Relaminarization of accelerated turbulent boundary layer under favorable pressure gradient with sink flow type (Coherent structure and two-point statistics)

Sink flow型順圧力勾配による加速乱流境界層の再層流化に関する研究(コヒーレント構造と空間2点統計量の変化)

The relaminarization process of a turbulent boundary layer under a sink flow was investigated experimentally. The boundary layer was accelerated because of the contraction of the flow area. The mean and fluctuating velocity components were measured using a hot-wire anemometer. With relaminarization, the fluctuating velocity, which was normalized by the free-stream velocity, decreased. The degree of decrease differed between the streamwise and wall-normal components, depending on the distance from the wall. The conditional probabilities that two hot-wire probes separated in the spanwise direction simultaneously observed turbulent and nonturbulent flows were obtained. A spanwise-wide turbulent region was spread near the wall, but its width decreased as the distance from the wall increased. When the layer was relaminarized, this decrease in the spanwise width started near the wall. The low-speed streak spacing of the coherent structure was obtained from the lateral correlation coefficient of the streamwise fluctuating velocity and average spanwise spectra, and both parameters were somewhat consistent. Both the spanwise spacing of the streaks and the vertical scale of the coherent structure increased because of relaminarization. The conditional lateral correlation coefficient of the streamwise fluctuating velocity based on turbulence or nonturbulence was calculated. The streak spacing was slightly wider under nonturbulent conditions. This trend is consistent with the spreading behavior of the streak spacing, owing to relaminarization. With relaminarization, coherent structures became less frequent.


Various information and complexity measures for analyzing the laminar-turbulent transition process in mixing layer

各種情報量を用いた混合層の層流―乱流遷移過程の解析(変動渦度と乱れエネルギー散逸率の解析)

In this paper, the laminar-turbulent transition process of a mixing layer downstream of a two-dimensional nozzle exit was analyzed based on various information and complexity measures. Shannon entropy, permutation entropy, and approximated Kolmogorov complexity were also obtained. To obtain the Shannon entropy, the temporal probability distribution of the hot-wire output voltage data was determined and analyzed. In addition to the fluctuating velocity, its time derivative and the square of this derivative were analyzed. The Shannon entropy of the time derivative and its square slightly decreased downstream, in accordance with the increase in the time scale of the turbulence. When the length of the extracted data was constant, the permutation entropy of the time derivative and its square increased around the peripheral region of the mixing layer, in accordance with the intermittent nature of the velocity signals. The region is at the 3-4 times farther from the jet centerline than the region where the fluctuating velocity becomes maximum. When the length of the extracted data was varied in accordance with the integral time scale of turbulence, the permutation entropy initially decreased in the potential core and subsequently increased after the disappearance of the potential core, as the transition progressed. The approximated Kolmogorov complexity of the time derivative and its square were smaller than that of the fluctuating velocity. Owing to the simplification of the data, they slowly increased after the disappearance of the potential core and then quickly decreased after the development of turbulence.

混合層の乱流遷移過程において，各種情報量と複雑度に基づいた解析を行った．変動速度の熱線出力電圧時系列信号，その時間微分係数及びその2乗の確率分布を求めて，シャノンエントロピー，順列エントロピー及び近似コルモゴロフ複雑度の特徴を比較考察した． 変動速度の時間微分係数及びその2乗のシャノンエントロピーは，下流での時間スケールの増加に対応してやや減少した．順列エントロピーは，データ列からの取り出し個数を固定した場合と時間スケールに応じて変化させた場合とで，乱流遷移に応じた変化が異なった．時間微分係数やさらにその2乗の近似コルモゴロフ複雑度の分布は，下流で変動が単純になることに伴う変化が現れる．


Analysis of laminar-turbulent transition process in mixing layer with various information measures

各種情報量を用いた混合層の層流―乱流遷移過程の解析

In the laminar-turbulent transition process of a mixing layer formed downstream of a two-dimensional nozzle exit, an analysis was performed based on various information measures. Shannon entropy, permutation entropy and Kullback-Leibler divergence were introduced, and former studies in which they were used in the turbulent analysis were then reviewed. In the present study, the probability distribution of time series of hot-wire output voltage data was obtained, then analyzed. The aim of the investigation was to clarify the effectiveness of the analysis for the transition and turbulent flow. In addition, equations which Shannon entropy must satisfy in the turbulent flow field were derived. The Shannon entropy of the fluctuating velocity changed monotonically in the downstream direction. Thus, it appears to measure the transition process in the mixing layer. The permutation entropy of the fluctuating velocity first increased, then decreased, then increased again, and decreased finally. It reflected the increase of the fluctuating velocity and change of fluctuation manner (from periodic to irregular fluctuation) during the transition process. The Kullback-Leibler divergence based on the probability density function of the fluctuating velocity increased first, then decreased downstream, and thus did not show a monotonic change during the transition process in the mixing layer.

混合層の乱流遷移過程において，各種情報量に基づいた解析を行った．変動速度の熱線出力電圧時系列信号の確率分布を求めて，シャノンエントロピー，順列エントロピー及びKLダイバージェンスの特徴を比較考察した．シャンノンエントロピーが乱流場で満たすべき方程式も導いた． 変動速度の確率分布のシャノンエントロピーは，混合層の乱流遷移過程を通して単調に増加して乱流遷移の測度となり得ることがわかった．変動速度の順列エントロピーは下流に進むと，遷移過程を反映して増加や減少を繰り返す．変動速度の確率密度関数のKullback-Leiblerダイバージェンスは，単調には変化しなかった．


Randomness representation in turbulent flows with Kolmogorov complexity (In laminar-turbulent transition due to periodic injection in an inlet boundary layer in a circular pipe)

コルモゴロフ複雑度による乱流のランダムさ表現(周期的吹き出しによる円管助走部境界層の乱流遷移の場合)

The complexity or randomness of the laminar-turbulent transition process of an inlet boundary layer in a circular pipe was analyzed by use of Kolmogorov complexity which is a very important measure of the randomness of various events. In the inlet region of the circular pipe, a jet that triggered a turbulent patch in the flow was periodically injected radially, and then propagated downstream periodically. Periodic velocity data which satisfies the phase constancy obtained from a hot-wire anemometer were compressed using a compression program running on a Windows PC. From the compressed data, theapproximated Kolmogorov complexity, named AK, and normalized compression distance NCD were obtained. Although the distribution of AK of irregularly fluctuating velocity in the flow showed a slight discrepancy from the profile of fluctuating velocity intensity and intermittency factor, they exhibited qualitative consistency. Therefore, the objective judgment of the laminar-turbulent transition process based on the approximated Kolmogorov complexity mostly supports the conventional judgment. In conclusion, our study established the validity and usefulness of Kolmogorov complexity or algorithmiccomplexity to describe objectively the laminar-turbulent transition process in the mixing layer, flat plate boundary layer and pipe flow. With the aid of the AK we can distinguish the complexity within the turbulent region; on the other hand, the intermittency factor cannot.

