Non-axisymmetric wall-thinning downstream of elbow-orifice pipeline in swirling flow

The non-axisymmetric wall-thinning leading to a pipeline break is studied in a scaled model experiment in a water tunnel. The pipeline consists of an elbow, an orifice and a straight pipe between them. The measurement of velocity field is carried out downstream of the orifice using stereo PIV and the spatial correlation of velocity fluctuations is analyzed by snapshot Proper Orthogonal Decomposition (POD), while the mass transfer coefficient is measured by a benzoic acid dissolution method. These measurements are carried out at Reynolds number Re = 3 × 104 with and without swirl. It is found that the non-axisymmetric flow and mass transfer is found downstream of the orifice due to the combined influence of the secondary flow in the elbow and the swirling flow. The POD analysis indicates that non-axisymmetric velocity field is generated in the first two POD modes, which suggests the structural change in the velocity field downstream of the orifice, such as the non-axisymmetric growth of the velocity and turbulent energy in the lower POD modes. It is also found that the near-wall turbulent energy distribution is correlated with the measurement of mass transfer coefficient.