Mode merging design method for non-locally reacting liner with porous bulk materials

• The Mode Merging Design Method (MMDM), a theoretical design method further developed based on the Cremer concept, for non-locally reacting liners with porous materials is first proposed and established. The acoustic properties of such non-locally reacting liners are determined by the combined action of porous materials in the chamber and perforated plate adjacent to porous backing and grazing flow, which are described by the Delany & Bazley (DB)-like models and the combined Guess & Kirby-Cummings (Guess-KC) impedance model in this study, respectively. According to the structure characteristics of bulk liner, the porous chamber depth Lc and flow resistivity σ, are selected to be optimized to maximize the sound attenuation at a target frequency when a single circumferential mode is incident. In the spirit of the mode merging theory, the eigen equation and the branch point equation for this physical problem are derived, from which the merging double eigenvalue/mode can be solved, in turn, the optimum chamber depth Lc and flow resistivity σ can be simultaneously determined, which can produce theoretically maximum sound attenuation. Then, a Finite Element (FE) sound propagation model is established to validate the liner design of theoretical optimization by MMDM. The accuracies of the eigen-analysis method, the DB model, the Guess-KC model and the FE model are validated through several benchmark cases. Further, the MMDM is applied in four design cases of bulk liners with finite length, and the results indicate that the MMDM can accurately aim at a given condition of grazing flow Ma, circumferential mode order m and target frequency f to effectively optimize the structural parameters for actual bulk liners. Finally, an optimality analysis performed through two concrete cases demonstrates that the MMDM can avoid locally optimal solution and successfully find optimal structures for an infinite non-locally reacting liner, thus producing the maximum sound attenuation at target frequency.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Maskinteknik -- Farkostteknik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Mechanical Engineering -- Vehicle Engineering (hsv//eng)

Nyckelord

Acoustic impedance

Acoustic wave propagation

Aeroacoustics

Eigenvalues and eigenfunctions

Merging

Perforated plates

Porous materials

Structural optimization

Circumferential modes

Impedance modeling

Optimal structures

Optimality analysis

Structural parameter

Structure characteristic

Target frequencies

Theoretical design

Structural design

Publikations- och innehållstyp

ref (ämneskategori)

kon (ämneskategori)