円管助走部境界層の乱流遷移過程の複雑さやランダムさを，コルモゴロフ複雑度によって検討した．円管助走部で噴流を半径方向に噴出し，これが孤立乱流塊を発生した．熱線風速計から得られた周期的な速度データを，Windowsパソコン上の圧縮プログラムで圧縮した．近似コルモゴロフ複雑度と正規化圧縮距離を求めた．不規則変動速度のAKの変化は，不規則変動速度自身や間欠係数の変化と完全には一致しないが，孤立乱流塊が平板境界層乱流斑点型である間は大まかには合い，コルモゴロフ複雑度に基づく乱流遷移進行の客観的な判断は，従来の間欠係数による判断をほぼ支持する．このようにこれまで混合層と平板境界層の乱流遷移過程で確認されてきた事実が円管助走部境界層でも確認された．下流に進んで孤立乱流塊が円管発達流の乱流スラグ型になると，乱流塊外で間欠係数や不規則変動速度が小さくても，AK やNCD が大きい領域が壁面近くで存在して，変動の複雑度を反映する．不規則変動速度のAK やNCD を用いることにより，間欠係数では区別できない乱流領域内部の複雑さを区別することができる．


Study of emulsification mechanism and droplet size estimation in a homogenizer

圧力式ホモジナイザーの乳化作用と液滴径予測に関する研究

A pressure type homogenizer consists of a plunger pump, and a valve part with a narrow channel. It generates effects such as a shear, a turbulent flow and a cavitation between fluid molecules at very short time, and makes a homogeneous emulsification state. If the flow pattern in a valve can be solved in more detail, the more efficient and stabilized emulsification will be attained. However, since it is difficult to measure the size, the pressure and the flow velocity in a narrow gap space by experiment, the details of the mechanism of emulsification by s shear, a turbulent flow, a cavitation and a collision have not been clarified enough. In this research, the size of gap is first calculated from the theoretical equation assumed to be laminar flow, based on the Reynolds number of the gap flow. Next, the pressure, the flow velocity, shearing stress, etc. are calculated. Then, the emulsification mechanism of each part of the valve is clarified by expressing the droplet size as a function of the gap size, the shearing stress and the exit velocity about two kinds of original solutions in which interfacial tension differs. Furthermore, the prediction expression of droplet size obtained by the emulsification is proposed.


Properties of the laminar-turbulent transition in a mixing layer by the low-frequency disturbance --- Effect of the anti-symmetrical disturbance

The laminar-turbulent transition of a mixing layer excited by oscillating flat plates at an exit of a two-dimensional nozzle was experimentally investigated. The plates oscillated vertically in relation to the mean flow. Upper and lower flat plates oscillated anti-symmetrically. The oscillation frequency, 5 Hz, was two orders of magnitude smaller than the fundamental frequency of the velocity fluctuation in the natural transition process. The results were compared with the previous case in which the plates oscillated symmetrically. Anti-symmetrical oscillation promoted the expansion of the mixing layer and promoted the disappearance of the potential core more than symmetrical oscillation. The fluctuations from time and phase averages in the anti-symmetrical oscillation were larger than those in the symmetrical oscillation. In the linear region of the transition, the irregular fluctuation grew exponentially. There were not any differences in the spatial growth rate between the streamwise and normal directions and among three oscillating states.

二次元ノズル出口の平板振動によって励起された混合層の層流-乱流遷移を実験的に調べた．平板は平均流に垂直に，上板と下板が逆対称的に振動する．振動周波数は5Hzで，これは自然遷移過程の速度変動の基本周波数よりも2オーダー小さい．実験結果は平板が対称的に振動した過去の実験結果と比較した．逆対称時は対称時よりも混合層の広がりを促進させ，ポテンシャルコア消滅を早める．逆対称時は時間平均や位相平均からの変動が対称時よりも大きい．線形領域においては，不規則変動が指数的に成長する．流れ方向や垂直方向成長率は，3振動様式間では差異がない．


On Behaviors of Pressure and Velocity in Duct with Tube Bank at Onset of High Level Sound

大音響騒音発生時における管群ダクト内の圧力・流量の挙動について

Vortices occur when gas flow passes through a duct with a tube bank of the heat exchangers, such as a gas heater and a boiler. Very high level sound called a "self-sustained tone" occurs due to the interference of the vortices and the sound field in the duct. There are many investigations concerning the generation mechanism and countermeasures of the self-sustained tones. However there are few investigations focusing on the behaviors of the pressure and the velocity in occurrence of the self-sustained tones. In the past, we experienced the failure of the fan blade used in the experiment. In this paper, the experiment was carried out to examine the behaviors of the pressure and the velocity in the duct with tube bank. As a result, the static pressure changes along the squared curve when the self-sustained tone does not occur. But it suddenly rises up when the self-sustained tone occurs and it is possible for this pressure rise to cause the blade failure due to the generation of the rotating stall. In addition, it was clarified that the flow velocity does not increase in proportion to the inverter frequency and its gradient decreases when the self-sustained tone occurs.

熱交換器内のダクト内管群から発生する渦の周波数とダクトの気柱共鳴周波数が一致して起きる共鳴や空力自励音が大きな問題でるが，その発生時にダクト内のガス流速や圧力がどのように変化するかについてはあまり報告されていない．そこで自励音発生時におけるガス流速や圧力の挙動を明らかにする実験を行った．自励音が発生していないときは管群列数が多いほどそれが流路抵抗となりダクト出口での流速分布の変化は小さくなるが，自励音が発生するとダクト幅方向音圧モードの影響を受けダクト出口の流速分布は大きくなることが明らかになった．


Randomness representation in turbulent flows with Kolmogorov complexity (In turbulence wedge developed from a single roughness element on a flat plate)

コルモゴロフ複雑度による乱流のランダムさ表現(平板上単一突起下流の乱流くさびの場合)

