Effects of notch geometry and sharpness on turbulent jets issuing from indeterminate-origin notched nozzles

Abstract

An experimental investigation using hot-wire anemometry to identify the effects of notch configuration and relative sharpness on notched indeterminate-origin turbulent jets at R e = 20,500 was carried out. The notches are characterized by their V- and A-shaped cuts, as well as their relative sharpness due to the design aspect ratio ( A R = 2 and 4) of the notch. Regardless of exact notch geometry, high aspect-ratio nozzles are shown to produce significant flow differences between measurements taken along peak and trough planes, in contrast to low aspect-ratio nozzles. Half-jet width results demonstrate that as the aspect-ratio increases, smooth peaks result in a constant increase within the measurement range while sharp peaks produce an initial decrease till some downstream location before increasing thereafter. In contrast, smooth and sharp trough produces significant nonlinear increases in the half-jet widths with the aspect-ratio increment. Cross-over points linked to axis-switching behaviour are observed for all nozzles except A R = 4 A-notched nozzle, when half-jet widths along peak and trough planes for each nozzle are compared. Increasing the aspect ratio also results in a 50% reduction in the distance away from the nozzle origin where the cross-over point occurs for V-notched nozzles. On the other hand, similar increase in the aspect ratio produces no cross-over point for A-notched nozzles. These results indicate that suitably configured notched nozzles are able to impart significant control over circular jet flow behaviour by inducing and manipulating axis-switching behaviour typically found in noncircular jets.