Aircraft Landing Gear Noise Research Articles

Retraction notice to “A component-based model for aircraft landing gear noise prediction” [J. Sound Vib. 312 (2008) 801–820

Retraction notice to “A component-based model for aircraft landing gear noise prediction” [J. Sound Vib. 312 (2008) 801–820

Experimental study of noise emitted by circular cylinders with large roughness

The aerodynamic noise generated by high Reynolds number flow around a bluff body with large surface roughness was investigated. This is a relevant problem in many applications, in particular aircraft landing gear noise. A circular cylinder in cross-flow and a zero-pressure-gradient turbulent boundary layer with various types of roughness was tested in a series of wind tunnel experiments. It has been shown that distributed roughness covering a circular cylinder affects the spectra over the entire frequency range. Roughness noise is dominant at high frequencies, and the peak frequency is well described by Howe׳s roughness noise model when scaled with the maximum outer velocity. There are differences between hemispherical and cylindrical roughness elements for both the circular cylinder and the zero-pressure-gradient turbulent boundary layer cases, indicating a dependence on roughness shape, not described by the considered roughness noise models. Cylindrical roughness generates higher noise levels at the highest frequencies, especially for the zero-pressure-gradient turbulent boundary layer case. Cable-type roughness aligned with the mean flow does not generate roughness noise, and its spectrum has been found to collapse with the smooth cylinder at medium and high frequencies. At low and medium frequencies the noise spectra have the same features as the smooth cylinder, but with higher shedding peak levels and fall-off levels, despite the decrease in spanwise correlation length. Roughness induces early separation, and thus a shift of the spectra to lower frequencies.

Effects of a boundary layer trip in the prediction of noise from flow past tandem cylinders

The use of boundary layer trips in wind tunnel experiments forces transition to fully turbulent flow, which affects the resulting acoustic signature. Boundary layer trips are often too small to be modeled geometrically in computational simulations, making it difficult to consider their influence. The goal of this study was to determine the best method for representing the effects of a boundary layer trip in the benchmark aeroacoustic problem of flow over tandem cylinders in a wind tunnel. This case is pertinent to the study of aircraft landing gear noise because periodic vortex shedding results in pronounced acoustic tones in addition to broadband noise from turbulent wake interactions. A hybrid lattice-Boltzmann Method/Ffowcs-Williams Hawkings technique was used to predict the transient flow field and the resulting noise. This study compared four methods for simulating the trip's effects: (1) applying a surface roughness on the upstream cylinder; (2) reducing the viscosity of the fluid; (3) forcing velocity perturbations in the incoming free stream; and (4) applying a ridge to the upstream cylinder that is one volume element thick. Preliminary results have shown that reducing the fluid's viscosity is an effective way to reproduce the highly turbulent flow patterns and the acoustic signature.

Identification and Attenuation of a Tonal-Noise Source on an Aircraft's Landing Gear

Aircraft landing gear noise is a major contributor to the overall airframe noise during the landing approach of a commercial aircraft. Fairings covering geometrically complex areas of the gears have proved to be very effective in noise reduction. However, in tests on an A340’s main landing gear, the overall benefit of the fairings was offset by both a slight increase in low-frequency broadband noise and a strong tonal noise. In this study, the identification and attenuation of the tonal-noise source has been carried out using a one-quarter-scale A340 main-landing-gear model. Aeroacoustic and aerodynamic tests were conducted in a closed-section wind tunnel, using a phased microphone array on the ceiling of the test section, flush-mounted pressure transducers on the model surface, and the particleimage- velocimetry technique. Far-field noise tests were then taken in an open jet aeroacoustic facility, using far-field microphones to verify the wind-tunnel test results. The experiments demonstrated the tonal-noise mechanism and a number of different control methods.

RETRACTED: A component-based model for aircraft landing gear noise prediction

This paper follows the general formulation of aircraft landing gear noise prediction to develop a component-based model, incorporating scaling laws of the theory of aerodynamic noise generation and correlations of these scaling laws with currently available test data. The method decomposes the landing gear noise into three spectral components, respectively, for the low, the mid and the high frequencies, which corresponds to cataloging the parts in the landing gear assembly into three groups, namely, the wheels, the main struts, and the small details. For all three spectral components, models are presented for their spectra, far-field directivities and amplitudes. The spectral characteristics of the three components are defined by normalized spectra, as functions of the Strouhal numbers based on the respective length scales of the three groups of parts in the landing gear assembly. Individual directivity factors are also presented for the three spectral components, with the low-frequency component having the smallest variations with emission angle and the high-frequency component having the largest variations. The amplitudes of the three spectral components are correlated to parameters unique to each group of landing gear parts, with the low- and mid-frequency noise essentially characterized by the physical dimensions of the wheels and the main struts, respectively, and the high-frequency noise, whose generation is associated with a large number of small details in practical landing gears, defined by a complexity factor. Quantities that affect this complexity factor are discussed and an empirical model is proposed for practical applications. The prediction model is validated by wing tunnel test data for an isolated Boeing 737 landing gear. In this case, the predictions agree well with data, both in parametric trends and in absolute noise levels.

Experimental Study on Aircraft Landing Gear Noise

An experimental investigation on aircraft landing gear noise is presented. The study includes systematic testing and data analysis using a full-scale Boeing 737 landing gear. The database covers a range of mean flow Mach numbers typical of landing conditions for commercial aircraft and various landing gear configurations, ranging from a fully dressed, complete gear to cleaner configurations involving only some parts of the complete gear. This enables the examination of noise radiation from various groups of the gear assembly and the derivation of functional dependencies of the radiated noise on the flow Mach number at various far-field directivity angles and on various gear geometry parameters. It is shown that the noise spectrum can be decomposed into three frequency components, namely, the low-, mid-, and high-frequency components, respectively, representing contributions from the wheels, the main struts, and the small details such as hoses, wires, cutouts, and steps. It is found that these different frequency components have different dependencies on flow parameters and gear geometry. Based on the spectral decomposition in the three frequency domains, normalized spectra are derived for all three components and a model for the overall sound levels is developed as a function of flow and geometry parameters.

A statistical model for landing gear noise prediction

This paper presents the development of a framework for aircraft landing gear noise prediction. A prediction model is derived that decomposes the landing gear noise into three spectral components, for the low, mid and high frequencies, respectively. This corresponds to cataloguing the parts in the landing gear assembly into three groups, namely, the wheels for low frequencies, the main struts for mid frequencies and the small details for high frequencies. The spectral decomposition is demonstrated by experimental data from a full-scale Boeing 737 landing gear test, which show different spectral characteristics of the noise in the three different frequency domains. In each frequency domain, asymptotic results are derived for the farfield noise, by making use of different length scales to simplify the phase behavior of the sources. The derived results require as input only some statistical descriptions of the surface pressure fluctuations and the geometry of the landing gear assembly. Some simple examples are given to demonstrate the features of the predicted noise, which show trends consistent with experimental data. The frequency domain decomposition also points to simple ways of obtaining the surface pressure properties required for noise prediction, which is also discussed in this paper.