The complexity or randomness was examined with the aid of Kolmogorov complexity for the flow about a turbulence wedge developed from a single roughness element on a flat plate. Velocity data obtained from a hot-wire anemometer and its time derivative data were compressed using a compression program running on a Windows PC. Approximated Kolmogorov complexity, AK, and normalized compression distance, NCD, were obtained. Although the AK variation of fluctuating velocity and that of its time derivative do not completely agree with that of the fluctuating velocity and the intermittency factor, they do roughly. Therefore, the objective judgment of the laminar-turbulent transition progress based on the Kolmogorov complexity mostly supports the judgment by the conventional intermittency factor. With the aid of the AK we can distinguish the complexity within the turbulent region; on the other hand, the intermittency factor cannot. The AK distribution of fluctuating velocity and that of time derivative are similar, and this suggests the similarity in the differentiation of complexity. The AK in the turbulent flow is larger than that in the non-turbulent flow. The AK decreases when the coherent structure has occurred in the turbulent flow. This means that the length of the algorithm is short if a computer expresses the coherent structure detected by the conventional method. Although the hot-wire signal within the coherent structure is random in appearance, it is coherent in the algorithm view. The difference in NCD on the time derivative of the fluctuating velocity between the turbulent and non-turbulent flow is larger than the NCD on the fluctuating velocity itself. That is, the difference in complexity appears in the fluctuating vorticity more than in the fluctuating velocity.

平板上単一突起から発生した乱流くさび周りの流れの複雑さやランダムさを，コルモゴロフ複雑度によって検討した．熱線風速計から得られた速度データとその時間微分データを，Windowsパソコン上の圧縮プログラムで圧縮した．近似コルモゴロフ複雑度と正規化圧縮距離を求めた． コルモゴロフ複雑度に基づく乱流遷移進行の客観的な判断は，従来の間欠係数による判断をほぼ支持する． 変動速度やその時間微分係数の複雑度は，間欠係数では区別できない乱流領域内部の複雑さを区別することができる． 非乱流よりも乱流の方が複雑度は大きいが，その乱流中でも，組織構造が発生しているときの複雑度は小さく，組織構造はアルゴリズム的に組織的である．


Study on Effect of Absorbent on Acoustic Damping of Duct

吸音材の諸元がダクト内音場の音響減衰に及ぼす影響について

The acoustic material has been used inside ducts as a countermeasure of the self-sustained tone generated from heat exchangers and boilers. However the effects of the amount of acoustic material and its patching position in a lined duct on the acoustic damping in its duct have not been established. It can be expected that we can suggest the guideline of absorbing treatment at the design stage to avoid the generation of the self-sustained tone. In this study, the experiment and the analysis are carried out to clarify the problems mentioned above. First the usefulness of the analytical method by BEM is shown by comparing experimental results referring to the acoustic damping in the duct. Next, the effects of the amount of acoustic material and its patching position relative to the noise source on the acoustic damping in the duct are examined by BEM analysis. As a result, it was confirmed that the analytical method due to BEM was useful to predict the acoustic damping because the analytical results of acoustic damping were in good agreement with the experimental ones. And the acoustic damping was also clarified to be affected strongly by the positional relation between the noise source and the acoustic material. In addition, it was effective to patch the acoustic material near the noise source.

熱交換器から発生する空力自励音と呼ばれる大音響の異音を抑制する手段としての吸音処理法について着目した．熱交換器内の管群に流体が通り抜けるときカルマン渦が発生し，その脱落周波数とダクトの気柱共鳴周波数が接近した時，共鳴あるいは空力自励音が発生する．この対策として用いられている吸音材による音響減衰を解析で求めた．吸音材中心位置が音源位置と一致するように貼り付けると効果的であった．


Laminar-turbulent transition of an inlet boundary layer in a circular pipe induced by periodic injection --- Turbulence within isolated turbulent patches and its growth mechanism

The laminar-turbulent transition of a boundary layer induced by a jet injection in the inlet region of a circular pipe was experimentally investigated. The jet was periodically injected radially from a small hole in the inlet region into the pipe flow. Axial velocity was measured by a hot-wire anemometer. The turbulent patches originated by the jet. Turbulent fluctuations within the patch were maximum a little inside from the leading edge in the axial direction and a little inside from the peripheral interface in the circumferential direction. Non-turbulent fluid was entrained into the patch through the leading and trailing edges. This was the main reason for the axial growth of the patch downstream. If the entrainment is suppressed, the axial growth is inhibited.

円管内助走部層流境界層の小孔からの周期的噴流噴出による乱流遷移を実験的に調べた．軸方向速度を熱線風速計で測定した．噴流によって孤立乱流塊が発生した．孤立乱流塊内部の不規則変動は，軸方向や周方向から少し内部に入った位置において最大となる．乱流塊外の非乱流流体を取り込んで乱流化されており，これが孤立乱流塊の軸方向成長の原因である．この非乱流流体の取り込みが少ないと，乱流塊内の変動速度は小さくまた軸方向成長は弱い．


Acoustic Characteristics of Flow Noise Generated from Air-Conditioning Duct of Rail Vehicle

Noise from an air conditioning duct of a rail vehicle is annoying for passengers especially when the rail vehicle is in a resting state. Then the noise reduction is very important from the point of view of keeping the car room comfortable and is one of the differentiating techniques. This paper described experimental results of flow noise characteristics. In this study, the flow noise characteristics generated from the air conditioning duct have been studied experimentally by using the duct with four holes. As a result, it was clarified that the noise reduction effect of the absorbing treatment could be neglected when the noise source was made only by the flow and is much when the fan noise is greater than the flow noise.

空調機のダクトや乗物からの騒音は深刻な問題である．そのため騒音低減は重要な課題である．本研究は流体騒音問題の実験的研究である．本研究では空調機ダクト内の空気からの騒音特性を4穴ダクトを用いて実験した．吸音材の騒音低減効果は，騒音源が流体である場合は無視できファン騒音が流体騒音より大きい場合は効果が大きいことが明らかになった．


Laminar-Turbulent Transition of an Inlet Boundary Layer in a Circular Pipe Induced by Periodic Injection --- Shape of Isolated Turbulent Patches and Their Growth

The laminar-turbulent transition of a boundary layer induced by an ejection of jet in the inlet region of a circular pipe was experimentally investigated. The jet was periodically inserted radially from a small hole in the inlet region into the pipe flow. Axial velocity was monitored by a hot-wire anemometer. The difference of properties in laminar-turbulent transition from developed Hagen-Poiseuille flow was examined. Isolated turbulence patches were generated by the jets, and then they propagated downstream. The leading and traiking edges of the turbulent patch were similar to those of a turbulent spot in a flat-plate boundary layer. The threshold value of the jet flow rate to generate the turbulent patch decreased and saturated finally with the increase in jet duration. The normalized jet duration when the threshold value was saturated and the normalized threshold flow rate were different from those of the developed region. With the increase in jet flow rate beyond the threshold value, the duration of the turbulent patch increased, though the fluctuating velocity within the patch did not increase. The propagation velocities of the leading and trailing edges, the duration and fluctuating velocity within the turbulent patch were almost constant irrespective of the jet ejection frequency.

