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Development and Applications of Oceanic Engineering
Number of Followers: 2

This is an Open Access Journal

Open Access journal
ISSN (Print) 2325-3754 - ISSN (Online) 2325-3762
Published by Science and Eng Pub Co.

[34 journals]

Unsteady Wake Rollup Modeling Using a Mollifier Based Filtering Technique
- Abstract: Unsteady Wake Rollup Modeling Using a Mollifier Based Filtering Technique
  Pages 1-28
  Author Gerasimos Politi
  3-D BEM formulations of unsteady lifting flow problems are paradigms of free boundary problems. The free boundary enters in the BEM formalism as the necessary spatial support of the velocity discontinuity, generated at the trailing edges of the lifting bodies. In the context of a BEM, this velocity discontinuity, alternatively termed a shear layer, is simulated by a surface dipole distribution or its equivalent singular vortex sheet. Free vortex sheets are inherently unstable and amenable to two well-known instabilities: the Kelvin-Helmholtz instability and the roll-up of their free edges. As a result, they show chaotic behavior with the passage of time. On the other hand, experimental evidence on flows around lift producing devices shows that the wake vorticity is organized in specific, problem dependent rollup patterns. In this paper we present a filtering technique, which by introducing artificial viscosity to our problem, suppresses the smaller scale instabilities, leaving the larger scale organized vortices to determine the rollup pattern of the free wake vorticity. Flow simulations are presented for a steadily advancing wing, a biomimetic wing at two different Strouhal numbers, a naval propeller at two different advance coefficients and a novel flexible oscillating duct propulsion device. The effect of the filtering parameters to the shear layer wake rollup pattern as well as to the calculated unsteady forces and moments is shown and discussed.
  PubDate: 2016-0

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