Yuji Ohya

Kyushu University | Kyudai · Research Institute for Applied Mechanics

We developed a new wind turbine system that consists of a diffuser shroud with a broad-ring brim at the exit periphery and a wind turbine inside it. The shrouded wind turbine with a brimmed diffuser, which we called a “wind lens turbine” (WLT), has demonstrated power augmentation by a factor of about 2–5 compared with a bare wind turbine for a give...

Wind solar towers constitute a fairly new scheme for harvesting renewable energy from solar and wind energy sources. In such a tower, solar radiation is collected and hot air is enforced to go fast through the tower, a process called thermal updraft, which fuels a wind turbine to generate power. Using vortex generators at the top of the tower creat...

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...

In order to design a large-scale wind farm, it is highly important to understand the wake of multiple wind turbines. Wind tunnel experiments with two arrangement patterns were conducted to approach the interference of the wakes arranging two wind turbines. Results have shown that when the blade posisions of the two scaled Horizontal-Axis Wind Turbi...

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 pla...

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 o...

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 win...

The most common wind turbine is the single–rotor, horizontal axis wind turbine. In order to reduce the cost of energy, upscaling of single–rotor wind turbines has been a major trend. Recent studies however show that for a given technology, the cost usually rises when upscaling, notably due to increased masses. To reach capacities beyond 10 MW, mult...

Diffuser augmented wind turbines (DAWTs) can significantly increase the performance of the rotor. Multi-rotor systems (MRSs) have a lot of merits such as significant saving mass and overall cost of the wind turbine system. A MRS is defined as containing more than one rotor in a single structure. In the present research, DAWTs are studied in a MRS....

Wind lens is a new type of wind power system consisting of a simple brimmed ring structure that surrounds the rotor causing greater wind to pass through the turbine. As a consequence, the turbine's efficiency of capturing energy from the wind gets dramatically increased. A Wind lens turbine can generate 2–5 times the power of an existing wind turbi...

The offshore turbine system was installed on a floating platform moored in Hakata Bay, offshore of Fukuoka, Japan. An identical turbine system was also installed at the adjacent waterfront. The separation of the two turbines was 3.7 km. Wind flow tends to be more stable and the average wind speed is often larger in offshore areas than adjacent land...

A new type of solar tower was developed through laboratory experiments and numerical analyses. The solar tower mainly consists of three components. The transparent collector area is an aboveground glass roof, with increasing height toward the center. Attached to the center of the inside of the collector is a vertical tower within which a wind turbi...

A multi-rotor system (MRS), in which multiple wind turbines are placed on one tower, is a promising concept for super-large wind turbines at over 10 MW due to the cost and weight advantages. The coherence effects on an MRS were investigated in this study. Although a wide range of coherences were measured so far, a decay constant of C = 12 is recomm...

Up-scaling of wind turbines has been a major trend in order to reduce the cost of energy generation from the wind. Recent studies however show that for a given technology, the cost always rises with upscaling, notably due to the increased mass of the system. To reach capacities beyond 10 MW, multi-rotor systems (MRS) have promising advantages. On t...

The effects of using a wind acceleration device (wind lens) with vertical-axis wind turbines in wind tunnel experiments were examined. A wind lens consists of a diffuser and flanges, and this study investigated the optimum parameters of their configuration with regard to the power augmentation of the turbines. The wind lens with a flat-panel-type d...

The trend of wind turbine industry is making a wind turbine larger and larger, because its electric capacity depends on swept area. Those huge wind turbines cause many problems as like increasing cost and weight. As one solution for these problems, multi-rotor system (MRS) has been proposed. MRS has many advantages such as weight decrease and cost...

In 1989, a pilot plant of a solar chimney was erected in Manzanares Spain to evaluate the feasibility of the solar tower as a new source of renewable energies. Since then, the solar tower was discussed in the press, but no commercial plant succeeded the research. A reason for this could be the relative low power output compared with other renewable...

The wind turbine industry has seen innovations leading to growing size of turbines of currently over 160 min diameter. However, as pointed out by some recent studies, up-scaling of blades has its limitations and therefore advantages of multi-rotor system concepts have been suggested by Jamieson et al. The so-called wind lens turbine, which was deve...

