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Science history of fluid mechanics research in Japan is reviewed for the time during the first half of 20th century. Three distinguished persons, Torahiko Terada, Itiro Tani and Isao Imai, were more or less associated with the Aeronautical Research Institute. Before the establishment of the Institute, von Karman and Prandtl were invited to the Institute to give series of lectures. Terada discovered a sequence of rolling eddies in the boundary layer cooled from above (or heated from below). Tani studied wing shapes and proposed a new wing which keeps its boundary layer laminar as long as possible. Imai resolved a paradox of divergence problem in an asymptotic solution starting from the Oseen equation, for a flow around a solid body placed in a uniform stream., 資料番号: AA0063908007, レポート番号: JAXA-SP-07-026E

A search for a precise definition of hydraulically smooth wall is carried out. It is argued that in the case of transitional flows such definition can be based on the onset of flow instabilities. Flow in a channel with distributed surface roughness is considered as a case study. Results of the linear stability analysis show that the presence of the roughness destabilizes the traveling-wave instability as well as introduces a new instability that manifests itself in the form of streamwise vortices. The critical conditions for the occurrence of both instabilities are given for different classes of roughness shape. It is shown that these conditions can be predicted with a reasonable accuracy in the case of an arbitrary (but Fourier transformable) roughness by considering only the leading Fourier mode (wavy-wall model). A segment in the parameter space where the roughness does not induce any instability regardless of its shape has been identified; this segment identifies conditions under which the rough wall behaves as a hydraulically smooth wall., 資料番号: AA0063908006, レポート番号: JAXA-SP-07-026E

Laminar-turbulent transition is a crucial phenomenon appearing in a variety of industrial applications. However the involved physical mechanisms as well as methods for reliable and accurate prediction of transition are still a matter of active research. In the present contribution, we give a brief overview on recent advances in the simulation and prediction of transitional and turbulent wall-bounded shear flows. The focus is on Large-Eddy Simulations (LES), which differ from Direct Numerical Simulations (DNS) by resolving only the large-scale, energy-carrying vortices of the fluid flow, whereas the fine-scale fluid oscillations, assumed to be more homogeneous, are treated by a SubGrid-Scale (SGS) model. The application of LES to flows of technical interest is promising and LES is getting more and more applied to practical problems. The main reason for this is that LES provides an increased accuracy compared to solutions of the (statistical) Reynolds-Averaged Navier-Stokes equations (RANS), while requiring only a fraction of the computational cost of a corresponding fully-resolved DNS. Nevertheless, LES of practical transitional and turbulent flows still require massive computational resources and the use of large-scale computer facilities., 資料番号: AA0063908005, レポート番号: JAXA-SP-07-026E

The free shear layer is suitable for understanding the basic mechanism of randomization. Sound from a loud-speaker was used for introducing ordered velocity fluctuation in the layer. Three kinds of shear layer were tested and compared. A quantitative expression of the degree of randomness was accomplished by the elementary-wave analysis. The concept of neighbor randomness was introduced for another way of describing randomization. The randomization process of three shear layers does not show any significant difference., 資料番号: AA0063908001, レポート番号: JAXA-SP-07-026E

SST-CFDワークショップ.次世代超音速機の数値シミュレーション利用技術に関する国際ワークショップ 航空宇宙技術研究所 20011203-20011205 東京 日本, SST-CFD Workshop. International Workshops on Numerical Simulation Technology for Design of Next Generation Supersonic Civil Transport National Aerospace Laboratory 20011203-20011205 Tokyo Japan, 資料番号: AA0063609063, レポート番号: JAXA-SP-06-029E

