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Experimental studies on rectangular jets with trapezoidal tabs

Published online by Cambridge University Press:  27 January 2016

A. Arokkiaswamy ,
S. B. Verma  and
S. Venkateswaran
A. Arokkiaswamy*
Affiliation:
Council of Scientific and Industrial Research, National Aerospace Laboratory, Bangalore, India
S. Venkateswaran*
Affiliation:
Council of Scientific and Industrial Research, National Aerospace Laboratory, Bangalore, India
*
argy_swamy@hotmail.com
venkatesh_w@hotmail.com
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Abstract

An experimental investigation was carried out to study the flow development of a jet issuing from a 2:1 rectangular nozzle with mixing tabs using two-component hotwire anemometry. A pair of tabs of trapezoidal configuration (with 2% total blockage area) is placed on the minor-axis side of the rectangular nozzle and tested for two tab inclination angles of 135° and 45°, with respect to the flow direction. Tests were conducted for a nominal jet exit velocity of 20m/sec corresponding to a Reynolds number based on nozzle equivalent diameter of 5·013 × 104. Relative to the plain jet, the jet with tabs show significant reduction in jet-core length (by 67%) followed by a faster decay in jet centreline velocity (U/Ue). This is also accompanied by a significant upstream shift in peak centreline turbulence intensity (u’/Ue). The presence of tabs is observed to inhibit the jet growth along the minor-axis plane thereby introducing large distortion in the jet cross-sectional development that ultimately leads to jet-core bifurcation along its major-axis. While a mushroom-like flow structure develops behind the tab with 135° inclination, the flow structure behind a 45° inclined tab rather takes the shape of the tab itself. The former flow development is seen to enhance the jet growth more along the minor-axis while the latter improves the jet growth more along the major-axis plane. From application point of view, since both tab inclinations result in more or less similar jet characteristics, a 135° inclined tab would be preferable over a 45° inclined tab from the view of improved jet mixing.

Type
Research Article
Information
The Aeronautical Journal , Volume 117 , Issue 1191 , May 2013 , pp. 505 - 517
Copyright
Copyright © Royal Aeronautical Society 2013 

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