  A transient two-dimensional acoustic boundary element solver is coupled to a
potential flow boundary element solver via Powell's acoustic analogy to
determine the acoustic emission of isolated hydrofoils performing
biologically-inspired motions. The flow-acoustic boundary element framework is
validated against experimental and asymptotic solutions for the noise produced
by canonical vortex-body interactions. The numerical framework then
characterizes the noise production of an oscillating foil, which is a simple
representation of a fish caudal fin. A rigid NACA 0012 hydrofoil is subjected
to combined heaving and pitching motions for Strouhal numbers ($0.03 < St < 1$)
based on peak-to-peak amplitudes and chord-based reduced frequencies ($0.125 <
f^* < 1$) that span the parameter space of many swimming fish species. A
dipolar acoustic directivity is found for all motions, frequencies, and
amplitudes considered, and the peak noise level increases with both the reduced
frequency and the Strouhal number. A combined heaving and pitching motion
produces less noise than either a purely pitching or purely heaving foil at a
fixed reduced frequency and amplitude of motion. Correlations of the lift and
power coefficients with the peak root-mean-square acoustic pressure levels are
determined, which could be utilized to develop long-range, quiet swimmers.
