Abstract
An experimental investigation on the mixing characteristics of Mach 1.5 rectangular jet emanating from aspect ratios (ARs) 2 and 3 convergent-divergent nozzles is carried out at nozzle pressure ratios (NPRs) 3, 3.69, 4 and 5, respectively. At overexpanded (NPR3), correctly expanded (NPR 3.69) and underexpanded (NPRs 4, 5) levels of Mach 1.5 jet, the Pitot pressure measured along the centerline of AR2 and AR3 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 AR2 jet is shorter than AR3 jet at all the NPRs, which indicates faster mixing of AR2 jet with ambient fluid as compared to AR3 jet. But after core, the decay of AR2 and AR3 jets in the characteristic decay region remained almost same at all the NPRs except at correctly expanded NPR of 3.69, the AR3 jet decays slightly faster than AR2 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 AR2 and AR3 jets along minor axis than along major axis. Both the jets are found to switch axes between 8D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> to 10D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> . The shadowgraph visualization reveals the complex structure of waves present in the major axis and minor axis planes of AR2 and AR3 rectangular jets.
Highlights
It is well known that the evolution of jet is strongly dependent on the initial conditions at the exit of nozzle
The shadowgraph results of AR2 and AR3 jets at nozzle pressure ratios (NPRs) 3, 3.69, 4 and 5 presented in Figures 11 and 12 show that the core length of both the jets increases with increasing NPR and at the same time the wave strength increases with NPR
The present experimental investigation of Mach 1.5 rectangular jets from rectangular C-D nozzles of AR2 and AR3 clearly shows that the influence of aspect ratio is dominant in the near field
Summary
It is well known that the evolution of jet is strongly dependent on the initial conditions at the exit of nozzle. For underexpanded rectangular jet from moderate aspect ratio convergent nozzle, the increased growth rate of jet along minor axis than along major axis is observed for pressure ratios 3 to 4.5 [15]. In the present work, the Mach 1.5 rectangular jets from aspect ratios 2 and 3 convergent-divergent rectangular nozzles are studied experimentally at different levels of expansion. For both the nozzles, the experiments are conducted for nozzle pressure ratios (NPRs) 3, 3.69, 4 and 5, covering overexpanded (NPR 3), correctly expanded (NPR 3.69) and underexpanded (NPRs 4, 5) levels of Mach 1.5 jet. A detailed Pitot pressure measurement is made to quantify the mixing characteristics of Mach 1.5 rectangular jets from AR2 and AR3 nozzles. The visualization is carried out with continuous illumination and the shadowgraph images projected on a screen are recorded using a still camera
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