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It's studied how thermals, which cause guerrilla-heavy rainfall in future, are generated from urban area like Kobe City and break through atmospheric boundary layer (ABL). In particular, the phase that thermals and vortex tubes connect to genesis of cumulous and cumulonimbus. I think that aggregation may play an important role at the phase. But, by radar observation, this mechanism isn't clear yet. Hence it is better to compute by using urban meteorological large eddy simulation. In this study, I conducted idealized experiments in order to investigate on how the behavior of thermals and vortex tubes is around or above ABL.

This study investigated the severe winds occurred in the Kinki District and the surrounding areas during the passage of Typhoon Jebi (2018) that developed in September 2018. This typhoon has induced currently the most costly meteorological damages to Japan. The analyses of the surface observational data indicated that the gust factors in urban areas amount to 2.0 or greater, which are significantly higher than those typically known at meteorological stations in a climatological sense. The coupled analysis of both a mesoscale meteorological model and a large-eddy simulation model demonstrated that the maximum wind gust in the analysis area of Osaka City was estimated as 60-70 m/s, which is comparable to the wind speed at the height of about 300 m.

都市の暑熱環境は，将来の気候変動下において重要性を増す社会的課題である．本報では都市キャノピー上における熱輸送について実例を用いて解説した．大気中で熱を鉛直上向きに輸送するのは暖気の上昇と冷気の下降であるが，大気成層が不安定な状態においてキャノピー上での熱輸送を担うのは，上昇する暖気であった．不安定性が強くなるほど，回数は少ないが強い乱流変動によって熱が輸送されていた．キャノピー上での暖気上昇が，日射で加熱された建物壁面での上昇流と関連している例を示した．, Turbulent heat transport in urban atmospheric boundary layer was investigated through the quadrant analysis with a field observation data. Heat flux above the buildings was dominated by upward ejection of warmer air in unstable stratification. In more unstable conditions, less frequent but stronger eddies accounted for a dominant portion of the turbulent heat transfer. An example was shown for a linkage in which the ejection above buildings corresponds to the buoyancy-driven upflow at the building walls.

Intensive observations of turbulence in the atmospheric boundary layer (ABL) during the winter season were conducted in the suburbs of Kyoto City. In the afternoon, strong winds in the lower ABL were intermittently observed by Doppler lidar. Radiosonde observations suggest that turbulent mixing in the ABL extends the high-speed layer, which is located in the upper levels, toward the lower position. Large-scale turbulence structures with temporal scales of more than 100 s were detected in the time series of the streamwise velocity component measured by sonic anemometer. The occurrence of large-scale structures is likely related to the intrusion of the high-speed layer toward the surface.

Although a suction vortex is one of the most common vortices appearing in everyday life, its internal structure has not been fully understood yet. We experimentally generate directly a superfluid suction vortex with a superfluid stirring system. A quantum vortex line carries all the microscopic circulation, and the distribution of vortex lines can be measured by combining two acoustic techniques. The results show that the vortex lines accumulate in the narrow region around the axis of symmetry. However, the vortex lines are not a simple bundle of straight vertical lines, but most of them incline in the horizontal direction.

流路壁面での熱伝達促進機構を明らかにするために，平行平板間流路内に正方形柱を設置した流れを対象にLESを用いた数値計算を行った．角柱から放出されるカルマン渦に同期して壁近傍に孤立渦が発生する．角柱後流の広範囲にわたり，カルマン渦対間の壁面方向流れにより熱伝達が促進される．一方，孤立渦は下流側から冷たい流体を巻き込み，熱伝達促進に寄与する．, Numerical computation with Large Eddy Simulation (LES) has been conducted in a channel flow disturbed by a square cylinder in order to clarify the mechanism of heat transfer enhancement at the channel wall. Discrete vortices appear near the channel wall in phase with the Karman vortices shed alternately from the cylinder. Heat transfer is enhanced by the Karman vortices due to the wallward flow between the Karman vortex pair in the extensive downstream region of the cylinder. On the other hand, the discrete vortices entrain cooler fluid from the downstream side and contribute to the enhancement of the wall heat transfer.