航空宇宙技術研究所 27-29 Sept.2000 東京 日本, National Aerospace Laboratory 27-29 Sept.2000 Tokyo Japan, e(exp N)法を使用した遷移位置の予測には、空間成長速度Nに及ぼす外部擾乱の定量的評価が強く求められるため、2次元翼流れ内の層流-乱流遷移に及ぼす音響騒音の影響を実験的に検討した。最初に、同一モデルに対する自然遷移を異なる5風洞中で調べた。各因子の貢献度は分離不可能であるが、大音響騒音および/または大残留主流乱れを用いた風洞では早期遷移を観測した。そこで、測定胴内に設置したスピーカを使って人工音響騒音を導入した。大きな励起が遷移過程を促進することを確認した。Nと音圧レベル(SPL)間の経験的関係N=-0.6×SPL+74を提案した。, Influence of acoustic noise on laminar-to-turbulent transition in 2-D wing flow is investigated experimentally, since the quantitative evaluation of external disturbances on spatial growth rate N is intensively required to predict the transition location by the use of the e(exp N) method. At first, natural transition on an identical model is examined in five different wind tunnels. Early transition is observed in the wind tunnels with large acoustic noise and/or large residual free-stream turbulence, although the contribution of each factor is not separable. Therefore artificial acoustic noise is introduced by means of a loud speaker installed in the settling chamber. Larger excitation is confirmed to facilitate the transition process. An empirical relation between N and Sound Pressure Level (SPL) is proposed as N = -0.6 x SPL + 74., 資料番号: AA0028637014, レポート番号: NAL SP-48T

境界層遷移の解明と制御研究会 宇宙航空研究開発機構.東北大学流体科学研究所 20070313-20070316 宮崎 日本, JAXA Workshop on Investigation and Control of Boundary-Layer Transition, Japan Aerospace Exploration Agency. Institute of Fluid Science, Tohoku University, 20070313-20070316, Miyazaki, Japan, 資料番号: AA0063908000, レポート番号: JAXA-SP-07-026E

航空宇宙技術研究所 27-29 Sept.2000 東京 日本, National Aerospace Laboratory 27-29 Sept.2000 Tokyo Japan, 平面Poiseuille流内の2種のバイパス遷移を並列計算機上で直接シミュレーションを行った。バイパス遷移のひとつは、流れの中に存在する大きな初期擾乱により誘発され、他は底壁からの吸込み・吹出しにより誘発される。遷移を誘発する擾乱のしきい値振幅をレイノルズ数の関数として決定した。吸込み・吹出しにより誘起した2つの斜行波が流れの遷移を誘発する大きな流れ方向モードを励起する。, Two kinds of by-pass transitions in the plane Poiseuille flow are directly simulated on a parallel computer, one of which being triggered by a large initial disturbance existing in the flow and another by a suction/blowing from the bottom wall. Threshold amplitude of the disturbance, which triggers the transition, is determined as a function of Reynolds number. Two oblique waves induced by a suction/blowing excite a large streamwise mode, which triggers the transition of the flow., 資料番号: AA0028637029, レポート番号: NAL SP-48T

27-28 Sept. 1999 (25th). 27-28 Mar. 2000 (26th), 層流-乱流遷移過程における再層流化流の受容性を検討した。回転する内球を持つ球クエット流で隙間比β=0.14を対象に、1個のトロイダル型TG(Taylor-Goertler)渦を使って超臨界流モードの中に外部擾乱を導入した。トロイダル型TG渦、スパイラル型TG渦および進行波の初生レイノルズ数は外部擾乱の影響を受けない。しかし、再層流化の初生レイノルズ数はこれら渦の影響を受ける。外部擾乱に対する超臨界撹乱モードの受容性は低Re領域よりも再層流化Re領域で大きい。, Receptivity of relaminarizing flow in the laminar-turbulent transition process has been investigated by the introduction of outside disturbances into the super-critical flow modes with one toroidal TG (Taylor-Goertler) vortex for clearance ratio beta = 0.14 in the spherical Couette flow with an inner rotating sphere. The onset Reynolds number of toroidal TG vortex, spiral TG vortex and traveling waves are not influenced by the outside disturbance. However, the onset Reynolds number of the relaminarization is influenced by them. The receptivity of the super-critical disturbance modes to the outside disturbances is greater in the relaminarizing Re-range than the lower Re-range., 資料番号: AA0028636017, レポート番号: NAL SP-47