円管内助走部層流境界層の小孔からの周期的噴流噴出による乱流遷移を実験的に調べた．軸方向速度を熱線風速計で測定した．発達流との差異を検討した．孤立乱流塊が発生して下流に移動した．その前縁，後縁は平板境界層の乱流斑点と同様だった．孤立乱流塊発生に必要な噴流流量の敷居値は，噴出時間の増加と共に減少し，最後に飽和した．この飽和する噴出時間の無次元値や敷居値の絶対値は発達流とは傾向が異なった．孤立乱流塊が発生した後に，噴流流量を増加させても，乱流塊内部の変動は増加せずに乱流塊継続時間が増加した．孤立乱流塊の前縁や後縁の伝播速度，継続時間や内部の変動の大きさは噴流噴出周波数によらず一定である．


Randomness Representation in Turbulent Flows with Kolmogorov Complexity (In Mixing Layer)

The Kolmogorov complexity which measures the randomness were introduced. Numerical and graphic data in the mixing layer which was formed downstream of two-dimensional nozzle exit were compressed with the aid of a compression program. Approximated Kolmogorov complexity, AK, and normalized compression distance, NCD, were obtained. The AK indicated the regularity of the laminar flow and the randomness of the turbulent flow quantitatively. The NCD of the numerical value varied with data length. Between the same data, it approached zero, yet, on the other hand, between different data, it approached unity as the data length increased. The NCD of the numerical value in the natural transition process in the mixing layer increased monotonically downstream. Thus the NCD appears to be the measure of the transition process.

ランダムさを表現する測度であるコルモゴロフ複雑さを紹介した．そして2次元ノズル出口下流に形成される混合層の乱流遷移過程の数値データや画像データを圧縮した．近似コルモゴロフ複雑さAKや正規化圧縮距離NCDを求めた．AKは層流の規則性や乱流のランダムさを定量的に表示することができる．数値データのNCDはデータ個数によって変化し，データ個数が多いほど同一データ間のNCDは0に近づき，異なるデータ間のNCDは1に近づく．混合層の自然遷移過程における数値データのNCDは下流方向に単調に変化して，遷移進行の測度となり得る．


Effect of Local Periodic Disturbance on Mixing Layer Downstream of Two-Dimensional Jet(Effect of amplitude and frequency of the disturbance)

2次元噴流出口混合層に及ぼす局所周期撹乱の効果(撹乱振幅と周波数の影響)

The laminar-turbulent transition of a mixing layer induced by oscillating flat plates at the exit of a two-dimensional nozzle was experimentally investigated. The plates oscillated vertically in relation to the jet. The oscillation frequency was two orders of magnitude smaller than the fundamental frequency of the fluctuating velocity. As the flow proceeds downstream, the mixing layer entrains the surrounding quiescent fluid. This entrainment is affected by the oscillating frequency rather than the oscillating amplitude. The variation of the streamwise velocity with the oscillating phase is much affected by the oscillating amplitude rather than the oscillating frequency. For an irregularly fluctuating velocity, a linear region where the velocity grows exponentially first exists. The spatial growth rate in this region is the same between the streamwise and normal components, and does not differ with various oscillating amplitudes and frequencies.

二次元ノズル出口の平板振動によって励起された混合層の層流-乱流遷移を実験的に調べた．平板は平均流に垂直に，上板と下板が対称的に振動する．振動周波数は自然遷移過程の速度変動の基本周波数よりも2オーダー小さい．下流に進むと周囲の静止流体を混合層内に取り込んで，混合層内の流量は増加するが，この取り込みは振動振幅よりも周波数の影響を受ける．流れ方向速度の位相に対する変化の大きさは，成分は板振動振幅の影響を受けるが，周波数の影響はあまり受けない．不規則変動は，初期は指数関数的に成長し，成長率は，速度の流れ方向成分と垂直方向成分間の差異はなく，また振動振幅や周波数間の差異もない．

Transactions of The Japan Society of Mechanical Engineers, Series B

日本機械学会論文集(B編)


Study of Emulsification Mechanism in a Pressure Type Homogenizer

圧力式ホモジナイザーの乳化メカニズムに関する研究

Emulsification technique is used in broad fields, such as food, chemistry, and medical treatment, and the range of use has been spreading still more. A pressure type homogenizer consists of a plunger pump and a valve part with a narrow channel. It generates the effects of shear, a turbulent flow and cavitation at very short time, and then makes a homogeneous emulsification state. If the flow pattern in the valve can be solved in more detail, the more effective and stabilized emulsification will be attained. However, since the measurement of the size, the pressure and the flow velocity in a narrow gap space by experiments is difficult, the details of the mechanism of emulsification by the shear, the turbulent flow, the cavitation and a collision have not been clarified enough. In this research, the size of gap is first calculated from the theoretical equation assumed to be laminar flow, based on the Reynolds number of the gap flow. Next, the pressure, the flow velocity, shearing stress, etc. are calculated. Then, the emulsification mechanism of each part of the valve is clarified by expressing the droplet size as a function of the gap size, the shearing stress and the exit velocity.

日本機械学会論文集(B編)


Study on a Countermeasure of Self-Sustained Tone by a Baffle Plate in Boiler Tube Banks

In heat exchangers such as boilers and gas heaters, tube banks are set in a duct such that water passes through inside the tubes and warm gas outside the tubes. Due to the external flow, the resonance phenomenon called the self-sustained tone occurs at a certain velocity. The self-sustained tone might cause noise problems in the surroundings, cause losses due to plant shutdown etc. The insertion of baffle plates in the duct is one of a few countermeasures of the self-sustained tone. However, the mechanism of suppression of the self-sustained tone is not understood. Thus, the purpose of this study is to clarify a new mechanism of suppression of the self-sustained tone by baffle plate insertion and the best insertion conditions for baffle plates in tube banks.