Mud flows were occurred in the west part of the Izuoshima Island on 16 October 2013. The Izuoshima Island is a volcanic island and the land surface is covered by the volcanic ash sediment in about 1m depth. The laminar layer is formed in the debris flow from the bed to the fluid surface. On the other hand, the laminar flow is restricted near the bed in the mud flow and the turbulence flow is formed on the laminar flow layer. As a result, the equilibrium slope of the mud flow becomes smaller comparing to the debris flow. In this study, the horizontal two dimensional mud flow model considering the both the laminar and the turbulence flows is developed. Subsequently, the model is applied to the mud flow occurred in the Izuoshima Island and discussed the applicability of the model. The differences of the horizontal flow areas between the simulated results and the field data are discussed and it was found that the outline of the horizontal shape of the flow areas is reproduced well. Furthermore, the horizontal distribution of the erosion and deposition area is reproduced by the numerical analysis well except for the residential area.

雑誌掲載版, 著者らはかねてより排尿時の尿動態計測用の空中超音波ドプラシステムを開発しているが、どの医療機器もそうであるように、実患者による臨床テストに先立ちシステムの開発および校正、また計測の正当性の評価に「ファントム」を必要とするのは本件開発も例外ではない。本研究においてはそのような主旨でヒトの放尿を模擬するためのウオータージェットファントムを開発し、試作試用したのでその要点を報告する。ヒトの放尿はただ管路の断端をノズルとしてしかるべき流速流量の水を層流として放出しただけでは正しく模擬出来ず、特に男子の場合、外部尿道口の直前にある舟状窩の前後における流路の形状変化に由来する層流から乱流への「ひねり」の場面を正しく再現して初めて正しく模擬できる。装置は中型の小便小僧立像にまとめられ、開発中の尿動態計測用ウエアラブル空中超音波ドプラシステム(1)〜(4)とともに2012年度大学見本市(Innovation Japan 2012)にて公開実演(5)、好評を博した。

本論文ではパーティクル法とウェーブレット解析を用いた高速な乱流シミュレーション手法を提案する．高速に流体の流れを再現するためにパーティクル法の一種であるSPHを用い，そのパーティクル間の相互関係から直接ウェーブレット解析により乱流が発生する領域を検出する方法を提案する．検出された領域にウェーブレットノイズに基づき渦場を付加することで乱流を再現する．さらに，乱流エネルギーに基づきパーティクルを分割・回転させることで，サブパーティクルスケールでの乱流を実現する．最後にこれらの処理のほとんどはGPU上で容易に実装可能であり，リアルタイムに近い速度で実行できることを示す．This paper presents a fast simulation method for turbulent flow which uses a particle method and wavelet analysis. To simulate fluid flow, the method uses smoothed particle hydrodynamics (SPH), which discretizes the fluid into a collection of particles, and detects regions where turbulent flow will occur by using wavelet analysis without a spatial grid. By taking the curl of wavelet noise, the turbulent flow is then appended as a divergence-free turbulence velocity field. Additionally, by using a particle splitting, which characterize the vortex features of turbulence, a sub-particle-scale representation of turbulent flow is proposed. Implementing almost all processes on a graphics processing unit (GPU), simulations are performed in near real time.

