Seminars Archive
Studying and Controlling Turbulence
Abstract
Workshop on Studying and Controlling
Turbulence
Thursday, September 9, 2003, 9:30
Seminar Room, ground floor, Building "T"
Sincrotrone Trieste, Basovizza
09:30 - 10:30
Joseph Niemela
Fluid turbulence at very low temperature
( The Abdus Salam International Centre for Thereotical Physics )
Abstract
Fluid turbulence is widespread, indeed almost the rule, in natural
and
engineering flows, and is important as a paradigm for nonlinear systems
with many interacting degrees of freedom. Low temperature helium
has many
advantages for the study of fluid turbulence, most notably its extremely
small viscosity. Special attention will be given to the use of
cryogenic
helium gas for producing very turbulent thermal convection under
controlled laboratory conditions, where the dynamical control parameter
can be varied over nearly eleven orders of magnitude in a single
experiment. Below the superfluid transition, turbulence can be
significantly influenced by quantum effects. Recent experimental
progress
will be discussed, as well as plans for new experiments at Elettra.
10:30 - 11:00 Coffee Break
11:00 - 12:00
Katepally R. Sreenivasan
The polymer and the flow
( The Abdus Salam International Centre for Thereotical Physics )
Abstract
It is known from numerous observations that the addition of small
amounts of long-chain polymers, of the order of a few parts per million
by weight, can have profound consequences on the turbulence in the
solvent fluid. For instance, the pressure drop in a turbulent pipe
flow
can be reduced by as much as 80%. (Hence firefighters in New York City
have often used polymers to be able to shoot water to the top of tall
buildings.) The effect is major, and its understanding will clearly
tell
us something worthwhile about both the polymer and turbulence. However,
this empirical result has not yet been explained satisfactorily, and
there are only fragments of a theory. Experiments have not been done
under sufficiently controlled conditions to help decide which theory,
if
any, is correct.
The talk will discuss a few basic experimental observations and outline
some existing theories. It will be more in the spirit of opening up
the
problem than present a solution, and will not assume too much special
knowledge of the audience.
