Vortex Identification Issues in Turbulent Boundary Layer Modeling
| When |
Feb 02, 2016
from 10:45 to 12:00 |
|---|---|
| Where | Centre Blaise Pascal |
| Attendees |
Luca Moriconi |
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A structural description of turbulent boundary layers (TBLs) has been a promising direction of research, strongly supported by an increasing number of fluid dynamicists along recent years. We discuss in this talk a particularly simple statistical vortex model, inspired by the picture of the TBL as a “gas” of hairpin-vortex configurations, which is able to reproduce, with remarkable agreement, important qualitative features of streamwise velocity fluctuations. In order to refine the model, with the help of numerical and experimental feedback, it is absolutely necessary to work with vortex identification methods, which, however, lose accuracy in a dramatic way in the inner layer of TBL flows. Focusing on one of the most popular vortex identification methods - the swirling strength criterion - we critically discuss its main problematic issues as (i) vortex image deformation and suppression due to the near presence of intense vortical structures; (ii) artificial vortex merging; (iii) introduction of “ghost” vortices in many-vortex configurations and (iv) in the presence of background shear. We, then, propose an alternative vortex detection criterion, based on the curvature properties of the vorticity profile, which is shown to clearly improve over the results obtained with the swirling strength criterion in a number of relevant two-dimensional case studies.