昨今, 流体の流れからエネルギーを収集するエネルギースキャベンジングが注目されている.本研究では, 乱流も含めた流体の流れからエネルギーを回収する方法として, 流体中にさらした梁を振動させることによりエネルギーを回収する機構を考える.乱流は, 一次元的にはカオス的な振動とスペクトル部分において類似性があることから, 本報告では静磁場中に置いた強磁性体の弾性梁をカオス的に励振し, 表面に貼った圧電膜から得られる電気エネルギーの見積りを試みる., In this research, we explore the possible model to sacavenge energy from fluid including turbulence. The energy can be extracted from a beam oscillation excited hydrokinetically. One demension of turbulence is similar to chaotic oscillation in the spectrum distribution. In this report, exciter vibrates a magnetoelastic beam chaotically in static magnetic field. We can estimate the amount of energy scavenged from PZT attached on the beam., 本文データは学協会の許諾に基づきCiNiiから複製したものである

２次元の保測写像である標準写像と標準写像を結合した４次元のFroeschlé写像における相空間上のカオス軌道の相対拡散の統計的性質を数値的に調べた。標準写像において、通常拡散が生じるパラメータK＝3.86では、相空間上のカオス軌道の２点間の平均２乗変位は、１点拡散の平均２乗変位のほぼ２倍になった。一方、異常拡散が発生する パラメータK＝6.9115では、相空間上の２つのカオス軌道の間の平均２乗変位は、１点拡散の平 均２乗変位の２倍とのズレが通常拡散に比べて大きくなる傾向が出た。 Froeschlé写像において、結合定数がμ＝0.0、K1およびK2が標準写像において加速モードが安 定に存在するパラメータ（K1＝6.9115,K2＝6.4717）では、相空間上の各点の平均２乗変位の指 数ζ1,ζ2が異なり、相対拡散の平均２乗変位の指数ζは、その中間の値となった。結合定数μ が正（μ＝0.001）、K1およびK2が標準写像において加速モードが安定に存在するパラメータ（K1＝6.9115,K2＝6.4717）でも、各点の平均２乗変位の指数ζ1,ζ2が異なり、相対拡散の平均２乗 変位の指数ζは、その中間の値となった。また、結合定数μが正の場合の方が、μ＝0 の時に比べて相対拡散、１点拡散の平均２乗変位の指数ζ, ζ1, ζ2が大きくなった。

In the present study, we establish statistical DNS (Direct Numerical Simulation) database in a turbulent channel flow with passive scalar transport at high Reynolds numbers and make the data available at our web site (http://murasun.me.noda.tus.ac.jp/turbulence/). The established database is reported together with the implementation of large-scale simulations, representative DNS results and results on turbulence model testing using the DNS data., 資料番号: AA0063742015, レポート番号: JAXA-SP-07-016

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

ほぼ中立な大気境界層における乱流構造を潮岬と信楽において観測した結果を解析した。連続ウェイブレット変換の方法を用いて下降する強風域による乱流構造の様子を明らかにした。これは，本質的にはこれまで乱流境界層に対する実験により示された組織構造の一種である。大きな時間スケールを持った強風の乱流構造は下方への運動量輸送に大きな寄与をなしている。乱流運動についての四象限解析により，スウィープ(高速流の下降運動)が運動量輸送に重要な役割を演じていることが明らかにされたが，この結果はおそらく大きな規模の強風の乱流構造と関連している。, Turbulence structures in the nearly neutral atmospheric boundary layer observed at Shionomisaki and Shigaraki are analyzed. Using the method of integral wavelet transform, the pattern of the descending high-speed turbulence structure is depicted. Essentially this structure is a kind of coherent structure which has been shown previously in experiments for the turbulent boundary-layer flows. High-speed turbulence structures with long time scales make a large contribution to downward momentum transfer. Quadrant analysis of turbulent motion reveals that the sweep motion (high-speed downward motion) plays an important role in momentum transfer. This result of quadrant analysis is probably related to the large-scale high-speed turbulence structures.

