Search

Kyucho around the east coast of Noto Peninsula in the Japan Sea consists of the first strong current after passing an atmospheric disturbance and following periodical currents. The first strong current with highest flow speed has been discussed from two points of view: density currents and near-inertial internal waves. In this study, we discuss which phenomena and dominant in a Kyucho occurred in September 2006. The first strong current appeared in the period of rapid temperature increase, while the current speed was reduced when the temperature reached a maximum. Unlike this, for the following periodical currents, temperature and current speed varied in phase, showing a character of progressive waves. Besides, after the first strong current, the offshore water mass north of the peninsula was found in Toyama Bay suggesting a large scale water mass exchange. These facts indicate that the first strong current is a density current in a rotating system; propagation of the offshore warm water which had been piled up to the northern coast of the peninsula by southwesterly winds. On the other hand, following periodical currents are flows accompanied by propagation of coastal trapped waves generated by scattering of near-inertial internal waves at the northern part of the peninsula.

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

Using the prediction system of boundary-layer transition, the spatial growth of traveling waves is examined in the boundary layer over the outer wing of the NEXST-1 semispan model. It is found from the computational results that TS waves are dominant to transition on the wing. Moreover, it is noted that TS waves directed to the leading edge are amplified even in the accelerated boundary-layer flow near the leading edge. However, the growth of TS waves is suppressed around the designed angle of attack., 資料番号: AA0045948035, レポート番号: NAL SP-57

航空宇宙技術研究所 Sep. 1994 (15th). Mar. 1995 (16th) 東京 日本, National Aerospace Laboratory Sep. 1994 (15th). Mar. 1995 (16th) Tokyo Japan, 下面加熱矩形ダクト内混合対流の線形不安定性を、コロケーション法で数値的に検討した。チェビシェフ多項式で2重拡大法を用いて得られた固有値問題と、それによって発生した一般化固有値問題を数値解析した。進行横ロールはレイノルズ数が、ある臨界値よりも小さい時に、最も不安定な攪乱であることが分かった。一方、縦ロールは、レイノルズ数がこの臨界値以上の場合に、最も危険になる。, The linear stability of mixed convection in a rectangular duct heated from below is investigated numerically by a collocation method. The eigenvalue problem obtained by making use in the double expansion method in Chebyshev polynomials and the resulting generalized eigenvalue problem is solved numerically. It is found that the traveling transverse roll is the most unstable disturbance when the Reynolds number is less than a certain critical value, while the longitudinal roll is most dangerous when the Reynolds number is larger the critical value., 資料番号: AA0000109016, レポート番号: NAL SP-28

航空宇宙技術研究所 Sep. 1994 (15th). Mar. 1995 (16th) 東京 日本, National Aerospace Laboratory Sep. 1994 (15th). Mar. 1995 (16th) Tokyo Japan, 3次元境界層に固有な横流れ不安定場での点状連続攪乱の形成と成長を実験的に検討した。攪乱は、小さな孔から境界層流中に連続的に空気を噴出する空気噴流柱により、人工的に起こした。熱線測定の結果、静的モードも進行モードも楔形になる。これは、進行波が分散しながら正常方向にも局部外向流の方向にも伝搬するからである。, The formation and development of a point-source disturbance in a three-dimensional boundary layer subject to crossflow instability has been investigated experimentally. The disturbance was artificially initiated by an airjet column, which was continuously issued into the boundary layer flow through a small hole. Hot-wire surveys showed that both stationary and traveling modes evolve into a wedge shape as the traveling waves dispersively propagate in both directions approximately normal to local external flow., 資料番号: AA0000109012, レポート番号: NAL SP-28

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, 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 7-9 Oct. 1998 (23th). 24-26 Mar. 1999 (24th) 東京 日本, National Aerospace Laboratory 7-9 Oct. 1998 (23th). 24-26 Mar. 1999 (24th) Tokyo Japan, 安定な回転成層流体中に存在する定在および伝播平面波について検討した。それらのほとんどは3次元摂動に対して不安定であることを示した。不安定性の成長率は、一般に撹乱の波数が増えるに従って大きくなり、大きな波数以下でのWKB(ウェンツェル・クラマース・ブリュアン)解析により予測された値に近づいて行く。最も危険な不安定モードは、基本定在波の節面近くに集中していた。短波長不安定性が弱いパラメータ領域では、3波共鳴相互作用による長波不安定性がより早く成長した。, Standing and propagating plane waves in a stably stratified rotating fluid are considered. It is shown that almost all of them are unstable with respect to three-dimensional perturbations. The growth rate of the instabilities increases as the wavenumber of the disturbance increases, generally. It approaches the value predicted by a WKB (Wentzel-Krammers-Brillouin) analysis from below at large wavenumbers. The most dangerous instability modes are concentrated near the node-planes of a basic standing wave. In the parameter region where the short wave instabilities are weak, long wave instabilities, which are due to resonant triad interactions, grow faster., 資料番号: AA0001960007, レポート番号: NAL SP-43

航空宇宙技術研究所 Sep. 1994 (15th). Mar. 1995 (16th) 東京 日本, National Aerospace Laboratory Sep. 1994 (15th). Mar. 1995 (16th) Tokyo Japan, 容器中でパラメトリックに励起された定常波(ファラデー共鳴)上に浮遊する微粒子のドリフト運動を研究し、粒子の変位とドリフト速度を統計的に解析した。粒子軌跡はビデオ画像で再現した。ドリフト運動は、部分的ブラウン運動として特性化できることを明らかにした。, Drift motion of small particles floating on standing waves excited parametrically in a container (Faraday resonance) is studied, and particle displacements and drift speeds were analyzed statistically. Particle trajectories were reproduced from video images. It is found that the drift motion is characterized as the fractional Brownian motion., 資料番号: AA0000109004, レポート番号: NAL SP-28

一様な風洞気流中において大振幅で進行波運動を行なうゴム膜の乱流境界層を，熱線流速計技術ならびに流れの可視化技術を用いて，レイノルズ数10^6付近において測定した．乱流境界層は，波速が一様流の速度の程度よりも小さいとき，山の背部で剥離する．しかし，波速が一様流の速度の程度よりも大きいときには剥離しない．乱れ，表面摩擦力および境界層厚みは波速の増大とともに減少する．