The Molecular Tagging Velocimetry (MTV) is a well-suited technique for velocity field measurement in rarefied gas flows. Typically, a line is tagged by a laser beam within the gas flow seeded with luminescent acetone molecules. Positions of the luminescent molecules are then observed at two successive times and the velocity field is deduced from the analysis of the tagged line displacement and deformation. However, this displacement is affected by molecular diffusion, and consequently, there is not a direct and simple relationship between the velocity field and the measured displacement of the initial tagged line. In this paper, the role of the tracer molecules diffusion is investigated using the Direct Simulation Monte Carlo (DSMC) method. The simulations demonstrate that the diffusion of these molecules closely depends on the flow regime, and becomes significant as the degree of rarefaction of the gas flow increases. A simple reconstruction algorithm based on the advection-diffusion equation has been developed to obtain the velocity profile form the displacement field. This reconstruction algorithm has been numerically tested on DSMC generated data. It is shown that the reconstruction becomes less effective as the degree of gas flow rarefaction increases. As expected, DSMC tests demonstrate that the reconstruction error is reduced as the binary diffusion coefficient decreases.
|Titolo:||Role of Diffusion on Molecular Tagging Velocimetry Technique for Rarefied Gas Flow Analysis|
|Autori interni:||FREZZOTTI, ALDO|
|Data di pubblicazione:||2014|
|Appare nelle tipologie:||04.1 Contributo in Atti di convegno|
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