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, CFD (Computational Fluid Dynamics) analyses of flow around NAL's non-powered supersonic experimental airplane are conducted. The results are compared with those of corresponding wind tunnel tests. In this paper, agreements and discrepancies between them are discussed in aspects of correspondence between calculation and test models., 資料番号: AA0063609058, レポート番号: JAXA-SP-06-029E

SST-CFD Workshop. International CFD Workshops for Super-sonic Transport Design 航空宇宙技術研究所 19980316-19980317 東京 日本, SST-CFD Workshop. International CFD Workshops for Super-sonic Transport Design National Aerospace Laboratory 19980316-19980317 Tokyo Japan, Most current turbulence models involve explicit wall distance in their formulation. However, wall distance is ambiguous in all but the simplest topologies. Besides, it is not at all evident that it bears a relationship to the structure of turbulence. Thus it is desirable to base modeling practice on wall proximity indicators which are local (pointwise) in nature and convey the influence of walls indirectly, based on parameters that 'measure' this proximity. Examples are the turbulence Reynolds number, k(exp 2)/(nu x epsilon), and various dot products of gradients such as (delta tau/delta x(sub j))(delta k/delta x(sub j)) where tau = k/epsilon, the turbulence time scale. Adhering to this modeling practice retains full generality of the model, since the entire formulation is local. Thus wall-distance-free models are tensorially invariant and frame-indifferent, applicable to arbitrary topologies and moving boundaries. They are also usable in conjunction with solvers based on either unstructured or structured book-keeping, executed on any computer architecture, including massively parallel processors. This paper illustrates the pointwise approach to turbulence modeling by introducing several such models of both linear and nonlinear types, and by demonstrating their performance in 2D and 3D flow eases., 資料番号: AA0063609008, レポート番号: JAXA-SP-06-029E

SST-CFD Workshop. International CFD Workshops for Super-sonic Transport Design 航空宇宙技術研究所 19980316-19980317 東京 日本, SST-CFD Workshop. International CFD Workshops for Super-sonic Transport Design National Aerospace Laboratory 19980316-19980317 Tokyo Japan, 資料番号: AA0063609007, レポート番号: JAXA-SP-06-029E

Behavior of the fine sediment around vegetation is still unknown because knowledge of complex flow around vegetation is limited. Moreover, only limited research has been done on flow resistance and fine sediment transport inof open channel flow wherewith vegetation that considers a growth type, which includinge emergent plants, submerged plants, and land plants, etc., has been considered are hardly researched. This study considered the growth type of vegetation and analyzed the flow of water with vegetation that considers a growth type of vegetation by using laboratory experiments that includeds various methods such as LDV and numerical simulations employing turbulence model. For emergent plants, it was found that the lateral momentum of transport reachedtakes a peak value at a certain vegetation density which wasis much larger than the density of the actual reed field, and the cause of this wascause related greatly to the shape of the horizontal vortex. WhenFor the case in which the ratio of a vegetation group's length to width wasis nearly 1:.7, the horizontal eddies were generated at the boundary of the vegetation group's region, and the momentum of transport reachedtakes a peak value. A numerical computation employing SDS&2DH turbulence models was introduced to investigate the resistance and the roles of the surface and submerged vegetation layers, and the effect of generated turbulence. Theseis models allowed us tocan predict the mean velocity of the surface and submerged vegetation layers, and provided information on the shapes of vortices, lateral distributions of the depth averaged flow velocity, and turbulence statistics. A phenomenon involving wavy motion of very flexible submerged vegetation (termed honami) was observed, and the displacement of the plants was found to be closely associated with the structure of the turbulent flow, which yieldeds a larger Reynolds stress near the top of the vegetation layer. Finally these experiments and simulations applyied to the development of methods for catching fine sediment method for the wetland conservation.