ボイラなどの熱交換機ではダクト内に管群が存在し，管内を冷水が，管外を熱気体が流れる．ある速度で共鳴現象が自励振動を発生させ，騒音が深刻な問題となる．バッフル板をダクト内に挿入すると自励音を抑制することができるが，その機構は未知であった．本研究はバッフル板挿入による自励音抑制の機構を明らかにし，バッフル板の最適挿入条件を明らかにした．


Study on Acoustic Characteristics of Lined Duct

Lined ducts are widely used to reduce the noise generated from various equipments. The noise reduction of non-lined ducts is usually predicted by using the FEM and the BEM techniques. In this research, the analytic value of BEM was compared with the actual measurement value for the attenuation quantity within a lined duct. Then, a noticeable gap was caused between both results in specific frequency. Thus, the cause was probed with a viewpoint of the specific acoustic impedance ratio used for BEM. As a result, it was found that the prediction of sound attenuation of the duct agrees with the experimental result.

直線ダクトは各種装置から発生する騒音を低減させるために広く用いられている．非直線ダクトの騒音低減は通常はFEMやBEMで予測されている．本研究では，BEMの解析値を直線ダクトの実験値と比較した．特定の周波数では顕著な差があった．その原因をBEMを用いた比音響インピーダンスの見地から考察し，実験結果と一致した．

Journal of Frontiers in Construction Engineering


Laminar-Turbulent Transition of an Inlet Boundary Layer in a Circular Pipe Induced by Periodic Injection --- Turbulence within Isolated Turbulent Patches and Its Growth Mechanism

周期的吹き出しによる円管助走部境界層の乱流遷移 --- 孤立乱流塊内部の乱れと乱流塊の成長機構

日本機械学会論文集(B編)


Effect of Local Periodic Disturbance on Mixing Layer Downstream of Two-Dimensional Jet (Spatial Structure and Quantitative Representation of Laminar-Turbulent Transition Process)

The laminar-turbulent transition of a mixing layer induced by oscillating flat plates at an exit of a two-dimensional nozzle was experimentally investigated. The plates oscillated vertically in relation to the mean flow. The oscillation frequency was two orders of magnitude smaller than the fundamental frequency of the velocity fluctuation. In the oscillating state, the same phenomenon as in the natural transition process appeared more upstream. In the early stage within the nonlinear region, the growth of fluctuating velocity attenuated and the Reynolds shear stress component decreased. The decrease in their production rate due to the expansion of the mixing layer contributed to the attenuation and decrease. The randomness factor appeared to be a reasonable indicator of the present transition process, especially in the process in which the periodic velocity fluctuation became irregular. However, this factor certainly indicated the same value at two streamwise positions.

二次元ノズル出口の平板振動によって励起された混合層の層流-乱流遷移を実験的に調べた．平板は平均流に垂直に対称的に振動する．振動周波数は自然遷移過程の速度変動の基本周波数よりも2オーダー小さい．非線形領域初期においては，混合層の広がりのために，流れ方向及び垂直方向変動速度やレイノルズせん断応力の生成率が減少して変動速度の成長は鈍化する．レイノルズせん断応力はいったん減少した後に再増加するが，これに伴って，レイノルズせん断応力に寄与する両変動速度が同符号になる確率が減少し，後に増加する．雑然度は，速度の周期変動が不規則変動に変化する過程では単調に増加して乱流遷移進行の測度として有効と思われるが，それよりも上流の，層流から周期変動が支配的になる過程においては，雑然度は単調に減少する．


Laminar-Turbulent Transition of an Inlet Boundary Layer in a Circular Pipe Induced by Periodic Injection --- Shape of Isolated Turbulent Patches and Their Growth

周期的吹き出しによる円管助走部境界層の乱流遷移 --- 孤立乱流塊の形状と成長

日本機械学会論文集(B編)


Randomness Representation in Turbulent Flows with Kolmogorov Complexity(In Mixing Layer))

コルモゴロフ複雑度による乱流のランダムさ表現(混合層の場合)

日本機械学会論文集(B編)


Effects of Splitter Plates on Turbulent Quantities on a Boundary Layer Developing on a Flat Plate near the Trailing Edge

平板後縁近傍境界層の乱流場の発達に及ぼすスプリッター板の影響

An experimental investigation was made on a turbulent boundary layer near the trailing edge on a long flat plate with a blunt trailing edge. The flow was controlled by an additional splitter plate attached to the trailing edge along the wake center line. Measurement of fluctuating velocity was made under the freestream zero pressure gradient. Almost independent of the installation of the splitter plate, the turbulent intensity and the Reynolds shear stress in the inner layer decreased when approaching the trailing edge of the flat plate. The effect of the plate length on turbulent quantities was shown just upstream of the trailing edge upon close comparison, and was classified into two groups. The tendency of the turbulent energy production terms approaching the trailing edge coincided with the decrease in the streamwise turbulent intensity and in the Reynolds shear stress.

長い平板の後縁近傍の乱流境界層に関する実験的研究を行った．平板後縁中心線上に分割板を設置した．零圧力勾配の下で，変動速度分布を測定した．分割板があってもなくても，内層の乱れ強さおよびレイノルズせん断応力は平板後縁に近づくと減少した．板長さの効果は後縁直前の乱流量の変化傾向に現れ，二群に大別される．後縁に向う乱れエネルギの生成項の減少傾向は，乱れ強さおよびレイノルズせん断応力と一致する．

日本機械学会論文集(B編)


Laminar-Turbulent Transition of an Inlet Boundary Layer in a Circular Pipe Induced by Periodic Ejection --- Condition for Generating an Isolated Turbulent Patch

The laminar-turbulent transition of a boundary layer induced by an ejection of jet in the inlet region of a circular pipe was experimentally investigated. The jet was periodically inserted radially from a small hole in the inlet region into the pipe flow. Axial velocity was monitored by a hot-wire anemometer. The difference of properties in laminar-turbulent transition from developed Hagen-Poiseuille flow was examined. Isolated turbulence patches were generated by the jets, and then they propagated downstream. The leading and traiking edges of the turbulent patch were similar to those of a turbulent spot in a flat-plate boundary layer. The threshold value of the jet flow rate to generate the turbulent patch decreased and saturated finally with the increase in jet duration. The normalized jet duration when the threshold value was saturated and the normalized threshold flow rate were different from those of the developed region. With the increase in jet flow rate beyond the threshold value, the duration of the turbulent patch increased, though the fluctuating velocity within the patch did not increase. The propagation velocities of the leading and trailing edges, the duration and fluctuating velocity within the turbulent patch were almost constant irrespective of the jet ejection frequency.


