Shunji Enomoto

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.

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.

3D Unsteady Flow Computations in a Slat Cove Using Large Eddy Simulation

A zonal Large-Eddy Simulation and Reynolds-averaged Navier-Stokes (LES/RANS) hybrid method is used to focus on the unsteady 3D flow structure inside the deployed slat of high-lift configuration. The power spectral density (PSD) of pressure coefficient is compared with that of the wind tunnel experiment, which was also performed at Japan Aerospace Exploration Agency. Not only high frequency narrowband peak, but also low frequency broadband component is observed in the simulation and the results are consistent with the experiment. Also, the effect of the grid resolution, order of numerical scheme, and number of sub-iterations for the implicit time integration to the PSD are examined. From careful observation of the validated unsteady computational data, longitudinal vortical structures under the lower surface of the slat are observed and these are estimated as the cause of the broadband component.

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.

On the Modification of the Ffowcs Williams-Hawkings Integration for Jet Noise Prediction

This paper proposes a modification on the end-cap treatment for the Ffowcs Williams and Hawkings (FW-H) equation with permeable control surface, aiming at jet-noise simulations by the use of time-accurate numerical methods. It is a known issue that a closed end cap affects the accuracy of the permeable FW-H equation, as turbulent jet flow passes through the control surface. This is essentially an outcome of the neglected volumetric quadrupole term. Based on our previous study of the quadrupole correction, evaluated at an end-cap surface for uniform mean flow, we derive a mathematical extension to nonuniform convection velocity. By introducing locally frozen assumption for convecting vortices, a modification factor is obtained as a convergent series if the deviation of convection velocity from mean flow is subsonic. The derived formulation is applied to a simple subsonic round jet at ReD = 1 × 10 and Ma = 0.9. Although the present jet-flow simulation fails in accurately reproducing mixing-layer transition behind a nozzle exit, which leads to a significant overestimate of far-field noise, our modification on the FW-H formulation suppresses the spurious noise due to closed end-cap surface, as well as a more empirical, disk averaging approach proposed by Shur et al. (2005)

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.

Large-Eddy Simulation of High-Subsonic Jet flow with Microjet Injection

Large-Eddy Simulation of high subsonic jet with microjet injection was performed using UPACS-LES code which is developed in JAXA. Large scale (476M grid point) simulation was executed on JAXA Supercomputer System using 980 processors. The result shows good agreement with the experimental data in terms of velocity fluctuation and far-field noise level. Far-field noise prediction using FW-H method from the LES results show that the LES successfully predict noise reduction by microjets for lower frequency component emitted in 30 deg. observation angle, while it still has difficulty in predicting reduction of higher frequency noise emitted in 90 deg. observation angle.

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.

A Common CFD Platform UPACS

NAL(National Aerospace Laboratory) is developing a common parallel CFD Platform UPACS(Unified Platform for Aerospace Computational Simulation), for the purpose of the efficient CFD programming and the aggregation of the CFD technology of NAL. UPACS is coded based on three-dimensional Navier-Stokes equations and supports multi-block grids. It is parallelized by MPI message passing library. In this paper the concept and the structure of UPACS is described and its computational performance is evaluated on NAL NWT(Numerical Wind Tunnel) supercomputer.

Quadrupole Corrections for the Permeable-Surface Ffowcs Williams–Hawkings Equation

This paper focuses on the spurious noise of the Ffowcs Williams and Hawkings equation with a permeable integral surface, which is now commonly used in far-field noise prediction for computational a...