Aspect Ratio Effect on Mach 1.5 Rectangular Jet Mixing

An experimental investigation on the mixing characteristics of Mach 1.5 rectangular jet emanating from aspect ratios (
AR
s) 2 and 3 convergent-divergent nozzles is carried out at nozzle pressure ratios (
NPR
s) 3, 3.69, 4 and 5, respectively. At overexpanded (
NPR
3), correctly expanded (
NPR
3.69) and underexpanded (
NPR
s 4, 5) levels of Mach 1.5 jet, the Pitot pressure measured along the centerline of
AR
2 and
AR
3 rectangular jets showed that the influence of aspect ratio on the jet mixing is not as strong as expected. The effect of aspect ratio is noticeable only in the core of both the jets. The core length of
AR
2 jet is shorter than
AR
3 jet at all the
NPR
s, which indicates faster mixing of
AR
2 jet with ambient fluid as compared to
AR
3 jet. But after core, the decay of
AR
2 and
AR
3 jets in the characteristic decay region remained almost same at all the
NPR
s except at correctly expanded
NPR
of 3.69, the
AR
3 jet decays slightly faster than
AR
2 jet. For all the cases, the jets have become fully developed together at far downstream location. The pressure profiles taken along major axis and minor axis of Mach 1.5 rectangular jets confirm the faster spreading of
AR
2 and
AR
3 jets along minor axis than along major axis. Both the jets are found to switch axes between
$8D_{e}$
to
$10D_{e}$
. The shadowgraph visualization reveals the complex structure of waves present in the major axis and minor axis planes of
AR
2 and
AR
3 rectangular jets.