Kyushu University [Yuji Ohya (Post-doctoral Fellow) Research Institute for Applied Mechanics, Division of Renewable Energy Dynamics]

Department of Aeronautics and Astronautics
Graduate School of Engineering

092-583-7777

092-583-7779

Wake interference of a row of normal flat plates arranged side by side in a uniform flow

Wind engineering, Fluid dynamics, Atmospheric boundary layer, Wind energy

Wind engineering section performs experimental and numerical research on problems of fluid dynamics, related to wind environments such as airflow over complex terrain and urban canopy, and to wind forces on buildings and structures, and to wind energy as clean and renewable energy. Current areas of research projects are: 1) Turbulence structure and transport characteristics of the atmospheric boundary layer; 2) Prediction of wind systems over local topographic features; 3) Aerodynamic characteristics and flutter phenomena of bluff bodies; 4) Development of wind energy and new wind turbine system; 5) Development of a hybrid energy generation system using solar heat and wind in a wind-solar tower; 6) Computational fluid dynamics in wind engineering. In order to conduct these researches, various wind engineering facilities consisting of a large boundary-layer wind tunnel, thermally stratified wind tunnel and water tanks are effectively utilized.

Research Interests

A hybrid renewable energy system by solar heat and wind in a wind-solar tower
keyword : solar heat, wind aloft, solar chimney, wind-lens vertical type, co-generation, triple-generation
2015.01.
Development of a multi-rotor system using wind-lens turbines
keyword : diffuser-augmented wind turbine, multi rotor system, wind energy, wind turbine
2014.01.
Development of a high-density Floating-body Energy farm
keyword : Wind, Solar, Tidal current, Wave
2010.10.
Development of high efficiency mini water energy system using Water-lens turbine
keyword : Windlens, Water-lens turbine, Micro/mini water energy, river
2011.04.
Research on the utilization of wind energy
keyword : Wind-lens turbine, Shrouded wind turbine, Brimmed diffuser
1999.04Development of high-performance wind turbine with a brimmed-diffuser.
Reserch on the Atomospheric Boundary Layer
keyword : Atomospheric Boundary Layer, Turbulance, Stratified Flow, Wind tunnel experiment, Numerical simulation
1993.04Resarch on atmospheric boundary layer by using wind tunnel and numerical analyses.
Research on the prediction method of wind system
keyword : Wind pattern, Numerical simulation, Wind tunnel experiment, Atomospheric environment
1996.04Development of a prediction method for local wind pattern and atmospheric environment.
Research on the bluff-body flow and the aerodaynamics of them
keyword : Aerodynamics characteristics, Flow visualization, Numerical caliculation, Wind tunnel experiment
1981.04Bluff body flow and aerodynamics.

Current and Past Project

Using wind energy due to wind-lens turbines, the electricity will be provided to an electroric station. A couple of elecrtoric cars are provided the electlicity through the station. The operation system of the electroric cars will be established.
We will initiate an irrigation project using wind energy in a desert area in the northwestern district in China. For this purpose, we will develop a wind turbine with a compact brimmed diffuser, called wind-lens turbine, which is expected to be suitable to a desert area with good wind condition.
Research on the integraded renewable energy including solar, wind , hydrozen, etc.
Development of high-performance wind turbine
Research on a huge floating body which has wind turbines, solar panels, tidal current turbines and wave energy conversion system.

Academic Activities

Books

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1.	Y. Ohya, A. Okajima and M. Hayashi, Wake Interference and Vortex Shedding, Encyclopedia of Fluid Mechanics, Vol.8, Gulf Publishing Co., N. P. Cheremisinoff Ed., Wake and interference, pp.323-389, 1989.12.

Reports

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1.	Offshore Wind Power-Floating Integrated Energy Platform in Corporation eith Fishery.
2.	Wind-Lens Turbine and Offshore Floating Energy Farm.
3.	Yuji Ohya, Floating energy farm offers windy bounty, NATURE JOBS, 2013.03.
4.	Wind Lens Turbine（Development of a Highly Efficient Wind Turbine).

