Yuzuru Yokokawa

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.

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.

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 on Noise Generation of a Two-Wheel Main Landing Gear

This paper deals with results of noise measurements for a 40% of two-wheel type aircraft main landing gear in lowspeed wind tunnel experiments. In order to accurately assess a noise source location and far-field characteristics during the approach phase, scale model with complex geometry which was equipped with small components such as link mechanism, hydraulic tubes and electrical wiring as well as a tire, a cylinder, a piston, doors, and a sidebrace was used. Model geometry was based on LEG (Landing gear noise Evaluation Geometry) which was designed by a gear manufacturer assuming 100-PAX class regional jet airliner. Experimental results obtained in two kinds of wind tunnels, which were 2m by 2m lowspeed wind tunnel in JAXA and large scale anechoic facility of Railway Technical Research Institute of Japan, showed dominant noise sources around a tire, a sidebrace, some parts of the door and also the junction between the cylinder and the sidebrace. Among these prominent noise sources, the tire and the sidebrace were large contributor to the total of noise level. It was found that noise characteristics around 1kHz was important not only in the amplitude but also in directivity for an actual aircraft scale. Representation of small components and geometry of an actual landing gear even in a scale model seemed to be effective of several decibels in noise level.

Aerodynamic/Aeroacoustic testing in Anechoic Closed Test Sections of Low-speed Wind Tunnels

This paper describes new anechoic closed test sections in Japan Aerospace Exploration Agency (JAXA) and Virginia Tech (VT) not only for an aeroacoustic but also for an aerodynamic testing ability in Low-speed wind tunnels. The anechoic closed test section with Kevlar wall is an innovative concept and had been originally developed at VT. It was later applied to JAXA’s 2m x 2m wind tunnel. By using a high-lift device model, the JAXAs new test section was evaluated and validated acoustically by comparing to VT anechoic test results. Moreover, the aerodynamic characteristics in the new test section were also evaluated by comparing to results of the same model in JAXAs closed hard-wall test section. New wall interference correction procedure is proposed for the Kevlar wall test section, and it showed very good agreement with well-known corrected hard-wall results. This anechoic test section is useful and a promising tool for both aerodynamic and aeroacoustic testing.

Phased Array Measurement of High Lift Devices in Low Speed Wind Tunnel

The aeroacoustic measurement using a half-span aircraft model equipped with high lift devices was carried out for the first time in JAXA 6.5m x 5.5m low speed wind tunnel. As the result of this test, the noise sources located at main wing tip, slat tracks, slat tip, flap tip, the slat-pylon region and so on are observed. The noise generated from wing tip and outboard flap tip had a strong dependence on Reynolds number and angle of attack. However, the noise generated from slat tracks and the slat-pylon region didn’t have a dependence on neither Reynolds number nor angle of attack. In this paper, a phased array system in JAXA is introduced, then the results of noise measurements for high lift devices are presented.

Numerical Simulation of NACA0012 Wingtip Flow Leading to Noise Generation

In this study, a flow around a blunt-tipped wing is solved using Reynolds averaged Navier-Stoke (RANS) equations, detached eddy simulation (DES) and large eddy simulation (LES) in order to simulate flap edge flow structure with a simple one-element wing. A rectangular wing with NACA0012 airfoil section is chosen as a model. A preliminary analysis around this configuration using RANS indicated that the flow structures are similar to that of the flap edge, and consequently the noise generation mechanism is expected to be similar as well. The computed results are compared with that of wind tunnel experiments, which were also performed at JAXA for the purpose of CFD validation. The present unsteady computation using LES indicates the existence of two different noise sources, one around the side edge and the other over the upper surface.

Simulation of the Broadband Noise From a Slat Using Zonal LES/RANS Hybrid Method

This study focuses on the unsteady 3D flow structure inside the deployed slat of high-lift configuration to investigate the noise generation mechanism. The power spectral density (PSD) of pressure coefficient (Cp) is compared with that of the wind tunnel experiment to validate the computational results. Not only high frequency narrowband peak, but also low frequency broadband components are simulated and the results are consistent with the experiment. Using the validated data, noise sources around the slat are investigated, especially focusing on the low frequency broadband component. From the spatial distribution of the PSD of Cp, it is found that the levels of the low frequency broadband fluctuation are high around the lower surface of the slat near the trailing edge (T.E.) and at the downstream of the T.E. Since the level around the latter is higher than the former region for wide range of frequency, this region is assumed to be the cause for the low frequency broadband noise. It is estimated that broadband fluctuation around the reattachment point flows to the downstream and when passing by the T.E., broadband fluctuation is generated. Additionally, the turbulent kinetic energy (TKE) and its production term are visualized. It became apparent that velocity fluctuation component normal to the slat lower surface near the T.E. is the dominant contributor.

Numerical Investigation on Change of Airframe Noise by Flap Side-edge Shape

This paper presents computational and experimental studies on the flap side-edge noise using a three-element rectangular high-lift wing model with a full-span slat and a part-span flap for high-lift device noise research in JAXA. The main purpose of this paper is focused on the numerical investigation of change of the flowfield and far-field noise by the flap sideedge shapes. Several flap side-edge configurations with rounded flap side-edges, a cavity side-edge, and a protruding-type device on the lower surface of flap are investigated in this paper. By the computations and wind tunnel tests, mechanisms of the noise generation and reduction of flap side-edge noise are discussed.