Wind lens turbines, developed by Kyushu University have increased performance due to the duct surrounding the rotor [1]. A Multi rotor system is a promising concept to upscale wind turbine systems beyond 20MW [2]. Results of experimental research on a seven turbine array have shown no loss in performance with closely spaced rotors [3]. In the prese...

Wind tunnel experiments were conducted to investigate the influence of the flanged diffuser on the dynamic behavior of the blade of a 3 kW wind turbine shrouded with a flanged diffuser. The blade was fabricated by the skin of carbon fiber reinforced plastic and solid foam core. Tests were carried out for three wind velocities (6.9 m/s to 11.6 m/s)...

The solar chimney prototype, operated in Spain from 1982 to 1989, verified the concept of the solar chimney. The power generation mechanism in this system is to turn the wind turbine placed inside a high rise cylindrical hollow tower by an induced thermal updraft. As long as the thermal updraft is induced inside the tower by the solar radiation, th...

Some interesting phenomena of vortex flows we have found in past experimental research are described. For a given flow configuration, multiple flow patterns can exist and a sudden change from one flow pattern to another can occur. We observed the alternate switching of the flow patterns with irregular periods around a bluff body. The change of vort...

PIV methods coupled with smoke wire techniques have been studied. The wire arrangements of these methods were perpendicular to the wind tunnel flow until now, however in our new proposal, the arrangements are parallel to the main flow direction of wind tunnel. The former wind speed, which was available to the flow observation, had been restricted o...

The purpose of this study is to improve the efficiency of the power generation system of a solar tower using fluid dynamics. The power generation system of a solar tower can be designed and constructed at relatively low cost. However, the energy output tends to be low for its physical size compared with other renewable energy production systems. Th...

A fluid machine, a wind turbine, and a method for increasing velocity of an internal flow is provided. A basic shape of the casing has a cycloid curve having a convex portion at a throat section between the front and rear edges. The throat section and a vortex generating face disposed downstream of the throat section to generate the negative pressu...

In this paper, a potential flow based numerical model is proposed for analysis of dynamic response of an offshore floating wind turbine system, with the consideration of hydrodynamic loads on the floating platform by the potential theory, the mooring lines by the catenary theory, and the aerodynamic loads on the wind turbine by the blade element mo...

In the World, renewable energy has been developing such as Solar power, geothermal energy, biomass energy and Wind energy. We are also conducting research on renewable energy such as wind energy in our laboratory. It has issued the results of many studies of the wind turbine with using the wind-lens technology developed in the field of wind energy...

Wind tunnel experiments were conducted to study the aerodynamic characteristics of the spinning soccer balls with variously oriented spinning axes, of which balls are observed in a real game. Ball suspension apparatus with the piano wire strings and a shaft-bearing system through a soccer ball are studied with the cautions to obtain good linearity...

A novel idea of hybrid power generation system has been proposed that can be characterized as a simple and renewable method to achieve sustainable utilization of renewable resources. The new hybrid system utilizes a solar chimney to produce electricity with a windmill. Geothermal heat will be used as a heat source to achieve desirable air speed ins...

This paper presents recent experimental and numerical work on dynamic analysis and load prediction of a floating platform. A new offshore renewable energy platform is designed for the second stage on-sea experiment of Kyushu University. An experiment is carried out in the towing tank with a 1/50 scale model, to verify the hydrodynamic performance o...

The strange three-dimensional flight behaviour of slowly spinning soccer balls is one of the most interesting and unknown phenomenon associated with the trajectories of sports balls. Many spectators have experienced numerous exciting and emotional instances while observing the curious flight behaviour of these balls. We examine the aerodynamic mech...

The authors study the radar signature of a new type of wind turbine, named the Wind Lens. This design includes a flanged shroud around the turbine which concentrates the wind flow past the turbine blades and hence improves the efficiency. The design also offers improved safety and reduces acoustic noise. Furthermore, it may offer a significantly lo...

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 × 10 3-1.2 × 10 4 and stratification parameters k d 0-2.0. The non-dimensional parameter k d is defined as k d = Nd/U, where N is th...

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...

Renewable energy resources including wind power generation are receiving more and more attention these days.In Japan,however,because of small land area,steep terrain,and population concentration in plane area,it is difficult to construct massive wind farm on land.The concept of offshore wind farm can overcome this problem.We have developed a wind t...