Papers

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1.	Yuji Ohya, Bluff body flow and vortex-its application to wind turbines, Fluid Dynamics Research, 10.1088/0169-5983/46/6/061423, 46, 6, 061423, 2014.12.
2.	Yuji Ohya, Takanori Uchida, Tomoyuki Nagai, Near Wake of a Horizontal Circular Cylinder in Stably Stratified Flows, Open Journal of Fluid Dynamics, 10.4236/ojfd.2013.34038, 3, 4, 311-320, 2013.12, The near wake of a circular cylinder in linearly stratified flows of finite depth was experimentally investigated by means of flow visualization and measurements of vortex shedding frequencies, at Reynolds numbers 3.5 × 103-1.2 × 104 and stratification parameters kd 0-2.0. The non-dimensional parameter kd is defined as kd = Nd/U, where N is the Brunt-Vaisala frequency, d, the diameter of the cylinder, and U, the approaching flow velocity. The study demonstrates that as kd increases from zero, the vortex shedding from a circular cylinder progressively strengthens, while the Strouhal number gradually becomes lower than that for homogeneous flow. This phenomenon can be explained by the effect of the increasingly stable stratification which enhances the two-dimensionality of the near-wake flow of the circular cylinder; the enhanced two-dimensionality of the flow strengthens the roll-up of the separated shear layer. Above a certain value of kd, however, vortex formation and shedding are strongly suppressed and the Strouhal number rises sharply. This observation is attributable to the development of stationary lee waves downstream of the circular cylinder because the lee waves strongly suppress vertical fluid motions..
3.	Takeo Mizota, Kouhei Kurogi, Yuji Ohya, Atsushi Okajima, Takeshi Naruo, Yoshiyuki Kawamura, The strange flight behaviour of slowly spinning soccer balls, Nature SCIENTIFIC REPORTS, 10.1038/srep01871, 3, 2013.05, サッカーボールなどでよく言われる無回転シュートが、なぜ左右上下にランダムに揺れるかの理由を解明した。.
4.	Shuhei Takahashi, Yuta Hata, Ohya Yuji, karasudani takashi, Uchida Takanori, Behavior of the Blade Tip Vortices of a Wind Turbine Equipped with a Brimmed-Diffuser Shroud, Energies2012, 10.3390/en5125229, 5, pp.5229-5242, 2012.12, To clarify the behavior of the blade tip vortices of a wind turbine equipped with a brimmed-diffuser shroud, called a “Wind-Lens turbine”, we conducted a three-dimensional numerical simulation using a large eddy simulation (LES). Since this unique wind turbine consists of not only rotating blades but also a diffuser shroud with a broad-ring brim at the exit periphery, the flow field around the turbine is highly complex and unsteady. Previously, our research group conducted numerical simulations using an actuator-disc approximation, in which the rotating blades were simply modeled as an external force on the fluid. Therefore, the detailed flow patterns around the rotating blades and the shroud, including the blade tip vortices, could not be simulated. Instead of an actuator-disc approximation, we used a moving boundary technique in the present CFD simulation to simulate the flow around a rotating blade in order to focus especially on blade tip vortices. The simulation results showed a pair of vortices consisting of a blade tip vortex and a counter-rotating vortex which was generated between the blade tip and the inner surface of the diffuser. Since these vortices interacted with each other, the blade tip vortex was weakened by the counter-rotating vortex. The results showed good agreement with past wind tunnel experiments..
5.	Ohya Yuji, Takanori Uchida, Takashi Karasudani, Masaru Hasegawa, Hiroshi Kume, Numerical Studies of Flow around a Wind Turbine Equipped with a Flanged-Diffuser Shroud using an Actuator-Disk Model, Wind Engineering, 36, 4, 455-472, 2012.08, Unsteady 3-D direct numerical simulations based on the finite-difference method (FDM) were performed for flow fields around a wind turbine equipped with a flanged-diffuser shroud. Generally, it is difficult to numerically simulate the flow around rotating bodies such as the blades of wind turbines because of the unsteady flow generated by moving bodies with complex geometry. Therefore, we have devised an actuator-disk model for a wind turbine for simulating the drag and rotational forces exerted on the fluid by the wind turbine. By incorporating the body forces derived from the actuator-disk model into the external terms in the Navier-Stokes equations, the unsteady flow around a wind turbine can be simulated. The results of numerical simulations were compared with the results from wind tunnel experiments and showed good agreement for the velocity and pressure fields..
6.	Yuji Ohya, Takashi Karasudani, A Shrouded Wind Turbine Generaring High Output Power with Wind-lens Technology, Proceedings of Renewable Energy2010, CD-ROM, 2010.07, 風力エネルギーの有効利用に関する研究である。特色は，風エネルギーを集中させて風力発電の効率を飛躍的に高めた新しいタイプの風力発電システムの開発(レンズ風車と名付けた)と、数値風況予測の高精度シミュレータ (リアムコンパクトと名付けた)にある。数年に亘る研究の結果、従来の風車と比べ，２-５倍の発電出力の増加を達成し，小型(1-5kW機)・中型(100kW機)のレンズ風車を開発した。風力エネルギーのより大きな獲得のため、海上展開を図った。博多湾に直径18mの六角形浮体を浮かべ、3kWレンズ風車2基と1.5kWソーラーパネルを搭載した世界で初めての浮体プラットホーム式のエネルギーファームを実現した。.
7.	Yuji Ohya, Takanori Uchida, Near Wake of a Horizontal Circular Cylinder in Stably Stratified Flows, 九州大学応用力学研究所所報, Vol.138, pp.13-22, 2010.03, The near wake of a circular cylinder in linearly stratified flows of finite depth was experimentally investigated by means of flow visualization and measurements of vortex shedding frequencies, at Reynolds numbers 3.5×103–1.2×104 and stratification parameters kd 0–2.0. The non-dimensional parameter kd is defined as　kd=Nd/U, where N is the Brunt-Väisälä frequency, d, the diameter of the cylinder, and U, the approaching flow velocity. The study demonstrates that as kd increases from zero, the vortex shedding from a circular cylinder progressively strengthens, while the Strouhal number gradually becomes lower than that for homogeneous flow. This phenomenon can be explained by the effect of the increasingly stable stratification which enhances the two-dimensionality of the near-wake flow of the circular cylinder; the enhanced two-dimensionality of the flow strengthens the roll-up of the separated shear layer. Above a certain value of kd, however, vortex formation and shedding are strongly suppressed and the Strouhal number rises sharply. This observation is attributable to the development of stationary lee waves downstream of the circular cylinder because the lee waves strongly suppress vertical fluid motions..
8.	Yuji Ohya, Takashi Karasudani, A Shrouded Wind Turbine Generaring High Output Power with Wind-lens Technology, Energies, 10.3390/en3040634, 3, 634-649, 2010.03.
9.	Development of a highly efficient wind turbine and its future.
10.	Tomohiro Hara, Yuji Ohya, Takanori Uchida, Ryohji Ohba, Wind-Tunnel and Numerical Simulations of the Coastal Thermal Internal Boundary Layer, Bundary Layer Meteorology, Vol 130, PP.365-381, 2009.02.
11.	Yuji Ohya, Takanori Uchida, Laboratory and Numerical Studies of the Atmospheric Stable Boundary Layers, Journal of Wind Engineering and Industrial　Aerodynamics, Journal　of Wind Engineering & Industrial Aerodynamics 96(2008),pp.2150-2160, 2008.05.
12.	Yuji Ohya, Takashi Karasudani, Akira Sakurai, Ken-ichi Abe, Masashiro Inoue, Development of a Shrouded Wind Turbine with a Flanged Diffuser, Journal of Wind Engineering and Industrial　Aerodynamics, vol. 96, Issue 6, pp.524-539, 2008.03.
13.	Yuji Ohya, Reina Nakamura, Takanori Uchida, Intermittent Bursting of Turbulence in a Stable Boundary Layer with Low-Level Jet, Boundary-Layer Meteorology, vol. 26, No. 3, pp. 349-363, 2008.01.
14.	Y. Ohya, T. Karasudani, Development of a Shrouded Wind Turbine Generating High Output Power with the Wind-Lens Technology, Proc. of the RENEWABLE ENERGY 2006（再生可能エネルギー2006国際会議）, CD-ROM, 2006.10.
15.	Yuji Ohya, Takashi Karasudani,Akira Sakurai, Masahiro Inoue, Development of a High-Performance Wind Turbine Equipped with a Brimmed Diffuser Shroud, Transactions of the Japan Society for Aeronautical and Space Sciences, 49, 163, 18-24, 2006.05.
16.	Yuji Ohya and Takanori Uchida, Laboratory and numerical studies of the convective boundary layer capped by a strong inversion, Boundary-Layer Meteorology, 10.1023/B:BOUN.0000027913.22130.73, 112, 2, 223-240, Vol.112, pp.223-240, 2004.08.
17.	Yuji Ohya, Drag of circular cylinders in the atmospheric turbulence, Fluid Dynamics Resrearch, 10.1016/j.fluiddyn.2003.10.002, 34, 2, 135-144, 34, pp.135-144, 2004.01.
18.	R. Ohba, T. Hara, S. Nakashima, Y. Ohya and T. Uchida, Gas diffusion over an isolated hill under neutral, stable and unstable conditions, Atmospheric Environment, 10.1016/S1352-2310(02)00642-8, 36, 36-37, 5697-5707, Vol.36, pp.5697-5707, 2002.01.
19.	Y. Ohya, Wind tunnel study of atmospheric stable boundary layers over a rough surface, Boundary-Layer Meteorology, 10.1023/A:1018767829067, 98, 1, 57-82, vol.98, pp.57-82, 2001.01.

