Effect of Tab Geometry on the Development of a Jet Issuing from a Rectangular Nozzle

Abstract

An experimental investigation was carried out to study the effect of tab geometry on the flow characteristics of a jet issuing from a 2:1 rectangular nozzle using two-component hotwire anemometry. A pair of tabs of trapezoidal and square configurations (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^°, respectively. Tests were conducted for a nominal jet exit velocity of 20 ms^-1 corresponding to a Reynolds number based on nozzle equivalent diameter of 5.02×10⁴. Relative to the plain jet, the potential-core length of the jet with trapezoidal tabs shows a reduction of 62% while the jet with square tabs shows a reduction of 75%, respectively. This is also accompanied by a significant upstream shift in peak centerline turbulence intensity (u'/U_e). The tab inclination of 135^° results in further enhanced jet characteristics in each case. The presence of each tab configuration 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. However, it is observed that while the jet with trapezoidal tabs switches its axis at some downstream location, the jet with square tabs does not switch axis at all. This indicates a strong influence of tab geometry on the overall jet flow development.