Quantitative Assessment of Flow Structural Changes via Similarity Analysis Using Dynamic Mode Decomposition

Structural changes in fluid flows are commonly observed in phenomena such as vortex formation, breakdown, and separation. This study presents a data-driven framework for quantitatively assessing similarity in flow dynamics by integrating Dynamic Mode Decomposition (DMD), which extracts dominant flow features, with a Grassmann kernel-based metric. Simulations of flow over an airfoil were conducted across a range of angles of attack, and changes in the lift coefficient and DMD modes were examined. The similarity analysis revealed a sharp decline near an angle of attack of 16°, corresponding to the onset of stall associated with boundary layer separation, thereby providing a quantitative characterization of the transition in the flow structure. The proposed approach offers a practical and interpretable tool for analyzing and comparing complex fluid dynamic behaviors.