Effect of Local Periodic Disturbance on Mixing Layer at Exit of Two-Dimensional Jet

The laminar-turbulent transition of a mixing layer induced by oscillating flat plates at an exit of a two-dimensional nozzle was experimentally investigated. The plates oscillated vertically in relation to the mean flow. The oscillation frequency was two orders of magnitude smaller than the fundamental frequency of the velocity fluctuation. The oscillation was found to be effective in enhancing the mixing. The disturbance traveled downstream as the convective instability, though it was damped only far downstream. The downstream development rate of fluctuating velocity in the normal component was larger than that in the streamwise one. Streamwise variation of the fluctuating velocity and fluctuating energy production and convection rates, which contribute to the velocity, were examined. The streamwise variation in the streamwise component did not correspond to that of the normal component.

二次元ノズル出口の平板振動によって励起された混合層の層流-乱流遷移を実験的に調べた．平板は平均流に垂直に対称的に振動する．振動周波数は自然遷移過程の速度変動の基本周波数よりも2オーダー小さい．混合層の下流における広がりは振動板によって促進することができた．本撹乱は対流不安定となって増幅するが，下流では対流的に減衰した．線形領域における変動速度の流れ方向への成長は，流れ方向成分よりも垂直方向成分の方が大きかった．流れ方向変動速度の増加には生成項・対流項以外が寄与している．垂直方向変動速度の増加には生成項・対流項が主に寄与している．


Effect of Local Periodic Disturbance on Mixing Layer Downstream of Two-Dimensional Jet(Spatial Structure and Quantitative Representation of Laminar-Turbulent Transition Process)

2次元噴流出口混合層に及ぼす局所周期撹乱の効果(乱流遷移過程の空間構造と定量的表示)

Transactions of The Japan Society of Mechanical Engineers, Series B

日本機械学会論文集(B編)


Effects of Splitter Plates on Turbulent Quantities on a Boundary Layer Developing on a Flat Plate near the Trailing Edge


2次元噴流出口混合層に及ぼす局所周期撹乱の効果

2次元噴流出口混合層に及ぼす局所周期撹乱の効果

日本機械学会論文集(B編)


Laminar-Turbulent Transition of an Inlet Boundary Layer in a Circular Pipe Induced by Periodic Ejection --- Condition for Generating an Isolated Turbulent Patch)

周期的吹き出しによる円管助走部境界層の乱流遷移 --- 孤立乱流塊の発生条件

日本機械学会論文集(B編)


Flow Structures above the Trunk Deck of Sedan-Type Vehicles and Their Influence on High-Speed Vehicle Stability 2nd report: Numerical Investigation on Simplified Vehicle Models using Large-Eddy Simulation

SAE International Journal of Passenger Cars - Mechanical Systems


The Effects of Splitter Plates on Turbulent Boundary Layer on a Long Flat Plate Near the Trailing Edge

An experimental investigation has been made for a turbulent boundary layer near the trailing edge on a long flat plate. The flow was controlled by an additional splitter plate fitted to the trailing edge along the wake center line. The length of the splitter plate was varied from a half, to five times the trailing edge thickness. Measurements of base pressure behind the trailing edge and of mean velocity and pressure distribution in the turbulent boundary layer on the flat plate were made under the freestream zero-pressure gradient. The absolute value of base pressure coefficient of the long flat plate was considerably smaller than that of the short flat plate (bluff body) without splitter plate. A significant increase in the normalized base pressure coefficient (about 50% as same as short one) was achieved with the splitter plate fitted to the long flat plate. Within an inner layer in the turbulent boundary layer near the trailing edge, mean velocity increased than that in the upstream position, especially in the case without splitter plate. With splitter plate, however, the base pressure rise made mean velocity distribution come closer to that of fully developed turbulent boundary layer.

長い平板の後縁近傍の乱流境界層に関する実験的研究を行った．平板後縁中心線上にスプリッター板を設置した．スプリッター板長さと平板厚さの比を0.5から5まで変えた．零圧力勾配の下で，背圧，平均速度，圧力分布を測定した．スプリッター板がないときの背圧係数は短い平板のそれよりも小さかった．スプリッター板を設置すると背圧は約50%回復した．平板後縁近傍の乱流境界層は，スプリッター板がないときは加速したがスプリッター板を設置するとこの加速は緩和され加速される領域も縮小した．

Journal of Fluids Engineering - Transactions of the ASME


長平板背後の渦構造に及ぼすスプリッター板の影響

長平板背後の渦構造に及ぼすスプリッター板の影響

長い平板の後縁近傍の乱流境界層に関する実験的研究である．平板後縁中心線上にスプリッター板を設置した．スプリッター板長さと平板厚さの比を0.5から5まで変えた．零圧力勾配の下で，渦放出周波数，速度変動波形，渦形成領域，再付着点位置を検討した．長平板と短平板との差はスプリッター板がないときの渦放出周波数の著しい差として生じた．スプリッター板を設置すると渦放出周波数は短平板ほど顕著ではないがいずれのスプリッター板長さでも増加した．その渦放出周波数に及ぼすスプリッター板の効果を調べ説明した．

日本機械学会論文集(B編)


Laminar-Turbulent Transition of a Boundary Layer Induced by a Single Roughness Element in an Inlet Region of a Circular Pipe Flow --- 定常乱流領域の発達過程

円管助走部境界層の単一突起による遷移 --- 定常乱流領域の発達過程

円管助走部境界層の乱流遷移に関する実験的研究である．単一突起を設置することによって下流に形成される定常な乱流領域の平均·変動速度を熱線風速計を用いて測定した．乱流領域の輪郭線は平面に展開するとくさび形である．くさびの頂点は突起位置に一致し，突起直後は直線であるが，次第に外側に向かって曲がる．これは平板上の乱流くさびと同様である．また広がり角も，同程度のレイノルズ数における平板上の乱流くさびと同程度である．乱流領域内の速度変動は中心線上で最大にはならず，周囲の層流領域との界面で最大になる．そこでの乱流領域内部の速度変動は乱流領域中心部よりも大きい．

日本機械学会論文集(B編)


平板後縁近傍乱流境界層の発達に及ぼすスプリッター板の影響

平板後縁近傍乱流境界層の発達に及ぼすスプリッター板の影響

長い平板の後縁近傍の乱流境界層に関する実験的研究である．平板後縁中心線上にスプリッター板を設置した．スプリッター板長さと平板厚さの比を0.5から5まで変えた．零圧力勾配の下で，背圧，平均速度，圧力分布を測定した．スプリッター板がないときの背圧係数は短い平板のそれよりも小さかった．スプリッター板を設置すると背圧は約50%回復した．平板後縁近傍の乱流境界層は，スプリッター板がないときは加速したがスプリッター板を設置するとこの加速は緩和され加速される領域も縮小した．

日本機械学会論文集(B編)


Properties of a Turbulence Wedge Which Develops from a Single Roughness Element in a Flat Plate Laminar Boundary Layer

平板層流境界層内の単一突起から発達する乱流くさびの特性

A turbulence wedge that develops downstream from a single roughness element placed in a laminar boundary layer on a flat plate was experimentally investigated. Streamwise vortices, development mechanisms of the wedge in the wall-normal and spanwise directions and development process of the turbulent quantities in the downstream were clarified. Many streamwise vortices appear within the wedge just behind the roughness. Further downstream, on the other hand, a pair of streamwise vortices are found on both interfaces between the wedge and the outer laminar region. The development mechanism of the wedge in the spanwise direction may be governed by the streamwise vortices ; the mechanism in the spanwise direction is different from that in the wall-normal direction. The fluctuating velocities and the Reynolds stresses just behind the roughness are larger than those of the developed turbulent boundary layer because of the many streamwise vortices. Further downstream, they more closely resemble those in the developed turbulent boundary layer.

