大山 聖

The Mach number effect on the riblets’ drag reduction performance in turbulent transitional flow regimes is investigated by direct numerical simulations. We focus on the transitional flow occurred by the Tollmien-Schlichting instability. For freestream Mach numbers of 0.2,0.6and 0.85, it is found that the riblets reduce the frictional drag in the turbulent flow region independently of the Mach number, while they tend to increase it in the transitional flow regions. Interestingly, the rate of the drag reduction in the turbulent region decreased with increasing the Mach number. This is because the non-dimensional groove width in the turbulent region changes as the Mach number changes. In other words, the relation between the groove width of the riblets and the size of the longitudinal vortices in the turbulent flow changes as the Mach number changes. The turbulent kinetic energy spectrum in the turbulent region supports these results. The difference in the spectrum between the smooth and riblet surfaces became smaller as the Mach number increased, indicating that the flow structure changes as the Mach number changes. From these results, it is recommended that for high-speed vehicles such as transonic aircraft, riblets be designed in compressible flow rather than incompressible flow.

In this study, direct numerical simulations are conducted to reveal the optimal groove width of the riblet at the mainstream Mach number ! = . , the typical cruise speed of a transonic aircraft. Additionally, the study aims to clarify the effect of Mach number on the drag change ratio by comparing it with the incompressible flow condition, ! = . . The results at ! = . show that the lowest drag change ratio, around − %, is observed at " =, and . As for the Mach number effect, the drag change ratio is smaller in the case of ! = . than in the case of ! = . for the same non-dimension groove width ". This is because the drag reduction amount with increasing Mach number is larger on the riblet surface than on the smooth surface since the ejection and sweep intensities on the riblet surface decrease more with increasing Mach number than on the smooth surface. It is also found that the robustness of the drag reduction effect against the change in " is improved for ! = . compared to ! = . .

Pit craters on Mars are assumed to be used as manned exploration bases and it is highly possible that life signature would be discovered there since its temperature is appropriate and it is less affected by radiation. Regarding pit crater exploration, helicopter which can climb and descend quickly is expected to be utilized. This paper introduces blade shape optimization of Mars helicopter exploring pit craters. Definition of a mission, selection of aircraft types, conceptual design, optimization of blade twist angle and airfoil, and rotor test are conducted. As a result, hexa-rotor which has robustness, resistance to gust, and fault tolerance is proposed. Moreover, it is confirmed that the mission can be accomplished, carrying instruments on the helicopter within payload weight. Hovering performance of the helicopter is improved by optimizing blade twisting angle and airfoil. And it is found that there is a good correlation between experiment and numerical simulation with respect to the helicopter's hovering performance.

The methods that measure the turbulence statistics distribution of high-speed flow with high spatial resolution using particle-image-velocimetry images are proposed, and their performances are verified. Two methods are proposed, and the problems caused by blurring the particle shape due to the high-speed movements are resolved. While the conventional method approximates the unique particle shapes with a circular distribution for image pairs, the first proposed method approximates the different particle shapes with an ellipse for first and second images of pairs and reduces the effects of the blur in the flow direction of the particles. Meanwhile, the second proposed method treats the general particle shapes such as the blur of temporally changing laser intensity and adopts the deconvolution analysis using a Fourier transform. Synthetic particle images were created and a supersonic jet test was performed, and the proposed methods were evaluated to be superior to the previous method for the estimation of turbulent fluctuation using those data.

<title>Abstract</title> A fixed-wing aircraft called Mars Airplane Balloon Experiment −2 (MABE2) developed by the authors was the subject of high-altitude flight demonstration test in this paper, which can simulate the near-actual environment of a Martian atmospheric flight. Although the flight condition is in the low-Reynolds-number region due to low density at high altitude, the wing suffers from aeroelastic deformation given the relatively high dynamic pressure load in the pull-up phase. Stereophotogrammetry was applied in the 6.5 m × 5.5 m low-speed wind tunnel at the Japan Aerospace Exploration Agency (JAXA), aiming to optically measure MABE2’s aeroelastic deformation under dynamic pressure loads equivalent to high-altitude flight test, with the MABE2’s reinforced structural strength. The results of the accuracy test indicated that stereophotogrammetry measures aeroelastic deformation at high accuracy of ±0.1 mm around the image center and ±0.3 mm around the edge. A slight deflection of up to 4 mm was observed on the main wing, whereas both the main and tail wings were hardly twisted. Compared with flight-simulation-assumed errors, these deformations are extremely small and have a negligible effect on the high-altitude flight test. The study results confirmed the practicality and efficiency of this optical measurement technique in aeroelastic deformation measurement for a real light aircraft.

