PIV Experimental Study on Oscillatory Flow of Liquid in U-tube Induced by Gas-liquid Coupling

Abstract

The characteristics of oscillating flow field have always been one of the hot issues in fluid mechanics. However, compared with the study of oscillating disturbance flow superimposed on the stable mainstream, there are relatively few theoretical or experimental studies on the instability of pure oscillating flow. Based on this, this paper uses a peristaltic pump to alter gas pressure gradient and induce reciprocating flow in a vertical U-tube (Rc/D=2.5). The particle image velocimetry (PIV) technology is used to build a visual experimental platform, and the pure oscillating flow field experiments in the U-tube under different oscillation periods are carried out. We modeled the fluid dynamics of the coupled gas-liquid interaction. Analyze the period variation law, the flow field characteristics of Oscillatory Reynolds number (111 ≤ Re δ ≤ 226，Based on Stokes layer thickness), Womersley number (1.69≤Wo≤2.21), transient velocity flow field and vorticity distribution of alternating pipe flow under different oscillation frequencies (0.28-0.49Hz). Experiments show that the interaction of inertial force and viscous force affects the fluid oscillation when the gas-driven liquid flows in a vertical U-tube. The velocity of the flow field changes periodically. The maximum instantaneous velocity of the flow center at different positions is consistent, and the axial velocity has no obvious gradient. The vector peak is affected by the period and phase. when increases, the instability of the liquid flow field intensifies also, and a complex gas-liquid mixed flow multiphase flow mode appears in the U-tube. This research aims to advance understanding and application of unstable pure oscillating flow fields, offering valuable experimental insights for related researchers.