Benchmarking a simplified model for acoustic streaming in SAW acoustofluidics

Computational modeling of acoustic streaming in surface acoustic wave (SAW) devices is crucial for acoustofluidic application design. While simplified models offer reduced computational cost compared to traditional approaches like the Reynolds stress method (RSM) and the arbitrary Lagrangian-Eulerian (ALE) method, their validity remains poorly investigated. This study systematically evaluates an effective simplified model that employs a viscous acoustic body force and a slip velocity for the simulation of acoustic streaming in SAW devices under the Stokes-slip boundary condition. By introducing a model difference factor (D), we delineate its applicability for both standing SAW (SSAW) and traveling SAW (TSAW) devices across a range of normalized channel height (h). The results establish that the simplified model is valid (D≤0.2) for h≥0.8 in SSAW and h≥1.5 in TSAW devices, achieving a significant reduction in computational cost. Furthermore, we identify a critical height (h_c≈0.43-0.58) marking the transition from boundary-driven (Rayleigh) to bulk (Eckart) streaming. Beyond this threshold, specifically for h≥1.1 in SSAW and h≥2.0 in TSAW devices, the slip velocity becomes negligible, and analytical approximations of the viscous body force are shown to be applicable. We also demonstrate that an improved layered approach, effective under no-slip conditions, fails for the physically correct Stokes-slip boundary. This work provides clear guidelines for the accurate and efficient simulation of acoustic streaming, enabling optimized device design across different operational regimes.