This paper investigates the applicability of a multi-element polynomial chaos method based on edge detection for uncertainty quantification of discontinuous responses in aerodynamic problems. This paper presents numerical experiments for the supersonic flow problem of Busemann’s biplane airfoil, which exhibits a discontinuous response of the drag coefficient to the uncertainty associated with the freestream Mach number caused by the flow choking. The numerical experiments show that the proposed method can sharply and efficiently capture the discontinuous response by accurately locating the discontinuity, while the conventional polynomial chaos method yields spurious oscillatory solutions.

The Japan Aerospace Exploration Agency, in partnership with academia and industry, are developing the Air Turbo Rocket for Innovative Unmanned Mission (ATRIUM) engine: an air turboramjet + rocket combine cycle propulsion system intended to replace conventional liquid rocket engines in Vertical Takeoff Vertical Landing applications, such as reusable sounding rockets. A subscale Flight Test Bed (FTB) vehicle is also being developed to demonstrate the ATRIUM engine in a flight environment. In this paper, the ATRIUM engine and FTB vehicle are introduced, and current progress in their development is summarized. Future test plans and practical applications are also discussed.

In the present work, we propose some new modifications of an existing constraint handling technique (CHT) for single-objective optimization problems. The base CHT is generalized multiple constraint ranking (G-MCR), which is already a modified version of the original CHT, MCR. Despite that G-MCR significantly outperformed the original MCR in the previous study, it is found that G-MCR tends to generate very few feasible individuals on a certain real-world like engineering design problem. In the present work, G-MCR is further modified to strike a better balance between feasible and infeasible individuals on each generation in an adaptive way so that the interaction between feasible and infeasible regions can be maintained, thus providing more efficient search towards constrained global optimum. Based on the investigation on 78 benchmark problems, we obtain that some of the proposed modifications produce more robust convergence performance by obtaining significant superiority on many types of problems. On real-world like engineering design problems, we also observe that the feasibility ratio generated on each generation might have an important role in improving the convergence performance.

The effectiveness of closed-loop flow control using a deep Q network (DQN), such as deep reinforcement learning algorithm, was experimentally researched for a NACA0015 airfoil. The system used a dielectric barrier discharge plasma actuator as the flow control device, and the experiment was conducted at the chord Reynolds number of 6.3 x 10(4). The closed-loop control system selected a nondimensional burst frequency of the actuator by analyzing the time series of the surface pressure data. The neural network of the DQN was sequentially trained at the angles of attack of 12 and 15 deg. As a result, the closed-loop control successfully generated a higher control gain compared with the open-loop control using a fixed burst frequency. Particularly, at 15 deg there was a significant control gain that could not be obtained by the open-loop control. The closed-loop control keeps the flow attached and preserves it for a longer time by periodically switching the actuator on and off.

© 2020 The Japan Society for Aeronautical and Space Sciences Aerodynamics of an owl-like wing model at low Reynolds numbers (Re = O(104-5)) are investigated using large-eddy simulations with high-resolution computational schemes. The airfoil shape of the owl-like wing model is constructed based on a cross-sectional geometry of the owl wing at 40% wingspan from the root. The chord-based Re ranges from 1.0 © 104 to 5.0 © 104 and the angle of attack (¡) varies from 0 to 14 deg. The time-averaged lift (Cl) and drag coefficients computed are in reasonable agreement with the results of force measurement. The results computed clarify a nonlinear change in the Cl curve slope, which is due to an increase in the suction peaks in conjunction with the change in type of separation, the formation of a laminar separation bubble (LSB), and pressure recovery on the pressure side. The generation of the LSB on the suction and/or pressure sides at the Re of 2.3 © 104 and 4.6 © 104 are seen, while reattachments are observed only on the pressure side at the Re of 1.0 © 104 due to the camber of the wing. Furthermore, the owl-like wing model demonstrates favorable aerodynamic performance in terms of a maximum lift-to-drag ratio in comparison with several airfoils at the Re range considered. This is due to the strong suction peaks and distribution of surface pressure on the pressure side. It is emphasized that the concave lower surface enhances the time-averaged aerodynamic performance at all of the ¡ even though the LSB is generated and fluctuation in lift history is induced at low ¡.

To apply MOEAs to industrial problems, the estimation of the ideal and nadir points becomes crucial in order to handle the differently scaled objectives by normalization and to handle the unknown Pareto Front. In this paper, the impact of the estimation methods of the ideal and nadir points for decomposition-based multi-objective evolutionary algorithms is examined on some constrained optimization problems whose constraints are explicitly designed to have the characteristics of the practical problems. The numerical experiments show that the estimation method has great impact on the performance of MOEAs.

