Dynamics of the Flow Past a Bluff-body
October 9, 2006 — October 13, 2006
Coordinator:
- Daniela Tordella (Politecnico di Torino, Torino, Italy)
The external flow past an object is a formidable topic for the study and application of fluid dynamics. This is due to the large variety of flow patterns that occur as the principal control parameter, the Reynolds number (Re), is changed. Both in nature and technology, a very wide range of Re can be encountered. As an example, let us consider the following sequence: motion of bacteria 10–6, mushroom spores 10–3, tadpoles 102, humans 106, submarines 109, astrophysical objects from 1012 to infinity. As an indication of the diversity of the possible patterns, let us consider two examples:
I – A flow past a blunt body, such as a circular cylinder, usually experiences boundary layer separation and strong flow oscillations in the wake region behind the body. This regular pattern of vortices is called the Karman vortex street. It is characterized by a discrete frequency that is correlated to the Reynolds number of the flow. The periodic nature of the vortex shedding phenomenon can sometimes lead to unwanted structural vibrations, when the frequency matches one of the resonant frequencies of the body structure or an aero-elastic coupling is excited.
II – When molecular diffusion dominates, as in very slow motion, or for very small objects, or in very viscous fluids, the Re is small compared to unity. In the limiting case, when Re = 0, vorticity spreads only through diffusion. A dipolelike steady distribution of vorticity is typical. The observed symmetry before and after the body is surprising, since a certain asymmetry is expected because of the directionality of the flow. This configuration is of theoretical interest, and is a useful approximation in applications with very small Re.
The course aims to supply an overview of the advances that have been made in the physics, mathematical and experimental investigation of the bluff-body flow. We shall illustrate the link between theory and experiments. In the last few decades several hundred papers have appeared. It would therefore be impossible to discuss this subject in any depth or completeness. The course makes no such pretension, but it focuses on a few topics to suggest the nature of the progress that has been made. The course will cover symmetry breaking, similarity solutions, linear stability analysis, weakly nonlinear analysis, Strouhal-Reynolds-number relationship, vortex-shedding, secondary instability, 3-dimensional flow around the circular cylinder, bifurcations, entrainment. With regards to laminar configurations, the course will present the mathematical and physical aspects that have recently received much attention due to developments in biological flows. The course is addressed to researchers, graduate students and post-doctoral fellows in the areas of engineering, science and applied mathematics who wish to improve their knowledge of the dynamics of the external flows past bluff-objects and to have an update on recent research results and new applications.
FINAL ROUND TABLE
Friday, 11.00 – 12.30 (sponsored by SCUDO Scuola di Dottorato of the Politecnico di Torino, Prof. Mario Rasetti, director).
Chairman: Prof. Paolo Luchini
The round table will be preceded by an extended lecture of 90 minutes by P. Luchini entitled Linear Stability Analysis of the Flow Past a Bluff Body, 9.00 – 10.30.