Effect of Sudden Expansion on Entrainment and Spreading Rates of a Jet Issuing from Asymmetric Nozzles

Abstract

Turbulent free jets issuing from five different nozzle geometries; smooth pipe, contracted circular, rectangular, triangular, and square, are experimentally investigated by using TSI 2-D laser Doppler velocimetry (LDV) to assess the effect of nozzle geometry and quarl (i.e. a cylindrical sudden expansion) on jet entrainment and spreading. The centerline mean velocity decay and the jet half-velocity width, which are indicators of jet entrainment and spreading rates, are determined for each nozzle's flow configuration, i.e. with and without sudden expansion. Furthermore, turbulence quantities, such as the flow mean velocities and their mean fluctuating components, as well as Reynolds shear stresses, are all measured along the centerline plane of the jet to facilitate understanding the extent of the effect of nozzle's geometry (i.e. nozzle's orifice shape and sudden expansion) on jet's entrainment and spreading. The main results show that the jet flow with the presence of sudden expansion exhibits higher rates of entrainment and spreading than without. In addition, these results reveal that sudden expansion exercises a greater effect on the asymmetric jet characteristics, especially for the triangular and rectangular nozzles compared to their axisymmetric counterparts (i.e. circular contracted nozzle).

Effects of Noncircular Inlet on the Flow Structures in Turbulent Jets

“…From a literature survey, previous studies were conducted on the turbulent flow of a jet issuing from differrently shaped nozzles [1][2][3][4][5]. From their results, it was found that the near-field flow of the jet is strongly influenced by the three-dimensional structure dependent on the loss of axisymmetric nature.…”

On the Stability of a Turbulent Non-Premixed Methane Flame

“…To the best knowledge of the present authors, all published literature addressed a central jet issuing from a circular pipe surrounded by an annulus of swirling air. Recent studies summarized in Iyogun and Birouk (2008, 2009a, 2009b have shown that asymmetric fuel nozzles have the potential of inducing various turbulent structures compared to a simple pipe counterpart. Therefore, the main purpose of the present study was to examine some of the stability features of non-premixed swirling flame as subjected to both large scales induced by the swirl and relatively smaller scales generated by the asymmetric fuel nozzle.…”

Free jet issuing from a pipe with a triangular collar: A numerical simulation

“…However, recent development showed that noncircular injectors would enhance further the mixing process between a jet and its surroundings. Pertinent literature has recently been briefly reported in, for example [1,2]. These recent studies, indeed, revealed that the use of such passive control methods can in fact lead to increasing mixing between a jet and its surrounding medium.…”

“…It was reported that these vortex pairs can have a significant impact on jet mixing [5]. Another recently proposed passive method for increasing jet mixing and spreading uses a collar, which is a sudden expansion of the nozzle [1,[16][17][18][19]. Husain et al [16] studied an elliptic whistler (i.e.…”

“…It was shown that maximum spreading angle and maximum decay rate increased with the expansion ratio of the orifice. Iyogun and Birouk [1] studied experimentally the effect of a circular sudden expansion on a jet issuing from non-axisymmetric nozzles. They reported that sudden expansion increases further jet mixing.…”