青山 剛史

第51回流体力学講演会/第37回航空宇宙数値シミュレーション技術シンポジウム (2019年7月1日-3日. 早稲田大学早稲田キャンパス国際会議場), 新宿区, 東京 51st Fluid Dynamics Conference / the 37th Aerospace Numerical Simulation Symposium (July 1-3, 2019. International Conference Center, Waseda University), Shinjuku-ku, Tokyo, Japan A CFD solver “FaSTAR-Move” that enables analysis around moving and deformed objects have been developed by JAXA, and was applied to the analysis of separation of mounted objects, etc. Currently, the rotorcraft analysis module has been added to FaSTAR-Move in order to meet industrial needsdemands for the rotorcraft analysis . In this paper, comparisons and validations of the developed module with experiments of hovering rotor are performed and it is shown that reasonable results are obtained. 形態: カラー図版あり Physical characteristics: Original contains color illustrations 資料番号: AA1930011017 レポート番号: JAXA-SP-19-007

第49回流体力学講演会/第35回航空宇宙数値シミュレーション技術シンポジウム (2017年6月28日-38日. 国際オリンピック記念青少年総合センター), 渋谷区, 東京 49th Fluid Dynamics Conference /the 35th Aerospace Numerical Simulation Symposium (June 28-30, 2017. National Olympics Memorial Youth Center), Shibuya-ku, Tokyo, Japan The wake behind a wind turbine can decrease the power generated by wind turbine farther downstream because tip vortices impedes recovery of velocity inside the wind turbine wake. From the viewpoint of cost effectiveness, collective installations of wind turbines are desired to reduce costs for maintenance and power transmission lines. However, the interference of wake makes it difficult to implement collective installations. This paper discusses about the characteristics of tip vortex in wind turbine wake via the use of Computational Fluid Dynamics (CFD), focusing on the dependency of tip speed ratio (TSR). TSR is an operational parameter of wind turbine and defined as the ratio of tip speed to inflow speed. It is important to assess the influence of TSR to the wake structure because it often changes in an operational wind turbine. In this work, CFD solver rFlow3D is used for capturing the characteristics of vortices and the velocity distributions in wind turbine wake. The CFD results are validated by comparing with the Model Experiments in Controlled Conditions (MEXICO) experiments. The tip vortices in wake region are clearly visualized, then it is found that TSR can change the distribution of vortices and the timing of vortex breakdown, which influences the velocity recovery in wake region. 形態: カラー図版あり Physical characteristics: Original contains color illustrations 資料番号: AA1730011008 レポート番号: JAXA-SP-17-004

第49回流体力学講演会/第35回航空宇宙数値シミュレーション技術シンポジウム (2017年6月28日-37日. 国際オリンピック記念青少年総合センター), 渋谷区, 東京 49th Fluid Dynamics Conference /the 35th Aerospace Numerical Simulation Symposium (June 28-30, 2017. National Olympics Memorial Youth Center), Shibuya-ku, Tokyo, Japan The purpose of this study is to understand the effect of release frequency of tip vortices which are shed from blade tips on a wind turbine wake. In wind farms, wind turbines are installed collectively and that results in a reduction of power generation. This problem requires proper designs of wind farms and knowledge about a wind turbine wake. Recent studies have revealed that tip vortices have a strong influence on wind turbine wakes. In this study, wakes from Mie University wind turbine of varying operating conditions are calculated by using Computational Fluid Dynamics (CFD), and energy transitions in the wind turbine wakes are examined. In the calculations, release frequencies of tip vortices are changed by changing tip speed ratio and the number of blades. The CFD results show the same trend of kinetic energy transition when the vortex release frequency is close. And the CFD results also show that when vortex release frequency becomes higher, a minimum value of energy becomes smaller and energy recovery rate becomes larger. This tendency is considered to be caused by the fact that when the frequency becomes higher, the interval between the vortices becomes narrower and the barrier effect which restrains momentum exchange between a wake and a mainstream becomes greater. 形態: カラー図版あり Physical characteristics: Original contains color illustrations 資料番号: AA1730011007 レポート番号: JAXA-SP-17-004

© 2017 by American Helicopter Society International, Inc. All rights reserved. Aerodynamic characteristics of a small-scale concept model of a compound helicopter are examined. Experiments are carried out with the side propellers and the pusher propeller without the main rotor. Influences of aerodynamic interactions of the fuselage, the main wing and the propellers are examined using various configurations. Results shows that the wake of the side propellers increases the thrust of the pusher propeller and the lift force on the main wing. The pusher propeller does not affect the aerodynamic characteristics of the airframe and the side propellers significantly.

