Modular flow accelerator for a wind power plant
with a vertical rotation axis
A.A. Bubenchikov
I.S. Lebedev
T.V. Bubenchikova
A.A. Zakharov
E.A. Manakova
Energy Department
Energy Department
Energy Department
Energy Department
Energy Department
Omsk State Technical Omsk State Technical Omsk State Technical Omsk State Technical Omsk State Technical
University
University
University
University
University,
Omsk, Russia
Omsk, Russia
Omsk, Russia
Omsk, Russia
Omsk, Russia
privetomsk@mail.ru
lisnick@bk.ru
Antech-energo@mail.ru a.n.dr.e.w@mail.ru manakova_helen@mail.ru
Abstract. The design version of a power generating
unit of a multi-tiered wind turbine type with a vertical
rotation axis is considered in this article. The results of
mathematical modeling and the operation principle of the
tier elements of the power generating area with a vertical
rotation axis are examined both separately and in
combination with each other, forming a complete
arrangement. The total average coefficient acceleration
values of air flow passing through a power generating
unit at different ram flow velocities are determined.
Keywords: convergent tube, concentrator, air flow
acceleration, air flow diffusion, wind power plant with a
vertical rotation axis, power generating unit.
I.
INTRODUCTION
Currently, using wind power plants in the central part
of the Russian Federation is not absolutely profitable.
This is due to the fact that most of wind power plants
available on the market are designed for a wind velocity
of 10 m/s. Since power produced by a wind turbine
depends on the velocity cubed, such installations in our
region, where the wind velocity is in the range of 3-5 m/s,
will produce no more than 30% of its committed capacity
and the payback period will reach about 150 years.
The instability conditions of the low-velocity air mass
flow, which are typical for low-rise buildings and regions
remote from a world of waters, require the development
of wind power systems capable of stabilizing and
selecting wind flow power [1-3]. This will be caused by
using special geometric designs for vortex-type
installations. The proposed development is a wind power
system unit and it gives the possibility to combine three
tiers (concentration, acceleration and dispersion) of a
power generating unit (PGU) of a wind turbine (WT),
obtaining the optimal power generation effect.
II.
PROBLEM SETTING
The proposed installation consists of three modules.
The first module is designed to concentrate and reorient
air flow from horizontal to vertical direction. There is
acceleration and additional flow ejection in the second
module. The third block is used to create a zone of
reduced pressure for additional suction of the operating
flow and its acceleration in power take-off area. The
installation shape is a sandglass.
To determine the optimal geometry of the first module
The work was performed with financial support of RF President
Grant MK-5446.2018.8
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designs, forming five converging chambers and channels,
which are a cone at the base, as well as the outer case for
a converging channel will be investigated.
Using the second module, conditions for obtaining a
compacted laminar flow changing the main movement
direction will be created. It is important to emphasize that
both modules should also be oriented to an additional
flow turn relative to the horizontal axis.
The third module will be designed taking into account
the dispersion and final corner rotation of outward air
flow parallel to external environment flow.
The effective proper use of separate structural
members of PGU which in the first approximation are
represented by different areas of production is proved by
their operation practice of (table. 1): for the first module
they are TPP cooling plants (cooling towers), for the
second one– the elements of water intake from great
depths, for the third one – ventilation systems.
The design of PGU is based on previously known
ideas of effective use of air flow accelerator elements [46]. The distinctive feature of this article is a proposed
design version, permitting to study the complete cycle of
air flow within PGU in analyzing driving forces at power
take-off area.
III.
THEORY
In any power plant, special attention should be paid to
a power generation (selection) unit along with subsequent
optimization of mechanical and electrical components
taking up electromechanical power loads.
Getting obviously large efficiency values is due to
using optimal solutions of the interaction between a power
generating unit (PGU) and the requirements of the power
plant placement and operation.
In the present study an aerodynamic concentrator
confuser-diffuser installation of a tower-modular type is
presented as a power take-off unit.
