Previous studies demonstrate that the presence of liquid strongly influences the pressure pulsation amplitudes of flow induced pulsations. In particular, in case of annular flow (thin liquid film on the walls) the pulsations can be eliminated. The present study aims at evaluating the contribution of the liquid film to the pulsation reduction.
Experiments have been performed in a tandem configuration with two side branches upward oriented. The side branches have the same diameter as the main pipe.
A first set of experiments has been conducted with the injection point located far upstream the upstream side branch. To isolate the sole effect of the film, a second and a third set of experiments have been performed with the injection point located close upstream the T-junction with the injection such that a thin film only was generated.
In the first configuration (far upstream), the pulsation level decreases with increasing liquid rate. The reduction in amplitude compares well with the assumption of added damping in the length between the two side branches.
A similar decrease in pulsation amplitude was obtained in the second configuration. However, the amplitude reduction depends on the local liquid flow pattern at the (upstream) side branch and in particular on whether liquid bypasses the side branch or it interferes with the shear layer.
This indicates that acoustical damping is the main effect and small amounts of liquid do not significantly interfere with the shear layer.