Microphone array designs

Non-uniform array for circular mode detection in aircraft engines
At NLR microphone arrays were designed for several applications:
  • wind tunnel measurements (for open jet & closed test section),
  • measurements on wind turbines,
  • circular mode detection (in intake and exhaust ducts of engines),
  • radial mode detection (with a slowly rotating rake).

Wind tunnel acoustic processing tools

Software was made for:
  • cross-spectral matrix calculations,
  • several methods for phased array beamforming, including the widely-used deconvolution method CLEAN-SC ,
  • acoustic transmission from a source in an open jet to a microphone outside the flow,
  • the calculation of “real life” fly-over data from measurements on scale model in a wind tunnel.


Beamforming on moving sources

Software was made for:
  • moving sources (applied to flying aircraft),
  • rotating sources (applied to wind turbines).
Acoustic sources on an Airbus A340 in approach


Acoustic field modelling

Acoustic field modelling software was made for the following applications:
  • propagation of sound through a lined flow duct (extensions to existing software, with bulk-absorbers and multiple lined segments),
  • propagation of sound through a C-shaped duct,
  • Green’s functions in non-uniform parallel flow,
  • rotor-stator interaction (extension to existing software).
                                                                        Acoustic source in open jet