Venturi effect is the base of operating all wind power
concentrators, as a result of Bernoulli law. It is that
pressure drops and velocity increases when gas flow
passes through a narrowed pipe part [4]. Therefore, it can
be stated that power increase can be obtained by reducing
cross-sectional flow area with its simultaneous increase in
velocity. Hence, accelerating air flow is the main
development tendency to improve the efficiency of wind
power plants (WPP).
TABLE I.
MAIN COMPONENTS (TIERS) OF A POWER GENERATING
UNIT
Tier name
1. Spiral converging
tube
2.1 Ejection and
acceleration chamber
Objects and examples of
using structural elements
Cooling towers, aerators
Gas-liquid pumps
Fuselage and wing elements in
the field of low velocity aero
building
3. Deflector
Ventilation
and
air
conditioning systems
Taking into account the experience of designing and
operating wind-dynamic systems under low wind pressure
[7], it can be argued that the most optimal installations
will be vertical-axial wind turbines for the considered
conditions. In this case, the hypothesis proving greater
efficiency in using concentric surfaces than rectangular
bodies in PGU designs will be tested (Fig. 1-3)
To facilitate the task of finding optimal design
solutions in general, any PGU is divided into separate
parts – modules which functions can have both similar
and different purposes. Operating a power generating unit
is based on the following processes: concentration,
direction reorientation, contraction, ejection, air flow
rarefaction and diffusion, increasing its velocity and
density [8-9].
According the world practice, constructing modules is
expedient based on the principle of similarity
(analogization) to the geometries of the living world,
using:
– the Golden ratio between installation components;
– spatial logarithmic spiral kinematics,
– the configuration of low-dimensional mathematical
topology,
– internal spatial areas in Gaussian distribution.
Using the above methods permits to obtain
hypothetically efficient power systems, which efficiency,
as well as the legitimacy of mathematical apparatus
selection, are specified in the subsequent mathematical
modeling and full-scale designing.
The whole considered power system should take into
account the peculiarity of its operation in the conditions of
low wind flow velocities. This makes a large set of source
data comparable with those of kinematic processes values
be considered. However, the dynamics of low velocities
today remains poorly understood and this creates
additional complexity in the wind turbine development.
The constant dimensional air flow redirection in
modules 1 and 2 enables to maintain and increase the total
forces of centripetal accelerations, which allow to
maintain the laminar-vortex structure of the main flow.
The laminar-vortex structure of the air flow permits to
concentrate the driving forces in a certain area of
mechanical energy removal. Depending on the driving
forces nature, it is necessary to use the appropriate
geometry of the power impeller surface fixed to the power
take-off shaft.
2.2 Additional
acceleration chambers
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An additional kinetic energy increment in the area of
its removal is due to the functions of the third PGU
module: ejection, air flow rarefaction and dispersion.
And the mechanical rotation energy transmitted to the
power take-off shaft by means of mechanical systems
(gearbox) makes the electric generator rotate. Thereby
power is supplied to the inverter through the regulator
unit. After the system start-up, the mode of its operation is
quickly stabilized, and the conditions for electrical energy
removal from the inverter terminals appear.
Since the structure of the electromechanical system is
quite complex, it requires the constant operational
adjusting and surveying.
Setting up mathematical correspondence of the
considered dynamic system will require final full-scale
experiments.
IV.
EXPERIMENT RESULTS
The PGU operation principle includes: concentration,
direction reorientation, contraction, additional ejection, air
flow rarefaction and dispersion (Fig. 1).
Fig. 1. Longitudinal cross section of PGU
There is an obstacle downwind in the form of
statically located cone 1 and channels 2, built along the
trajectory of a three-dimensional logarithmic spiral
twisted around the cone 1 of the first module. The effect
of concentration and reorientation of wind direction in the
earth's surface plane by 72 degrees takes place. The
geometry of the cross-sectional area of the channels 2
resembles an elongated drop, which space decreases
proportionally as the air flow passes upwards, thereby
creating the effect of contraction and its twisting.
