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A new technique for the simultaneous measurement of velocity and concentration fields is described. We describe here applications in liquid-phase flows, but the methodology can be extended to gas-phase flows with appropriate tracers. In this single-laser, two-tracer approach, molecular tagging velocimetry (MTV) based on the use of a phosphorescent compound is combined with laser induced fluorescence (LIF) using fluorescein as a tracer. Results show that one can design experiments with minimal cross-talk between the LIF and MTV signals. Applications of the simultaneous MTV-LIF technique are demonstrated by performing simultaneous flow visualization and vorticity measurements in a low Reynolds number forced wake and simultaneous velocity-concentration measurements in a turbulent mixing layer. Preliminary data on the mean and RMS fluctuation of velocity and concentration are presented, together with the correlation between velocity and concentration fluctuations.

The character of axial flow in the core of a concentrated line vortex is studied using flow visualization. Results show that axial flow can be initiated when the no-slip boundary condition is imposed on the vortex core over a spatial extent comparable to the core diameter. It is further demonstrated that no-slip is not a necessary condition to generate the axial flow; a region of spanwise shear (i.e., a slip boundary) is sufficient. Two distinct axial flow velocity profiles are observed; they are either jetlike or spatially undulated corresponding to a maximum axial speed occurring at the core center or outer edge, respectively.

Abstract. This work reports our recent developments of novel techniques for velocimetry and studies of the Lagrangian evolution of mixing interfaces based on molecular tagging approaches. These developments take advantage of a class of newly engineered phosphorescent supramolecules that are water soluble. Previous implementations using photochromic molecules and caged fluorescein are briefly discussed and compared. The application of molecular tagging velocimetry is demonstrated in several flow fields, including examples which illustrate its capability in flows with significant out-of-plane motion and its potential for simultaneous passive scalar and velocity measurements.