Numerical study on the self-induced U-tube oscillation

In the double tank system having two independent free surfaces and circulating flow, a manometer oscillation was self-excited by flow without any other external force, i.e. 'self-induced U-tube oscillation'. This tank system was composed of an upstream tank where the flow entered and a downstream tank which was connected to the upstream tank through a joint space and having a drain. In the present study, the simulation of self-induced U-tube oscillation was carried out. The flow with free surface in the upstream tank was calculated, using a two-dimensional laminar code based on Boundary Fitted Coordinate method (BFC). While, the flow motion in the downstream tank and joint space were modeled respectively, based on the lumped constant assumption. The simulated results were verified qualitatively. The characteristics of this phenomenon were evaluated using the simulated results. It was observed qualitatively that the flow variation from inlet to outlet in the upstream tank played an important role to the self-excitation. Furthermore, the reduction of resonant frequency was predicted by simulated results, which was considered to be caused by the flow pattern transition. (author)