In principle I think that they can get
some more power out of it. As JF is telling
this concept is not new and it already
has been proved to be somewhat successful.
I have earlier written that there are some
other research papers indicating that
you might somehow utilize air currents
from the middle to the tips of the blades.
Betz limit is based on the idea that
the air goes straight through the turbine
and that idea is probably not valid.
An extract from my previous post
http://www.fieldlines.com/comments/2004/4/26/93024/1936/13#13
************
From an article:
Alexander N. Gorban
Professor and Deputy Director,
Institute of Computational Modeling,
Krasnoyarsk, Russia Assoc. Mem. ASME
Alexander M. Gorlov
Professor Emeritus,
Hydro-Pneumatic Power Laboratory
Northeastern University,
Boston, MA 02115
e-mail: amgorlov@coe.neu.edu Mem. ASME
Valentin M. Silantyev
Graduate Student,
Department of Mathematics,
Northeastern University,
Boston, MA 02115:
Limits of the Turbine Efficiency
for Free Fluid Flow
...
The most interesting finding
of our analysis is that
the maximum efficiency of
the plane propeller is
about 30 percent for free fluids.
This is in a sharp contrast
to the 60 percent given
by the Betz limit,
commonly used now for decades.
It is shown that the Betz
overestimate results
from neglecting the curvature
of the fluid streams.
We also show that
the three-dimensional
helical turbine is more efficient
than the two-dimensional propeller,
at least in water applications.
Moreover, well-documented
tests have shown that
the helical turbine
has an efficiency of 35 percent,
making it preferable
for use in free water currents.
@DOI: 10.1115/1.1414137#
...
The principal assumption of
the Betz model was that
the fluid flow remains rectilinear
when passing through the turbine
and maintains a uniform distribution
of the fluid pressure on the turbine.
Such a distributed load leads
to overestimating the forces
and torque applied to
the turbine and, as a result,
to overestimating the turbine's
power and its efficiency.
In reality, the fluid streams
are deflected from the rectilinear
direction near the barrier,
changing their motion to curvilinear
trajectories and reducing
their pressure on the turbine,
as can be seen in Fig. 1~b!:
By taking account of
the curvilinear trajectories
for the streams,
one obtains a more correct
turbine power and efficiency limit.
...
*
********
I'm not sure, if it is the
best way to put the air going
through the blades.
I've been supporting the idea that
it might help if you'll make
the blades wider on the tips than
on the roots.
(Contrary to the common practice.)
But I hope that further research
will be done on this jet principle, too.
- Hannu
