512Small scale turbulence and related gradient statistics


26 October 2009 – 29 October 2009


Turin, Italy


Prof.  Daniela Tordella
Politecnico di Torino
Dipartimento di Ingegneria Aeronautica e Spaziale
Corso Duca degli Abruzzi 24,
10129 Torino

phone: +39 011 564 6812 
fax: +39 011 564 6899 
email: daniela.tordella@polito.it


Prof.  K.R.Sreenivasan
The Abdus Salam International Centre for Theoretical Physics 
Strada Costiera 11
34014 Trieste

email: krs@ictp.it

Turbulent flows are known to contain a wide range of scales, each range being characterized by its own physics. For instance, the energy dissipation takes place at small-scales. Yet, the process is linked to the large scales of the system. One central problem of turbulence is to compute the large scale phenomena by modeling or parameterizing the small scales; this is the goal of sub-grid scale (SGS) models. Another example deals with modeling micromixing (relevant to chemical industry and combustion), in which small scales are the important feature.

Laboratory and numerical results are continuously being generated on the small-scale features of turbulence dynamics. One fundamental question is: are the small scales universal? If so, under which conditions? If not, when? In particular, what is their connection to the large scale motion?
The basis for the near-universal behavior of small scales is provided by Kolmogorov’s theory (1941 and 1962). The gaps in this theory are becoming increasingly certain. The objective of the Colloquium is to establish a possible consensus on new ideas, post- Kolmogorov, dealing with the non-universality of small scale dynamics. A manifestation of the non-universal behavior of small-scales is closely related to small-scale anisotropy. This feature can be recast and presumably explained in different ways. For example,
  • Local structure of turbulence from a kinematic point of view. It is interesting to detect the role of local velocity gradients, under the effect of strain and rotation. Particular attention must be paid to the dissipation rate of the scalar variance, as well as to its local anisotropic behavior.
  • Statistical approach, when the small scales are explicitly linked to the turbulence forcing.
  • Role played by coherent structures.
  • Effects of rotation, stratification and such other body forces.