OBJECTIVES

PIANO aims at enabling future low noise tilt-rotor aircrafts with an improved interior acoustic comfort. This is achieved by developing a robust system characterization for interior noise control, as well as improved dedicated solutions for interior noise abatement without weight penalty.

The associated high-level objectives to the overall goal are the following:

  • Improve tilt-rotor vibro-acoustic characterization for a more accurate assessment of noise abatement measures
  • Improve the accuracy of numerical modelling of aircrafts through experimental techniques
  • Enable aircrafts with enhanced interior acoustic comfort without weight penalization and at a reasonable cost

Technical objectives are described as follows:

  1. Identification of the tilt-rotor subsystems from a 3D model of the aircraft. A novel methodology based on direct transfer paths and clustering techniques will be applied to identify the different subsystems of the tilt-rotor. This subsystem list will be used as a valuable input for the definition of the ATPA test.
  1. Obtention of noise paths and contributions of a tilt-rotor, quantifying air-borne and structure-borne noise through the ATPA technique. An ATPA test will be performed in the tilt-rotor, for certain flight conditions. This method allows to quantify noise paths (from sources and from panels) to a certain receiver, distinguishing air-borne from structure-borne transmission paths, covering a wide frequency range.
  1. Obtention of SEA factors from ATPA results in real case. A methodology to deduce SEA coupling and loss factors from ATPA results will be applied. This methodology uses the energetic direct transfer functions and global transfer functions from the ATPA analysis.
  1. Implementation of an efficient Local Active Noise Control (LANC) system at a passenger headrest level (“quite bubble” concept). At a first priority, efficient ANC systems for generation of local quiet zones around the passenger heads (LANC).will be considered due to their simplicity and effectiveness. The current high TRL LANC systems of TechnoFirst  and DSL-NTUA will be adapted to the project needs and further extended and improved towards the following directions:
  • Reduction of weight and cost
  • Enhancement of the extent, robustness and frequency range of the quiet zone around the passenger head
  • Implementation of advanced active noise control systems, such as broad-band feed-forward and hybrid approaches, sub-band adaptive filtering and binaural and psychoacoustic ANC
  1. Implementation of a supplementary Global Active Noise Control system (GANC) at a cabin level. After evaluating the effectiveness of the LANC and following the results of ATPA, a GANC approach will be followed. The GANC will complement LANC in two directions:
  • Cancellation of low frequency global modes (e.g. well below 100Hz).
  • Better spatial localization and enhancement of the extent of the quiet zones, especially at cabin areas with high noise level and poor LANC results.

For this reason, several advanced GANC approaches will be considered:

  • Acoustic mode cancellation
  • Wave-Field synthesis and Multichannel Equalization
  • Non-linear and Artificial Intelligence Based Approaches

Advanced optimization approaches for the selection of the number and the proper location of the GANC loudspeakers and microphones will be implemented, especially of the heavy low frequency loudspeakers (woofers). Constraints shall ensure that the overall noise level due to the ANC intervention does not exceed the permissible limits at any point in the cabin. Robustness will be ensured in case of failure of critical control elements.