The formed air flow in each of the channels 2 enters
the second module - the placement zone of the first
corrugated diffuser ring 3. Corrugation is represented by
five flange-shaped troughs with their displacement by 72
degrees (the plane of the earth's surface), coinciding with
air flow trajectory along the diffuser circle. Then the flow
moves to the zone of the second saddle-shaped diffuser
ring 4 (module 3), which region is dissected by five floworiented blades 5 twisted by 144 degrees (the plane of the
earth's surface), directed also along the main trajectory of
air movement. The profile of both rings is comparable to
the mixing ejector [6] in geometric parameters, which
experimentally proves its structural efficiency. Moreover,
the cross-sections of the diffuser ring walls 3 and 4 are
made in the form of a low-velocity wing profile (long and
thin). To increase the pressure and integrity of the formed
flow in the body of the diffuser ring 4, structural elements
in the form of elliptical air intake/air dispersion openings
6 are added. At the outlet of the second diffuser ring 4, the
air flow will enter the dispersion zone.
At the air flow outlet from the channels 2, the wind
wheel 11 is installed in front of the corrugated diffuser 3.
This wheel acquires additional dynamics of movement
due to the ejection effect of external wind flow through
the structural formation of gaps between the channel
group 2 and the corrugated diffuser 3. Additionally, in the
channels 2, oriented downwind, there is the cross-flow of
operating air masses (reverse thrust), increasing the
driving moment. Moreover, the module two is installed on
the module one, taking into account the technological
overlap of dimension projections. An additional
improvement in the quality of flow twisting and its
distribution is obtained by placing the entire system in the
core diffuser 3 presented by a drop 7. The second half of
the core 7 is closed by the second diffuser 4 with an outlet
to flow dispersion area.
The kinetic energy of the air flow is converted into
rotational motion of the wind wheel 11 by sensing area air
pressure on the blade. Further torque is transmitted to the
gearbox by means of the shafting line on which the wind
wheel 11 (power take – off impeller) is mounted, and then
to the generator (not specified in figure 1). They are
located at the convergent tube base – cone 1 of the first
module.
Module three is a chamber of reorientation, rarefaction
and dispersion of the working and external flows.
The total oriented flow, leaving the module two, is
entrained by an additional wind flow of external
environment, which enters the air intake ducts 6. Besides
an additional external flow meets the installation, entering
the air cavities between the diffuser ring 4 and the dome 8
with an opening in the center. The air flow inside the
module 3 after the rarefaction stage is divided into two
components, scattering between the diffuser ring 4 and the
dome 8, and also, reorienting along the guides 9, and
comes out between the dome 8 and the cap 10.
The diameters and heights of concentration,
acceleration and dispersion modules are also determined
by the following structural elements (parameters):
1. The scale of spiral turns of a static blade (this
affects on the angle of the wind flow rotation and the
channel width) -in our case it equals to 72according to
the laboratory tests [10].
2. The number of twisting turns (affecting on the
channel width) was determined earlier, on the conducted
studies basis [10], it is possible to determine the optimal
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number of sections for the first tier (module) as 5 in
number.
3. The geometry of a guide channel (affecting on
the wind flow rotation angle) – it is simulated according
to the geometry of a three-dimensional logarithmic spiral.
4. The conjugation form of an extended static blade,
providing a smooth entry of the wind flow into the wind
turbine convergent tube (affecting on the concentrator
flow inlet area) – two options are proposed in using:
straight and rounded ones.
5. The shape and rotation angles of the blades 5 and
guides 9 in the second module body (affecting on the
density and flow rate).
6. The height of the convergent tube – the constant
parameter of 1500 mm is defined.
7. The height of the lower dome boundary of the
convergent tube above the ground surface (air inlet
channels) – proposed options are in the range from 450 to
1200 mm.
8. Dimensions and conjugation angles of the second
and third tier elements of a power generating unit [10].
9. Cross-section profiles of diffuser rings 3 and 4,
dome 8 and cap 10
10. Configuration of air intake openings 6.
To ensure optimal efficiency of the installation, it is
necessary to observe the condition of the exhaust air flow
outlet parallel to the external one. This factor is necessary
in constructing the geometry of modules deploying flow
to certain angle values, which total sum must be multiple
of 180 degrees.
