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An experimental study was conducted to investigate transition process on 10-deg cone. There are two goals of this study. One is to validate transition prediction numerical code LSTAB, which is recently developed. Instability wave is detected by use of flush-mounted a pressure transducer and a hot-film sensor, and its frequency is confirmed to agree with the numerically predicted value. The second goal is to clarify the effects of freestream acoustic disturbances on the boundary-layer transition in supersonic flow. Intensity of freestream disturbances was controlled by a strip of sand paper or distributed roughness, which were attached on the floor or sidewall near the throat. High-frequency disturbance increased in freestream when sand paper was attached on the floor, though freestream disturbance was not affected by larger roughness on straight sidewall. The effect of roughness on the wind tunnel wall is pointed out to be different with the position and condition., 資料番号: AA0045947015, レポート番号: NAL SP-56

Infrared-image technique has been prevailingly applied to diagnose laminar-turbulent transition in compressible boundary layers. The purpose of the present paper is to establish this technique for low subsonic flow. To produce measurable temperate difference between laminar and turbulent states above ambient temperature, the model was pre-heated by a hair-drier prior to each measurements. Infrared image captured in two-dimensional boundary layer was quantitatively reduced to evaluate transition location. It was found that reduced results are in good agreement with those by means of conventional methods such as hot-wire anemometer and Preston tube., 資料番号: AA0032827015, レポート番号: NAL SP-54

Transition on the natural laminar flow wing of a non-powered scaled supersonic experimental airplane was measured by hot-film sensors and an infrared camera at Mach 2. In order to supress crossflow instability which dominates the transition on the highly swept wing, the pressure falls very rapidly in the vicinity of leading edge of the wing, so as to minimize the crossflow velocity components. The unit Reynolds number had no effect on the transition Reynolds numbers of the wing. The transition Reynolds number was 0.8 million at 70 percent semi-spanwise location at Mach 2 at the angle of attack of 2 deg. Transition location in flight was estimated by conducting transition measurement in a quiet low Reynolds number wind tunnel and in a variable unit Reynolds number wind tunnel which has moderately low turbulence. The transition at 70 percent semi-spanwise position at the angle of attack of 2 deg at Mach 2 in flight was predicted to be located downstream of 60 percent chordwise position., 資料番号: AA0032827008, レポート番号: NAL SP-54

