Axisymmetric and Non-Axisymmetric Initiation of Vortex Breakdown
Abstract
The onset of axisymmetric (bubble) and non-axisymmetric (spiral) modes of breakdown is studied numerically for swirling pipe flows. The authors have found that the onset of axisymmetric vortex breakdown occurs when the vortex attains local criticality. A transient simulation of the evolution of vortex breakdown revealed that downstream-running waves are trapped approximately at the location of flow criticality. These trapped waves are slowly amplified and eventually result in the bubble breakdown region with reversed flow and enlarged core size. Non-axisymmetric disturbances were found to decay on columnar base flows; however, for base flows with bubble breakdown, non-axisymmetric disturbances were amplified. These amplified disturbances resulted in the formation of spiral breakdown. If the base flow inlet swirl was only slightly larger than that leading to axisymmetric breakdown, a nearly columnar solution was obtained, suggesting that weak asymmetry may help to stabilize the columnar solution branch. The numerical simulations also revealed that most of the energy in spiral breakdown is contained in the first few non-axisymmetric modes of variation. (10 figures, 38 refs.)
Document Details
- Document Type
- Technical Report
- Publication Date
- Mar 01, 2003
- Accession Number
- ADA418955
Entities
People
- Andrew W. Cary
- David L. Darmofal
Organizations
- Boeing