Development of vorticity family and the role of its family members to the flow phenomena and structures are discussed., 資料番号: AA0063156017, レポート番号: JAXA-SP-06-013

An advanced Large Eddy Simulation (LES) technique with high accuracy and resolution is proposed with the Approximated Deconvolution Method approach, 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 capture the laminar to turbulent transition phenomena in the order of Reynolds number of 106. 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 eN method and discussed., 資料番号: AA0063156020, レポート番号: JAXA-SP-06-013

An experiment was made in the wake behind a strip of screen in the uniform flow. The wake was excited by various kinds of sound introduced from a loudspeaker. One purpose is to compare the turbulent wakes created by various sounds. The close similarity was found. Another accomplishment is the quantitative expression of randomness of randomizing wakes. The random components in the randomizing process were also clarified., 資料番号: AA0063156016, レポート番号: JAXA-SP-06-013

To obtain a better understanding of the mechanism for supersonic boundary layer transition, experiments are made at Mach number 2.0 by using a small supersonic wind-tunnel, with focusing efforts on finding non-linear disturbances governing the transition. We examine a boundary layer along the nozzle wall and its transition process by means of quantitative schlieren optical system. It is found that vortical structures our schlieren system visualizes are mostly similar to each other in shape, being stick-like and inclined at about 30 to 70 degrees to the wall, and start to grow often forming a group at streamwise stations where the momentum thickness Reynolds number is around 580 and the transition proceeds as they increase in number to cover the whole boundary layer. We examine the statistical feature of such oblique vortical structures using 1,800 samples and show that these structures are important non-linear disturbances as the mechanism of supersonic boundary layer transition., 資料番号: AA0063156009, レポート番号: JAXA-SP-06-013

Phased-Array Microphone system has been developed at 2 m x 2 m Low-speed Wind Tunnel (LWT2) of JAXA. As a function checkout of the system, NACA0012 airfoil was tested. The results of this test were observed distinctly the noise generated near or on the trailing edge. In this paper, the outline of the results is reported., 資料番号: AA0063156011, レポート番号: JAXA-SP-06-013

Inhomogeneous turbulence is studied statistically using the cross-independence closure hypothesis for the equations of multi-point velocity distributions. First, the turbulent velocity field is decomposed into the mean flow and turbulent fluctuation around the mean. The equations for the mean velocity and the distributions of turbulent velocity are derived. These equations are closed by applying the cross-independence closure hypothesis which has been successfully used for homogeneous turbulence (Tatsumi & Yoshimura, 2004, 2006). The closed equations are obtained for the mean velocity and the one- and two-point velocity distributions. At large Reynolds numbers, these equations are shown to give the inertial normal velocity distributions in the outer range and the non-normal velocity distributions in the local range respectively., 資料番号: AA0063156015, レポート番号: JAXA-SP-06-013

Streamwise interfaces between laminar and turbulent regions in a flat-plate boundary layer are investigated using a rake of single hotwire probes. Two pieces of piezo-ceramic actuators are used to generate trapezoidal shaped turbulent regions, which have a wide leading edge in the spanwise direction. Its aim is to eliminate the contamination between the side interfaces and the downstream interface that are unavoidable in turbulent spot experiments. Experimental results show that a turbulent region has a sharp leading edge and a gradual trailing edge. It is shown that when a turbulent region passes by, the RMS (Root Mean Square) value remains high for a while although there is little disturbance remaining. It is also shown that inside this region, known as the calmed region, because the flow returns laminar away from the wall, the turbulent flow near the wall is accelerated, which may be causing the inverse-transition., 資料番号: AA0063156021, 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

We perform numerical simulations of the radial circulation of the dust in weak turbulent protoplanetary disks, taking the effect of radiation pressure of the central star and puffed-up inner rim of the disk into account. We confirm that the following dust circulation mechanism will be realized: at the inner edge of the disk, the infalling dust aggregates partially evaporate and break up into fine grains, which are stirred up to the upper irradiated region by magnetorotational instability and are blown outward by the radiation pressure. Most of the blowing grains reenter into the disk within approximately 1 AU and settle to the midplane, joining inwardly-migrating dust aggregates. We find that in the shadowed region of the disk the outflow mass flux in the surface layer is comparable to the inflow mass flux in the disk interior. Dust circulation occurs efficient in the shadowed region if the turbulent intensity in the innermost region of the disk and the stellar luminosity are sufficient higher. In a steady state, the surface density distribution of the dust is enhanced by dust circulation in the inner shadowed region. Therefore, the enhanced abundance of the dust may cause gravitational instability for planetesimal formation., 資料番号: AA0063350034

