Cross and clover shaped orifice jets analysis at low Reynolds number

Abstract

The jet coming from a cross-shaped orifice with an open center has been shown in the past, to provide substantial increase in the near field convective transport-mixing, in comparison to a classical round orifice jet. Detailed information has been reported in previous works on the role played in the jet mixing enhancement by the crow of vortices composed of counter-rotating pairs of secondary streamwise structures which are developing in orifice's troughs. A trough in the cross-shaped jet generates a local shear like the one generated by a triangular tab in a square jet. In the present study we are interested by the modification of local shears in the troughs of the cross-shaped jet, when orifice geometry is modified, such as the center of the orifice becomes closed, leading to a clover- shaped orifice. The general motivation is to understand the effect of using a set of combination of longitudinal structures, themselves produced by the superposition of local shear regions, in mixing performance of a cross jet. It is shown that lower entrainment rates in the clover jet is a results of an additional internal crown of vortices which opposes the external one due to inner shears generated by closing the center of the orifice.