Direct Numerical Simulation of Naturally Evolving Free Circular Jet

Direct numerical simulation (DNS) of incompressible, spatially developing circular jets at a moderate Reynolds number of 1030 is performed to understand the details of the evolution of the flow field. The axisymmetric shear layer rolls up in the near field of the jet forming vortex rings. The rings tilt as they convect downstream before becoming turbulent in the far field. The evolution of vortical structures reveals the presence of a helical structure in the flow field along with the occurrence of vortex pairing. The time-averaged streamwise velocity distribution shows self-similarity in the far field. The cross-streamwise distribution of the Reynolds stresses also shows weak self-similarity downstream as the flow is not fully developed within the streamwise length of the computational domain. A detailed comparison with experiments is carried out and the computed time-averaged as well as statistical data shows excellent match with the experimental results. Numerical simulation also reveals various transitions during flow evolution in the streamwise direction.