A novel strategy for numerical analysis of nonharmonic laser-induced acoustic streaming

Acoustic streaming in microfluidics has traditionally been driven by harmonic acoustic waves generated from on-chip ultrasound transducers. Laser-induced acoustic streaming (laser streaming) offers a transducer-free, light-driven approach to microfluidic actuation. However, the highly nonharmonic nature of laser streaming hinders its analysis using conventional methods. This work introduces a novel strategy to bridge this gap and enables quantitative numerical modeling of laser streaming. This method decomposes the nonharmonic ultrasonic field generated by pulsed laser heating into harmonic components using Fourier series expansion. The dominant components, selected from energy spectrum analysis, are then solved using successive approximations to yield the time-averaged streaming force, which incorporated into second-order streaming equations to determine the streaming field. The simulation results demonstrate good agreement with experimental data and other numerical models. This new strategy significantly reduces the computational costs while enhancing insights into the laser streaming physics. It also provides a versatile tool for analyzing general forms of acoustic streaming induced by nonharmonic sources.