層流境界層の乱流遷移に関する実験的研究である．乱流くさび領域の平均·変動速度を熱線風速計とV型，X型熱線プローブを用いて測定した．突起直後の断面においてはくさび内に多数の縦渦が存在し，突起からある程度下流に進んだ断面内においては，くさびと周囲の層流領域との界面に一対の縦渦が存在した．乱流のときは，よりくさびの外側に向かうような横方向運動が存在し，これによって乱流くさびは外側に広がることがわかった．この横方向への発達機構には縦渦が影響を与えていると考えられ，境界層厚さ方向と横方向間では発達機構は異なる．突起直後における変動速度，レイノルズ応力は，発達した乱流境界層の分布よりも大きな値を示した．これは突起直後の多数の縦渦によるものと考えられた．またこれらの値の下流方向への変化より，下流に行くに従って乱流が発達することが示された．

日本機械学会論文集(B編)


The Flow over in Inclined Fence in a Turbulent Boundary Layer

平板乱流境界層内に設置された傾斜フェンスまわりの流れ

The purpose of this paper is to study in detail the flow over an inclined fence in a turbulent boundary layer, as basic research which issues from promoting heat transfer and the decrease of the pressure drop. The fence height h set in a turbulent boundary layer is 3 mm (u_τh/ν≒75, u_τ : friction velocity, ν : kinematic viscosity) and setting angle of a fence is 20° in the free stream direction. The time averaged velocity profiles in the downstream of the fence ware measured by using a 3-hole pitot tube. We investigated velocity profiles by utilizing polar diagram, logarithmic velocity distributions and velocity defect law. Consequently, It was found that the spanwise velocity profiles are cross-over profiles. We clarified the relaxation process from streamwise direction velocity. Further we investigated in detail the flow direction on the wall which shows the wall shear direction by the oil flow visualization.

平板上に設置された傾斜フェンス下流の流れについて熱線風速計によって平均速度の測定を行い，流れ場の基本現象の解明を試みた．フェンスによって横方向速度を生じるねじれた三次元境界層になることが明らかになった．そのねじれは正負が同程度ではないことも示された．また限界流線角度や剥離領域を流れの可視化によって特定した．

日本機械学会論文集(B編)


Properties of a Relaminarizing Turbulent Boundary Layer under a Favorable Pressure Gradient

Behavior of the turbulent boundary layer on a flat plate in a relaminarization process with flow acceleration due to a convergenceof the sectional area is experimentally investigated. Statistical properties are measured and the turbulent structure is examined in detail. The bursting phenomena are also investigated. In the relaminarization process, low-amplitude fluctuating portions appear intermittently in the velocity signal. In the relaminarization process, vorticity increases in a large eddy and decreases in a small one. The small eddies become large, and the contribution from the high wave number decreases. It is considered that the relaminarization changes the ejection and sweep, though it does not particularly attenuate the bursting in the inner layer. This phenomenon is qualitatively explained with the aid of the mean velocity profiles and mixing length concept.

乱流境界層の再層流化に関する実験的研究を行った．この再層流化は流れを縮小させて順圧力勾配を加えることによって行った．境界層内の平均•変動速度を熱線風速計とI型熱線プローブを用いて測定し，速度分布，乱流統計量，バースト構造について考察した．再層流化過程では低振幅変動が間欠的に発生した．再層流化過程では，乱流領域の境界層内に占める割合が減少し，渦塊は大型化して高周波成分の寄与が減少した．再層流化は境界層内層のバーストを特別には弱めないが，イジェクション，スイープには変化を及ぼすことが混合距離を用いた考察から示された．


入口案内羽根による貫流ファンの高性能化に関する研究

入口案内羽根による貫流ファンの高性能化に関する研究

高圧力係数を持つ貫流ファンを開発するため入口案内羽根が内部流れや，ファン性能に及ぼす影響を検討した．入口案内羽根によって流入流れを制御し，回転と逆方向の適切な予旋回を与えれば入口案内羽根がないものと比べて高い圧力係数が得られるとともに，高効率が得られることを示した．

Transactions of The Japan Society of Mechanical Engineers, Series B

日本機械学会論文集(B編)


順圧力こう配下の再層流化乱流境界層の特性 --- VITA法によるバースト構造の解析

乱流境界層の再層流化に関する実験的研究である．この再層流化は流れを縮小させて順圧力勾配を加えることによって行った．境界層内の平均·変動速度を熱線風速計とI型熱線プローブを用いて測定し，VITA法を用いてバースト構造について考察した．再層流化は乱流境界層の外層部分から発生するという従来の推測が支持される結果を得た．また再層流化するとバーストの発生は減少する．しかしこの周波数をテイラー微小時間で無次元化すると圧力勾配にかかわらず一定になる．再層流化は境界層内層のバーストを特別には弱めないが，イジェクション，スイープには変化を及ぼすことが混合距離を用いた考察から示された．

日本機械学会論文集(B編)


Unsteady Fluid Forces on a Blade in a Cross-Flow Turbine

The experimental and theoretical studies for determination on fluid forces on the blade in a cross-flow turbine are conducted. In the experiment, the tangential and radial forces are measured. In the theoretical study, they are calculated numerically using the unsteady momentum theory. The calculated results are compared with experimental data and good agreement between them is demonstrated. Furthermore, the maximum forces are found to occur immediately before the blade leaves the nozzle exit in both the experimental and theoretical results.