This work presents a new rank-based constraint handling technique (CHT) by implementing a modification on Multiple Constraint Ranking (MCR), a recently proposed rank-based constraint handling technique (CHT) for real-world engineering design optimization problems solved by evolutionary algorithms. The new technique, namely MCR-mod, not only maintains MCR's superior feature, i.e. balanced assessment of constraints with different orders of magnitude and/or different units, but also adds some more good features, such as more proper rank definition that the best feasible solution in the population always has better rank than the best infeasible solution, involvement of good infeasible solution, and easier way of implementation. Numerical experiments on benchmark problems from IEEE-CEC 2006 competition and engineering design are conducted to assess the accuracy and robustness of MCR-mod. From 25 independent runs on each problem, MCR-mod has proven its robustness compared to MCR, by its ability to produce better feasible optimal solution in most problems. Based on nonparametric statistical tests, there are indications that MCR-mod yields significant superiority in terms of accuracy compared with MCR on problems whose most constraints are inequality and active constraints, indicating that all added features of MCR-mod produce some improvements on the constraint-handling performance.

Several studies report that the solutions obtained by indicator-based evolutionary algorithm (IBEA) with the binary additive epsilon indicator are biased to specific regions in the objective space. This paper reveals the reason of the bias is due to the asymmetricity of the epsilon indicator without considering the dominance relationship. This paper also proposes a modified epsilon indicator to obtain uniformly distributed solutions in the objective space. The proposed indicator uses indicator value based on Chebyshev distance when the dominance relationship does not exist between two solutions. The results of the experiments show that the diversity of IBEA is enhanced by the proposed indicator on WFG5 problem.

In this paper, we investigated and compared the performance of various constrained surrogate-based optimization (SBO) techniques on solving low-fidelity, low-speed airfoil design problems. We aim to better understand the strengths and weakness of various constrained SBO algorithms on handling non-algebraic real-world problems. Low-fidelity problems are chosen since they allow us to perform multiple independent runs of optimization algorithms, but still in the domain of non-algebraic real-world problems. To be specific, the optimization methods that we compared are Kriging-based efficient global optimization (EGO) with the probability of feasibility (PoF), ConstrLMSRBF, COBRA, and COBYLA. Results on four airfoil design problems show that ConstrLMSRBF is the most robust method in terms of convergence and consistency of performance. On the other hand, EGO-PoF found high-quality solutions on two airfoil problems, but its robustness decreases as the dimensionality increases. We also observe that COBRA is significantly better than EGO-PoF on one high-dimensionality problem, but its general performance is not as good as that of ConstrLMSRBF. Finally, COBYLA is the worst performer, which implies that methods based on linear interpolation are not accurate for the problems considered in this paper.

To enhance the coverage performance of MOEA/DM2M, we propose a modified nadir point called a dystopian point and propose to use the dystopian point as the origin of the direction vectors of MOEA/D-M2M. The performance of the proposed algorithm is tested on 16 artificial test problems and a real-world-like problem, which have the feature of difficultto- approximate PF boundaries. The experimental results show that the existing MOEAs, including the standard MOEA/DM2M, performs not very well with respect to coverage while the proposed algorithm performs well. The results on the real-worldlike problem indicate that the balance between convergence, diversity, coverage, and feasibility is all important.

This paper reports the results of the aerodynamic deformation measurements of the meter-scale, entire shape, actual UAV in the wind tunnel using a video grammetry technique. The measured airplane was the airplane for Mars exploration being developed by Japan Aerospace Exploration Agency (JAXA) and Japanese universities. Its main wing span length was 2.4 m. The video grammetry measurement was performed using VICON’s system. Retroactive markers and stickers were put on the airplane. JAXA’s 6.5 m × 5.5 m Low-Speed Wind Tunnel was used. The airplane was mounted on the strut support with pitch-free or pitch-locked conditions. The deformations of the main wing bending, the main wing twisting, the tail boom bending, and the elevator deflection angle change were revealed quantitatively. The bending stiffness of a main wing spar that was designed as a safety factor of 2.8 at load factor of 5 was sufficient. The main wing spar was located around a center of pressure of an airfoil and it showed enough stiffness for twisting at nominal condition. The effects of the main wing bending and twisting, and the tail boom bending on the aerodynamic performance were estimated but they were in an acceptable range from the standpoint of the controllability of the aerodynamic performance using control surfaces. Even though the servo motor was located near the elevator and the linkage between the servo motor and the elevator was short, the measured elevator deflection angle was at most 4% smaller than the angle at no-wind condition. The obtained results and presented method are useful for control, flight data analysis, and design of lightweight airplanes.