LOX/LH2 subscale rocket nozzle flow fields are computationally simulated using three-dimensional compressible Navier-Stokes equations. The area ratio of the nozzle is 140 and film coolant hydrogen gases are injected from 30 film cooling holes which are distributed circumferentially at the area ratio of 13. The experimental nozzle throat Reynolds number indicates that the boundary layer of the nozzle is in its transition region as the size of the nozzle is small. Both the turbulent and laminar computations are carried out to investigate the effect of the boundary layer conditions to the nozzle performance. The computed results show that the structure of the separated flow down stream of the film cooling injection significantly changes between the turbulent and laminar conditions. Since clear difference in performance between the laminar and turbulent conditions are also shown, the computed result confirms that the experiment boundary layer condition is in its transition region. The nozzle wall temperature also influences the nozzle performance and the computed nozzle performance shows rather laminar flow performance when the film coolant temperature and the nozzle wall temperatures are set to be close., 資料番号: AA0049212035, レポート番号: JAXA-SP-05-017

The SST (Shear-Stress Transport) turbulence model has been implemented in UPACS, a CFD platform developed in JAXA. Four test cases with increasing level of difficulty were used to validate the present implementation. Three basic test cases included flat plate, backward-facing step, and transonic airfoil RAE2822. For more practical application, the flow simulation around the DLR-F6 transport aircraft was performed. Validations were carried out by comparing the present numerical results with those of other numerical methods and experimental method. Numerical results obtained from the computations above show that the present implementation is valid. We believe that this effort has extended UPACS's applicability to more complicated flow fields., 資料番号: AA0049212001, レポート番号: JAXA-SP-05-017

Two methods of numerical solution of an elastic beam performing large bending oscillation together with LES simulation of both air and canopy flows have been proposed, Transition professes to turbulence through the K-H type shear flow instability mechanism are analyzed using 3D bird's eye view of the flow field. Turbulent canopy flows are shown to have a multiple structure consisted of the longitudinal vortices common to wall turbulence and lateral vortices accompanied by low pressure zones, which supply energy to the former by elongation of vortices. Prevalence of sweeping motion in canopy flow is shown. 3D structure of the so-called micro-front characterizing canopy flow is composed of vertical curtains extending downstream., 資料番号: AA0049208007, レポート番号: JAXA-SP-05-012

In this paper we attempted to develop a low-noise 'Active Turbulence Generator (ATG)' for aerodynamic noise measurement in a large scale turbulent flow field. The aerodynamic noise from the developed ATG was only 10 dB larger than that of the conventional wind tunnel. Aerodynamic noise from a rearview mirror was measured to estimate sound generation effect on turbulence intensity. The experimental result showed that the edge tone of the rearview mirror was disappeared in the case of strong turbulent flow field. Aerodynamic noises strongly depend on the turbulence intensity and eddy scale of incoming flow. The turbulence of incoming flow is important parameter to estimate flow around real cars. The active turbulence generator is one of the useful devices to simulate real road simulations in wind tunnels., 資料番号: AA0049208017, レポート番号: JAXA-SP-05-012

Breakdown process of the Klebanoff mode and origin of turbulence are experimentally investigated in detail. An acoustic excitation using a 2D roughness attached on the wall are used for T-S wave generation. Piezo-ceramic actuators are used to introduce the Klebanoff mode fluctuation. It is found that another shear layer, in which the spike phenomenon takes place and the turbulence starts, exists between the Lambda structures aligned in rows. The spreading of the turbulence along the shear layer induced by the Lambda structures is newly found., 資料番号: AA0049208011, レポート番号: JAXA-SP-05-012

