VORTICAL STRUCTURES ANALYSIS IN JET FLOWS USING A CLASSICAL 2D-PIV SYSTEM AND TIME RESOLVED VISUALIZATION IMAGE PROCESSING

摘要

An optical field measurement technique and a high-speed visualization technique enriched by a low-level image processing are associated in the vortex dynamics analysis of the near field of jet flows. In a round jet the entrainment is produced in the braid regions being interrupted in the presence of the Kelvin-Helmholtz ring. The latter crush the streamwise vortices altering their self-induction role. Conversely, a lobed cross-shaped orifice geometry allows a cutting of the Kelvin-Helmholtz structures into discontinuous ring segments. Consequently, streamwise large-scale structures are developing in these discontinuity regions. The streamwise structures control and enhance the jet entrainment which is not altered by the Kelvin-Helmholtz structures passing.