a b s t r a c tAerodynamic noise from a generic two-wheel landing-gear model is predicted by a CFD/FW-H hybrid approach. The unsteady flow-field is computed using a compressible Navier-Stokes solver based on high-order finite difference schemes and a fully structured grid. The calculated time history of the surface pressure data is used in an FW-H solver to predict the far-field noise levels. Both aerodynamic and aeroacoustic results are compared to wind tunnel measurements and are found to be in good agreement. The farfield noise was found to vary with the 6th power of the free-stream velocity. Individual contributions from three components, i.e. wheels, axle and strut of the landing-gear model are also investigated to identify the relative contribution to the total noise by each component. It is found that the wheels are the dominant noise source in general. Strong vortex shedding from the axle is the second major contributor to landing-gear noise. This work is part of Airbus LAnding Gear nOise database for CAA validatiON (LAGOON) program with the general purpose of evaluating current CFD/CAA and experimental techniques for airframe noise prediction.

Wheels are one of the major noise sources of landing gears. Accurate numerical predictions of wheel noise can provide an insight into the physical mechanism of landing gear noise generation and can aid in the design of noise control devices. The major noise sources of a 33% scaled isolated landing gear wheel are investigated by simulating three different wheel configurations using high-order numerical simulations to compute the flow field and the FW-H equation to obtain the far-field acoustic pressures. The baseline configuration is a wheel with a hub cavity and two rim cavities. Two additional simulations are performed; one with the hub cavity covered (NHC) and the other with both the hub cavity and rim cavities covered (NHCRC).

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Leading edge noise reductions caused by serrations have been shown to be sensitive to the length scales of vortical disturbances. In order to improve the understanding of wavy leading edge airfoils as a noise reduction technology, this paper examines the effects of anisotropy on turbulence-airfoil interaction noise by means of computational aeroacoutic simulations. A synthetic turbulence method is used to generate fully three-dimensional, divergence-free, homogeneous anisotropic turbulence, which is injected in a linearized Euler equation solver to model the noise generation. Moderate variations in turbulence length scales, which are representative of the anisotropy in aero-engine fan wakes, are tested for a NACA 0012 airfoil with a wavy leading edge. This work focuses on the noise sources in the near-field by examining the distortion of the turbulent structures and velocity spectra in the vicinity of the noise sources, the unsteady pressure and its spectral density on the airfoil surface, the magnitude-squared coherence between velocity and pressure fluctuations on the noise sources, and the correlation between noise sources along the span for various degrees of anisotropy. Numerical results show that small variations in the turbulence length scales can produce significant changes in the spectral content of the noise sources at the peak and root regions. The loudest noise source is always located in the root region for the cases examined and this source is mainly affected by the transverse velocity fluctuations. To reduce the correlation between noise sources in the peak and root regions, the ratio between the chordwise length scale and the amplitude of the serrations, and the ratio between the spanwise length scale and the wavelength of the leading edge should satisfy lx/(2hw) < 1 and lz/λw ≤ 0.5, respectively.Recent experimental, numerical, and analytical studies 6,8,14,15 highlighted the importance of the length scales of the vortical disturbances or turbulence as a key parameter in the noise reduction of wavy leading edge airfoils. However, the majority of previous works were based on the flat plate assumption 8, 16 and used simplified representations for the turbulence, such as harmonic gusts 14 or isotropic turbulence. 8 Unlike previous works that focused on flat plates and isotropic turbulence, the present work studies the noise generation mechanisms of an airfoil with wavy leading edge in the presence of anisotropic turbulence. Although the effects of anisotropic turbulence have been shown to be limited in airfoils with straight leading edge, 17 wavy leading edge airfoils are expected to be more sensitive to anisotropic turbulence due to additional three-dimensional mechanisms caused by the amplitude and wavelength of the leading edge serrations. In this work, Computational AeroAcoustic (CAA) simulations are performed by means of a synthetic turbulence method to generate fully three-dimensional anisotropic turbulence and a linearized Euler equation (LEE) solver for the noise generation. The following top...

A semi-empirical analytical model is developed that predicts the noise produced by a rotor ingesting a boundary layer in proximity to a hard-wall. The rotor boundary layer ingestion noise source is an important source to include when a rotor is installed close to an aircraft fuselage. This is the case for a tail mounted

When an unsteady wake from an upstream body impinges on a downstream body, the resultant interaction noise can be significant. The use of distributed blowing through the surface of a cylinder to reduce this source of noise was investigated in a series of experiments. The two bluff bodies in tandem were a cylinder and an H-beam. Two configurations were tested, one with the cylinder upstream of the H-beam (OH configuration) and the other with the H-beam upstream of the cylinder (HO configuration). The default separation distance was / = 2. These two configurations modelled the interaction noise due to large perturbations in the wake generated by an upstream component inducing unsteady pressure fluctuations on a downstream component. Blowing was used to break down the large flow structures in the wake and to modify the shear layers. The mean velocities and velocity fluctuations were determined in the flowfield. The application of blowing to the OH configuration reduced the ′ ′ component of the stress term. This resulted in a peak reduction of 9.3 dB at a Strouhal number of 0.2. There was a broadband noise reduction of 3.2 dB averaged over the frequency range 0.05 < < 5. The effect of blowing on the HO configuration was to inhibit the strong crossflow fluctuations ( ′ ′ ) between the Hbeam and the cylinder by delaying the reattachment of the shear layers onto the surface of the cylinder. This resulted in a large noise reduction of 13.2 dB at a Strouhal number of 0.8. There was a broadband noise reduction of 4.3 dB averaged over the frequency range 0.05 < < 6.3. The effect of blowing produced additional high frequency noise. This additional noise was minimised with blowing applied through a sintered plate with a very small pore diameter. NomenclatureBlowing area, m 2 Pressure coefficient Blowing coefficient Pore diameter, ṁ Volume flow rate, m 3 /s Distance to microphone, m Reference area, m 2 Strouhal number based on cylinder diameter Component separation distance, m Lighthill stress tensor, N/m 2 Perforated plate thickness, m , , Non-dimensional cartesian components of velocity vector ′ ′ , ′ ′ , ′ ′ Non-dimensional components of Reynolds stress tensor ∞ Freestream velocity, m/s , , Cartesian coordinates, positive downstream, positive to port, positive up Distance from separation line in direction, m

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Wind-tunnel experiments are presented in this paper for two different models, single wheel and tandem wheels. The tests are performed in the 2.1 m × 1.5 m wind tunnel at the University of Southampton. The aims of the experiment are to gain a better understanding of the flow past simple landing-gear components and to generate a CFD validation database. Since the model is designed to study basic landing-gear components, the wheel geometry is simplified, with no detailed elements in the assembly. The tandem-wheel configuration is formed of two in-line wheels that can be tested at different inter-axis distances and various angles of attack. Mean and unsteady data of aerodynamic loads and on-surface pressures are measured. A vibration test is performed in situ on the model assembly to validate the unsteady-load measurements. Particle Image Velocimetry (PIV) is used to acquire the velocity fields in the wake downstream of the model. The results highlight the low sensitivity of the measured quantities to the three versions of the wheel hub on the single wheel. The mean drag coefficients of the tandem wheels show a low sensitivity to the inter-axis distance, which has stronger effects on the mean lift coefficients and the unsteady aerodynamic loads. The angle of attack determines relevant changes in both mean and unsteady quantities. The pressures on the wheel surface are used for gaining a better understanding of the flow regimes and the effect of tripping the flow. Additionally, the PIV data are used to compare the velocity profiles in the wake and identify the wake vortical structures.