Kazuomi Yamamoto

Comparison Study of Drag Prediction for the 4th CFD Drag Prediction Workshop using Structured and Unstructured Mesh Methods

Comparison study of computations for the 4th AIAA CFD Drag Prediction Workshop (DPW-IV) is performed on the NASA Common Research Model using the structured grid solver UPACS and the unstructured grid solver TAS-code. The results on the all test cases of DPW-IV (Grid convergence, Downwash, Mach sweep and Reynolds number studies) are shown and sensitivity of the drag prediction by the two different mesh methods is discussed. Additional discussion including the effect of grid resolution and the anisotropic Reynolds stress tensor on the flow separation at wing-body juncture corner for higher angle of attack and its influence on the aerodynamic performance is also described.

Comparison Study of Drag Prediction by Structured and Unstructured Mesh Method

Comparison study of computations for the Third AIAA Computational Fluid Dynamics Drag Prediction Workshop is performed on the DLR-F6 wing-body configurations with and without the wing-body fairing using the structured grid solver UPACS and unstructured grid solver TAS code. Grid convergence study at a fixed C L using a family of three difference density grids and the results by a sweep are discussed. The self-made multiblock structured grids and mixed-element unstructured grids are employed. Another participants grid is also compared. Comparisons between the two codes are conducted using the same turbulence model. Moreover, the detailed comparisons are conducted on the grid topology at the comer of the wing-body junction, the turbulence models, and the thin-layer approximation in viscous terms using the multiblock structured grids. The reconstruction schemes to realize the second-order spatial accuracy are also compared on unstructured grids. By comparing the results, the sensitivity of drag prediction to these factors is discussed.

Three-Dimensional Unsteady Flow Computations Around a Conventional Slat of High-Lift Devices

Three-dimensional unsteady flow structure inside a deployed slat of high-lift configuration is simulated numerically to investigate the cause of slat noise. Because the Reynolds number of the flow is high and the geometry is complex, a zonal large eddy simulation/Reynolds-averaged Navier-Stokes hybrid method is used to reduce the overall computational cost. The power spectral density of the pressure coefficient is compared to the experiment, and some issues regarding grid resolution, order of numerical scheme, and number of subiterations for implicit time integration are discussed. Two different types of fluctuations (high-frequency narrowband and low-frequency broadband) are observed, and the computational results are consistent with the experiment. Careful observation of the unsteady computational data reveals longitudinal vortical structures under the lower surface of the slat, which is consistent with the previous studies. The low-frequency broadband fluctuation becomes large around this region. Therefore, it is assumed that these longitudinal vortical structures are causing the broadband noise from the slat.

Experiment and CFD of a High-lift Configuration Civil Transport Aircraft Model

This paper presents the results of the first wind tunnel testing for a high-lift configuration aircraft model in JAXA. Main objective of the research is to develop the design methodology for a high-lift system. During the research process, validation data for a complex configuration assuming actual aircraft was essential for an advancement of CFD technology with high accuracy and reliability. As the step of our research, a civil transport aircraft model equipped with high-lift devices, fuselage, nacelle-pylon, slat tracks and Flap Track Fairings (FTF) was newly designed and produced, then lowspeed wind tunnel test was conducted. The first testing was aiming to store large amount of basic aerodynamic information by various measurement techniques to provide the experimental data for CFD validation and to understand flow physics. Navier-Stokes computation was performed on unstructured hybrid mesh, simultaneously. As a result of the testing, two kinds of Reynolds number effects within linear region and also at stall region were observed. Analysis of static pressure distribution and flow visualization gave the knowledge to understand the aerodynamic performance. CFD could capture the whole characteristics in basic aerodynamics even for such a complicated model geometry and its flow field, while differences between the experimental results and CFD were shown.

Effect of a Nonlinear Constitutive Relation for Turbulence Modeling on Predicting Flow Separation at Wing-Body Juncture of Transonic Commercial Aircraft

This paper presents an improvement in numerical prediction of aerodynamic characteristics for transonic commercial aircraft using the Reynolds-averaged Navier-Stokes equations. With turbulence models base on the Boussinesq eddy-viscosity approximation, the shock-induced flow-separation at wing-body juncture-corner is sometimes overestimated at higher angle-of-attack, which often results in wrong prediction of aerodynamic force and moment of aircraft. To improve it, we focus on effect of anisotropy in the Reynolds stress at the corner flow. A simple nonlinear constitutive relation is employed to introduce the anisotropy of the Reynolds stress for the turbulence models. The obtained results show that the size of the flow separation considerably shrinks with the nonlinear model and fairly good comparison with experimental results. The detailed flow in boundary-layer at the corner is discussed for better understanding of physics that results in the improvement of prediction.

Designing of Slat Cove Filler as a Noise Reduction Device for Leading-edge Slat

The purpose of this study is to design noise reduction devices for leading-edge slat which is called as a slat cove filler (SCF), from both aerodynamic and acoustic points of view. From the previous studies, a SCF seems to have an effect on reducing broadband noise by forming substantially continuous shape instead of a slat cusp configuration. However, there are some studies which indicate the decrease of aerodynamic performance when the SCF is attached. Since the primary feature of high-lift-devices is to increase aerodynamic performance, reduction of maximum lift coefficient or stall angle etc. is not acceptable even if the device is effective in reducing noise. In order understand both features, two kinds of flow solver, UPACS and UPACS-LES codes, are used to simulate steady and unsteady flows around slats. The UPACS code is used mainly for aerodynamic force prediction, and UPACS-LES is used to understand the noise generation and reduction mechanism. Based on the simulations, it became apparent that if the SCF is designed while maintaining the geometry around the slat trailing edge and the main element leading edge, the aerodynamic performance will be the same as that of the baseline. Also, to suppress the noise as much as possible, it is important to reduce small separation along the lower surface of a SCF, which seems to be caused by adverse pressure gradient. Additionally, wind tunnel experiments are performed for verification purpose. The SCF designed in this study satisfies both aerodynamic and acoustic performance successfully.