© 2017 by the American Helicopter Society International, Inc. All rights reserved. Influences of the walls on the performance of the multiple rotor type drones are numerically simulated. With current wide spreading applications of the autonomously flyable UAVs, there are potential needs to use the drones for inspections and observation near various structures, such as buildings and bridges. The flowfields around multiple rotors are significantly influenced with the existence of an upper or a side wall, so that the thrust and required torque and other forces and moments are changed. It is found that when a rotor is approaching an upper wall, as the distance between the rotor and the upper wall is less than a diameter of the rotor, the thrust suddenly increases that causes the rotors to collide onto the upper wall. When an isolated rotor is operated near a side wall, the thrust decreases and a rolling moment appears to tilt the rotor toward the wall as the distance becomes shorter. For a multiple rotor drone near a side wall, the rotors have different distances from the wall, which causes the whole aircraft tilts toward the wall. From a view of safety operations, the multi-rotor drone should be kept away from both the upper wall and the side wall at least 1.5 times of the rotor diameter to prevent unexpected motions of the aircraft caused by the wall during hovering flight.

<p>The computational grid dependency is an important problem for CFD. We have computed aerodynamics on NASA-Common Research Model (CRM) with FaSTAR and various grids to investigate the grid dependency. We employed four grids: two Cartesian-based unstructured grids, a tetrahedral unstructured grid, and a hexahedral structured grid. The computational conditions are based on the test cases of Aerodynamics Prediction Challenge (APC). First, the grid convergence at a fixed angle of attack and the trend of an angle-of-attack sweep are compared between the four grids. The lift coefficients computed with the two similar Cartesian-based grids are different, and this is caused by the grid difference around the leading edge. However, the overall trend of angle-of-attack sweep is almost same between the four grids. Next, we computed aerodynamics on NASA-CRM with a support device to investigate the support interference. It is found that the support interference on the drag and pitching moment is large and should be considered.</p>

<p>Summary of Second Aerodynamics Prediction Challenge (APC-II) is presented. The APC-II is a domestic CFD prediction workshop that was held on July 6, 2016. The test cases include aerodynamic prediction of NASA-CRM with and without support effects, and buffet prediction. We compare the CFD results with JAXA's wind tunnel measurements. There are 9 participants from national research agency, academia, industry, and commercial software vendor. The CFD results submitted from the participants are compared and discussed in the presentation.</p>

<p>これまでに開催された米国，欧州，日本のCFD（Computational Fluid Dynamics）ワークショップについて振り返り，各国のワークショップの特徴を述べ，開催することで得られるメリットを整理する．次に，今回開催したCFD ワークショップ「Aerodynamics Prediction Challenge（APC）」の開催趣旨，概要について述べる．最後に，今後の展望について述べる．</p>

第48回流体力学講演会/第34回航空宇宙数値シミュレーション技術シンポジウム (2016年7月6日-8日. 金沢歌劇座), 金沢市, 石川 48th Fluid Dynamics Conference /the 34th Aerospace Numerical Simulation Symposium (July 6-8, 2016. The Kanazawa Theatre), Kanazawa, Ishikawa, Japan Aerodynamic interactions between 6 rotors on a multi-copter type drone are numerically simulated. The pitch angle of the rotor blades and the distance between the rotors are varied. It is found that 2-6/rev fluctuations in the resultant forces and moments are significant due to the interactions between these 6 rotors. These oscillating forces and moments are considered to be the main sources of vibrations on the multi-copter type drone. The thrust of the drone is controlled by change of the rotor pitch and the fluctuations change in nearly same proportion with the resultant thrust. When the distance between the rotor is below half of the rotor radius, the intensity of the interaction increases abruptly to about 3 times while the rotor performance improves about 20% compared with the wide rotor distance cases. 形態: カラー図版あり Physical characteristics: Original contains color illustrations 資料番号: AA1630031017 レポート番号: JAXA-SP-16-007

&lt;p&gt;Aerodynamic interaction between 6 rotors on a multi-copter type drone is numerically simulated. Variable pitch controlled rotors are modelled. It is found that 6/rev fluctuations in the resultant forces and moments are significant due to the interactions between these 6 rotors. These oscillating forces and moments are considered to be the main sources of vibrations on the multi-copter type drone. The thrust of the drone is controlled by change of the rotor pitch and the fluctuations change in nearly same proportion with the resultant thrust.&lt;/p&gt;

Aerodynamic interactions between multiple rotors on so-called multi-copter UAVs are simulated. The multicopter UAVs have seen a very rapid and wide spread of applications recently and been mainly used as visual recording platforms. Severe vibrations are often encountered so that gimbal-stabilized camera bases are required. One of the main sources of vibrations is found due to the aerodynamic interactions between the rotors even during hovering flights. A CFD code, rFlow3D, developed in JAXA has been extended to handle multiple rotors. A variable pitch angle controlled hexa-copter is considered with the variation of distance between rotors. The relationship between the oscillatory aerodynamic forces and the rotor distance is investigated. It is found that when the rotor distance is less than half of the rotor radius, the oscillation increases rapidly to nearly 2 times while the rotor performance improves about 10%.

