Dense volumetric velocity field reconstruction with time-segment assimilation

The time-segment assimilation (TSA) method levers upon the spatio-temporal information from a finite number of successive time samples of particle velocity, coming from PTV and STB, into a refined spatial reconstruction of the velocity field of the flow. The method recently introduced by Schneiders and Scarano (2018) is elaborated here further in its working principle and hypotheses. Three regimes of operation are identified, with respect to the normalized length of the time segment, of which, the adjacent tracks regime is found to be the most promising in terms of spatial resolution and computational viability. The ability of TSA in delivering high-resolution velocity reconstructions is inquired by a numerical and experimental assessment. The numerical study is based upon a synthetic field of a 3D sine-wave lattice, popular among previous works. The amplitude modulation of sinusoids appears to be increased when moving from the assimilation of a short time sequence, towards a longer time segment. Furthermore, it is observed that the result of the numerical process is independent of the time interval chosen for time-marching, provided that the CFL condition is respected. The experimental analysis regards experimental data from a multichannel swirling jet. The initial results demonstrate that a richer vorticity field can be retrieved when the assimilation is conducted with time segments that approach the stringy regime.