Spontaneous Break of Symmetry in Unconfined Laminar Annular Jets

Abstract

Numerical investigations show that the spontaneous break of symmetry in annular incompressible jets occurs in the laminar flow regime and is controlled by both the Reynolds number and the blockage ratio. In the blockage ratio range between 0.50 and 0.89 the transition critical Reynolds number decreases with increasing blockage ratio, according to a defined formula. Transition to asymmetry happens in the steady regime, before the transition to the unsteady flow. Asymmetry is characterized by a preferential flow direction from one side of the jet boundary layer to the diametrically opposite side. The plane of preferential direction passes through the geometry centerline and represents the single plane of flow symmetry. Experiments reported in literature have confirmed the existence of flow asymmetry in an annular jet flow.

Symmetry breaking and vortex precession in low-swirling annular jets

“…The mechanism of disturbances proposed by Del Taglia et al 11 is unable to explain the low frequency motions of the stagnation point since the frequencies associated with their convective timescales are much higher. Therefore, we suggest a model which involves feedback from the stagnation point back to the inner shear layer.…”

“…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. In order to study the large scale motions of the wake, a POD decomposition of the wake is performed.…”

“…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.…”

Experimental investigation of the precessing vortex core in annular swirling jet flows in the transitional regime

“…The shape of this zone can be controlled by varying Reynolds number and nozzle dimensions, mainly the blockage ratio of the bluff body. The studies of del Taglia et al [11] and Vanierschot et al [12] showed that in non-swirling conditions, the CRZ symmetry breaks up above a critical Reynolds number. Even though the turbulent behaviour of the CRZ can be characterized according to flow velocity, the position of the stagnation point solely depends on the nozzle geometry in isothermal and non-swirling conditions.…”

Proper orthogonal decomposition analysis of coherent motions in a turbulent annular jet

“…Although the flow has both a symmetric geometry and symmetric boundary conditions, the investigations on turbulent annular jets have shown that spontaneous break of symmetry of the time-averaged flow field could appear [9][10][11][12][13][14] . This type of asymmetry is observed in laminar annular jets as well, if the Reynolds number is above a certain threshold value, which is around 150 for the geometry used in this study [15] .…”