Study of the parabolic and elliptic approaches validities for a turbulent co-flowing jet

Abstract

An axisymmetric turbulent jet discharged in a co-flowing stream was studied with the aid of parabolic and elliptic approaches. The simulations were performed with two in-house codes. Detailed comparisons of data show good agreement with the corresponding experiments; and different behaviors of jet dilution were found in initial region at different ranges of velocities ratios. It has been found that the two approaches give practically the same results for the velocities ratios Ru ? 1.5. Further from this value, the elliptic approach highlights the appearance of the fall velocity zone and that?s due to the presence of a trough low pressure. This fall velocity has not been detected by the parabolic approach and that?s due to the jet entrainment by the ambient flow. The intensity of this entrainment is directly related to the difference between the primary (jet) and the secondary flow (co-flow). In fact, by increasing the velocities ratios Ru, the sucked flux by the outer stream becomes more important; the fall velocity intensifies and changes into a recirculation zone for Ru ? 5.