Unsteady 3-D direct numerical simulations based on FDM are carried out for flow fields around a wind turbine equipped with a flanged diffuser. Generally, it is difficult to simulate numerically the flow around rotational bodies like rotors of wind turbines, because of unsteadiness due to a moving body and complex geometry. Therefore, we have devise...

A new type of wind turbine system with wind power enhancement technology, named "Wind Lens", has been developed and reported in various publications, showing power augmentation by a factor of 2-5 compared with conventional turbines. This study reports further development of the system and its application including floating off-shore integrated ener...

This paper reviews the potential for wind-power generated electricity in ASEAN countries with special attention to Malaysia. ASEAN countries comprises of Brunei, Cambodia, Indonesia, Laos, Malaysia, Myanmar, Philippines, Singapore, Thailand and Vietnam. Big progress in renewable energy most probably comes in wind, because ASEAN countries have b...

A detailed wind synopsis analysis was performed for the Asokurumagaeri wind farm (operation of this wind farm was initiated in October, 2005) in cooperation with the Kumamoto Prefectural Enterprise Bureau. In this simulation, high-resolution terrain elevation data which included the latest land development information were utilized. The simulation...

Because a significant portion of the topography in Japan is characterized by steep, complex terrain, which results in a complex spatial distribution of wind speed, great care is necessary for selecting a site for the construction of Wind Turbine Generators (WTGs). We have developed a CFD model for unsteady flow called Research Institute for Applied...

This paper reviews the potential for wind-power generated electricity in ASEAN countries with special attention to Malaysia. ASEAN countries comprises and Vietnam. Big progress in renewable energy most probably comes in wind, because ASEAN countries have big potential for wind energy as it occupies less land. Besides, land in these countries is qui...

We present the results of measurements of the radar signature of a new type of wind turbine, named the Wind Lens. This design includes a shroud around the turbine which concentrates the wind flow past the turbine blades and hence improves the efficiency. The design also offers improved safety, and reduces acoustic noise. Furthermore, it may offer a...

The wake of a wind turbine generator (WTG) operated at the optimal tip speed ratio is compared to the wake of a WTG with its rotor replaced by a stationary disk. Numerical simulations are conducted with a large eddy simulation (LES) model using a nonuniform staggered Cartesian grid. The results from the numerical simulations are compared to those f...

Because a significant portion of the topography in Japan is characterized by steep, complex terrain, which results in a complex spatial distribution of wind speed, great care is necessary for selecting a site for the construction of wind turbine generators (WTG). We have developed a CFD model for unsteady flow called RIAM-COMPACT (Research Institut...

In the present numerical study, we carried out the large-eddy simulation (LES) of the wake generated behind the wind turbine generator under optimal tip speed ratio. Particular emphasis was placed on the effect of inflow turbulence on the wake region generated behind the wind turbine generator. Through comparisons between three cases with and witho...

We have developed a new wind turbine system (WLT, WindLens Turbine) that consists of a difluser shroud with a brim at the exit periphery and a wind turbine inside it. WLT has a bigger power output compared with a general same size wind turbine. This is because a low-pressure region due to a strong vortex formation draws more mass flow to the wind t...

In the present study, two doubts concerning the wind tunnel experiment by using the scale model were investigated. First, the comparison between an I-type hot wire probe and a split film probe was paid to attention in the eddy region. In the case using the I-type probe, a negative value is not reproduced for the mean velocity profile. Consequently,...

This paper describes the numerical study of a non-stratified airflow over real complex terrain. Attention is focused on a mechanism of a local strong wind induced by a topographic effect. As a result, the airflow has converged to the col and a local strong wind has been generated leeward along the slope of the col. Furthermore, the influence of the...

This paper describes the numerical study of a non-stratified airflow past a two-dimensional escarpment in a uniform flow. The Reynolds number, based on the uniform flow and the height of the escarpment, is about 104. The slope gradient of the escarpment is 25, 35 and 45 degree. Attention is focused on an influence of a slope gradient on airflow cha...

This paper proposes of real wind speed prediction method over complex terrain by using CFD. It is an attempt to convert the wind distribution on the computer into the scalar wind speed of a real scale in consideration of the correlation with the observed data. The reproducibility and the accuracy of the real wind speed were performed by using the h...

