Research project: Airbus Noise Technology Centre

Aerodynamics and Aeroacoustics of Flap-Side Edge

An experimental and computational investigation was carried out to determine the aerodynamics and aeroacoustics of a flap side-edge. A porous side-edge treatment was applied to the flap side-edge in an attempt to reduce airframe noise. The application of a porous flap side-edge had two favourable effects. Firstly, it reduced the magnitude of vorticity in the turbulent shear layer and the vortex. This reduced the magnitude of the hydrodynamic instabilities induced by the flap side-edge vortex. Secondly, it displaced the vortex further away from the flap surface due to the finite mass flux allowed through the porous material. This reduced the magnitude of the disturbances that interacted with the solid flap surface by moving them further away.

 

Aeroacoustic Measurement Techniques for Closed-Section Wind Tunnels

The aim of this research is to develop accurate acoustic array measurement techniques for use in closed-section wind tunnels. This is for research and development work, such as for aircraft components, and also to provide better methods that can be used for full aircraft wind tunnel test programmes. This work successfully developed microphone array systems that are now extensively used by the ANTC at Southampton and in the Airbus low-speed wind tunnel in Filton, UK. Our research is focussed on techniques to remove the reverberation effects encountered in closed-section wind tunnel testing. The overall aim is to improve methods so that this testing is accurate enough to be used to provide certification checking as an integral part of any aircraft wind tunnel test programme.

Aeroacoustic Control of Landing Gear Noise using Perforated Fairings

A study was performed to investigate and optimize the application of perforated fairings for landing gear noise control. The sparse knowledge about this new subject has necessitated a more fundamental study involving a basic fairing-strut configuration, followed by wind tunnel tests on a simplified landing gear configuration incorporating perforated fairings. The synthesis of the conducted studies has shed new light on application of perforated fairings for landing gear noise control.

Slat Aerodynamics and Aeroacoustics with Flow Control

This study primarily investigated the flow and aeroacoustics associated with the slat of a three-element aerofoil in approach conditions. The factors investigated were aerofoil incidence, slat angle, slat cusp geometry, fixing transition and blowing in the slat cove. The study involved PIV, pressure taps, force balance, flush mounted microphones and acoustic array measurements along with DES simulations. Three distinct tonal features were identified along with the settings where they occurred. Broadband sound was recorded over a wide range of settings to identify the trends and test for noise reductions.

Low Noise Landing Gear Design

The design of landing gears has to be fully integrated with the design of the whole aircraft so as to satisfy the many structural, weight and safety constraints. Identifying acceptable ways of reducing landing gear noise is thus a complex task requiring careful development and testing of new concepts. In collaboration with Airbus, the University has developed an engineering design tool to predict the potential benefits of new landing gear concepts, and is using this to assist in a number of EU, DTI and Airbus funded projects.

Aerodynamic Control of Bluff-Body Noise using Splitter Plates

Landing gears have been identified as a major noise source contributor during the approach to landing phase of an aircraft. Techniques such as fairings to alter the flow around the landing gear components have shown a noise reduction. This study investigates a method to further improve the fairing performance as well as a method to reduce the noise produced by a bluff body without the using a fairing. The control device used was a splitter plate which, for the fairing-strut configuration, was placed between the faring ad the strut and behind the bluff body for the H-beam configuration. Aerodynamic measurements using particle image velocimetry (PIV), shown here as well as hot wire anemometry, pressure and force measurements were used to investigate the flow. Free-field acoustic measurements where conducted in an anechoic open jet facility. The splitter plate affected the shedding of vortices as well as the unsteadiness around the model and in the near wake leading to a noise reduction for both the configurations.

Development of Interface between High-Order CFD and CAA Solvers

A high-order interface is developed under a Centre for Fluid Mechanics Simulation (CFMS) project to link a high-order CAA solver for noise propagation with a high-order CFD solver for near field noise generation. Therefore the interface allows the use of optimal grids for and solvers for each part of an aeroacoustic simulation. Conventional high-order interpolation polynomial functions are adopted to preserve flow disturbances in structured Computational aeroacoustic (CAA) grids with high accuracy. A method is also proposed to account for the effects of complex geometry in the CFD flow domain without physically presenting them in the CAA grids.

Computational Aeroacoustic Modelling of Aircraft Sound Propagation and Radiation

A suite of high-order, time-domain computational aeroacoustic programs have been developed to model sound propagation and radiation from airframe components and aero engine intake and bypass/exhaust ducts. The method is based on multi-block, structured grids and high-order compact schemes [1-3] and is capable of modelling the effect of liner, bifurcation, etc. Simulations have been performed of noise propagation/radiation problems associated with high lift devices (HLDs), e.g. slats, flaps, spoilers, and both engine intake and bypass ducts. New features are being implemented including efficient computation of broadband noise content for engine applications. New formulations of linearised Euler and acoustic perturbation equations are also being developed.

Efficient Computation of Sound Radiation on Adaptively Refined Mesh

A new computational tool was developed to efficiently predict sound radiation with block-structured adaptive mesh refinement (AMR) algorithm. The basic idea was to use grids of fine resolution only for the area where sound propagates. As a result the required grid number is reduced and the computational efficiency can be increased. The work includes parallel implementation of the AMR algorithm, a high-order solver, and linear models for acoustics. Practical problems, such as spinning modal radiation from an aero engine duct, were studied with the tool. Compared to the computation performed on a fixed mesh, the computational efficiency by the AMR method is increased extensively while the accuracy of the solution is still maintained.

Plasma Actuators for Bluff-Body Interaction Noise Control

Initial experimental works have been carried out to investigate effects of plasma actuators on the control of the broadband noise interaction on a bluff body (circular cylinder) with attached oblique struts, which represents some components of landing gear. Two types of plasma actuators, i.e. dielectric barrier discharge (DBD) and sliding discharge (DBD+DC), were performed on the bluff body arranged in tandem. The induced wind by each discharge was measured with a glass pitot tube senor, and their effect on the local flow and aeroacoutics were studied by near- and far-field microphone array and particle image velocimetry (PIV).

Slat Noise Attenuation with Acoustic Liner Treatment

Numerical simulations were performed to investigate the generation and farfield propagation of the slat noise generated by a high-lift wing model. A numerical approach was developed that combines nearfield flow computation with an integral radiation model to predict the farfield acoustic signals. A time domain impedance boundary condition was implemented to simulate the effect of the liner material directly. The noise generation was calculated using large-eddy simulation (LES) with a 6th-order accuracy spatial scheme. The calculated noise sources were then used to drive the acoustic perturbation equations (APE) to simulate the noise propagation and the attenuation by acoustic liners. The farfield acoustic signals were calculated by solving the Ffowcs Williams and Hawkings equation. Results show that attenuation is achieved by the acoustic liner treatment.