Multi-objective evolutionary algorithms (MOEAs) are an active research topic for multi-objective design problems. MOEAs are population-based global optimization algorithms and it is said that the performance of the MOEAs depends on the population size. It is well-known that the population size should be large enough to guarantee the diversity of the solution while the large population size makes the convergence slow. This study is on the trade-off of the convergence speed and the diversity of the solutions and the trade-off is visualized from the view point of the efficiency of the algorithms against the population size. It is clearly shown that there is an optimal population size with regard to the efficiency for each problem and for a target quality of the solutions. To shift the optimal population size toward larger, i.e, to make the convergence fast with good diversity property, two methods are employed. First method is the multi-objective-to-multi-objective (M2M) decomposition and the other is a newly proposed elitist mate selection based on binary tournament (termed EBT). Experimental studies on MOP test instances show that NSGA-II incorporated with the M2M decomposition and the EBT (NSGA-II-EM2M in short) shows the highest and fastest performance with better efficiency over NSGA-II and NSGA-II-M2M with different mate selection schemes.

In the present work, we propose an efficient infill criterion of surrogate model specifically for computationally expensive, severely-constrained optimization problems. Basing on a rank-based constraint handling technique (CHT) called multiple constraint ranking (MCR), we devise a rank-based infill criterion to overcome the drawbacks of the widely-known infill criterion called constrained expected improvement (CEI), namely CEI-MCR. In the framework of efficient global optimization (EGO), we conduct optimization on various kinds of benchmark problems to investigate the performance of the proposed infill criterion, CEI-MCR, compared with other currently existing infill criteria, CEI and EGOcons. Results of statistical significance tests on the optimization of the benchmark problems bring about a indication that the performance of CEI-MCR is either significantly more superior or equivalent compared with CEI and EGOcons by the end of EGO on all problems selected in the present work. In the last part of the present work, we conduct an airfoil design optimization and notice that CEI-MCR also performs with significant superiority or equivalently compared with CEI and EGOcons.

The flow structure and near field acoustic profile of a supersonic jet at a Mach number of 2.0 and Reynolds numbers of 105 and 106 were investigated by particle imaging velocimetry, schlieren visualization and acoustic measurement using a microphone. The effect of the disturbance in the shear layer was also investigated. In the case of higher Reynolds number jet, the presence of disturbance does not significantly affect the flow and acoustic fields because the shear layer state has already been turbulent even without the disturbance. However, presence of disturbance significantly affects the flow and acoustic fields in the case of moderate Reynolds number jet (Re=105) because the initial condition of the shear layer without disturbance is laminar and disturbance promotes the turbulent transition which has the strong influence on flow and acoustic fields. The sound pressure level decreases with adding disturbance because the promoted turbulent shear layer is smoothly growing instead of rapid growth in the vicinity of the transition which leads to strong acoustic wave emission.

Freestream turbulence effects on laminar separation bubbles in low-Reynolds-number flow over a flat plate are investigated using large eddy simulations. To this end, the framework of the Fourier-series-based synthesized turbulence is introduced to make inflow turbulent fluctuation. The results show that the freestream turbulence accelerates the laminar-turbulent transition and the length of the separation bubble decreases. Consequently, the pressure distributin of the simulations with the freestream turbulence shows closer distributions to an experimental result than the simulation without freestream turbulence. Moreover, a parametric study shows that the length scale of turbulence, as well as the intensity of turbulence, affects the flow reattachment point. This fact may indicate that we have to pay attention to the turbulent length scale in addition to the turbulent intensity on wind tunnel tests.

<p>We redesigned the Mars Airplane Balloon Experiment Two (MABE-2) based on MABE-1 to improve the vehicle's stability and controllability. Following the redesign, the MABE-2 vehicle had a larger horizontal tail volume than that of MABE-1 for improved stability performance. In addition, to further improve the stability and control characteristics, a rectangular planform was employed for the horizontal tail wing; in contrast, MABE-1 had a tapered planform. The vertical tail position of MABE-2 was moved to the end of the horizontal tail wing, because the vertical tail of MABE-1, which was positioned at the mid span of the horizontal tail wing, showed aerodynamic interaction with the horizontal tail wing. In this paper, we discussed the aerodynamic performance of a control surface based on computational fluid dynamics with variation in the deflection angle between the control surface and the horizontal tail (elevator), and we examined the effects of this redesign on longitudinal control characteristics. Numerical investigations confirmed the linear variation in the pitching moment and the aerodynamic force with the changing elevator deflection angle in MABE-2. Surface pressure observations indicated that MABE-2 shows a smooth variation in the pressure distribution with changing elevator deflection angle, while MABE-1 does not. These results demonstrate that the aerodynamic control characteristics of MABE-2 were improved in comparison to those of MABE-1.</p>

