Image registration algorithm for molecular tagging velocimetry applied to unsteady flow in Hele-Shaw cell
Florent Brunet, Emmanuel Cid, Adrien Bartoli, Emmanuella Bouche, Frédéric Risso, Véronique Roig
Experimental Thermal and Fluid Science, Volume 44, 897-904, January 2013
Abstract
In order to develop velocimetry methods for confined geometries, we
propose to combine image registration and volumetric reconstruction
from a monocular video of the draining of a Hele-Shaw cell filled
with water. The cell’s thickness is small compared to the other two
dimensions (e.g. 1 x 400 x 800 mm^3). We use a technique known as
molecular tagging which consists in marking by photobleaching a pattern
in the fluid and then tracking its deformations. The evolution of
the pattern is filmed with a camera whose principal axis coincides
with the cell’s gap. The velocity of the fluid along this direction
is not constant. Consequently, tracking the pattern cannot be achieved
with classical methods because what is observed is the integral of
the marked molecules over the entire cell’s gap. The proposed approach
is built on top of direct image registration that we extend to specifically
model the volumetric image formation. It allows us to accurately
measure the motion and the velocity profiles for the entire volume
(including the cell’s gap) which is something usually hard to achieve.
The results we obtained are consistent with the theoretical hydrodynamic
behaviour for this flow which is known as the Poiseuille flow.