Multiphase flow can induce high amplitude vibrations in piping systems. Several experimental campaigns focused on the force spectrum on a single bend. To evaluate the evolution of the forces from bend to bend, experiments have been done on an air-water, one inch pipe system consisting of six bends at near-atmospheric conditions. In a first phase, all individual bends were clamped to measure the phase relation and correlation of the flow-induced forces on the subsequent bends. In a second phase, all clamps were removed to measure the free vibrations. In this paper which focusses on the phase 2 results, the vibration measurements were compared to the calculated vibrations. For the excitation forces and phase relations, the measured force spectra from phase 1 are used. Damping values are based on experimental results from phase 2. The results show a good match between modeled and measured vibrations levels. Including the measured correlation between forces at multiple bends, improves the modeled results for slug flow cases. It is possible to directly use extract damping values from the measured signals, however, robustness of the damping estimation needs to be improved. Using average damping values currently leads to the best match.

We study the relation between large-scale structures in the concentration field with those in the velocity field in a dye-seeded turbulent jet. The scalar concentration in a plane is measured using laser-induced fluorescence. Uniform concentration zones of an advected scalar are identified using cluster analysis. We simultaneously measure the two-dimensional velocity field using particle image velocimetry. The structures in the velocity field are characterized by finite-time Lyapunov exponents. The measurement of the scalarand velocity fields moves with the mean flow. In this moving frame, turbulent structures remain in focus long enough to observe well-defined ridges of the finite-time Lyapunov field. This field gauges the rate of point separation along Lagrangian trajectories; it was measured both for future and past times since the instant of observation. The edges of uniform concentration zones are correlated with the ridges of the past-time Lyapunov field, but not with those of the future-time Lyapunov field.

We report results on the instantaneous drag force on plates that are accelerated in a direction normal to the plate surface, which show that this force scales with the square root of the acceleration. This is associated with the generation and advection of vorticity at the plate surface. A new scaling law is presented for the drag force on accelerating plates, based on the history force for unsteady flow. This scaling avoids previous inconsistencies in using added mass forces in the description of forces on accelerating plates.

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