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

27-28 Sept. 1999 (25th). 27-28 Mar. 2000 (26th), CFD(数値流体力学)手法を用いて自然層流翼に適用することを意図したNALのSST(超音速輸送機)計画に関連して境界層遷移計測を実施した。実験の目的は最先端的な境界層遷移に関するデータベースを構築して翼上の遷移点予測の参考とし、また高度な計測技術を確立して航空機の飛行試験に適用することにある。本論文では、代表的な2つの予備実験の結果を報告した。ひとつはビーチクラフト機を使った飛行試験で、低乱流環境下における遷移過程を把握し、飛行試験の諸課題を明らかにするために実施した。Tollmien-Schlichting波が前縁近傍領域で検出され、スペクトルの振幅分布がSALLY(3次元層流境界層安定性解析)コードを使った数値予測値と非常によく一致したことから、風洞内で行う遷移計測が好結果を得ることが分かった。もうひとつは、超音速風洞内においてSST実験機の半裁模型に対して行った計測である。設計点、すなわち、迎角α=2.7度の時のマッハ数M=2では、層流状態は少なくともX/C=0.5に耐えることが分かった。自然層流翼はSST実験機の飛行試験で実現すると期待されている。, Boundary-layer transition measurements have been conducted associated with the NAL SST (Supersonic Transport) project, which is designed to apply natural laminar flow wing using CFD (Computational Fluid Dynamics) technique. The purpose of experiments is to construct the database on boundary-layer transition most advanced which will be referred to predict the transition point on the wings, and to establish high quality measurement techniques, which will be applied to the flight test of the airplane. In this paper, the results of two typical preliminary experiments are introduced. One is flight tests using Beachcraft airplane, which are performed to grasp the transition process under low disturbance environment and to clarify the problems of flight test. Transition measurement as conducted in wind-tunnel was found to be successful, because Tollmien-Schlichting wave is detected at the region near the leading edge, and its amplitude distribution of the spectrum is in very good agreement with the numerical prediction by SALLY (3D laminar boundary layer stability analysis)-code. Another is the measurement on a half-model of SST experimental airplane in a supersonic wind tunnel. At the design point, i.e. Mach number M = 2 at an angle of attack alpha = 2.7 deg, it is found that the laminar state sustained at least to X/C = 0.5. Natural laminar flow wing is expected to realize on the flight test of SST experimental airplane., 資料番号: AA0028636001, 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, 超音速輸送機を目的とした無推力実験機の自然層流翼上の遷移測定をマッハ数2.0と1.2で行った。翼弦沿いに設置した熱フィルム流速計に対する出力信号の振幅中の摂動増加が層流から乱流境界層への遷移を示す。熱フィルム流速計およびPreston管による測定結果は遷移点が翼の半弦の下流に位置していることを明らかにした。, Transition measurement on the natural laminar flow wing of non-powered experimental airplane for supersonic transport was conducted at Mach 2.0 and 1.2. Increase of perturbation in amplitude of output signals for hot-films placed along the wing chord indicates transition from laminar to turbulent boundary layer. Results by hot-film and Preston tubes proved that transition point is located downstream of the half chord of the wing., 資料番号: AA0028637019, 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, 流線曲率モードより横流れ進行モードを分離するため、円盤上の孔から点源撹乱を導入した静止空気中の回転円盤流の実験的研究を行った。実験結果は、両方のモードの明確な分離が、点源の下流の楔状領域で、分散関係に従って現れることを示していた。また、増幅していく撹乱の特性については、複素特性曲線法を用いた線形安定性理論とよく一致した。本論文の最後では、斜め円柱の場合と比較として、なぜ回転円盤流や後退翼では、横流れ不安定の定在モードが支配的となりがちなのかを議論した。, An experimental investigation in rotating-disk flow in still air was made to separate the crossflow traveling mode from the streamline-curvature mode introducing a point-source disturbance through a hole on the disk. The experimental results show that the definite separation of both modes appeared in wedge-shaped region downstream of the point source in accordance with the dispersion relation. It is also shown that the characteristic features of growing disturbances are in good agreement with the linear stability theory making use of the method of complex characteristics. In the last part of this paper, the reason is discussed why the stationary mode of the crossflow instability is prone to dominant appearance on rotating disk and swept wing compared to yawed circular cylinder., 資料番号: AA0001960006, レポート番号: NAL SP-43

航空宇宙技術研究所 26-28 Mar. 1997 東京 日本, National Aerospace Laboratory 26-28 Mar. 1997 Tokyo Japan, 斜め円柱における3次元境界層の不安定性を実験的に検討した。流れの不安定特性を明らかにするため円柱上の点源から人為的に非定常撹乱を導入した。横流れ不安定の定常モードの影響により振幅は変調するが、レイノルズ数が線形安定理論の予測と一致するある一定の範囲内では、流線曲率不安定が横流れよりも支配的であることを確認した。, Instability of the three-dimensional boundary layer on a yawed circular cylinder is investigated experimentally. An unsteady disturbance is artificially introduced from a point source on the cylinder to clarify instability characteristics of the flow. Streamline-curvature instability is confirmed to dominate rather than cross-flow instability in a certain range of Reynolds number in agreement with the prediction of linear stability theory, although the amplitude is modulated by the effect of stationary mode of cross-flow instability., 資料番号: AA0001320001, レポート番号: NAL SP-36

資料番号: NALSP0015021, レポート番号: NAL SP-15

The three-dimensional boundary-layer experiments were conducted on a 45 degrees swept wing in the ASU unsteady Wind Tunnel. Crossflow-dominated transition was produced on a very smooth surface with contoured end liners to simulate infinite swept-wing flow. The model surface was carefully polished and buffed up to plus or minus 3 mum to minimize roughness effects on transition. Fixed-wavelength vortices, traveling wave and inflectional breakdown were subsequently observed prior to turbulent state as before, but the transition location moved further 10%-20% downstream of the chordlength. In order to control traveling wave and inflectional breakdown, two kinds of acoustic sounds, which tune up the traveling wave and breakdown, respectively, were introduced visualizing the surface flow via two-or three-dimensional roughness elements. No acoustic effect was observed in visualization., 資料番号: NALSP0015020, レポート番号: NAL SP-15