We have developed a new wind turbine system that consists of a diffuser shroud with a broad-ring brim at the exit periphery and a wind turbine inside it. The shrouded wind turbine with a brimmed diffuser has demonstrated power augmentation by a factor of about 2–5 compared with a bare wind turbine, for a given turbine diameter and wind speed. This...

We have already investigated the effects of inflow turbulence on the flow around a three-dimensional steep isolated-hill. For this purpose, two cases of large-eddy simulation (LES) are carried out: one is a numerical condition in which the hill is immersed in a fully-developed turbulent boundary layer; the other is a numerical condition in which a...

It is highly important in Japan to choose a good site for wind turbines, because the spatial distribution of wind speed is quite complicated over steep complex terrain. We have been developing the unsteady numerical model called the RIAM-COMPACT ® (Research Institute for Applied Mechanics, Kyushu University, COMputational Prediction of Airflow over...

It is highly important in Japan to choose a good site for wind turbines, because the spatial distribution of wind speed is quite complicated over steep complex terrain. We are developing the unsteady numerical model called the RIAM-COMPACT^<[○!R]> (Research Institute for Applied Mechanics, Kyushu University, Computational Prediction of Airflow over...

Wind-tunnel experiments in a thermally stratified wind tunnel and direct numerical simulations were performed to simulate the thermal internal boundary layer (TIBL) that developed over a coastal area in a sea-breeze flow. The results of the simulations were analyzed to investigate turbulence structure in the TIBL. To study the effects of the atmosp...

It is highly important in Japan to choose a good site for wind turbines, because the spatial distribution of wind speed is quite complicated over steep complex terrain. We are developing the unsteady numerical model called the RIAM-COMPACT (Research Institute for Applied Mechanics, Kyushu University, Computational Prediction of Airflow over Complex...

The wind turbines with a flanged-diffuser shroud-so called “wind lens turbine”-are developed as one of high performance wind turbines by Ohya et al. In order to investigate the flow characteristics and flow acceleration, the paper presents the flow velocity measurements of a long-type and a compact-type wind turbines with a flanged-diffuser shroud...

Less spinning soccer ball aerodynamics are studied by wind tunnel experiments. Aerodynamic force of unsteady lift and side ones acting on the ball at rest are measured and estimated flight trajectory. Well agreements of flight shift magnitude in lateral direction between observed and calculated ones are obtained. As a result, the cause of this stra...

It is highly important in Japan to choose a good site for wind turbines, because the spatial distribution of wind speed is quite complicated over steep complex terrain. We are developing the unsteady numerical model called the Research Institute for Applied Mechanics, Kyushu University, COMputational Prediction of Airflow over Complex Terrain (RIAM...

Large eddy simulation (LES) of the flow field over a surface-mounted prism under two different conditions, namely smooth and turbulent inflows, are carried out. A higher-order scheme, in which artificial dissipation is controllable, is used. The simulations are validated through comparison with experimental measurements. The results present new phy...

We have investigated the turbulence phenomena of SBLs for a wide range of stability, particularly focusing on the effects of strong stratification on turbulent boundary layers, using a thermally stratified wind tunnel. In parallel with wind tunnel experiments, to understand the turbulence features and fluid dynamics in detail, we have also performe...

We are developing the numerical model called the RIAM-COMPACT (Research Institute for Applied Mechanics, Kyushu University, Computational Prediction of Airflow over Complex Terrain). The object domain of this numerical model is from several m to several km, and can predict the airflow and the gas diffusion over complex terrain with high precision....

We have developed a new wind turbine (Wind Lens Turbine) which consists of a diffuser shroud with a broad-ring brim at the exit periphery, a rotor and a nacelle. We are now researching this type of wind turbine of large scale. When this type of wind turbine becomes large, we have to consider the wind load to the wind turbine. In order to decrease s...

We have observed the two wind turbines which built in two areas with different wind conditions. And we have investigated the wind turbine performance in various flows with dynamic wind direction fluctuations and different turbulent intensities and scales with wind tunnel. As a result, the power outputs of the wind turbine in turbulent flows with la...

Less spinning soccer ball aerodynamics are studied by wind tunnel experiments. Aerodynamic force of unsteady lift and side ones acting on the ball at rest are measured and estimated flight trajectory. Well agreements of flight shift magnitude in lateral direction between observed and calculated ones are obtained. As a result, in this stage the caus...