航空宇宙技術研究所 27-29 Sept.2000 東京 日本, National Aerospace Laboratory 27-29 Sept.2000 Tokyo Japan, 修正e(exp N)法を使って3次元境界層の遷移予測を数値的に検討した。主要概念は、最増幅擾乱波に相当する波数を単独で決定するためe(exp N)法の中に複素放射線理論を組み込むことである。後退角50度の片揺れ円筒回りの流れに対する計算から、N.Itoh(1986)が得た理論的結果とN因子を除きよく一致することが分かった。, Transition prediction of three-dimensional boundary layer is numerically investigated by the use of a modified e(exp N) method. Main idea is the corporation of a complex ray theory into the e(exp N) method so as to uniquely determine a wave number, which corresponds to a most amplified disturbance wave. From the calculation for a flow around a yawed circular cylinder with sweep angle 50 deg, it is found that the results agree well with a theoretical one obtained by N. Itoh (1986) excepting the N factor., 資料番号: AA0028637001, レポート番号: NAL SP-48T

航空宇宙技術研究所 27-29 Sept.2000 東京 日本, National Aerospace Laboratory 27-29 Sept.2000 Tokyo Japan, 局所化した撹乱により起こる回転円板流中の3次元境界層の層流から乱流への遷移過程を実験的に検討した。熱線解析の結果は、点撹乱が乱流パッチに発達することを示した。くさび領域内で伝播する乱流パッチは、いわゆる直交流と流線曲率モードで構成される2種の進行波を伴う。乱流領域の平面形態の配置は三日月状でBlasius境界層における矢じり形乱流斑点とは異なる。, A laminar to turbulent transition process of a three-dimensional boundary layer in rotating-disk flow initiated by localized disturbances was experimentally investigated. The hot-wire analyses showed that the point disturbance develops into a turbulent patch. The turbulent patch propagating in the wedge region is accompanied by the two families of traveling waves, which consist of the so-called cross-flow and streamline-curvature modes. The configuration in the plane view of the turbulence region is a crescent, which is different from an arrowhead-shaped turbulent spot in a Blasius boundary layer., 資料番号: AA0028637007, レポート番号: NAL SP-48T

航空宇宙技術研究所 27-29 Sept.2000 東京 日本, National Aerospace Laboratory 27-29 Sept.2000 Tokyo Japan, 大半の層流-乱流遷移の最終段階では、ストリーク構造の崩壊は局所変曲速度分布内の強い非粘性不安定性のため遷移シナリオを終了する。2次元および3次元粘性事例に対し、この変曲不安定性の基準および成長速度を線形安定性理論を用いて検討した。反対称分布に対する一般基準とパラメータを計算から導出した。3次元事例に対する結果は、この基準がストリーク構造の一般的崩壊に対して拡張可能であることを示した。, In the final stage of most laminar-turbulent transitions, breakdown of the streaky structures finalizes transition scenario due to strong inviscid instability in a locally inflectional velocity profile. The criteria and growth rates of this inflectional instability for both two-dimensional and three-dimensional viscid cases have been investigated with linear stability theory. The general criterion and parameters for anti-symmetric profiles were derived from the calculation. Results for a three-dimensional case show the possibility that this criterion is extended for general breakdown of streaky structures., 資料番号: AA0028637026, レポート番号: NAL SP-48T

航空宇宙技術研究所 27-29 Sept.2000 東京 日本, National Aerospace Laboratory 27-29 Sept.2000 Tokyo Japan, チャネル流の安定性に及ぼす分散表面粗さの影響を考察した。粗壁の形状はフーリエ展開を使って表現した。解析は粗面壁を覆う流れの決定からなり、続いて線形安定性解析を行った。得られた結果は、粗さの存在が、流れ方向渦の形状に表れる不安定性を誘起することを示した。, The influence of distributed surface roughness on the stability of channel flow is considered. The shape of the rough wall is represented in terms of Fourier expansions. The analysis consists of determination of the flow over such a wall followed by a linear stability analysis. The available results show that the presence of the roughness induces an instability that manifests itself in the form of streamwise vortices., 資料番号: AA0028637012, レポート番号: NAL SP-48T