Multi-Objective Aerodynamic Exploration of Elements' Setting for High-Lift Airfoil Using Kriging Model

A multi-objective design exploration for a three-element airfoil consisting of a slat, a main wing, and a flap was carried out. The lift curve improvement is important to design high-lift system, thus design has to be performed with considered multi-angle. The objective functions considered here are to maximize the lift coefficient at landing and near-stall conditions simultaneously. Genetic algorithm is used as an optimizer. Although it has the advantage of global exploration, its computational cost is expensive. To reduce the computational cost, the Kriging surrogate model, which was constructed based on several sample designs, is introduced. The solution space was explored based on the maximization of expected improvement (EI) value corresponding to objective functions on the Kriging surrogate models. The improvement of Kriging surrogate model and the exploration of the optimum can be advanced at the same time by maximizing EI value. In this study, a total of 90 sample points are evaluated using the Reynolds-averaged Navier-Stokes simulation for the construction of the Kriging surrogate model. Through the present exploration process, several designs were obtained with better performance than the baseline setting in each objective function. To obtain the information of the design space, functional analysis of variance, which is one of the data mining techniques showing the effect of each design variable on the objectives, is applied. Main effects of the design variables are calculated to recognize which design variable has the effect on the objective functions. This result suggests that the gap and the deflection of the flap have a remarkable effect on each objective function and the gap of the slat has an effect at near-stall condition.

Knowledge Discovery in Aerodynamic Design Space for Flyback-Booster Wing Using Data Mining

The data mining has been performed for the aerodynamic design optimization result of two-stage-to-orbit reusable launch vehicle flyback booster wing. Three data mining techniques were used such as self-organizing map, functional analysis of variance, and rough set theory. The optimization problem had four aerodynamic objective functions and 71 design variables regarding wing shape. The optimization obtained the result as the hypothetical design database with 302 all solutions including the 102 non-dominated solutions. Consequently, the knowledge in the design space was acquired regarding the correlation between objective functions, and the influence of the design variables to the objective function, for non-dominated and all evaluated solutions, respectively. The features of three data mining techniques were revealed. Although the combination among three techniques discovered detailed design knowledge, self-organizing map was especially a key technique for knowledge discovery. Moreover, design knowledge from all solutions conserved the information from non-dominated solutions. Data mining was essential to solve multi-objective optimization problem.

High-Lift Device Testing in JAXA 6.5M X 5.5M Low-Speed Wind Tunnel

To obtain detailed validation data for a complicated high-lift system including aerodynamics, aeroacoustics, flow visualization, and so on, half-span large-scale high lift device model was tested in JAXA 6.5m x 5.5m Low-speed Wind Tunnel. Five-component aerodynamic force and aeroacoustic noise with phased array microphones were measured simultaneously, and surface pressure with pressure taps and Pressure Sensitive Paint (PSP), unsteady pressure using surface mounted pressure sensors, and velocity distribution around the model using Particle Image Velocimetry (PIV) were obtained. Surface flow visualization with oil flow and china clay method were also carried out. Here, overview of the testing and verification data for CFD which were successfully obtained is reported. Moreover, those various measurements were able to reveal important aspects of flow field around nacellepylon which dramatically affected to aerodynamic force, surface pressure, and also aeroacoustic noise.

Experimental Study of Slat Noise from 30P30N Three-Element High-Lift Airfoil in JAXA Hard-Wall Low-Speed Wind Tunnel

Aeroacoustic measurements associated with noise radiation from the leading edge slat of the canonical, unswept 30P30N three-element high-lift airfoil configuration have been obtained in a 2 m x 2 m hard-wall wind tunnel at the Japan Aerospace Exploration Agency (JAXA). Performed as part of a collaborative effort on airframe noise between JAXA and the National Aeronautics and Space Administration (NASA), the model geometry and majority of instrumentation details are identical to a NASA model with the exception of a larger span. For an angle of attack up to 10 degrees, the mean surface Cp distributions agree well with free-air computational fluid dynamics predictions corresponding to a corrected angle of attack. After employing suitable acoustic treatment for the brackets and end-wall effects, an approximately 2D noise source map is obtained from microphone array measurements, thus supporting the feasibility of generating a measurement database that can be used for comparison with free-air numerical simulations. Both surface pressure spectra obtained via KuliteTM transducers and the acoustic spectra derived from microphone array measurements display a mixture of a broad band component and narrow-band peaks (NBPs), both of which are most intense at the lower angles of attack and become progressively weaker as the angle of attack is increased. The NBPs exhibit a substantially higher spanwise coherence in comparison to the broadband portion of the spectrum and, hence, confirm the trends observed in previous numerical simulations. Somewhat surprisingly, measurements show that the presence of trip dots between the stagnation point and slat cusp enhances the NBP levels rather than mitigating them as found in a previous experiment.