The present experiment focused on revealing effect of scales and directional components of free stream turbulence on boundary layer transition, especially the growth rate of the disturbance energy in the streamwise direction. Free stream turbulence generated by a turbulence grid mounted upstream of the contraction has typical character of axisymmetric turbulence with strong anisotropy. The experimental results with the anisotropic free stream turbulence show the non-modal growth disturbance even at 0.7 percent turbulence intensity. The correlation between the filtered free stream fluctuation and growth rate of the disturbance suggests that the wall-normal velocity fluctuation in the free stream dominates the disturbance growth., 資料番号: AA0049208004, レポート番号: JAXA-SP-05-012

We tried to generate quasi-isotropic homogeneous turbulence fields with high Reynolds numbers in the multi-fan wind tunnel. The fans making flow and counter flow were arranged like a checkered pattern and they were driven by a fluctuating signal transformed from continuous spectra with - 5/3 slope, The Reynolds number of the resultant turbulence fields ranged from 330 to 560. The turbulence fields realized in the multi-fan wind tunnel are expected to be very useful to study high Reynolds number turbulence, though their uniformity and isotropy were not so good., 資料番号: AA0049208023, レポート番号: JAXA-SP-05-012

Kites are the most popular toy in the world. In Japan people enjoy carps swimming in the fragrant May wind. They belong to the same family from the fluid dynamical viewpoint. We have made wind-tunnel experiments on the performance of carp model. As a simplified model we chose straight round hollow cylinder of various size and weight. If a model is light enough, it floats in the flow by a single support thread attached to the mouth. Obviously, the lift force acting on the cylinder supports the model. If a model us heavy, it start violent oscillations. The reason for the oscillation seems to be due to the stall of cylinder wing. Models of carps suspended in the wind tunnel show similar performance. The best way in realizing a stable swimming is the choice of connecting corps to a rod., 資料番号: AA0049208022, レポート番号: JAXA-SP-05-012

中立に近い安定度の大気境界層における乱流の構造を潮岬風力実験所と信楽MU観測所において観測した結果を解析した。時間スケール200 秒程度の比較的大きな強風域の構造による運動量輸送への寄与は平均値に比べて2倍程度まで大きい。地表近くでの運動量輸送への寄与は100 秒程度のスケールの乱流変動によるものが大きく，また，イジェクション（低速流の上昇運動）よりもスウィープ（高速流の下降運動）の乱流運動による運動量輸送の方がやや寄与が大きい場合が見られる。そして，これらのことと強風域の構造との関連が示唆される。, Turbulent structures in the nearly neutral planetary boundary layer observed at Shionomisaki Wind Effect Laboratory and Shigaraki MU Observatory is analyzed. Structures of high wind speed with larger time scale (about 200s.) make large contribution to momentum transfer which is up to about 2 times of average values. Near the surface large contribution to momentum transfer by turbulent fluctuations with time scale of about 100s. Is shown. The sweep turbulent motion (downward high speed motion) may dominate the ejection motion (upward low speed motion) for the momentum transfer. Some relation of these results to the structures of high wind speed is suggested.

一定の位相速度で進行する風波上の気流に3次元直接数値計算を適用することにより，気流の乱流特性を調べた。7種類の波齢（ c /u* =0, 4, 8, 10, 12, 16 and 20）で，それぞれについて乱流が統計的に定常状態になるまで計算した。その結果，気流及び乱流の挙動に強い波齢依存性が見られた。また，波によりゆがまされた流れは，臨界高さ近傍で大きく変化した。その結果，波の発達率と強い関係がある波による運動量フラックス(wave-induced momentum flux)は臨界高さより低い場所では正，高い場所では負となることがわかった。, Characteristics of the airflow over a train of waves moving at a constant speed are investigated using a direct numerical simulation. We simulate the flow for various wave ages ( c /u* =0, 4, 8, 10, 12, 16 and 20), where c is the phase speed of the wind wave and u* is the friction velocity on the wave surface. The results show that both the mean flow profiles and the turbulent statistics depend strongly on the wave age. For example, the mean-flow speed in the log layer generally decreases at small wave ages, I. E., when the wave growth rate is positive. Vertical profiles of the flow change significantly at the critical height zc , where the mean flow speed and the wave speed c agree. Then, the wave-induced vertical flux of the horizontal momentum is positive below zc , decreases rapidly near zc , and becomes negative above zc .