Works, Software and Database

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Presentations

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1.	Yuji Ohya, An efficient wind turbine with wind-lens technology and offshore floationg energy farm, The 2nd Pacific Rim Energy and Sustainability Conference, 2013.08.
2.	Yuji Ohya, A highly efficient wind and water turbine with windlens technology and an offshore folating renewable energy farm, COME2013, 2013.05.
3.	Yuji Ohya, Bluff body flow and vortex, IUTAM2013, 2013.03.
4.	Yuji　Ohya, Wind Power Generation and Windlens, 日本－デンマーク　Future Green Technology, 2012.12.

Membership in Academic Society

JAPAN ASSOCIATION FOR WIND ENGINEERING
THE JAPAN SOCIETY OF FLUID MECHANICS
THE JAPAN SOCIETY OF AERONAUTICAL AND SPACE SCIENCES
METEOROLOGICAL SOCIETY OF JAPAN
JAPAN　WIND　ENERGY　ASSOCIATION
JAPANESE SOCIETY OF APPLIED METEOROLOGY AND CLIMATE RESOURCES

Awards

DUNHUANG　AWARD
Experimental Studies of Stable Boundary Layers and Convective Boundary Layers in the Atmosphere

Other Educational Activities

2008.11.
2004.11.

http://www.riam.kyushu-u.ac.jp/