In experimental studies for the first module (tier) in
[10], the value of the optimal flow rotation angle was
determined, which value varies from 51 to 120 degrees.
For the third module – the dispersion unit, the values
of the flow twisting angles were laid according to the
experimental data obtained in operating full-scale models
and completed units. In our case of borrowing the
elements of the well-known deflector design [5], the flow
twisting interval was from 5 to 90 degrees.
Hence, considering two previous modules, the flow
twisting value for the second tier should be in the range
from 126 to 211 degrees. The value of 144 degrees was
determined experimentally.
In order to determine the final design of the PGU, it is
necessary to identify the most optimal design solutions for
separate module units at preliminary testing stages. It is
necessary to consider the conditions of the best
performance parameters for each unit separately.
However, there is a high probability that in some cases
operating the elements taken separately is ineffective or
simply impossible [9].
The refusal from rectilinear geometries, despite the
sufficient assembling and manufacturing simplicity in
favor of using concentric bodies in the PGU elements, is
due to the practice of comparing mathematical modeling
results in order to obtain the best acceleration coefficients
(Fig. 2-3).
Fig. 2. General view of the first tier versions
a)
b)
c)
d)
Fig. 3. Horizontal section of airflow outlet plane from a concentrator: a)
external structural elements of a convergent tube are presented by
symmetrical planes; b) convergent tube elements are smooth planes; c)
internal structures of a convergent tube are symmetrical planes; d)
internal structure of a convergent tube is presented by smooth planes
Fig. 3 a, b shows that in changing symmetrical planes
of an external convergent tube construction into smooth
concentric ones, velocities inside the convergent tube
body will get greater values.
A more uniform distribution of flow velocities inside
the convergent tube proved the necessity to divide the
internal space into five channels (Fig. 3b, C).
Organizing the internal space of channels by replacing
sharp corners with static blades allowed to localize an
operating channel and increase the velocity value inside it
(Fig. 3b, g).
For the selected geometry, the height of an external
truncated cylindrical dome was chosen. The data obtained
are presented in table 2.
Based on the data obtained, the most optimal
configuration of the first module (tier) was chosen for the
further power generating unit construction. The height of
the earth's surface indentation was 1000 mm.
The geometry of the second module construction is
similar to the proposed mixing ejector characteristics of
the scientific study [6].
When conducting mathematical research on obtaining
the highest acceleration values in module 2 it was
discovered that in adding capacity directed flange
channels of the first diffuser of a mixing ejector [6] the
effect of the supplemental local flow acceleration
appeared. This effect was taken as a basis and improved
in constructing shaped fence chambers– separate channels
in the module 1 (Fig. 4).
The cone parameters remained unchanged. It was
decided to replace the inner blades and the outer casing
with separate channels, which allowed to give them
influence of integrity and softness on the flow. The
generatrix (arc, R=275mm) and its trajectory (straight on
the surface of a cone with a twist of 72 degrees) were left
from the inner blade in the previous version, the contour
was closed by an arc (R=193mm).
To observe the conditions for maintaining and
increasing air flow density, it is necessary to sustain the
constant forced change of movement direction when
stabilizing the formation of vortex flow (especially in
extended and volumetric chambers). This is due to the
flow contraction by centrifugal forces. And in the
transition of the air flow from one element of the module
to another, it will be especially important to create this
effect of changing the dimensional flow direction.
The second tier outside is represented by the first
corrugated
diffuser ring (Fig.
5, hereinafter
"corrugation"), designed to create an ejection effect. The
lower edge of the ring is a set of channel profiles of the
first tier, formed into a ring. The corrugation is located
relative to the first tier in such a way that the first tier is
immersed in it by 44 mm, and the distance between the
outside channel walls and the corrugation is 1:1.63.
Constructing such geometry is due to the wall layer
presence in the flow [11], which kinematic viscosity is
much higher than the operating one, freely moving from
the channels to the corrugation inside.
a
DETERMINING THE ACCELERATION AIR FLOW
COEFFICIENT OF THE LOWER TIER (MODULE), DEPENDING ON THE
OVERALL PARAMETERS WHEN THE BASE CIRCLE DIAMETER IS 1567, 8 MM
b
TABLE II.
