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In this paper, the gamma-Re(sub theta) transition model proposed by Menter et al. is investigated. Correlations not described in the original paper are reproduced based on other literature and validated by several test cases: T3A- (Tu = 1 percent), T3A (3 percent), T3B (6 percent) for flat-plate boundary layers with bypass transition, and Schubauer & Klebanof (0.2 percent) for flatplate boundary layer with natural transition. T3LC test case is used for separated flow transition which is important for RANS simulation applied to separated flow problems. Transition position on flatplate for each free-stream turbulent intensity has good agreement with experiment, although transition lengths estimated for low free-stream turbulent intensity are too short. For T3LC test case, the length of laminar separation bubble is correctly predicted by using the present transition model., 資料番号: AA0063156010, レポート番号: JAXA-SP-06-013

An advanced Large Eddy Simulation (LES) technique with high accuracy and resolution is proposed. This method solves compressible 3-D Navier-Stokes equations with the Approximated Deconvolution Method approach as LES approach and has several sophisticated techniques such as highly tuned compact schemes, the generalized characteristic interface conditions, and the generalized Navier-Stokes boundary conditions. Several applications to flows around 2-D NACA0012 aerofoil are presented and discussed. Numerical results show that this method can solve very complicated subsonic flow including the laminar flow separation at the leading edge region, the transition in the bubble and the reattachment. It also has capability to capture the natural laminar to turbulent transition phenomena in the order of Reynolds number of 10(exp 6). In order to validate the present LES technique in more detail, the results are compared with existing wind-tunnel experiments and linear stability analyses with the e(sup N) method and discussed., 資料番号: AA0063154022, レポート番号: JAXA-SP-06-010

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

航空宇宙技術研究所 16-18 Jun. 1999 東京 日本, National Aerospace Laboratory 16-18 Jun. 1999 Tokyo Japan, チャンネル流の層流-乱流遷移を並列計算機上で直接数値シミュレーションを行った。シミュレーションは、基本流と様々なレイノルズ数に対応する異なるエネルギーレベルの小さな撹乱の和で与えられる初期流れで開始する。超臨界レイノルズ数の場合、以下の2つの機構により遷移が起こる。ひとつは初期撹乱が非常に小さい場合、流れの中で成長するトルミーン・シュリヒティング波であり、もうひとつは初期撹乱が大きい場合、流れの方向に軸を持つ縦渦の過渡的増幅である。一方、亜臨界レイノルズ数では、初期撹乱が非常に大きい場合にのみ過渡的増幅により遷移が起こる。過渡的増幅型遷移を引き起こす初期撹乱のエネルギーレベルは、レイノルズ数の-7/2乗に比例することが見出された。, Laminar-turbulent transition of channel flow is directly simulated on a parallel computer. The simulations are started with initial flows given as the basic flow plus small disturbances with different energy levels for various Reynolds numbers. In the case of supercritical Reynolds numbers, the transition is triggered by two mechanisms: one is Tollmien-Schlichting waves growing in the flow when initial disturbances are very small, and the other is transient growth of stream-wise vortices when initial disturbances are rather large. On the other hand, for subcritical Reynolds numbers, transition is triggered by the transient growth only when initial disturbances are considerably large. It is found that the energy levels of initial disturbances, which can trigger the transient-growth type transition, are proportional to -7/2 power of the Reynolds number., 資料番号: AA0001961054, レポート番号: NAL SP-44

航空宇宙技術研究所 24-26 Jun. 1998 東京 日本, National Aerospace Laboratory 24-26 Jun. 1998 Tokyo Japan, 超音速輸送機(SST)の揚抗比改善のためには摩擦抗力を低減する必要があるので、実際の空気動力学的設計への応用の観点から、Warp形状翼に関する超音速層流制御効果について検討してきた。今回、実験によりマッハ数M=1.4における吸い込みに起因する大幅な低減を実験的に確認し、また層流境界層の安定性を数値計算的に解析した。, Since the friction drag of an SST (Supersonic Transport) must be reduced to improve the lift-to-drag ratio, supersonic laminar flow control on a warped wing has been investigated from a viewpoint of applying it to real aerodynamic design. Then large reduction due to suction at M = 1.4 was experimentally confirmed and the stability of laminar boundary layer was numerically analyzed., 資料番号: AA0001958040, レポート番号: NAL SP-41

航空宇宙技術研究所 24-26 Jun. 1998 東京 日本, National Aerospace Laboratory 24-26 Jun. 1998 Tokyo Japan, e(exp N)法に基づく層流-乱流遷移予測システムを開発する目的で、NASAが開発したSallyコードを詳細に検討した。このコードは様々な形の問題に使用できるが、数値的精度はあまり保証していないことが判った。, In order to develop a prediction system of laminar-turbulent transition based on e(exp N) method, the Sally code, which was developed by NASA, is investigated in detail. It is found that, although this code can be used for the objects with variety shapes, the accuracy of numerical results are unfavorable., 資料番号: AA0001958042, レポート番号: NAL SP-41

e(sup N)法を用いた2次元および3次元境界層の乱流遷移位置の予測において外乱の影響を定量的に評価するため、一様流の残留乱れTuおよび騒音レベルSPLと遷移位置における撹乱の空間増幅率Nの相関関係を実験的に調べた。気流特性が異なる3つの風洞で同一の矩形翼NACA0012模型の遷移計測を実施した。その結果、模型を2次元と3次元形態のどちらに設置しても、NはTuの対数とSPLの1次関数で表されるが、外乱に対する感度は翼断面や後退角に依存することがわかった。この相関関係を用いることにより2次元の場合には遷移位置の予測精度が翼弦長の10％程度向上することが期待される。また低亜音速境界層の遷移位置検出手法として、赤外線力メラを用いた表面温度分布計測が有効であり、横流れ定在渦も可視化可能であることを示した。, A series of experimental investigations have been carried out to examine the influence of free-stream turbulence and acoustic noise on laminar-to-turbulent transition in boundary layers on an NACA0012 airfoil. The quantitative evaluation of the influence on the total growth rate N of the most amplified disturbance obtained from the e(sup N) method at the transition location is made in an empirical relation between the total growth rate N and both the residual turbulence Tu and the sound pressure level SPL. Consequently, the transition location is detected as a linear equation N = C(sub Tu) x ln(Tu) + C(sub SPL) x SPL + C for not only 2-D case with zero angles of both sweep and attack but also 3-D case with non-zero angles of both sweep and attack, though each coefficient in N depends on geometrical configuration of airfoil such as cross-sectional shape and swept angle. Accuracy of predicted chord length is expected to be improved 10 percent by use of the obtained empirical relation. Surface temperature measurement technique by use of infrared camera is shown to be efficient and useful for transition detection in low subsonic flow. Usefulness is also shown in visualizing cross-flow stationary vortices growing in 3-D boundary layer., 資料番号: AA0049194000, レポート番号: JAXA-RR-05-017