Instability in a Spatially-Periodic Channel: Aspect-Ratio Dependence

In channel flow with one wall textured with spanwise grooves distributed periodically in the streamwise direction, prior 2D simulations indicated a primary transition to stable waves similar to Tollmien-Schlichting modes at Reynolds numbers O(100), in contrast to transition in plane channel flow at Reynolds numbers O(1000). We present results from laboratory experiments and direct numerical simulations to compare instability onset measurements in large aspect-ratio channels with predictions from 2D and 3D simulations. Additionally, we investigate the onset of instability and the resulting flow behavior as a function of channel aspect-ratio.