ABSTRACT
The strategy of Scheme 4 may be extended to explore new directions in sensing that extend well beyond the world of chemicals. We have invented a new technique called molecular tagging velocimetry (or MTV) [304-307], which allows us to physically sense flow by precisely describing the velocity profile of a fluid. In the MTV experiment, the ternary complex is dissolved in water and a grid of laser lines is imposed upon a flow of interest by shining a laser beam off a grating. A glowing grid is defined by the luminescence from the ternary complex. The 10-ms luminescence lifetime of the ternary complex allows the grid to convect with flows moving as slowly as 0.02 m/s. The deformation of the grid as it moves with the flow is recorded with a CCD camera. By measuring the distance and direction each grid intersection travels and knowing the time delay between each image, the two velocity components in the grid plane may be determined (the out-of-plane velocity can be determined with a second CCD camera). Parameters important to the fluid physicist such as turbulence intensities, the Reynolds stress, and vorticity may be calculated. The solubility of the ternary complex in water has enabled us to use the MTV technique to specify fluid flows with Reynolds numbers that can be achieved in water tanks and tow facilities. Quantitative measures of swirl and tumble within the cylinder of an engine (rotational flow about and perpendicular to the cylinder axis, respectively) [308], two-phase liquid/solid flows [309,310], and other flow issues of concern at boundary layers of solid [311,312] and aerodynamic surfaces (e.g., a rotating airfoil [313]) have been characterized.
