Numerical simulations of a turbulent axial vortex
Abstract
Although the vortex is present in most flows of engineering interest, the turbulent structure of the vortex is not well understood. Current prediction capabilities are especially weak for the vortex as well as other strongly rotating flows. The objective of this work is to aid the development of turbulence models for the vortex as well as strongly rotating flows in general by using direct numerical simulations of the vortex. The present study focuses on the turbulent axial vortex with and without an external strain field. The numerical simulations of a turbulent axial vortex without strain, i.e. an isolated vortex, have been performed by using a pseudo spectral method for compressible flow. The results qualitatively match well with the experimental data. The isolated vortex is stable unless the mean axial wake flow has sufficient magnitude. During the period of decay of disturbances, the mean tangential velocity profile exhibits anti-diffusion because a negative eddy viscosity develops near the center of the vortex. With the disturbance growth, the isolated vortex develops large-scale helical vortex structures, but they eventually disappear during the period of relaminarization. The details of turbulent statistics have been examined. The turbulent structure is related to the in stability of the isolated vortex. The budgets for the Reynolds stresses reveal that the production term is the primary source term, but the pressure strain, pressure transport, and turbulent transport terms also make a large contribution to the budgets for the Reynolds stresses.
Degree
Ph.D.
Advisors
Blaisdell, Purdue University.
Subject Area
Aerospace materials|Mechanical engineering
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