1 Scope
This document specifies the general technical requirements for the design and verification of cabin acoustics during the development of transport category aircraft.
This document applies to the design and verification of cabin acoustics for transport category aircraft. Other aircraft types may also refer to this document for in-cabin acoustic design and verification.
2 Normative references
The contents of the following documents constitute the essential provisions of this document through the normative references in the text. Among them, note the date of the reference document, only the date of the corresponding version applicable to this document; do not note the date of the reference document, its latest version (including all the revision of the list) applicable to this document.
GB/T 3767 Acoustic sound pressure method for the determination of sound power level and sound energy level of noise sources ﹑ Engineering method for approximating the free field above the reflecting surface GB/T3947 Acoustic terminology
3 Terms, definitions and abbreviations
3.1 Terminology and definitions
The terms defined in GB/T 3947 and the following terms and definitions apply to this document.
3.1.1
Decibeldecibel
A unit describing the sound pressure level.
Note:Decibels are expressed in dB.
4 General requirements
4.1 Design basis
At the beginning of the design of transport aircraft, a comprehensive analysis of passenger comfort and the competitiveness of the aircraft market and other factors should be made to develop the noise level and requirements for cabin design. During the development process, a reasonable aircraft cabin noise control plan and design process should be prepared to carry out relevant work continuously:
4.2 Design guidelines
The acoustical design of transport aircraft cabins should be carried out in stages in accordance with HB 8525, usually following the following guidelines.
a) Consider the external sources, internal sources, structural acoustic design and other factors affecting noise levels in the cabin of a transport category aircraft, as well as
a) Consideration of external sources, internal sources, structural acoustic design, and measures such as acoustic insulation (AI) and damping for noise control. Among them:
1) External sources include engine radiation noise, as well as surface noise caused by high speed airflow over the external surfaces of the fuselage and turbulence noise caused by lifting devices, landing gear structures, etc.
5 Detailed requirements
5.1 Estimation of cabin noise and allocation of subsystem indicators
The aircraft cabin noise prediction covers the stages of aircraft requirements and proof of concept, preliminary design, detailed design, commissioning and verification. The basic methods of aircraft cabin noise prediction include finite element method, boundary element method, statistical energy method, hybrid method, sound line method, etc. Usually the finite element method or boundary element method is used for the low frequency band, the hybrid method for the medium frequency band and the statistical energy method or the sound line method for the high frequency band. The following requirements should be fulfilled when the noise in the cabin is expected and the subsystem indicators are assigned:
a) At different design stages, numerical simulation, engineering and other methods are used to assess the acoustic design status of the aircraft to ensure that the aircraft acoustic performance indicators meet the target requirements and, if necessary, to establish an acoustic model of the entire cabin;
b) Based on the results of the modelling and simulation analysis in the initial design phase, establish the maximum permissible noise levels and requirements for each system of the aircraft, in order to meet the design objectives and requirements for aircraft cabin noise, and carry out the allocation of cabin acoustic design indicators in accordance with 4.4.2; and
c) determine the main noise sources, noise transmission paths and control methods for the aircraft based on the predicted results
d) determine the noise loads on the fuselage and the sound insulation performance of typical wall structures
(e) the requirement of noise specifications to subsystem suppliers.
5.2 Acoustic design of wall panel structures and interiors
5.2.1 Sound insulation design requirements for wall panel structures
On the basis of the requirements of 4.4.4 a) and c), the cabin bulkhead structure, wing reinforcement bulkhead structure, hatch, porthole and floor structure shall meet the acoustic design requirements, as well as the sound insulation index requirements for each area of the bulkhead structure.
5.3 Acoustic design and installation of power systems 5.3.1 Engine anechoic nacelle design requirements
For aircraft with turbofan engines, anechoic nacelle structure can be used to inhibit the outward propagation of engine noise.
The design of the anechoic nacelle should be based on the main noise frequencies of the turbofan, the engine nacelle acoustic modes and other parameters, and optimise the nacelle acoustic lining structure parameters and installation layout to meet the requirements of the index limits of the outgoing engine noise. The engine nacelle acoustic design should avoid adverse effects of liquid emissions on the effectiveness of the acoustic liner.
5.3.2 Power system damping installation design requirements
5.4 Acoustic design of on-board systems
5.4.1 Ring control system fan acoustic design requirements 5.4.1.1 Ring control system fan radiation noise assessment
The sound power level of the noise radiated by the fan inlet and exhaust shall be measured using the reverberation chamber method or the free field method, and its contribution to the cabin noise shall be assessed according to its installation location and installation method in conjunction with the numerical model of the cabin noise.
6 Validation requirements
6.1 Wall panel structural sound insulation and interior sound absorption tests
6.1.1 Wall panel structural sound insulation performance test
Using half of the anechoic chamber reverberation chamber aviation wall panel structure sound insulation measurement standards to determine the wall panel sound insulation, for the wall panel structure selection and acoustic design plan to provide data support. The wall panel structure sound insulation performance test mainly includes:
a) sound insulation tests of wall panel structures in different areas of the cabin
b) Hatch structure sound insulation performance test;
c) structural sound insulation tests with portholes;
d) Acoustic performance tests of fuselage wall panels, thermal insulation and interior trim panels
e) Acoustic optimisation and selection tests of wall panel assemblies;
(f) vibration/acoustic characteristics test of the wall panel structure.
6.1.2 Sound absorption test of interior materials
In the impedance tube or reverberation chamber, the sound absorption coefficients and acoustic impedance characteristics of seat padding, carpet materials, side wall panels and bulkheads are measured in the cabin material absorption test to provide data support for the selection of cabin materials and the design of cabin sound absorption and noise reduction. The impedance tube method and the reverberation chamber method can be used to test the sound absorption properties of cabin materials, and are based on the provisions of GB/T18696,1, GB/T 18696.2, HB 7126, GB/T 20247. Acoustic performance test of cabin materials mainly includes:
a) seat cushion and backrest padding material sound absorption performance test
b) Acoustic performance test of carpet materials;
c) Acoustic performance test of side wall decorative panels and bulkheads.
6.2 Powertrain noise and vibration isolation tests
6.2.1 Power system acoustic performance test
6.3 Noise measurement of on-board systems/equipment
6.3.1 Acoustic tests of the environmental control system
The acoustic performance test of the EMS is carried out to verify whether the noise index of the EMS meets the design requirements. The requirements for the acoustic performance test of the EMS are as follows.
6.4 Cabin noise measurement
In accordance with the requirements of GB/T 20248 and other relevant standards, the noise test in the cabin section of the test chamber and the cabin noise test under flight condition are conducted to verify the sound pressure level (SPL), A-weighted sound level, reverberation time, speech interference level and cockpit speech transmission index at 1/3 octave and octave. The total sound pressure level (SPL) is measured for compliance with the specifications. The results can be used to improve acoustic simulation models and acoustic changes to the cabin. In-cabin noise testing consists mainly of:
a) Testing of the acoustic performance in the cabin section of the aircraft in the test chamber or on the ground at a standstill;
b) measurements of acoustic loads on the aircraft fuselage surfaces in flight and on the ground during driving conditions; and
c) In-flight testing to verify the acoustic design of the aircraft cabin in cruise conditions.
Appendix A (Informative) Acoustic design-related calculation equations
1 Scope
2 Normative references
3 Terms, definitions and abbreviations
4 General requirements
5 Detailed requirements
6 Validation requirements
Appendix A (Informative) Acoustic design-related calculation equations