クロスフロー水車の羽根にかかる流体力の実験的，理論的研究を行った．実験では，接線方向力，半径方向力を測定した．理論解析では，非定常運動量理論を用いた．計算と実験はよく一致した．さらに最大力は羽根がノズル出口を去る直前に発生することが明らかになった．

JSME International Journal, Series B: Fluids and Thermal Engineering


順圧力こう配下の再層流化乱流境界層の特性

順圧力こう配下の再層流化乱流境界層の特性

乱流境界層の再層流化に関する実験的研究である．この再層流化は流れを縮小させて順圧力勾配を加えることによって行った．境界層内の平均·変動速度を熱線風速計とI型熱線プローブを用いて測定し，速度分布，乱流統計量について考察した．また変動速度の確率密度関数の形状の変化をK-Lダイバージェンスを用いて定量的に説明した．再層流化は乱流境界層の外層部分から発生するという従来の推測が支持される結果を得た．再層流化過程では，乱流領域の境界層内に占める割合が減少し，渦塊は大型化して高周波成分の寄与が減少する．

日本機械学会論文集(B編)


往復流におけるクロスフロー形波力水車の作動特性

往復流におけるクロスフロー形波力水車の作動特性

対称形クロスフロー水車を用いた波力水車について往復流中の水車性能に及ぼす羽根車の慣性モーメントの影響を実験的に明らかにした．さらに本水車の相似則を考慮した運動方程式を導き，定常特性を準定常的に用いたシミュレーションによって慣性モーメントが変化した場合にも往復流中の回転数，効率などの作動特性を評価できることを示した．

日本機械学会論文集(B編)


波力水車の運転特性に関する研究

波力水車の運転特性に関する研究

対称形クロスフロー水車を用いた波力水車について上下往復流中の水車性能に及ぼすケーシング形状の影響を調べるとともに，一方向流中の定常特性を準定常的に用いて本水車の動特性のシミュレーションを行い，回転数，効率などの作動特性を評価できることを示した．

日本機械学会論文集(B編)


クロスフロー水車の羽根に働く流体力

クロスフロー水車の羽根に働く流体力

クロスフロー水車の羽根に働く非定常な流体力をひずみゲージ，スリップリングを用いて実験的に求めるとともに運動量法則を用いて数値解析を行い，計算値は実験とかなり良く一致すること，接線方向力，半径方向力ともに羽根がノズル出口の噴流から脱出するノズル先端近傍で最大値を示すことを明らかにした．

日本機械学会論文集(B編)


平板上の突起より発達する乱流くさびの構造の研究

平板上の突起より発達する乱流くさびの構造の研究

層流境界層の乱流遷移に関する実験的研究である．この遷移は3次元突起列によって強制的に生じさせるものである．層流境界層内に単一の3次元突起が存在すると，その下流にくさび形の乱流領域(乱流くさび)が形成される．この乱流くさび領域の平均·変動速度を熱線風速計とI型熱線プローブを用いて測定し，くさびの輪郭線や広がり角度を明確な定義に基づいて示した．また平均量は突起直後では十分発達しておらず，下流に向かって徐々に発達することが明らかになった．

日本機械学会論文集(B編)


多板式層流ファンに関する研究 --- スクロール広がり角が性能に及ぼす影響

多板式層流ファンに関する研究 --- スクロール広がり角が性能に及ぼす影響

低騒音であることが期待されるが，効率が低い多板式層流ファンの性能向上を目的としてスクロール広がり角の影響を検討した．本ファンは羽根車出口流れ角が極端に小さく，かつ流速が大きいため広がり角が1，2°の小さいスクロールを用いればスクロール流入時の減速損失が減少し，効率は増大するが，最高効率点が小流量側へ移動することを示した．

日本機械学会論文集(B編)


軸流中の回転円筒上の境界層に及ぼす単一突起の影響 --- 乱流くさびの間欠域の条件付き測定

一様な軸流中で回転する円筒上に設置した単一突起の下流に発達する乱流領域の流れについて乱流·非乱流の識別を行い，これによって条件を付けた平均·変動速度を円筒の一回転を一事象とするアンサンブルへ平均を求めた．周方向平均速度の周方向分布は非乱流平均値が先行側界面と後続側界面ではくさび外の速度に相対的にそれぞれ正負の値をとる．乱流くさび界面における縦渦を乱流平均·非乱流平均に分けて示すことにより，縦渦構成成分はほとんど乱流であることが示された．

日本機械学会論文集(B編)


軸流中の回転円筒上の境界層に及ぼす単一突起の影響 --- 速度比による乱流くさびの特性の変化

軸流中の回転円筒上の単一突起による乱流遷移に関する実験的研究である．単一突起下流に発生する乱流くさび内の速度を熱線風速計によって測定した．円筒の回転速度を変化させ，アンサンブル平均を求めてた．乱流くさび内の軸方向平均速度分布は，相対主流方向を中心としてほぼ対称的な分布を示した．コリオリ力は乱流くさびの非対称性には寄与するが，その程度は本実験の範囲ではくさびの広がりに現れるほど大きくない．

日本機械学会論文集(B編)


軸流中の静止および回転円筒上の境界層に及ぼす単一突起の影響 --- 乱流くさび領域の平均·変動速度

軸流中の静止及び回転円筒上の単一突起による乱流遷移に関する実験的研究である．単一突起下流に発生する乱流くさび内の速度を熱線風速計によって測定した．乱流くさびと外側の層流との界面に存在する縦渦がくさびの発達に本質的な役割を果たすことが明らかにされた．平均速度ベクトルはくさびの内·外及びくさび内部において，その大きさ，方向とも大きく変化し，その特徴を極線図で示すことができた．円筒回転時における乱流くさび領域は円筒に巻きつくねじれたものであるが，円筒とともに回転する系から見て，平面に展開すると下流に向かってほぼ直線的に増加した．

Transactions of The Japan Society of Mechanical Engineers, Series B

日本機械学会論文集(B編)


A New Measure for the Laminar-Turbulent Transition Process in Free-Shear Flows

自由せん断流の乱流遷移過程の新しい測度について

ランダムさを表現する測度であるコルモゴロフ複雑さを紹介した．そして2次元ノズル出口下流に形成される混合層の乱流遷移過程の数値データや画像データを圧縮した．近似コルモゴロフ複雑さAKや正規化圧縮距離NCDを求めた．AKは層流の規則性や乱流のランダムさを定量的に表示することができる．数値データのNCDはデータ個数によって変化し，データ個数が多いほど同一データ間のNCDは0に近づき，異なるデータ間のNCDは1に近づく．混合層の自然遷移過程における数値データのNCDは下流方向に単調に変化して，遷移進行の測度となり得る．

Journal of Japan Society of Fluid Mechanics