Th. Weisgraber et D. Liepmann, TURBULENT STRUCTURE DURING TRANSITION TO SELF-SIMILARITY IN A ROUND JET, Experiments in fluids, 24(3), 1998, pp. 210-224
The developing turbulent region of a round jet was investigated using
an improved implementation of digital particle image velocimetry (DPIV
). The two-dimensional flow field in planes normal and parallel to the
axial velocity was measured at locations between 15 and 30 diameters
downstream, for two Reynolds numbers of 5500 and 16,000. The study con
sisted of instantaneous snapshots of the velocity and vorticity fields
as well as measurements of velocity correlations up to third order. I
n this regime, the Reynolds number had a significant effect on both th
e instantaneous flow structure and the profiles of mean velocity acros
s the jet. Coherent streamwise structures were present in the jet core
for the lower Reynolds number. Additional structures whose evolution
was governed by time scales two orders of magnitude larger than the co
nvective scale inside the jet were observed in the entrainment field.
The velocity correlations provided further support for the validity of
DPIV turbulence measurements. The data was consistent with the equati
ons of motion and momentum was conserved. DPIV measurements of turbule
nt kinetic energy components agreed with the hot-wire measurements of
previous studies.