bombastic titles, little content – this the way to make news

Putting an end to turbulence (11/25/2008)

It is still unclear whether the new results also hold true for flows outside of pipes.

This is what I read in small letters down there. but the title: way far bombastic:

Putting an end to turbulence (11/25/2008)

well, that’s MatterNews. Judge it yourself.

When a flow reaches a certain speed, things get turbulent: The
fluid or the gas no longer flows in an orderly fashion but whirls
around wildly. However, in contrast to what researchers assumed until
now, this state is not permanent. Scientists from the Max Planck
Institute for Dynamics and Self-Organization in G๖ttingen, Germany, and
the Technical University in Delft, Netherlands, have shown that in pipe
flows, all turbulence will disappear with time. The new measurements
are significantly more precise than all previous experiments and
computer simulations concerned with this question. (Physical Review Letters, November 21st 2008)

Turbulent flows in pipes are of importance for many every-day
applications. What they all have in common is their appearance: They
travel down the pipe bubbling and gurgling like a mountain stream. The
flow only calms down when its speed is reduced. Scientists call this
calmer state laminar. Crucial for the difference between laminar and
turbulent flow are the inner forces that link the water molecule to
each other. Only if the influence of these inner forces is smaller than
the influence of the forces that accelerate the flow can turbulence
appear.

Until now, scientists assumed that a turbulent flow travelling with
a constant speed will always remain turbulent. However, scientists from
G๖ttingen and Delft have now found evidence that points to the
contrary. “Our measurements show that every turbulent flow in a pipe
will inevitably become laminar”, says Dr. Bj๖rn Hof from the Max Planck
Institute for Dynamics and Self-Organization. Depending on the exact
geometry of the pipe this transition may take many years. But just like
a ball inside a hollow, that always rolls back into the equilibrium
position, only the laminar flow is stable.

For their measurements the scientists let water flow through glass
pipes of up to 14 meters length and only a few millimetres in diameter.
With the help of a short water pulse from the side they created a
turbulent eddy in the otherwise perfectly laminar flow. They then
monitored closely, how this eddy changed as it travelled down the pipe.
From the probability with which it reached the end of the pipe they
could derive the basic principles that govern turbulence.

“In order to discern whether turbulence is stable or only has an
extremely long lifetime, our measurements had to be very exact”, says
Hof. For example, it was crucial to keep the temperature of the water
absolutely constant during the experiment. The measuring accuracy which
the scientists achieved in this way exceeded all previous experiments.
Even computer simulations cannot provide such precise data.

It is still unclear whether the new results also hold true for flows
outside of pipes. But even now the results could help in ending
turbulence in pipes in a controlled way. “Turbulent flow consumes more
energy than do laminar ones. In many applications such as oil pipelines
they are therefore bothersome”, explains Hof. Since the flows aspire to
turn laminar on their own, it could be possible to shorten the long
lifetime of the turbulence with the help of a small perturbation. This
could help save energy.

A turbulent eddy flowing through a thin glass pipe. The flow is laminar in front of and behind the eddy. -  Max Planck Institute for Dynamics and Self-Organization

A turbulent eddy flowing through a thin glass
pipe. The flow is laminar in front of and behind the eddy. – Max Planck
Institute for Dynamics and Self-Organization


Advertisements

Leave a Reply

Please log in using one of these methods to post your comment:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s