Detailed Image Analysis of Vortex-Flame Interaction under Acoustic Excitation of Coherent Structure Characterized by Geometrical Configuration

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Depending on their own geometric configurations, many types of coherent structures exist in the practical turbulent flow fields, such as jets, wakes and plane shear layers. Since these flow fields are employed as fundamental flow fields for practical turbulent combustion, detailed optical observations and image processing of vortex-flame interaction in the turbulent combustion enable modeling of basic flame structure. To make the latter possible, a variety of devices is necessary concerning optical observations and image processing. During the first term of this investigation, 2006, acoustic excitation of coherent structure has been introduced to make it conspicuous and to make optical observation easy, whereas detailed PIV measurements and their image processing are made to estimate the effects of baroclinic torque on the vorticity conservation equation. In the final term of this investigation, 2007, the concrete roles of baroclinic torque in the flame-flow interaction have been studi … More ed using an incompressible two-dimensional jet, being most simple among the above-mentioned flows. By means of PIV velocimeter using titanium-oxide powder and smoke of an joss stick of about 1 μm diameter as tracking particles, the behaviors of a single two-dimensional vortex ejected into both uniform and non-uniform density fields under micro-gravity of 0.1 m/s2 have been tracked and analyzed, as well as those under normal gravity. Some devices and improvements have been made, such as a tower system to realize the condition of micro-gravity in the normal room situation and an original PIV-imaging system for making clear the weak effects of baroclinic torque on vortex-flame interaction.It was found that, due to the combined influence of density-gradient and pressure-gradient, a symmetric vorticity is clearly generated along the boundary region of the vortex, and that the flow velocity within the vortex decreases discontinuously across the boundary region of vorticity generation. Also found was that, finally, the effects of baroclinic torque on vortex-flame interaction are selectively enhanced in the flame zone where a steep density gradient inevitably is produced Less