Acoustic Resonances in 2D Open Cavities

Acoustical resonances of a 2D open cavity of aeroacoustic interest are elucidated by a computational acoustic model and a fast and inexpensive experimental method. Numerical predictions of acoustic resonances (eigenmodes) of an open cavity are computed by solving a multi-dimensional Helmholtz equation, subject to appropriate Perfectly Matched Layer absorbing boundary conditions simulating the presence of the open domain. Spectral/hp element spatial discretization of the eigenvalue problem ensures accuracy and geometrical flexibility. The experimental approach consists of several steps. First, the impulse responses between tweeters and electret microphones in diff erent positions inside the cavity are measured. To equalize possible acoustic resonances of the tweeter, inverse filtering is then applied. Second, time-windowing is applied in order to select and process some, and reject other, parts of the measured signal. The transformation of these time-windowed impulse responses to the frequency domains provide the transfer functions between each tweeter-microphone pair whose peaks are identified as the acoustic resonances of the cavity. An excellent agreement is verified between experimental results and numerical predictions.