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We investigate the amplitude modulation of acoustic waves in acceleratingflows, a problem that is still not fully understood, but essential to manytechnical applications, ranging from medical imaging to acoustic remotesensing. The proposed modeling framework is based on a convective form of theKuznetsov equation, which incorporates the background flow field and is solvednumerically by a finite-difference method. Using acoustic black and white holeanalogues as model systems, we identify a modulation of the wave amplitude,that is shown to be driven by the divergence/convergence of the acoustic wavecharacteristics in an accelerating/decelerating flow, and which is distinctfrom the convective amplification accompanying an acoustic emitter moving at aconstant velocity. To rationalize the observed amplitude modulation, aleading-order model is derived from first principles, leveraging a similarityof the wave characteristics and the wave amplitude with respect to a modifiedHelmholtz number. This leading-order model may serve as a basis for thenumerical prediction and analysis of the behavior of acoustic waves inaccelerating flows, by taking advantage of the notion that any acceleratingflow field can be described locally as a virtual acoustic black or white hole.

Amplitude modulation of acoustic waves in accelerating flows quantified using acoustic black and white hole analogues