Taro Imamura

A Far-field Noise and Near-field Unsteadiness of a Simplified High-lift-configuration Model (Slat)

Airframe noise generation at the flap-edge is investigated on a simplified three elements high-lift configuration wing model. Lowspeed wind tunnel experiments for aerodynamics measurements in JAXA-LWT2 and noise measurements in Large scale anechoic facility of Railway Technical Research Institute as well as steady-state Reynolds-Average NavierStokes computation (RANS) has been implemented. Cross spectrum analysis and computational results connect the far-field noise and the near-field unsteadiness, and then show the noise generation mechanism around a flap-edge. Flap-edge noise component around 2.5kHz is caused by the oscillation of the merged longitudinal vortex, which is formed by the top-side vortex and the side-edge vortex, in downstream area. The vortex is excited by shear layer instability at a lower corner of the flap-edge. In addition, three kinds of the flap-edge shape modification are tested. As a result, reduction of the far-field noise is achieved with specific shapes. Most effective modification is LowerRound flap-edge which has rounded corner at the lower side and a sharp-edge at upper side. Furthermore, variations in the vortical structures at the flap-edge with/without low noise shape are discussed using the data provided by PIV measurement and computation.

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.

Investigation of Airframe Noise from High Lift Configuration Model

To investigate airframe noise from high lift devices, acoustic measurement was carried out at JAXA 2m x 2m Low-speed Wind Tunnel (LWT2) and Large-Scale Anechoic Wind Tunnel in Railway Technical Research Institute (RTRI) by using a simplified three-element wing model. Noise around slat, wing tip and flap side edge were observed as dominant airframe noise of this model from results of phased-array microphone measurement. The ratio of each noise spectrum to overall airframe noise was investigated and each noise source was evaluated by comparison of far-field noise spectra with integration value of each spectrum. In addition, the effect of two types of slat cove filler (SCF) which reduced slat noise was investigated by using spectra from beamforming quantitatively. From these results, the independent effects of slat noise reduction were validated by using two types of SCF.

Comparison of RANS Simulations of Multi-Element High-Lift Configurations

In this study, flow computations are performed on three-dimensional high-lift configurations on multi-block structured and unstructured meshes with two turbulence models, Spalart-Allmaras model and Menter’s Shear Stress Transport model. Two kinds of three-element trapezoidal wings with full-span flap or part-span flap are computed. The objectives of this paper are to investigate the mesh dependency and the effect of turbulence models and improve the reliability in simulating the flow around high-lift devices. First, the mesh dependency on unstructured meshes is investigated and the results on structured and unstructured meshes using the same turbulence model, Spalart-Allmaras model, are compared. Importance of the mesh resolution to resolve the separated corner flows near the wing-fuselage junction is shown to improve the accuracy of computational results. Next, difference of flows by turbulence models is evaluated using the unstructured mesh CFD code. The effect on the prediction of the stall is discussed. It is shown that the maximum lift and the angle at which it occurs are very sensitive to turbulence model and Menter’s model gives better results at higher angle of attack in the present computations.

Progress on Experimental and Numerical Research for Slat Noise in JAXA

This paper summarizes the progress on experimental and numerical research activity for better understanding slat noise in Japan Aerospace Exploration Agency (JAXA). A slat is a leading edge device which is used during take-off and landing of an aircraft to enhance its aerodynamic performance at low speed flight. However, this device is known to be one of the dominant noise sources, especially during the landing phase. To clarify the noise generation mechanism, both experimental and numerical researches are conducted at JAXA. Overall characteristic of slat noise is obtained through several wind tunnel experiments associated with aerodynamic measurements. Large scale computation using large-eddy simulation technique is also performed around the slat region to seek for the relevant unsteady features. Both experimental and numerical results indicate that the dominant noise source from the slat, which has broadband characteristics, is generated around the slat trailing edge.

High-lift Wing Design in Consideration of Sweep Angle Effect Using Kriging Model

In this paper, a multi-objective design exploration for a three-element airfoil which consists of a slat, a main wing, and a flap was carried out by paying attention to the span wise sweep angle effect for a civil aircraft. Reynolds Averaged Navier-Stokes Solver (RANS) was used for the evaluation during the design process. In this study, sweep angle effect is focused, and 2.5-dimensional span wise design was developed. In this calculation, two same planes were arranged along span wise direction. They were diagonally arranged to represent the sweep angle and periodic boundary condition was used for the simplified 2.5 dimensional span wise calculation. Kriging based Multi-objective Genetic Algorithm (MOGA) called efficient global optimization (EGO) and Analysis of Variance (ANOVA) were used for the design exploration. The objective functions were defined as the maximization of lift coefficient at landing and near stall conditions simultaneously. 90 sample points were evaluated for the construction of the Kriging model. Based on present evaluation method, the span wise flow was observed and it has an influence on the separation on the wing. Through the design exploration process, the differences of the designed results between 2.5D and 2D evaluation were observed by visualizing the design space. It was also observed that the span wise flow influences the separation point and suction peak on the wing elements.

Investigation of Near-field Flow Unsteadiness around a NACA0012 Wingtip using Large-Eddy-Simulation Approach

Three-dimensional unsteady flow around NACA0012 wingtip is simulated numerically to investigate the cause of flap-edge noise generation. The vortical flow structures around the NACA0012 are known to be similar to that of a flap-edge. Therefore, it is assumed that noise generation mechanism is similar as well, although its geometry is simpler than a flap-edge. Since the Reynolds number of the flow is high, a zonal LES/RANS hybrid method is used to reduce the overall computational cost. The power spectral density of the pressure coefficient is compared with the experiment, and several issues regarding, the number of sub iteration for implicit time integration, sensitivity to Smagorinsky constant, grid overlap points at block-block interface, and grid resolution, are discussed. Subsequently, two longitudinal vortical structures around the wingtip, that show different characteristics, are investigated to understand its generation mechanism. The broadband nature of flow unsteadiness around the wingtip will be discussed.

5314 Design Exploration of Shielding Effect for Aircraft-Engine Noise

The multi-objective design exploration of the two-dimensional shielding effect for engine noise using V-tale wing has been performed. Two objective functions are con- sidered as the minimization of the sound pressure level at the side and bottom locations relative to the fuselage, which values are evaluated by using the linearized Euler equation. Two design variables are defined as the wing length and the wing cant angle to set on the fuselage. The response surface method with kriging model is employed as the optimizer to reduce the time required for design exploration. As a result, there is no tradeoff between two objective functions, i.e., the sound pressure level at the side and bottom measuring locations can be reduced, simultaneously. The wing cant angle which is set at nearly 65 deg is most effective to shield the noise. It is justly the necessary condition to reduce the sound pressure level that the wing length becomes long. Moreover, a self-organizing map as a data mining technique obtains the knowledge in the design space regarding the correlation between the objective functions and the design variables.