Nonlinear Axisymmetric and Three-Dimensional Vorticity Dynamics in a Swirling Jet Model

By: Nasa, National Aeronautics and Space Adm

The mechanisms of vorticity concentration, reorientation, and stretching are investigated in a simplified swirling jet model, consisting of a line vortex along the jet axis surrounded by a jet shear layer with both azimuthal and streamwise vorticity. Inviscid three-dimensional vortex dynamics simulations demonstrate the nonlinear interaction and competition between a centrifugal instability and Kelvin-Helmholtz instabilities feeding on both components of the base flow vorticity. Under axisymmetric flow conditions, it is found that the swirl leads to the emergence of counterrotating vortex rings, whose circulation, in the absence of viscosity, can grow without bounds. Scaling laws are provided for the growth of these rings, which trigger a pinch-off mechanism resulting in a strong decrease of the local jet diameter. In the presence of an azimuthal disturbance, the nonlinear evolution of the flow depends strongly on the initial ratio of the azimuthal and axisymmetric perturbation amplitudes. The long term dynamics of the jet can be dominated by counterrotating vortex rings connected by braid vortices, by like-signed rings and streamwise braid vortices, or by wavy streamwise vortices alone. Martin, J. E. and Meiburg, E. Langley Research Center NAS1-19480; NSF CTS-9196004; RTOP 505-90-52-01...

• Format: Paperback
• Language: English
• ISBN: 172910780X
• ISBN13: 9781729107805
• Release Date: January 1
• Publisher: Independently Published
• Length: 32 Pages
• Weight: 0.22 lbs.
• Dimensions: 0.1" x 8.5" x 11.0"