Effect of Centrifugal Force on the Disturbance Wave Characteristics of Decay Swirl Liquid Film

The liquid film interfacial wave characteristics of vertical and swirling flow are experimentally investigated with the ultrasonic Doppler velocimetry and a high-speed camera under a liquid-phase Reynolds number (Rel) of 5.88 × 103–1.23 × 104, and a correlation for the disturbance wave frequency of swirling flow was developed based on the centrifugal-gravity ratio. The interfacial waves of swirling flow have no apparent periodicity and correlation, similar to the vertical flow. In swirling flow, centrifugal force promotes the accumulation of liquid film mass, reflected in the increase of the substrate liquid film. The circumferential velocity of the swirling flow increases the wall friction stress, reducing the disturbance wave velocity. The superposition of swirling streaks promotes the formation of disturbance waves. Still, the increasing centrifugal force forces the disturbance waves to transfer mass and energy to the ripples, suppressing the formation of disturbance waves. The established correlation for the disturbance wave frequency has a good prediction effect with a mean absolute percentage error of 19.89%.