研究発表

完全発達した管内乱流の速度場をステレオPIVを用いて計測し、平均速度ならびにレイノルズ応力の全成分を求めた。半円オリフィスを設けた流れ場においても同様の計測を行い、両者において計測の不確かさはほぼ同じ程度に収まることが確認できた。

オープンソースのCFDコード、OpenFOAMを用いて、モデルHDD内に発達する乱流場についてLES解析を行った。アームを模した物体に作用する変動流体力を求めた結果、トルクの変動は圧力変動により主にもたらされることが明らかになった。また、そのスペクトル解析を行ったところ、ディスク回転数とアーム加振力の間には相関がないことがわかった。

離散渦法による非定常複雑流れの解析手法開発を目的として、往復運動する平板周りに形成される非定常渦をテストケースに取り上げ、渦度拡散、壁面境界条件の取り扱い手法などの基礎的な検証を行った。過去の研究結果と比較して良好な一致が見られた。

Flow in the tip clearance of a hard disk drive model has been investigated with laser Doppler techniques. The velocity measurements were carried out with two different types of laser Doppler sensors. One was a conventional laser Doppler velocimetry and the other a novel laser Doppler velocity profile sensor with a spatial resolution in the micrometer range. The circumferential velocity component was measured along the axial and radial directions. The velocity statistics obtained with both sensors have good agreements in general, but those measured with the conventional velocimetry suffered from a spatial averaging effect.

Flow characteristics of a simple flapping wing model was investigated in the development of a measurement system for a periodically moving body such as flapping wing. Pressure distribution around the model was calculated by integrating the Poisson equation formed by the divergence of Euler equation and a two-mesh scheme.

The complex feature inside a prototype hard disk drive is investigated both experimentally and computationally. The experiment focuses on both flow dynamics and the disk vibration, where measurements of fluctuating pressure and velocity are undertaken at some representative points. Certain correlation between the disk vibration and the fluctuating pressure in the turbulent flow between disks is found in the spectra of each signal. The computational approach by LES provides information on the whole flow field as complementary to the point measurements. The experimentally observed fluctuation of pressure and velocity are partly due to the disk vibration and its contribution could be estimated by comparing the experiment with the LES results.

Turbulent flow behind a half-wing was characterized by measurement of fluctuating pressure inside the wing-tip vcrtex. A newly developed pressure probe was carefully caliburated and used in the measurement in water flow. The measured profiles of mean- and fluctuating-pressure agreed well with the results by previous experiments.

Turbulent flow characteristics inside a model hard-disk-drive was experimentally investigated. The model contained five disks of 3.5 in diameter, enclosed in a cylindrical case. The pressure fluctuation was measured along the shroud surface and its character was compared with that of the disk fluctuation. The change of the shroud from the flat wall to ribbed one caused an obvious reduction of the pressure fluctuation and hence the disk vibration.

ナノ秒パルス波を用いたDBD-PA の2 次元的な流れ，及び3 次元的な流れへ の制御評価を行った。2 次元的な流れである矩形翼G¨o 387 上に発達する流れでは，迎角の上昇とともに，翼上の剥離がスパン方向にほぼ均一に起こり，急激に揚力が減少した。3 次元的な流れである後退翼NACA65A005上に発達する流れでは，前縁渦は迎え角の増加とともに後方から徐々に崩壊し，緩やかな失速に至った。

ハードディスクドライブ内に発達する乱流をLESで数値解析し、データ読み書きヘッドを固定するアームに作用する流体力を求めた。アームの背後を通過する流量を変化させることでアームに作用する流体力を変化させ、その影響を、アームに作用する圧力変動トルク、粘性応力変動トルクで評価した。先年に行った類似の計算結果と比較しててわずかなアームの形状変更により流れ場に大きな変化が生じることが明らかになった。