To clarify the influence of sidewalls on flow instability in rectangular wavy channels with sinusoidal waveforms, this study employs numerical simulations to investigate both the location of flow instability and the local characteristics following the onset of instability under different channel widths. When the Reynolds number Re = 450 and the width-to-height ratio W/H ≥ 8, longitudinal vortices affected by the sidewalls propagate from the wall region toward the channel center, but these vortices remain stable. In regions not influenced by the sidewalls, the waviness triggers flow instability that first appears in a two-dimensional form, manifested as deformation and splitting of transverse vortices. This subsequently evolves into three-dimensional instability, generating longitudinal vortices and ultimately transitioning to a chaotic state—characteristic of a secondary instability of Görtler vortices. The onset location of instability is governed by the behavior of the transverse vortices.
 

flow, instability,,width,numerical simulation; wavy channel