資料番号: NALSP0012017, レポート番号: NAL SP-12

資料番号: NALSP0011010, レポート番号: NAL SP-11

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

低速風洞縮流胴に沿った境界層の遷移過程を可視化および熱線計測などにより実験的に研究した。縮流胴境界層の遷移過程は次のように幾つかの素過程に分けられる。レイノルズ数が低い場合、凹面領域にはゲルトラー不安定により、流れ方向に軸を持ち対になって回転する縦渦列が発生する。層流境界層はその縦渦列によって歪められて変曲点を持ち、2次不安定によって乱流へと遷移する。しかし、下流の凸面領域に至ると主流の加速によって境界層は再層流化され、縮流胴出口まで層流状態が維持される。レイノルズ数が高い場合、縮流胴入口における初期境界層はすでに乱流状態にあり、凹面領域を通過する間に境界層厚さはさらに増加するが、その下流の凸面領域では一旦層流化する。しかし、縮流胴出口付近において乱流斑点が自然発生することにより、境界層は再遷移する。測定部の主流流速を増加すると乱流斑点が発生する位置は上流側のより加速された領域へと移動する。乱流斑点は加速流中でも下流に向かって成長するので、レイノルズ数が高い場合には測定部の境界層が乱流になるのは避けられない。, The transition process of boundary layers on a low-speed wind-tunnel contraction wall was experimentally investigated using flow visualizations and hot-wire/hot-film measurements. The process has several classifications depending on the Reynolds number. For the low Reynolds number, a row of counter-rotating longitudinal vortex pairs is generated by the Gortler instability on the concave wall. The velocity profile of the laminar boundary layer distorted by the Gortler vortices has inflection points, and eventually the secondary high-shear-layer instability causes high-frequency velocity fluctuations. These growing disturbances lead the boundary layer to a turbulent state within the concave region of the contraction. However, the resultant turbulent boundary layer is laminarized by acceleration of the mean flow in the convex region free from centrifugal instability. For the higher Reynolds number, the initial boundary layer flow was already turbulent at the entrance of the contraction. The boundary-layer thickness increases downstream within the concave region. On the convex wall the turbulent boundary layer is laminarized; however, re-transition occurred with the naturally occurring turbulent spots under a favorable pressure gradient. With an increase in the mean velocity in the test section, the location of occurrence of spots moves forward into a more accelerated region. As the turbulent spots grow downstream even in the accelerated flow, the formation of a turbulent boundary layer is unavoidable on the test section wall at the higher Reynolds number., 資料番号: AA0046106000, レポート番号: NAL TR-1462

小型超音速ロケット実験機の自然層流翼の遷移特性をホットフィルムと赤外線カメラを用いて計測した。高後退翼の遷移を支配する横流れ不安定の発達を抑制するために、自然層流翼では前縁付近の急加速領域を狭くすることで横流れ速度成分を抑えている。本翼の遷移Reynolds数は単位Reynolds数に依存せず、設計迎角(α=2deg)において70％半翼幅位置における遷移Reynolds数は0.8 x 10(exp 6)であることがわかった。線形安定解析結果から本翼を支配する不安定性はTollmien-Schlichting不安定性であり、横流れ不安定は設計通り抑制されていることがわかった。表面粗さと主流乱れの影響を考慮すると、飛行試験 M=2、α=2deg (設計迎角)において70％半翼幅位置の遷移位置は約50％翼拡張と推定された。, Transition characteristics on the natural laminar flow wing of a nonpowered scaled supersonic experimental airplane was measured by hot film sensors and infrared camera in two supersonic wind tunnels at Mach 2. In order to suppress the growth of crossflow instability which dominates the transition on highly swept wings, the pressure falls very rapidly in the vicinity of leading edge of the wing, so as to minimize the crossflow velocity components. From test results, the unit Reynolds number had no effect on the transition Reynolds number of the wing. The transition Reynolds number was 0.8 million at 70 percent semispanwise location at Mach 2 at the angle of attack of 2 deg. Tollmien-Schlichting instability dominates the transition and crossflow instability was found to be suppressed on the wing. Considering the influence of surface roughness and free-stream turbulence, the transition at 70 percent semi-spanwise position at Mach at the angle of attack of 2 deg in flight is estimated to be located at 50 percent chordwise position., 資料番号: AA0032998000, レポート番号: NAL TR-1437

