Time-averaged, three-dimensional flow in a rectangular sudden expansion

An experimental study of a 2:1 aspect ratio rectangular jet that undergoes a 6:1 sudden expansion in area is being conducted to understand the three-dimensional dynamics of the asymmetric vortex rings formed in the confined shear layers and thus to understand entrainment and mixing in this type of configuration. LDV is used to measure three velocity components under forced and unforced conditions. Profound differences are found between the two axes of symmetry: in contrast to a conventional two-dimensional sudden expansion, no time-averaged recirculation is found in the minor axis plane. Along the major axis a normal size recirculation zone is found. Significant transverse velocities are the result of both rapid spreading of the jet on the minor axis and the effects of confinement by the duct on the developing jet. In this paper the time-averaged flow pattern is described, and mass fluxes are compared at two streamwise locations. These results are presented not only to illustrate new flow phenomena but also to serve as a database. The phase-averaged properties and a discussion of the vortex dynamics will be presented in a companion paper that is under preparation.