Lower dome generatrix height,
mm
Flow velocity, m/s
450 600 1000 1200
4.9 5.5
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5.8
5.5
Fig. 4. Views of the first module channel versions: a) general view, b)
side view
a
b
Fig. 5. Views of channel versions of combining the first and second
module: а) general view, б) side view
assembly. We can see the non-directional and nonstructured rarefaction and dispersion of the air flow,
which ultimately reduces power take-off efficiency at the
appropriate area.
The received data served the basis for forming the
third tier structure, which began to acquire the properties
of concentration, direction reorientation, ejection,
rarefaction and dispersion of the air flow, typical to the
deflector properties [5] and was determined in terms of
the transition diameter between the modules two and
three. Besides, for ordering the flow motion better,
additional elements such as a central guide (position 7,
Fig. 1), blades twisting around it (position 5, Fig. 1) and
elliptical openings (position 6, Fig. 1) placed on the
second saddle-shaped diffuser ring.
In analyzing the velocities picture of the mathematical
modeling results of a transition tube of the first and
second modules (Fig. 6) it can be stated that the twisting
corrugation nature has a great influence on the ejection
parameter values. The greater the twisting angle of
elliptical corrugation flanges along the flow movement,
the higher the velocity entering into the structure. With
more twisted ring the velocity of the incoming flow is in
the range of 6-7 m/s, with less spun one it is about 5 m/s.
Moreover, the high velocity area expands (Fig. 6).
Fig. 8. Velocity map of mathematical positioning of the developed
model in the general flow at a velocity of 5 m/s
а)
Fig. 6.
б)
Comparing twisting versions of ejector ring flanges a) spun at
72º, b) spun at 10º
The third tier became a chamber for the exhaust flow
removal outwards. And the installation is domed and
capped (position 8.10, Fig. 1). Guide blades are designed
taking into account the thickness gap of the wall layer
[11]. The twisting angle of five blades (position 9, Fig. 1)
is due to the exhaust flow outlet in the direction of the ram
environment air and amounted to 144º.
After measuring the main dimensional performance
parameters of PGU, data are summarized in table 3. The
data obtained indicate the performance of the system, but
with small efficiency. It provides maintenance,
distribution and acceleration of incoming flow, but
certainly requires further development.
Determining the optimal ratios of all the abovementioned structural parameters will allow to obtain the
greatest flow acceleration from 34% to 50% and increase
the power generated by a wind turbine from 2.2 to 3.3
times.
V.
Fig. 7. Flow pattern in an installation with the third tier ring (the
external flow moves along the glance trajectory, from an observer to
PGU)
After forming the second module geometry, the
question about the design of the second saddle-shaped
diffuser ring arose (Fig. 7). The result was obtaining the
visual air mass movement at the stage of step GPU
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CONCLUSION
The simulated design gives the possibility of
estimating the acceleration air flow coefficient. It allows
to analyze separate concentration units: direction
reorientation, contraction, additional ejection, rarefaction
and dispersion of the air flow. At the same time, the
functionality of the proposed flow acceleration system
will be minimally influenced by such factors as
temperature, intensity and frequency in wind direction
changes.
Constructing a wind flow accumulation unit through
the optimal combination of modules and additional
toppings, along with the process of increasing power and
averaging the air flow at the outlet, will also help to
TABLE III.
reduce the vibration loads both on structural elements
themselves and on adjacent territories. This is one of the
most important factors in locating wind turbines near
social facilities and residential infrastructure.
MEASUREMENT RESULTS
Obtained values of flow velocities at
an external wind of 5 m / s
Tier Name
separately, m / s
1. Spiral convergent tube
2.1 Ejection and acceleration
chamber
2.2 Additional acceleration
chambers
3. Deflector
5.35
5.5
3.88
3
While investigating it was revealed that the data
obtained by preliminary hypothetical analysis were
corrected by means of mathematical modeling. These
data will provide the basis for the further research of
the proposed designs with due account for the
influence of additional geometry elements in a power
generating unit.
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