航空宇宙技術研究所 28-29 Sep. 1992. 25-26 Apr.1993 東京 日本, National Aerospace Laboratory 28-29 Sep. 1992. 25-26 Apr.1993 Tokyo Japan, 主流に対して斜めに置かれた円柱に沿う3次元境界層の横流れ不安定について実験的に調べた。これまで長い間、根源的な擾乱と考えられていた定常的な渦の代わりに、はっきりした振動数をもつ時間進行波が熱線風速計による不安定流れ場の計測のうちに観察された。熱線風速計の配列を用いて詳細な計測を行い、この非定常擾乱が、線形安定理論によって最も不安定な擾乱と予言されている横流れ進行波と同一のものであることを確認した。しかしながら、理論予測と実験結果の間にはなお一致しない点が残っている。, Experimental investigations are made on crossflow instability of the three dimensional boundary layer along a yawed circular cylinder. Unsteady disturbances with definite frequencies instead of stationary vortices, which have long been considered as generic disturbances, are observed in hot-wire surveys of the unstable flow field. Detailed measurements with the aid of hot-wire arrays have confirmed that the unsteady disturbances are identical with the so-called crossflow traveling waves predicted by linear stability theory as the most unstable disturbances, although some discrepancies still remain between experimental results and theoretical predictions., 資料番号: AA0004170010, レポート番号: NAL SP-21

Characteristic features of a wave packet in a rotating-disk boundary layer were experimentally investigated. The point disturbance originating from a small hole on the disk forms an isolated wave packet which consists of two types of unstable waves. Comparison with the prediction by Itoh's linear stability theory enabled the identification of these waves; the streamline-curvature (S-C) modes with the smaller wave number in the circumferential direction and the higher frequency are observed prior to the appearance of cross-flow (C-F) modes with the larger wave number and lower frequency. The hot-wire analyses quantitatively show that such characteristic features of these modes are in good agreement with the theoretical results. Time trace of the edge of packet does not indicate the occurrence of absolute instability but shows that the wave packet convectively passes through the radius line corresponding to the critical Reynolds number for the absolute instability predicted by Lingwood., 資料番号: AA0045947029, レポート番号: NAL SP-56

Behavior of stationary vortices in rotating-disk boundary layer was experimentally investigated by hot-wire measurements. Sources of disturbance such as the disk vibration and free convection around the disk seem to affect the unsteadiness of the stationary vortices. The circumferential wave numbers and the position of vortices fluctuate for each rotation. The fluctuation was quantitatively evaluated. Small roughness elements have the effect of lowering the fluctuation although the nonlinear growth of the vortices becomes significant. This fact implies that the development of nonlinearity is not main cause of the unsteady behavior of the stationary vortices., 資料番号: AA0045947016, レポート番号: NAL SP-56

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, 最近の線形理論は、付着線上の流れに比較して極低レイノルズ数時に流れが不安定になる領域では多重不安定性が共存することを示している。不安定性が臨界レイノルズ数の低下に特に作用する現象を明らかにするため、付着線近傍の境界層不安定性に焦点を当てて実験的な検討を行った。これらの実験結果を理論計算と比較した。, The latest linear theory shows that multiple instabilities co-exist in the region, where the flow becomes unstable at very low Reynolds number compared to that on the attachment line. An experimental investigation has been done focusing boundary-layer instability near the attachment line to clarify the phenomena, especially on which instability devotes to the drop of the critical Reynolds number. These experimental results are compared with the calculations done by the theory., 資料番号: AA0028637009, レポート番号: NAL SP-48T

