An Analytical Solution for the Near Field of Axisymmetrical Turbulent Jet with Weak to Moderate Swirling

Abstract

An analytical model was developed to explore the effect of swirl action on the mean evolution of a near flow field of turbulent jet. The equations of motion for turbulent flow were integrated to obtain the theoretical model with the aid of boundary layer approximations and the concept of self-preservation of velocity profiles. Vortex breakdown at the core of the jet, a phenomenon associated with swirling jets, was taken into account through the axial velocity distribution. Axial velocity profiles were described in terms of Gaussian curves and azimuthal velocity profiles described in terms of sinusoidal curves. Expressions were obtained which describe the decay of axial and azimuthal maximum velocities and the growth of jet half width. The proposed model proves that the initial swirling degree significantly influences the time-averaged jet characteristics. Collected data from various sources, covering weak to moderate degrees of swirling, were used to verify the theoretical model. The simulated results for the decay of axial and swirling velocities and the jet spread agree closely with the existing experimental findings. Compared to a non-swirling jet, the growth of the jet width is considerably large, and velocity field is suppressed in a swirling jet, and also the core length becomes shorter.