Takashi Aoyama

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

<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>

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

<p>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.</p>

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.

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 "FaSTAR" 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.

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.

Focus boom emanating from a supersonic flight vehicle is analysed in this paper. A focus boom or the focusing of a sonic boom, occurs when a vehicle with a supersonic speed accelerates or maneuvers, which can be modeled by nonlinear Tricomi equation(NTE). In this paper, we solve NTE by splitting it into two equations in order to deal correctly with refraction and nonlinearity, respectively.