Direct numerical simulation of a fully developed turbulent channel flow has been carried out using Numerical Simulator 3 at JAXA. The Reynolds number is set to be Re(sub tau) = 1,020 where Re(sub tau) is the Reynolds number based on the friction velocity and the channel half width. It is known that this is one of the largest computations ever simulated in conjunction with this configuration, where about 1.4 billion grid points are required. In the present study, to perform large-scale DNS more efficiently, the parallelized computational program has been modified, and its computational performance is presented., 資料番号: AA0048469003, レポート番号: JAXA-SP-04-012

Detached-Eddy Simulation is applied to three airfoils with different stall types. The method combines the strong points of Reynolds-averaged Navier-Stokes and Large Eddy Simulation approaches. Spalart-Allmaras Model is basically used, which reduces to a RANS formulation near a solid surface and to a subgrid model away from the wall. LU-SGS implicit scheme is employed to solve the model in time. Compared with experiment data, it is found that stall angle can be reasonably predicted by the present method., 資料番号: AA0048469012, レポート番号: JAXA-SP-04-012

Some trials to detect fine-scale coherent vortices in turbulence are presented in the present paper. The simplest method is a conditional measurement using an X-probe. Various turbulence fields at R(sub lambda) = 19 to 2,300 could be measured by this method and the Reynolds number dependences of the characteristics of the fine-scale coherent vortex were obtained. But, such data showed an error caused by the third velocity component unmeasured. So employed was a double-X probe that can measure three components of instantaneous velocity fluctuation. The resultant data showed that the fine-scale coherent vortex was slightly different, from the Burgers' vortex. Also examined was the array of X-probe that can measure instantaneous 2-D velocity profiles. Though it is in progress of such experiments, the primary results showed the validity of the conditional measurement using single X-probe., 資料番号: AA0047776006, レポート番号: JAXA-SP-04-002

資料番号: AA0047901015

安定度が中立に近い大気境界層における乱流の構造について，その境界層全層にわたる空間構造を信楽MU 観測所において観測した。大気境界層下層においては，風上方向に傾いた強風域の構造が地表へ向かって下降してきている。また，比較的大きな時間スケールの乱流構造は，鉛直方向にかなりの拡がりを持っている。, Spatial turbulent structures for the whole layer in the nearly neutral planetary boundary layer areobserved at Shigaraki MU Observatory. In the lower boundary layer, upwind tilting structures of high-speedarea are approaching to the surface. The turbulent structures with larger time scale have considerably largevertical extent.

Direct numerical simulation of a fully developed turbulent channel flow has been carried out using new NS system at NAL. The Reynolds numbers are set to be Re(sub tau) = 180 and 1,020, where Re(sub tau) is the Reynolds number based on the friction velocity and the channel half width. To the present knowledge, DNS for Re(sub tau) = 1,020 is one of the largest computations ever simulated in conjunction with this configuration, where about 1.4 billion grid points are required to resolve all the eddies. In the present study, the Reynolds-number dependence on turbulence statistics is investigated up to Re(sub tau) = 1,020. Moreover, turbulence structures for Re(sub tau) = 1,020 are visualized in order to examine the characteristics of quasi-coherent structures such as high and low-speed streaks and vortices., 資料番号: AA0047427010, レポート番号: JAXA-SP-03-002