutomi, Yuji Ohya, Takanori Uchida, An Ignored Wind Generates More Electricity
A Solar Updraft Tower to a Wind Solar Tower, International Journal of Photoenergy, 10.1155/2020/4065359, 2020, 2020.01, A solar updraft tower is one of the wind power generation plants which utilizes solar energy. The purpose of this study was to ascertain whether the tower was also able to utilize crosswind energy. Wind tunnel experiments and numerical simulations were conducted simulating the crosswind. The results showed that suctioned updraft speed in the tower was proportional to the crosswind speed, and its conversion rate depended on the tower configuration. A diffuser-shaped tower with a vortex generator achieved to produce the updraft whose speed exceeded the crosswind speed. It was due to the low pressure created by the vortex atop the tower and to the diffuser effect. The crosswind utilization enables the simple power generation device to generate electricity during the night, and the hybrid utilization of renewable energies contributes to the increasing wind energy market..
2. Koichi Watanabe, Yuji Ohya, Takanori Uchida, Power output enhancement of a ducted wind turbine by stabilizing vortices around the duct, Energies, 10.3390/en12163171, 12, 16, 2019.08, A brimmed-diffuser augmented turbine (called a wind lens turbine: WLT) actively uses vortices around the brim to enhance its power output. However, the vortices are usually unstable and asymmetric. This study attempted to stabilize the vortices to enhance the power output of a WLT. Then, we investigated new approaches using vortex stabilization plates and polygonal brims in wind tunnel experiments and numerical simulations. Both approaches achieved a 1.5-3.8% increase in power output compared with a standard WLT. Our numerical simulations revealed a periodicity existing in a fluctuating vortex structure on the circular brim. Importantly, vortex stabilization plates and polygonal brims must be the same periodic scale to suppress the vortex fluctuation and stabilize the vortices effectively. In addition, a larger brim tended to enhance the stabilizing effects. We believe that this discovery provides an easy way to increase the power output of existing wind turbines. It is particularly important in light of advances in wind energy technology and the increasing wind energy market..
3. Ohya Yuji, Koichi Watanabe, A new approach toward power output enhancement using multirotor systems with shrouded wind turbines, Journal of Energy Resources Technology, Transactions of the ASME, 10.1115/1.4042235, 141, 5, 2019.05, 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..
4. Koichi Watanabe, Yuji Ohya, Multirotor Systems Using Three Shrouded Wind Turbines for Power Output Increase, Journal of Energy Resources Technology, Transactions of the ASME, 10.1115/1.4042971, 141, 5, 2019.05, Brimmed-diffuser augmented wind turbines (B-DAWTs) can significantly increase the performance of the rotor. Multirotor systems (MRSs) have a lot of merits such as significant saving mass and overall cost of the wind turbine system. In the present research, B-DAWTs are studied in a MRS. In wind tunnel experiments, the power output and aerodynamics of three B-DAWTs placed in close vicinity have been investigated. The results show a significant increase of up to 12% in total power output of the MRS with B-DAWTs compared to the sum of the stand-alone (SA) same turbines. The accelerated gap flows between B-DAWTs in a MRS cause lowered pressure regions due to vortex interaction behind the brimmed diffusers and draw more wind into turbines..
5. Power Output and Drag Characteristics of Multi Rotor Wind Turbine System Using Brimmed-Diffuser Augmented Wind Turbines (in Japanese).
6. Improvement of Power Output of Straight-Bladed Vertical Axis Wind Turbines with Surrounding Structures (in Japanese).
7. Koichi Watanabe, Yuji Ohya, Takanori Uchida, Tomoyuki Nagai, Numerical Prediction and Field Verification Test of Wind-Power Generation Potential in Nearshore Area Using a Moored Floating Platform, Journal of Flow Control, Measurement & Visualization, DOI:10.4236/jfcmv.2017.52002, Vol.5, No.2, pp.21-35, 2017.04.
8. Yuji Ohya, Jumpei Miyazaki, Uli Goeltenbott, Koichi Watanabe, Power Augmentation of Shrouded Wind Turbines in a Multi-Rotor System, The American Society of Mechanical Engineers, Journal of Energy Resources Technology, DOI:10.1115/1.4035754, Vol.139, Issue5, 051202, 2017.02.
9. Yuji Ohya, Takashi Karasudani, Tomoyuki Nagai, Koichi Watanabe, Wind Lens Technology and Its Application to Wind and Water Turbine and Beyond, Journal of Renewable Energy and Environmental Sustainability, DOI:10.1051/rees/2016022 , Vol.2, 2, 2017.01.
10. Yuji Ohya, Masaki Wataka, Koichi Watanabe, Takanori Uchida, Laboratory Experiment and Numerical Analysis of a New Type of Solar Tower Efficiently Generating a Thermal Updraft, Energies, DOI:10.3390/en9121077 , Vol.9, Issue12, 1077, 2016.12.
11. Koichi Watanabe, Shuhei Takahashi, Yuji Ohya, Application of a Diffuser Structure to Vertical-Axis Wind Turbines, Energies, DOI:10.3390/en9060406, Vol.9, Issue6, 406, 2016.05.
12. Application of a Wind Acceleration Device to Vertical Axis Wind Turbines (in Japanese).