Tohru Hirai

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.

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.

Numerical and Experimental Research of Low-Noise Slat Using Simplified High-lift Model

This paper focuses on numerical and experimental research for designing low-noise slat on a simplified high-lift configuration model (OTOMO). Two types of noise reduction devices are considered. First device is a slat cove filler (SCF). From the previous studies, SCF seems to have an effect on reducing broadband noise by forming substantially continuous shape instead of a slat cusp configuration. Several different geometries are designed and tested experimentally as well as numerically. The second device is called thin slat (TS). This device maintains the leading edge radius of the baseline slat and cusp region is shaved off to avoid separation from the cusp. Interestingly, the aerodynamic performance, such as maximum lift coefficient and stall angle, will be maintained while noise reduction is achieved. These results indicates that lower surface slat could be designed for the low noise configuration without aerodynamic penalties.

Tandem Cylinder Flow Simulations Using Sixth Order Compact Scheme

Flow around tandem cylinder is solved using UPACS-LES code developed in JAXA. Delayed detached-eddy-simulation (DDES) is used, and order of numerical schemes and grid density are changed to investigate their sensitivities to the near-field flow and far-field noise. The results are compared with the experimental results. It became apparent that near-field flow structures including both steady and unsteady components are sensitive to the numerical scheme and grid density. As spatial resolution is increased, the results tend to converge toward the experimental results. On the other hand, far-field noise is insensitive to the spatial resolution. The dominant noise is generated by the impingement of the upstream cylinder wake on the downstream cylinder, and this large scale feature is already captured by the lowest spatial resolution case which we have calculated. The highest resolution case with long spanwise length (18D) shows good agreement in terms of both tonal and broadband component.

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.