27-28 Sept. 1999 (25th). 27-28 Mar. 2000 (26th), 亜音速風洞縮流胴部の緩やかな曲率を持つ凹面領域における縮流境界層を検討した。平均速度分布は多分プレナム室内の上流ハニカムにより縮流胴入口においてスパン方向に3次元的に変形する。もっと下流では、ゲルトラー渦が流れ方向に増幅されることを流れの可視化および熱線流速計測定結果が示した。凹面壁におけるゲルトラー渦作用の結果として低・高運動量流体により境界層は厚くなり撹乱される。従って、平均速度分布は2重変曲点を持ち、より強力な乱流が出現する。加速流のため下流の凸面壁では、境界層は薄くなり、乱流は崩壊するにも拘らず、乱流強度の約4%が壁近傍に残留する。, A contraction boundary layer has been investigated in the moderately accelerated concave region along the subsonic wind-tunnel contraction. The mean velocity profile is three-dimensionally deformed in the spanwise direction at inlet of the contraction perhaps by the upstream honeycomb in the plenum chamber. Farther downstream, the flow visualization and hot-wire measurements showed that Goertler vortices are amplified in the streamwise direction. The boundary layer is thickened and is disturbed by low- and high-momentum fluids resulting from the action of Goertler vortices on the concave wall. In consequence, the mean velocity profile has double inflection points where the higher intensity of turbulence appears. Although the boundary layer is thinned and the turbulence is decayed on the downstream convex wall due to the accelerated flow, about four percent of turbulence intensity is retained near the wall., 資料番号: AA0028636012, 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, 航技研0.2m超音速風洞の縮流胴壁上の遷移の原因を探るために、対応する航技研校正用風洞での測定との比較により、下流の2ヶ所で境界層を調べた。亜音速および超音速縮流胴の実験観測に基づき、もっともらしい原因として2つの可能性を挙げることができた。, In order to seek the cause of transition on the contraction wall of the NAL 0.2 M Supersonic Wind Tunnel, the boundary layers at two downstream locations were investigated in comparison with the corresponding measurements in NAL Calibration Wind Tunnel. Two possibilities as the plausible cause are proposed based on the experimental observations in both subsonic and supersonic contraction., 資料番号: AA0001960019, レポート番号: NAL SP-43

An iterative calculation method was applied to identify two different instability modes in a three-dimensional boundary layer near attachment-line on a yawed cylinder. The point disturbance originating from a small hole on the cylinder was dispersed in the wedge-shaped region which consists of two types of unstable waves. Detailed hot-wire measurements illustrated the wave crests suggesting the each distribution of phase line for the two instability modes. The iterative calculation based on an assumption for the distribution function of the amplitude successfully provided the decomposition of the original experimental data into the two modes. The decomposition enabled us the comparison with the prediction by Itoh's linear stability theory and the identification of these modes, the streamline-curvature (S-C) modes and cross-flow (C-F) modes., 資料番号: NALSP0059012, レポート番号: NAL SP-59

Characteristic features of small disturbances originating from a point source on a yawed cylinder were experimentally investigated in order to decide the critical Reynolds number near the attachment line. Various frequencies were examined by hotwire measurements. The results showed that the disturbances propagate downstream in wedge-like regions and the cross-flow instability is dominant for all the frequencies examined here in comparison with the streamline-curvature instability. For lower frequency disturbances the neutral points were clearly observed in contrast to the higher ones. A critical Reynolds number for off attachment line was obtained. The value is about 7% lower than the well known critical Reynolds number Rc=583 for attachment-line instability., 資料番号: NALSP0059014, レポート番号: NAL SP-59

A fibre optic three-dimensional Laser-Two-Focus(L2F)-Velocimeter was introduced in the Aircraft Aerodynamics Division in 1988. The former half of the present report describes both an outline and the principle of this system for two-dimensional measurements. In the latter half, the L2F-Velocimeter is evaluated by using three types of flows, i.e., two-dimensional wake, three-dimensional boundary layer and quasi two-dimensional free jet with, and occasionally without, seeding particles. Furthermore, several seeding particles such as paraffine vapor, mosquito-repellent smoke and tobacco smoke are used for evaluations. The axial velocity component from the L2F-Velocimeter is pointwisely compared with a calibrated velocity. The comparison is extended to the transverse mean velocity component/fluctuating components with hot-wire measurements, in which great care was taken with the linearity and wire inclination. There is no incongruity in comparison except in low turbulence with less than 2％ intensity to the lal velocity .In summary, features of the fiber optic L2F-Velocimeter are its applicability to natural seed, wall-proximity and non-calibration measurements, although it is apriori known that the L2F-Velocimeter is not adaptable to both reverse flow and high turbulence measurements., 資料番号: NALTM0627000, レポート番号: NAL TM-627

