Dynamic Mode Decomposition DMD Gallery

Phase-averaged λci fields in the near wake region with different phase angles.
Streamwise components of typical dynamic modes with different characteristic frequencies: (a) 0.25f₀; (b) 1.0f₀; (c) 2.0f₀; (d) 3.0f₀.

Initial growth of a disturbance in a boundary layer influenced by a circular cylinder wake
Guosheng He, Jinjun Wang and ChongPan.
Beihang University, Beijing
Journal of Fluid Mechanics, (2013), vol. 718.

The initial growth of a disturbance induced by a near-wall circular cylinder in a flat-plate boundary layer was experimentally investigated using both PIV and hydrogen bubble visualization techniques.

The streamwise variation of the total disturbance energy within the boundary layer shows a two-stage growth: the first exponential growth stage, followed by a region with slower growth rate. Experiment revealed that these two stages of growth are related to the formation and the destabilization of the secondary vortex in the near-wall region.

Dynamic mode decomposition (DMD) was used to decompose the total disturbance into temporally orthogonalized modes. It shows that the first growth stage largely results from the increased disturbance at the same frequency as that of the wake vortex shedding, while the second growth stage comprises the disturbance growth in a number of frequencies, especially the lower ones.

MicroVec 2D TRPIV system was used with a continuous laser sheet. VGA resolution CCD camera was used to capture the iages at 100 fps.