An Individual Pitch Control (IPC) system to reduce the yawing and tilting moments on the hub of Horizontal Axis Wind Turbines (HAWTs) in Atmospheric Boundary Layer (ABL) is constructed and a trim routine is numerically simulated to check the effectiveness of the system. With 1/rev cyclic pitch control, it is found that for a three-bladed turbine, the averages can be trimmed to nearly zero while the 3/rev fluctuations cannot be effectively reduced. However, for a two-bladed turbine, the averaged moments can be reduced to nearly zero, and furthermore, the load fluctuations on rotor hub can also be significantly reduced. For both type of HAWTs, the oscillations of flapwise bending moment on the blade root can be remarkably reduced when IPC is applied.

This paper reports the results from the initial flight tests of a compound model helicopter by Japan Aerospace Exploration Agency. Technologies for high speed helicopter has been developed since the maximum flight speed of a conventional helicopter is relatively low compared to the fixed wing aircraft. In this study, compound helicopter is selected for the high speed helicopter since its hovering capability is higher than other high speed rotorcraft configurations such as tilt-rotor or tilt-wing. As a result, the model compound helicopter achieves stable flight and its flying ability is confirmed. From the remote controller pilot, the following comment is obtained; the control resembles to the fixed wing aircraft in high speed flight. On the other hand, from the flight data, it is found that the compound helicopter is easy to maintain the horizontal attitude and the attitude disturbance is slight, though its maximum flight speed was lower than the conventional helicopter during the initial flight tests.

It is effective to estimate the rotor performance of large scale wind turbines such as 10 MW-class wind turbines using Computational Fluid Dynamics (CFD), since it is necessary to capture complex flow fields in order to estimate the performance precisely. The CFD analysis targeted small scale wind turbines has been conducted and the results are consistent with those of wind tunnel tests. When applying the analysis conditions used in the CFD analysis of small scale wind turbines to that of large scale wind turbines, the effect caused by the difference of Reynolds number should be considered. In this study, we executed CFD analysis targeted 10 MW-class wind turbine with the analysis conditions used in the analysis of small scale wind turbines, then we validated the applicability of the analysis conditions through the comparison of the results between CFD and Blade Element Momentum Theory (BEM). Consequently, the stability of CFD analysis using analysis conditions of small scale wind turbines and the possibility of capturing the properties of complex flow fields using CFD are shown.

A CFD/CSD coupling analysis code rFlow3D, developed in Japan Aerospace Exploration Agency (JAXA) originally for rotorcraft, has been applied to predict the airflows around horizontal axis wind turbines (HAWTs) and validated with existing experimental data. It is used to simulate the flowfield around HAWTs in realistic complex operating conditions, such as yawed wind, atmospheric boundary layer inflow, rotor/tower interaction, and in the wake of an upstream HAWT. This paper will describe the results of the simulations for these representative complex flowfield around HAWTs.

To decrease blade mass for effectively reducing construction costs, the application of slender blades or two-bladed rotors to 10 MW-class wind turbines is proposed. Since few wind turbine designs have adopted this approach, it is important to investigate the effects of applying slender blades and two-bladed rotors. Considering this possibility and the relationship between the flow characteristics around the blade and the Reynolds number, it is useful to implement an aerodynamic analysis on actual-scale wind turbines using computational simulations such as blade element momentum (BEM) theory and computational fluid dynamics (CFD). In this study, we executed an aerodynamic analysis of two- and three-bladed 10 MW reference wind turbines proposed by the New Energy and Industrial Technology Development Organization. For the aerodynamic analysis, we used the fast CFD solver FaST Aerodynamic Routines (FaSTAR), which was developed by the Japan Aerospace Exploration Agency. First, we validated and confirmed rotor performance by comparing with the results obtained using BEM theory. The power and thrust coefficients (C P and C T ) obtained by FaSTAR are generally in agreement with those obtained using BEM theory. These results suggest that rotor performance can be captured correctly by FaSTAR. Furthermore, the 3D effects caused by flow separation are seen only in FaSTAR. Regarding the difference in the number of blades, the values of C P and C T for the two-bladed rotor change more gradually than those for the three-bladed rotor. Moreover, the 3D effects around the root in two-bladed rotors are more significant than those in three-bladed rotors.

