Numerical and Experimental Investigation of an Annular Jet Flow With Large Blockage

Abstract

Unsteady 3-D numerical simulations and 3-D LDA measurements of an annular jet with a blockage ratio of 0.89 and Reynolds number 4400 are presented. At these flow conditions, the flow inside of the recirculation zone is asymmetric, with a preferential direction. Very good predictions of the velocity fluctuation values are achieved with the unsteady simulation technique in the same region, as the fluctuations are mainly large scale, structure dominated. A frequency near to 10 Hz is identified in the simulations, which is attributed to the principal shedding behavior of the vortical structures.

Symmetry breaking and vortex precession in low-swirling annular jets

“…As can be seen on the figure, the wake behind the central tube is slightly asymmetric. This symmetry breaking of annular jets is also reported in literature by Del Taglia et al 10 In their numerical study, symmetry breaking occurred even for symmetric boundary conditions. A simple mechanism for the transition to asymmetry is proposed in another paper by Del Taglia et al 11 They stated that perturbations in the inner shear layer near the nozzle exit are convected towards the stagnation point and cause there a shift in location.…”

“…To derive a simple model for the influence of swirl on the precession, let us assume that the driving force for the precession is entrainment of the annular jet near the nozzle inlet at the base of the wake vortex. In a study by Del Taglia,10 this was stated as the region where the perturbations originate and are convected towards the stagnation point, creating the asymmetric flow. The frequency-swirl relation can be derived by assuming that the asymmetric wake rotates with the same angular frequency as the jet and therefore there is no slip between the two.…”

“…Although the annular jet geometry is axisymmetric, under some conditions the flow exhibits a spontaneous break in symmetry. Del Taglia et al 10,11 reported that for laminar, zero-swirl, incompressible annular jets the break of symmetry is controlled by the Reynolds number and the blockage ratio which can be combined into a state parameter λ. At a certain critical value of the state parameter λ c , the flow suddenly breaks symmetry.…”

Large eddy simulation of forced ignition of an annular bluff-body burner

“…The jet injected via this annular gap deviates slightly radially outward and envelops the central recirculating bubble, which continuously traps energy from the main streams and maintains the turbulence level. Farther downstream, the flow behaves similar to a fully established round jet [4]. The unique aerodynamics and flow field properties of such bluff-body configurations have motivated several research studies, both experimental and numerical [5,6,1,7,4,[8][9][10].…”

“…The unique aerodynamics and flow field properties of such bluff-body configurations have motivated several research studies, both experimental and numerical [5,6,1,7,4,[8][9][10]. Many of the reported numerical works concentrated on aerodynamics and cold-flow mixing in bluff-body burners; simulation of such complex aerodynamical configuration demands on unsteady numerical technique, such as large eddy simulation (LES), for fair description [11][12][13]4,14].…”