DEFINITION:

Helicopter aeroacoustics consists in:

• studying and identifying the aerodynamic phenomena causing noise generation and influencing noise radiation. The occurrence of these phenomena and their relative contributions to noise, strongly depend on flight conditions (take-off, descent, level flight at low, medium and high speed) and on the type of helicopter.
• Developing and validating computational tools for prediction of helicopter noise with the following objectives:
  • quantification of helicopter nuisance,
  • quiet helicopter design (rotor, turboshaft air intake and acoustic lining),
  • determination of low noise flight procedures (for civil applications)
  • determination of low detectability manoeuvres and flight procedures (for military purposes). Helicopter noise sources comprise main and tail rotors and turboshaft engines.

Research activities consist in:

• physical modelling and numerical simulations,
• wind tunnel or static tests and helicopter flight tests.

Key issues for an accurate numerical prediction of helicopter noise are:

• for rotor noise, a precise prediction of the main rotor wake and vortices which may interact with main rotor and even tail rotor blades, depending on flight conditions.
• for turboshaft engine noise, a precise prediction of acoustic propagation in the complex flow and geometry of the engine air intake.

(Source: ACARE Domain 211)

SUBDOMAINS:

1. Sub-domains according to the origin of the sources:
   1. main rotor noise
   2. tail rotor noise
   3. turboshaft engine noise
2. Sub-domains according to the nature of noise:
   1. Discrete frequency noise related to periodic aerodynamic phenomena. The nuisance from helicopter rotors is very much increased when a certain type of discrete frequency noise called «helicopter rotor impulsive noise» occurs. This «impulsive noise» includes Blade Vortex Interaction (BVI) noise in descent and low-to-medium level flight and High Speed Impulsive noise (HSI).
   2. Broadband noise, mainly due to interactions between rotating components (rotor and compressor blades) with incoming turbulence.