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Activity title

Aeroacoustics of Engine Installation for Military Air Vehicles

Activity Reference

AVT-233

Panel

Applied Vehicle Technology

Security Classification

NATO UNCLASSIFIED

Status

Active

Activity type

RTG

Start date

2014

End date

2017

Keywords

Aeroacoustics, Aeroacoustics of Propulsion Airframe Integration, Air Vehicle Noise

Background

Accurate prediction of the sound radiation from aircraft, using computational methods, would be valuable to influence the vehicle design process at an early stage where significant noise reduction is possible.

Objectives

To study installation effects on the radiated sound of generic vehicle models, to determine the shielding properties that can be used as an effective means of reducing noise and, to validate sound radiation prediction methods.

Topics

Source noise of military air vehicle classes, including open rotor- (propellers, helicopters, UAVs) and jet-powered. Source to receiver propagation, near field acoustic effects, relevance of available aircraft noise prediction methods with regard to propulsion system installation effects, and such other aeroacoustic phenomena as become pertinent. A focus on aero-acoustic installation is recommended because of the relevance to acoustic detectability. Prediction methods must be qualified to serve as reliable tools for the design of geometries which a) maximize the exploitation of acoustic shielding, and b) minimize installation related excess source noise. For this purpose it will be important to define/identify a generic, yet relevant reference vehicle (e.g. the SACCON configuration, possibly some UCAV or civilian blended wing body configuration), which allows the study of the installation effects on the source as well as the radiated acoustic installation/acoustic shielding properties. The studies in this group should include dedicated shielding tests using well-defined (i.e. very simple) sound sources in order to isolate source noise effects from pure acoustic installation effects. The influence of the flow, particularly the refracting boundary layers at the vehicle’s surface, on the resulting sound radiation needs to be studied experimentally and computationally to quantify errors arising from the neglect of convection and refraction effects. The position of the sources relative to the airframe should be varied. Both discrete frequency and broadband sources should be investigated since acoustic shielding exhibits different interference effects during diffraction and scattering by a vehicle. Where necessary, distributed sources should be used to represent propulsion systems during experimental studies and in prediction methods. If affordable, a simultaneous measurement of the surface pressure fluctuations is desirable since increasing structural vibration (cabin noise) excitation will potentially accompany an increasing exploitation of acoustic shielding. Installation related sources of sound should possibly be studied via the same reference vehicle. Although radiation from the engine intake is certainly relevant the more challenging issue is installed jet noise. For geometries with jets exhausting over an aft deck or shielding structure typically a jet/trailing edge interaction takes place, which may increase the radiated noise considerably. Again, if affordable within the timeframe of the TG, unsteady flowfield measurements should be acquired. It is recommended that an appropriate setup be defined, possibly with a generic cold jet, directed tangentially to the trailing edge of the vehicle. The effects of some simple trailing edge extension devices on the radiated jet noise should be studied experimentally and computationally, with the objective to qualify computation methods for a reliable prediction of source installation effects.

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