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CAbin NOise from Boundary Layer Excitation

Periodic Reporting for period 2 - CANOBLE (CAbin NOise from Boundary Layer Excitation)

Reporting period: 2018-03-01 to 2019-08-31

What is the problem/issue being addressed?

The CANOBLE project aims to address cabin & cockpit noise induced by the pressure loading on the fuselage structure. The Turbulent boundary layer (TBL) is responsible for two contributions:
1. A direct contribution with generation of self-noise source inside the TBL that by transparency radiates in the cockpit and the cabin
2. An indirect contribution with a pressure loading of the fuselage which by vibration generates noise inside the cockpit and the cabin
Controlling such noise sources requires a way to measure the excitation level as well as an accurate source and transmission path analysis model to predict the efficiency of the aircraft in design phase.
Given by the theory, the TBL loading is a space-time quantity controlling by the coherence length of the turbulence and the pressure fluctuation amplitude over the time. For both test and simulation, those two quantity must be characterized.
On the experimental side, this characterization is challenging because:
• To reproduce the right turbulent scale inside the boundary layer, a full scale model is required operating in realistic flow conditions
• The thickness of the TBL along a wall is very thin which requires a non-intrusive and local measurement
• The frequency spectrum of interest is very large from 300Hz up to 10kHz
• The pressure fluctuation level is high leading to an overload of standard microphone probe types while the various dynamic of the excitation (acoustic vs hydrodynamic) limits the use of dynamic pressure probe
• The spatial dependency requires to measure the
For all these reasons, no experimental data base are available at full scale. On the simulation side, model source are based on empirical methods mainly based on test data. By enriching the experimental data base with the CANOBLE project will help in improving the current state of the art in source modeling
The transfer path analysis in a vibroacoustic context is a second challenge in analyzing the TBL contribution. On the measurement side, a common way is to use intensity probe with masking technics. Such method allows for the measurement of accurate global indicator like the transmitted power of a panel but it is a long process and it is therefore difficult to execute such measurement during a flight test. In CANOBLE, it is expected to perform a complete transfer path analysis with vibration and inner noise measurements. For the inner noise, current intensity methods will be comparted with new methods based on acoustic array technics. On the numerical side, if the structure and acoustic modeling are yet well known, applying such random excitation in the medium and high frequency range requires an accurate coupling and a dedicated sampling strategy. Furthermore, the ability to produce a virtual prototype is a requirement due to the difficulty to perform full scale test in flight condition except on a real aircraft. A aero/vibroacoustic virtual prototype is a nice way to extrapolate results based on a data base measured at low speed.

Why is it important for society?

For business jet and large passenger aircraft, cabin & cockpit noise is of major interest for safety (audibility), for the health of the crew and for the comfort of the passenger. Ability to the measurement and to better predict the interior noise induced by the TBL has therefore a strong impact on all the human chain involved in the use of civil and private aircraft.
Furthermore, with the integration of new external devices to improve on-board communication (TV, web connectivity, big data, tracking, external probes for control, etc.) and the trend in design for larger cabin size like the Falcon 6X, TBL noise will have a stronger impact on interior noise in the next generation of civil aircraft.
For the competitiveness of the European industry, producing quitter aircraft is one differentiating criterion for the sales force towards competitors.
Finally, improving the understanding of the pressure wall excitation in the aeronautic context impacts directly other industries. Indeed for example:
• In the automotive industry, the increasing of the electrical engine will directly change the noise source contribution into the cabin with no more engine piston noise and the increase of the flow noise contribution
• for the marine and defense industry where underwater TBL loading is a source of excitation of the hulls and directly breaks the acoustic discretion feature of the vessels and reduces the accuracy of flush equipment like the sonar
• for the oil&gas and nuclear industries with the well-known AIV/FIV excitation due to high pressure surface loading in pipe which could lead by dynamic fatigue to equipment failure.

What are the overall objectives?

CANOBLE objectives are:
1/ Develop key TBL technologies:
1.1 To measure the fuselage & Cockpit pressure induced by the TBL using a non-intrusive, consumable and affordable pressure surface array
1.2 To develop an accurate TBL pressure surface model compatible with the industrial design constrains and generate a full aero/vibro-acoustic coupling method.
1.3 To validate in labs for various flow conditions the 1.1 and 1.2 development
2/ Perform a full scale validation:
2.1 Manufacturing of a full-scale cockpit and cabin mock-up
2.2 Perform low speed measurements in Wind Tunnel environment
2.3 Develop a virtual prototype to extend the results to flight conditions
1/ Development of an aero vibroacoustic modeling strategy including for heterogenous BL profile and a full CFD/FEM coupling

2/ design and manufacturing of TBL pressure array with delivery of first demonstrators

3/ Desing and manufacturing of a full scale mockup

4/ Wind tunnel test : Mockup specification and specification of the wind tunnel test campaign

5/ Development of a virtual AeroVibro-acoustics prototype

6/ EPDR : 7 scientific papers, 1 article, 1 open workshops including major aeronautics actors, 2 operational demonstration for Railway & Automotive industry
The CANOBLE project will set a non intrusive TBL measurement technology validated at full scale in an industrial context combined to a validated modeling approach for desing.
As ouput, the project team will be able to propose a unique set of skills to address the noise problem induced by a turbulent boundary layer with the ambition to propose on the market services and hardware to design a quieter and safer mobility and industrial equipment.