In this paper, an acoustic source localization method using the emerging technology of the deep neural network (DNN) is proposed. After the construction and training of the DNN, the capability of the DNN for source localization through a set of numerical simulations is verified. Next, experimental studies and demonstrations in a very shallow water tank with acoustic reflective walls are prepared, which enable the quick acquisition of a huge amount of experimental data for the training of a one-dimensional DNN-based source localization model. The development of the DNN-based source localization method and the corresponding numerical and experimental demonstration constitute the main contribution of this work. The associated performance is then evaluated at various frequencies. In particular, the localization results of the DNN are compared with readily available model-based localization methods, such as the conventional matched field processing method and the normal-mode based multiple signal classification method. The comparison shows that the proposed DNN approach is able to produce satisfactory accuracy in this reflective shallow water tank environment, for which a forward acoustic propagating model is not required. Last but not least, the generality of the proposed DNN approach from one-dimensional localization to progressively more complicated two-dimensional tasks is also considered.

In many aeronautics and marine applications, the unsteady forces generated by propulsion rotors due to turbulence ingestion are a significant source of noise and create serious concerns. The understanding of rotor turbulence ingestion and the rotor noise generation mechanisms is vital to achieve an optimal design or apply noise control strategy. The current study is the first attempt to numerically investigate an underwater rotor ingesting grid-generated turbulence by large eddy simulation combined with the Ffowcs-Williams and Hawkings equation. The flow characteristics of two directly simulated turbulence grids with a mesh spacing of 4 and 6 in. are investigated and proved to be adequate for the rotor turbulence ingestion study. The simulated unsteady force spectra of the rotor show better agreement with the experimental results in terms of amplitudes and frequency ranges of the first haystack and broadband components compared to previous theoretical and numerical studies. The unsteady forces and noise of the rotor downstream of the 4-in. grid are slightly higher than those downstream of the 6-in. grid. A far-field noise prediction approach based on the time derivatives of the rotor axial and radial unsteady forces are investigated and validated. The far-field noise spectra and the rotor noise directivities predicted by the time derivative approach agree well with the Ffowcs-Williams and Hawkings equation in the main frequency range of underwater rotor noise. The noise directivities are found to be dominated by axial force related dipole sources.

High resolution aeroacoustic source analysis is a prerequisite to address the noise concerns and release the full benefits of wake-ingesting propellers. In this work, the aeroacoustic sources of a two-bladed propeller ingesting the wake of an aerofoil are investigated using large eddy simulation in conjunction with two different source identifying approaches. The first approach is the numerical beamforming that utilizes both the classical and wavelet-based beamforming techniques, which determine the phase variations of sources at the low to mid frequencies and reveal that the high-frequency sources are phase-independent. To further improve the spatial resolution of source identification, a new near-field aeroacoustic source analysis approach based on the acoustic analogy is developed in this work. In particular, the on-surface source terms emanating the far-field noise are derived based on the Ffowcs Williams and Hawkings equation for low Mach number flows and constant rotating propellers. Through the incorporation of the simulation results into the proposed source analysis approach, various types of aeroacoustic sources are identified and studied by visualizing their distributions on the propeller surfaces, correlating to flow features and examining the noise spectra and directivity. While the leading edge sources are highly correlated with the wake interaction process, the sources at the mid-chord and the trailing edge of the blade can maintain their strength across most revolving angles. Overall, the proposed analysis approaches extend the capability of computational fluid dynamics and enable the detailed study of noise generation mechanisms of wake-ingesting propeller noise.