Tetsuya Kogaki

Numerical Investigation of Wind Conditions over a Rectangular Prism-Shaped Building for Mounting Small Wind Turbines:

This study investigated the wind conditions over a building from the viewpoint of mounting small wind turbines. Large-eddy simulations (LES) of the wind flow around a rectangular prism-shaped building, whose ratio of breadth, length, and height is 1:1:2, was performed. The LES results confirmed that above the vicinity of the buildings leading edge, wind power density is relatively large and velocity standard deviation is relatively small. It was also confirmed that the regions with higher values of standard deviation of the stream-wise wind velocity component that exceeds the value given by IEC61400-2 for the normal turbulence model are large.

Prospect of offshore wind energy development in Japan

In Japan, the cumulative capacity of wind turbine generation systems on land has increased steadily in recent years. To install a large number of wind turbines has inherent problems such as shortage of suitable land, and inadequate infrastructure such as power cables and roads. The necessity for development of offshore wind turbine generation systems has been recognised based on the above backgrounds. An expert committee to survey the prospect of offshore wind turbine generation in Japan was organised last year. In this paper, the prospect of offshore wind energy development in Japan is reported based on the discussion in the committee. As a result, it was found that there are some undesirable circumstances for offshore wind energy utilisation in Japan. For that reason, we need technological innovation as well as an increase in scale of wind farms in order to achieve an economical profit. The difficulty in realising of offshore wind farms in Japan relates to Japanese inshore conditions, various legal regulations and fishing rights issues.

Investigation of the Fetch Effect Using Onshore and Offshore Vertical LiDAR Devices

An offshore wind measurement campaign using vertical light detection and ranging (LiDAR) devices was conducted at the Hazaki Oceanographic Research Station (HORS) as part of an investigation into determining the optimal distance from the coast for a nearshore wind farm from a meteorological perspective. The research platform was a 427 m long pier located on a rectilinear coastline on the Pacific coast of the central Honshu Island in Japan. The relationship between the ratios of the increase of wind speed near the surface and fetch length within 5 km of the coast was analyzed via LiDAR observations taken at heights from 40 to 200 m. The results showed that the speed of the coastal wind blowing from land to sea gradually increased as the fetch length increased, by approximately 15–20% at 50 m above sea level around a fetch length of 2 km. Moreover, empirical equations were derived by applying the power law to the relationship between the increase of wind speed and fetch lengths at 1–5 km, as obtained from the LiDAR measurements. It was also found that the wind speed increase at a 2 km fetch length was equivalent to the effect of a 50–90 m vertical height increase on the coast in this region.

Assessment of the offshore wind resource in Japan with the ASCAT microwave scatterometer

ABSTRACT We analysed wind speed and direction off the coast of Japan using data from the satellite-borne Advanced Scatterometer (ASCAT) and the Weather Research and Forecasting model (WRF), validated these data using in situ wind measurements from 20 buoys, and evaluated the effect of the long time intervals from ASCAT observations on wind resource assessment. More than 25 km from the coast, and at heights of 10 m, the ASCAT wind speed has negative biases of up to 3.4% and root mean square errors of up to 18.5%; its wind direction has 11° to 27° of mean absolute error compared to buoy measurements at a height of 10 m. These accuracies are better than either the expected accuracies reported in the technical manual or those simulated with WRF with its spatial resolution of 10 km. We also evaluated long-term average ASCAT wind speeds in comparison to 4- and 5-year averages of in situ buoy wind speeds measured at three buoys, with resulting differences of –0.3%, –6.3%, and – 1.6%. Furthermore, wind roses show that appearance frequencies of the ASCAT wind direction for the long term are in a good agreement with those of the measurements at the three buoys. Our results show that the ASCAT-derived wind speed and direction are appropriate more than 25 km from the coast, and that the long time interval between ASCAT observations has an insignificant effect on wind resource assessment, if at least 4 or 5 years of averaged ASCAT data are used.

Modeling of Flow Acceleration Around Wind Farms

Recent measurements from operating wind farms demonstrate that the layout of the farm and interactions between turbine wakes strongly affects the overall efficiency of the wind farm. In some wind farms arranged in rectangular layouts, winds coming from the direction of the rectangular corner create a potential acceleration around the wind farm. This acceleration inherently leads to stronger local wind speeds at wind turbines downstream of the corner turbine, thereby increasing the power output of the downstream turbines. In this study, computational models are developed to predict this complex behavior seen in wind farms. The model used to examine these effects is a fully three-dimensional unsteady incompressible Navier-Stokes code, with the turbulence model turned off. Preliminary results show an optimum spacing configuration is possible. However, the results have yet to be verified at higher Reynolds number, which will be the effort of future work. Ultimately, these tools may lead to more optimal wind farm layouts.© 2007 ASME

Performance Improvement of Airfoil for Wind Turbines by Modified Vortex Generators

風力 ター ビンの性能 は,種 々の要素 によって影響 さ れ るが,そ の中で も風力 ター ビンブ レー ドを構成す る 翼型の性能 の影響 が最 も支配 的である と言 える.近 代 的 な水 平軸 プ ロペ ラ型風 力 ター ビンが 開発 され 始 め た1960~1980年 あた りまでは,中 ・小型航空機用 に開 発 され た低 レイ ノルズ 数翼型 が風力 ター ビン用 翼型 として用 い られ た.し か し,作 動 レイ ノル ズ数範囲 が 広 く,か つ変動風 が流入す る風力 ター ビンに対 しては, これ らの翼 型 は必 ず しも最適 で はな く十分 な性 能で はなか った.1980年 代以降,風 力 ター ビンの高効率化, 安定性能化のた めに,風 力 ター ビン用 に特化 した翼型 開発 が世界の研究機関 ・大学 で実施 され,産 業技術総 合研 究所風 力研 究チー ムで もMEL翼 型 を開発 して き た※1,2).し か し,翼 型 の開発 には コス ト及 び労力 が 必 要であるた め,ボ ル テ ックス ・ジェネ レー タを用 い た境界層 制御 に よ り比較 的低 コス トで既存 翼型 の性 能 改善 を行 うこ とも一つ の方 向性で あ る と考 え られ てい る.こ うした 考 えに基づ き,平 板 状 ボル テ ック ス ・ジェネ レー タを翼上面に取 り付け,風 洞実験に よ ってそ の有効性 を検 証 した※3).そ の結果,揚 力 が増 加 す るとともに性能 が安定化す る ものの,抗 力 も増加 す るため最大揚抗比 としては減少 し,必 ず しも満足の い く性能 改善 が達成 され ない こ とがわか った. 本研 究では,上 記の問題 を改善す るため,新 たな断 面形状を採用 した改 良型ボル テ ックス ・ジェネ レー タ を開発 した.改 良型ボルテ ックス ・ジェネ レー タの有 効性 を検証す るために,風 洞実験 を実施 し,レ イ ノル ズ数,設 置間隔,高 さ等 のパ ラメー タを変化 させた時 の影響を詳細 に調査 した.