The influence of turbulence on a columnar vortex with axial flow

Abstract

The interaction between a columnar vortex and external turbulence is investigated numerically. A q ‐vortex is immersed in an initially isotropic homogeneous turbulence field, which itself is produced numerically by a direct numerical simulation of decaying turbulence. The formation of turbulent eddies around the columnar vortex and the vortex‐core deformations are studied in detail by visualizing the flow field. In the less‐stable case with q = –1.5, small thin spiral structures are formed inside the vortex core. In the unstable case with q = –0.45, the linear unstable modes grow until the columnar vortex make one turn. Its growth rate agrees with that of the linear analysis of Mayer and Powell[1]. After two turns of the vortex, the secondary instability is excited, which causes collapse of the columnar q ‐vortex and the sudden appearance of many fine scale vortices. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

On the vortex parameter estimation using wide band signals in active acoustic system

“…The flow of an incompressible fluid of velocity u(r, t) is characterized by the Navier-Stokes equation, (1). At the same time, the flow is fully characterized by adding the mass continuity equation (2).…”

“…These equations may be formulated in terms of vorticity vector ω, and giving the suitable initial and boundary conditions, a desired vortical structure can be mathematically modeled to facilitate the determination of the vortical solutions describing any vortex model. We recall the two relations metioned above [1], [2]:…”

“…The analytical solution 3 of the equations (1) and (2) reflect directly the frequency signature of the vortex through the solution of ω. Therefore, it follows [1]:…”

“…This paper is organised as follows: in section 2, it is presented the relation between the vortex flow and vortex spectrum. The point of depart in this research was that the received Doppler spectrum is unambiguosly related with the spatial velocity distribution of a Rankine vortex [1]. The RPA method is described in section 3 and, then, the quantification of the diagonal lines specific for the recurrence matrix is highlighted.…”