A benchmark problem based on a real-world car structure design optimization1 is proposed. The benchmark problem is constructed by using a response surface method from the design optimization result of a car structure design optimization problem. Because this benchmark problem bases on actual car structure design optimization result conducted by Mazda, it contains features of real-world design optimization problems. Objectives are the minimization of the total weight of the different type of cars and maximization of the number of common gauge (standard plate thickness) parts among the different type of cars. This benchmark problem has 148 discrete design parameters and 36 design constraints for simultaneous design optimization of two types of cars and 222 discrete design parameters and 54 design constraints for simultaneous design optimization of three types of cars. Thus, it is a scalable and multiobjective design optimization problem with many and discrete design parameters and many and severe constraints. The benchmark problem is available on our website (http://ladse.eng.isas.jaxa.jp/benchmark/).

While many of real-world industrial design problems involve several constraints, researches on multiobjective evolutionary algorithms (MOEAs) for problems with many constraints or the benchmark problems themselves are limited. The novel constrained multiobjective optimization benchmark problem based on a real-world car structure design optimization problem, termed Mazda CdMOBP, has more desirable characteristics as a constrained benchmark problem than the existing ones. The experimental results with 12 constrained MOEAs on this problem suggest the importance of balancing all of three factors of convergence, diversity, and feasibility and knowledge of proper settings of not only MOEA and CHT but also these parameters are imperative for application of MOEAs to industrial design problems.

A design tool for simultaneous structure design optimization of multiple car models is developed and applied to simultaneous design optimization of MAZDA CX-5 (SUV car), MAZDA6 wagon (large car), and MAZDA3 hatchback (small car) to demonstrate feasibility of the developed design tool. This problem is a multiobjective design optimization problem where the objectives are minimization of total weight of three car models and maximization of number of common thickness parts. To find the nondominated designs efficiently, an evolutionary multiobjective optimization algorithm named Cheetah is adopted. For analysis of the obtained nondominated and dominated designs, an interactive data mining tool iSPM is used. To evaluate crash performances accurately, a finite-element software LS-DYNA is used for each crash mode. To overcome difficulty in computational time, the K computer is used, where the required computational time is more than 360 hours using 73,728 cores of the K computer. As a result, many designs that outperform the initial design developed by Mazda Motor Corporation are found. In addition, the obtained nondominated designs reveal the trade-off between the two design objectives of the simultaneous structure design optimization problem of multiple car models.

The stochastic behaviors of airfoil characteristics at low Reynolds numbers under uncertain flow conditions are investigated. The potential importance of considering multiple uncertainties including the Reynolds number effect on the stochastic response of the airfoil characteristics is highlighted at low Reynolds numbers.

A generic framework for incorporating constraint handling techniques (CHTs) into multi-objective evolutionary algorithms (MOEAs) is proposed to resolve the differences between MOEAs from algorithmic and implementation perspective with respect to the incorporation of CHTs. To verify the effectiveness of the proposed framework, the performances of the combined algorithms of five CHTs and four MOEAs on eight constrained multi-objective optimization problems are investigated with the proposed framework. The experimental results show that the outperforming CHT can vary by constrained multi-objective optimization problems, as far as examined in this study.

© 2018 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. The numerical analysis of the supersonic jet is conducted using large eddy simulations (LES) with high order schemes and the grid of approximately 650 million points. A Mach number and a Reynolds number are set to be 2.0 and 9.0×105, respectively. At first, we confirm the azimuthal grid resolution. As a result, it seems that the flow field and the acoustic field near the jet flow are slightly affected by changing the grid resolution, while the sound pressure level at far-field converges sufficiently with the present grid number. The computational flow field shows good agreement as compared with the experimental data. Moreover, it is shown that the sound pressure level at far-field can be predicted within 4dB difference as compared to the experimental data. Next, the effect of the jet temperature of the supersonic jet on the acoustic waves is investigated. The temperature ratio of the chamber to ambient air is set to be 1.0, 2.7, and 4.0 for the cold, mid-hot and hot jets, respectively. Mach waves are radiated from the supersonic jet toward downstream. we confirmed that the shorter potential core length, the higher sound pressure level, the larger angle of Mach waves with increasing jet temperature.