The structure of the flow field inside a torque converter was quantitatively evaluated using dynamic mode decomposition (DMD). The input time series data in the interference region of the cascade blades were measured using particle image velocimetry (PIV). The spatiotemporal flow field was decomposed by DMD into several modes. Each DMD mode corresponds to the frequency of the flow field fluctuation. The flow field frequency mainly consisted of blade passing frequencies and their harmonics. The flow field was visualized for each DMD mode. Positive and negative vortex structures were generated alternately in the direction of rotation of the impeller and turbine. It was found that the vortex structure became smaller at a lower speed ratio.
