The mechanics of a spark-induced coherent structure (called a 'spot') in the turbulent mixing layer of a 12. 7 cm diameter incompressible air jet has been investigated through phase-locked measurements at three streamwise stations. Data include phase-average time series of background turbulence intensities, coherent and background Reynolds stresses, vorticity and intermittency at different transverse positions. Spatial distributions of these properties over the extent of the spot have been presented as contour maps. The computed pseudo-stream-functions have been comapred with the phase-average streamlines inferred from the measured distributions of the velocity vector. The spark-induced spot is an elongated large-scale coherent vortical structure spanning the entire thickness of the mixing layer. The dynamics of the turbulent mixing layer spot, whose signature is buried in the large-amplitude background fluctuations, is much more complicated than that of the boundary-layer spot. The vorticity, intermittency and other turbulence measures, zone averaged over the extent of the spot, compare well with the time-average values. Refs.
|Number of pages||39|
|Journal||Journal of Fluid Mechanics|
|Issue number||pt 1|
|State||Published - 1980|