Showing papers by "Manoochehr Koochesfahani published in 1997"
TL;DR: Implementation of a two-detector system is described which relaxes the requirement that the initial tagging pattern be known a priori, eliminates errors in velocity estimates caused by variations in the grid pattern during an experiment, and makes it possible to study flows with non-uniform mixtures.
Abstract: The development and applications of a new class of water-soluble compounds suitable for molecular tagging diagnostics are described. These molecular complexes are formed by mixing a lumophore, an appropriate alcohol, and cyclodextrin. Using 1-BrNp as the lumophore, cyclohexanol is determined to be the most effective overall among the alcohols for which data are currently available. Information is provided for the design of experiments based on these complexes along with a less complex method for generating the grid patterns typically used for velocimetry. Implementation of a two-detector system is described which, in combination with a spatial correlation technique for determining velocities, relaxes the requirement that the initial tagging pattern be known a priori, eliminates errors in velocity estimates caused by variations in the grid pattern during an experiment, and makes it possible to study flows with non-uniform mixtures. This detection and analysis combination also solves one of the problems associated with using caged fluorescein to study high-speed flows. In addition to the traditional implementation for velocimetry, novel applications for studying the Lagrangian evolution of both reacting and non-reacting interfaces and obtaining combined passive scalar/velocity measurements are demonstrated.
161 citations
01 Jan 1997
TL;DR: This work reports the recent developments of novel techniques for velocimetry and studies of the Lagrangian evolution of mixing interfaces based on molecular tagging approaches that take advantage of a class of newly engineered phosphorescent supramolecules that are water soluble.
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 demonstrated in several flow fields, including examples which illustrate its Capability in flows with siginificant out-of-plane motion and its, potential for simultaneous passive scalar and velocity measurements.
41 citations
TL;DR: In this paper, the authors studied the spanwise structure and scalar mixing in a confined low Reynolds number wake forced at the Karman shedding frequency and found that the extent of three-dimensionalality is dependent on the forcing amplitude.
Abstract: The spanwise structure and scalar mixing are documented in a confined low Reynolds number wake forced at the Karman shedding frequency. Results show that the extent of three-dimensionality is dependent on the forcing amplitude. Data show evidence of streamwise vorticity initially in the form of a counter-rotating vortex pair near the side walls which evolves into a much more complex spatial structure farther downstream. The amount of mixed fluid can be significantly increased at high forcing amplitudes; the mixed fluid is estimated to occupy about 41% of the test section cross-sectional area at the farthest downstream station. The large mixing increase in this case is contained within the central portion of the span while the regions near the side walls are practically devoid of mixed fluid.
9 citations
29 Jun 1997
TL;DR: In this paper, the flow structure and the molecular mixing field were investigated in a liquid-phase low Reynolds number forced wake in a confining channel using chemically reacting LIT, and the absolute level of molecular mixing enhancement was quantified.
Abstract: The flow structure and the molecular mixing field are investigated in a liquid-phase low Reynolds number forced wake in a confining channel using chemically reacting LIT. The absolute level of molecular mixing enhancement is quantified. Results show that the amount of chemical -product can be dramatically increased when high amplitude forcing is used. Mixing at mid-span is enhanced by about a factor of 40 over the unforced case. More importantly, the maximum level of mixing is nearly three times that in high Reynolds number liquid-phase mixing layers, and 60% higher than that in gas-phase turbulent shear layers.
2 citations