美国SANDIA国家实验室关于垂直轴风力机的研究报告SAND74-0160

Ability
to accept
wind from
any direction. at ground level, tower without costly construction bevel and
The generator gearing, less
can be placed
and will thereby
CHORD LINE
Forces Airfoil
Acting
has rotating
airfoils,
it presents the absolute
a slightly wind speed.
different In-
is not simply
to the blade is the absolute velocity difference
will not cause
to bend and thus
the stresses
will be pure tension. axis wind turbine offers several advantages over the conventional propeller-
The verticaltype wind turbine: 1. 2.
reason.
increases,
the angle of attack,
Consequently,
the chordwise
component
of lift decreases
with decreasing
a (see Figure From
2).
Also,
the lift-toa comoccurs values at of
THE VERTICAL-AXIS WIND TURBINE “HOW IT WORKS”
In 1925, of windmill
G. J. M. Darrieus,
Paris,
France, of power.
proposed The patent,
for United States patent a new type issued in 1931 as Number ‘‘ 1, 835,Байду номын сангаас018, wind
allow simpler
maintenance. fabrication costs because of simple tower construction
3,
Lower
and reduced The operational of a wing (airfoil). forces are generally
is perpendicular
The angle between airfoil, section.
is c ailed the angle of attack. to the centerline
For a symmetric cross
as shown in Figure The general
up to the point where the flow separates to as stall. creases condition
the airfoil. large
This separation to cause stall,
is generally the lift-to-drag
Once the angle of attack is sufficiently angle of attack.
A similar
was independently Council
of the National
of Canada in the early a photograph in cross
Figure is a symmetric of uniform
1 shows airfoil
of a small-scale and is curved
RW/ V. L, and the drag of the
The forces force,
rotation
are determined
the lift force,
D, onto the direction (Figure
of the chord
line of the airfoil.
The chordwise sense,
component
lift force component
2) tends to cause opposes
rotation
in a counterclockwise
while the chordwise lift force is greater
of the drag force
this motion. torque
rotational
speed
(Rw / V),
the airfoil
be stalled t ational
In that the blade
stalls
at low relative
speeds,
the aerodynamic that cause
performance
will be very poor for small by projecting
is comparable of the available
to that of a conventional stream energy
horizontal-axis
wind turbine,
model
vertical-axis
wind turbine.
Each blade cable shape
section
in the shape that a perfectly axis.
flexible
density
and cross troposkien
section (from
would assume the Greek: shape,
drag ratio goes to zero posite picture
as the angle of attack goes to zero. performance speeds;
the above discussion, poor performance at intermediate
of the aerodynamic
above, stall.
the aerodynamic The performance As Ru/V
performance is also poor
rotational speeds
speeds
be-
at high relative
rotational a, decreases.
but for an
can be envisioned: best performance large
both low and high relative
RLU/V because
rotational
occurs
the angle of attack is sufficiently Figure 3 illustrates
if spun about a vertical TPOTTOS, urning; t
This blade
has been designated blades are preformed
and rJXotVIOV, rope), the blades
If the
in the troposkien
rotation
line corresponds airfoils
of the airfoil (L/D)
characteristic
of most
is that the ratio
of lift-to-drag from
increases
with increasing
angle of attack referred ratio de-
blade fabrication of the verticalover
costs. axis wind turbine forces is analogous to the aerodynamics These
principle
When a fluid flows divided
an airfoil,
with increasing
For optimum
aerodynamic
performance,
the stalled
should be avoided.
3
Figure
1.
Vertical
Axis
Wind
Turbine
4
A
o
Figure 2. Aerodynamic on a Rotating Because condition. stead, absolute the verticalaxis wind turbine First, the wind felt on a rotating of the wind relative RM. airfoil the velocity
with increasing speed
rotational
for a sufficiently However, portion
rotational
(Rw/V),
the airfoil
is never will ro-
a revolution. an appreciable
at a low relative of a revolution.
are exerted
on the airfoil. is parallel the chord
into lift and drag components; to the drag force.
the drag force
to the wind, line and the 2, the
while the lift force wind direction chord
wind velocity,
V, minus the 2. For a ro-
blade velocity,
This vector
is shown in Figure wind speed,
tating airfoil, line. tational
the angle of attack is the angle between in Figure 2, the angle of attack, angle, 0.
the relative u, depends In the figure, 12 degrees
W, and the chord V, the roso that
As illustrated speed,
on the wind speed,
Rw, and the blade position
V and RW are drawn at the blade position relative
designed
for the generation
was for a “turbine turbine Research
having its rotating developed
shaft transverse by the National 1970 ‘s.
to the flow of the current. Aeronautical Establishment
As long as the chordwise will always is poor be positive. at low relative
than the chordwise As stated cause entirely of airfoil different
drag force,
the driving
Rw/V corresponds
to an angle of attack of approximately the angle of attack decreases high relative
indicated, speed
For a given blade position, (R~/V). stalled Therefore, during over
for high values behavior.
of L/D but not large
enough
to cause
stall.
this anticipated
The efficiency
of the vertical-axis i. e. , about
wind turbine 40 percent