4 research outputs found
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Transition of a vortex ring measured by 3D scanning Tomo-PIV
A vortex ring with piston-based Reynolds number Rep=4650 is studied experimentally by means of time-resolved scanning tomographic PIV. The present measurement technique provides the so-called 4D flow field, thus enables revealing the vortex ring’s transition from laminar to turbulent. The evolution of the ring torus as well as the generation of secondary vortex filaments in transition are first observed through 3D visualization. Analysis on the quantities of the vortex ring, such as circulation and vorticity components, defines the three evolution phases, namely laminar, transition and turbulent. The ring median plane is also examined to provide further insights on flow structure exhibited in transition. The axial vorticity component and radial velocity component are studied respectively and they are found to be organized in a multi-layer concentric-ring pattern. Spectrum analysis on the radial velocity component along the ring core and inner ring where secondary vortical activity happens reveals the dominate wavenumber in transition and broad band of wavenumbers in turbulent phase
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Transition of A Vortex Ring Visualized by 3D Scanning TomoPIV
A vortex ring with piston-based Reynolds number Rep=4650 is studied experimentally by means of time-resolved scanning tomographic PIV. The present measurement technique provides the so-called 4D flow field, thus enables revealing the vortex ring’s transition from laminar to turbulent. The evolution of the ring torus as well as the generation of secondary vortex filaments in transition are first observed through 3D visualization. Analysis on the quantities of the vortex ring, such as circulation and vorticity components, defines the three evolution phases, namely laminar, transition and turbulent. The ring median plane is also examined to provide further insights on flow structure exhibited in transition. The axial vorticity component and radial velocity component are studied respectively and they are found to be organized in a multi-layer concentric-ring pattern. Spectrum analysis on the radial velocity component along the ring core and inner ring where secondary vortical activity happens reveals the dominate wavenumber in transition and broad band of wavenumbers in turbulent phase
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Investigation of the Vortex Ring Transition using Scanning Tomo-PIV
The transition of a vortex ring at ReΓ = 5030 is studied by time-resolved scanning tomographic PIV technique. The transition process is first analyzed through flow quantities such as circulation and vorticity components. Using the volumetric measurement technique, vortical organization of the vortex ring at early and late transition stages are visualized respectively. Focus is paid to the instability phenomenon associated with transition. The present 4D flow data allows analysis of the temporal evolution of the wavenumber spectra. The dominant wavenumbers in transition are identified and the growth of their amplitude is revealed. The vortex ring transition is finally studied through the particle trajectories. A phase difference between the axial velocity and radial velocity is found in the beginning of transition, however, it is subject to change following the progression of transition. Statistical analysis on the velocity components helps to identify the aft portion of the inner ring as the one that is first to lose the original phase relation in velocity, which is caused by the secondary vortical activity during transition