Although CFD tools are necessary for aerodynamic design, it is still time consuming and this is one of the big problems. In order to shorten the computational time, a fast CFD code &quot;FaSTAR&quot; has been developed. We combined two acceleration techniques. One is a convergence acceleration technique such as the multigrid method. A coarse-grid generation method using octree data of the Cartesian grid is proposed. This method is simple and it can generate high-quality coarse grids. The other is a programing technique such as data structure improvement and performance tuning. We demonstrate the high-speed performance of the code for aerodynamic computation of a standard aircraft model, NASA-CRM. The computational time is less than one hour using 10 million cells and 100 CPU cores. It is found that the multigrid method is beneficial for large-scale problems.

To shorten the time to simulate fluid flows, we develop a fast automatic grid-generation tool, HexaGrid, that produces Cartesian grids with body-fitted layers. The objective of the present study is to apply automatic grid generation to the drag prediction of the NASA Common Research Model. First, we generate a grid following the 4th Drag Prediction Workshop gridding guidelines as far as possible and discuss the capabilities and limitations of the automatic method. Then, we validate the computational-fluid-dynamics results computed with the grid by comparison with other solvers and grid generators. The HexaGrid results agree well with the other results, with the differences in predicted drag being less than five counts except at the stall angle. Additionally, we compare separated flows at the stall angle. The separation lines and C-p distribution are found to be greatly affected by grid topology.

A study group of future rotorcraft is formed in JAXA with participants from a wide spectra of organizations in Japan. Taking the helicopter market in Japan as a study case, four potential high speed rotorcraft (VTOL aircraft) missions are discussed. When a capability of hovering is required, compound helicopter is concluded as the most suitable design configuration. A simplified conceptual design process for a compound helicopter is described where a wing and propellers are added to a single rotor helicopter. A compound helicopter concept for high speed EMS (Emergency Medical Service) is proposed. The result of the conceptual design is compared with a conventional helicopter and the cost expense is illustrated. If also considering the cost to maintain a base hospital, a high speed rotorcraft with significant higher cost is acceptable which covers a much wider area providing effective first aid to critical patients.

Numerical simulations based on NREL (National Renewable Energy Laboratory) Phase VI and MEXICO (Model Experiment in Controlled Conditions) experiments using rFlow3D CFD code are conducted. The rFlow3D code is a multi-disciplinary analysis tool of flow-structure coupling, trim analysis, and noise prediction for rotorcraft developed at Japan Aerospace Exploration Agency. In this study, the numerical computation based on NREL Phase VI experiment with SA turbulence model is conducted to validate the accuracy of performance prediction of the horizontal axis wind turbines. Additionally, numerical computation for MEXICO experiment with a Navier-Stokes (NS) flow solver is conducted to confirm the ability of rFlow3D to predict the wake structure. The NREL Phase VI computational results indicate that the utilization of turbulence model improves the performance prediction in fully separated flow conditions. Meanwhile, MEXICO computation results show the solver can accurately predict the vortex structure and the axial velocity deficit in the wake. Copyright© 2014 by the American Helicopter Society International, Inc. All rights reserved.

本稿ではソニックブーム推算法としてJAXAが開発を進めている,近傍場圧力波形推算手法,中間場音響伝搬解析手法,近傍場/中間場マッチング手法,ソニックブーム強度評価手法について解説している.近傍場圧力波形推算手法としては,解析Fidelityや複雑形状への対応に難があるものの低ソニックブーム設計に有用なPanair+Aging補正法と,解析Fidelity,複雑形状対応ともに優れたUPACS/TAS重合格子法とHexaGrid/FaSTAR適用について紹介する.中間場音響伝搬解析手法としては,従来のThomas法と同等の機能に加え,熱粘性および分子振動緩和効果を考慮できる拡張Burgers方程式ベースの伝搬解析ツールXnoiseについて紹介している.近傍場/中間場マッチング手法としては,CFD解析で機体近傍場における周方向の格子密度が粗くなる課題を解決する方法としてMultipole Analysisを採用している.Xnoiseにより推算されたソニックブーム圧力波形は,ソニックブーム強度評価ツールBoomMetreにより各種メトリックによる評価ができる.

超音速飛翔体が加速やマニューバを行う場合,フォーカスブームと呼ばれる通常のソニックブームよりも数倍強いブームが発生することが知られており,フォーカスブームによる圧力上昇の予測が重要視されるようになってきた.本稿では,フォーカスブームのモデル方程式であるNonlinear Tricomi Equationの解析プログラムを実装し,実験結果と比較することでその妥当性について検討する.