A new method was developed for determining an exact slant hot-wire inclination to the axial flow direction in order to accurately measure the transverse velocity component. The method requires dual parallel laser beams near the focal point such as Laser-Two Focus velocimeter beams, one of which can rotate around the other. Since the squared hot-wire bridge output is proportional to the mean value of the beam intensity exposed on the hot-wire element, the bridge output indicates the maximum variation, when the slant wire is exposed to just dual beams. This beam rotating angle is referred to as the slant angle of the wire, if necessary, relative to the freestream angle, which is accurately given by the Laser-Two-Focus velocimeter. Furthermore, it was found in the wire-inclination measurement that the beams rotate in precession due to optical misalignment. This precession is prone to serious errors in this boundary-layer measurements., 資料番号: NALTR1078000, レポート番号: NAL TR-1078

A low-turbulence calibration wind-tunnel for laser velocimeters was newly constructed at NAL in the spring of 1988. Detailed flow-quality measurements in this facility have been successively achieved to obtain a better understanding of the characteristics of facility disturbances and identification of their sources, using two hot-wire anemometers, a microphone and an accelerometer. Experimental results show that overall residual turbulence levels in free-stream are 0.04％ and 0.06％ at fan speeds of 600 RPM and 1200 RPM, respectively. Extensive analyses of turbulence fluctuations show that the free-stream velocity is unexpectedly contaminated by acoustic disturbances, which are regarded as non-vortical fluctuations generated by fan blades and vibratory resonance of a portion of the wind-tunnel. Such pressure disturbances acoustically propagate into the flow direction. Cross-correlation measurements between two distant anemometers indicate that the contamination level reaches 70％ in the overall axial fluctuation energy at 600 RPM. It is estimated that the vortical turbulence level is about 0.022％ at this speed., 資料番号: NALTR1054000, レポート番号: NAL TR-1054

An anemometer using a heat wake method for low wind velocity was constructed. The aim is to indicate directly the mean flow velocity. The method makes use of three thin wires mounted on a simple body. The wires are held parallel to each other in the plane perpendicular to the flow direction. By heating the upstream wire with a periodical current, the thermal oscillation was introduced into the flow. The time taken for the thermal oscillation to connect between the two downstream wires which serve as thermal senssors, is inversely proportional to mean velocity. When the thermal frequency with the lowest value was adjusted to keep the ratio of the convection time and the thermal period constant, its frequency should become proportional to the velocity. Keeping the value of one half as this ratio, the system with two sensors about 0.4mm apart was calibrated on a towing truck with a constantly known speed in a calm air. The convection velocity of the thermal oscillation independent of its frequency was found to be equal to about 80 percent of the mean velocity. The mean velocity from 0.3m/sec to 2m/sec was successfully measured with good linearity to the heating frequency. If the ratio were reduced to one fourth or one eighth, the high-velocity limit for the velocity measurement could be easily extended to two or four times respectively larger than that in the present calibration., 資料番号: NALTR0727000, レポート番号: NAL TR-727

This report represents a production of a low noise hot-wire anemometer with a constant current mode. This instrument consists of a constant current circuit, a low noise amplifier and a frequency compensator. Newly designed circuits and several techniques that reduce electric noise are described in detail. A typical application for residual turbulence measurement in a wind tunnel is given. The performance of this instrument is satisfactory for the measurement of velocity fluctuations with a turbulence intensity of less than 0.05％ and with frequencies of up to 5kHz at the wind speed of 20m/s. If the heating current for the hot-wire is low, this system may be easily applied to a resistance thermometer., 資料番号: NALTR0697000, レポート番号: NAL TR-697

A simple method was developed to determine the focal point of the Laser 2 Focus velocimeter. The method requires only a conventional hot-wire anemometer, which is traversed across the dual beams at diverse beam-axis locations. The squared hot-wire bridge output indicates the mean value of the beam intensity exposed on the hot-wire element. Eventually, the maximal bridge output along the beam axis is referred to as the focal point. Furthermore, the method can be extended to measure laser-beam properties such as beam separation, beam diameter, relative beam intensity on the dual beams, beam divergence and cross-sectional beam-intensity distribution. Measurement error in determining the beam diameter is estimated by using a simple beam model., 資料番号: NALTR1043000, レポート番号: NAL TR-1043

資料番号: NALTM0472000, レポート番号: NAL TM-472