NL2030791B1

NL2030791B1 - A vertical axis turbine and use of a turbine

Info

Publication number: NL2030791B1
Application number: NL2030791A
Authority: NL
Inventors: Cabildo Fajardo Pablo
Original assignee: Cabildo Fajardo Pablo
Priority date: 2022-01-31
Filing date: 2022-01-31
Publication date: 2023-08-08

Abstract

The invention relates to a vertical axis turbine, comprising a rigid structure, a single or a multiple number of stators mounted to the rigid structure, and a rotor arranged for periodic movement relative to the single or multiple number of stators. The turbine further comprises a pre-stressed elastic element mounting the rotor to the rigid structure so as to enable the rotor to perform periodic movements relative to the single or multiple number of stators upon occurrence of a force oriented mainly transverse to a body axis of the rotor and induced by a ﬂowing ﬂuid surrounding the rotor.

Description

P131596NL00

Title: A vertical axis turbine and use of a turbine

The invention relates to a vertical axis turbine and use of a turbine.

In the XIX century, the coal-steam engine stroked the first blow to the history when the first train appeared in 1804 in the early times of the 1st

Industrial Revolution. In the XX century, the oil engine struck a second shot to history, after the first automobile appeared in 1886, in the middle of the 2nd Industrial Revolution. And so, the early years of the XXI century find humankind facing the results of decades of harming and polluting the Earth and its ecosystems, and thus seeking for a Green Energy Revolution, hosted by electric engines, and carried out by electric cars.

It 1s at this point where renewable power generators such as wind turbines can lead humankind one step further in the goal of achieving a sustamable, more efficient electric power generation, increasing the efficiency of the electric generators currently driving the Renewable Energy

Industry.

There is an extensive variety of generators used for. Different prototypes depending on the renewable energy it is tried to take advantage of, but most of them share structural elements, with the most typical conformation being the Turbine prototype, composed by four main elements: blades/vanes, rotor/impeller, shaft, and stator and bearings.

Hence, two main generator families can be remarked. Considering the position of those elements within the fluid they try to obtain power from, there are Horizontal Axis and Vertical Axis Turbines. Horizontal Turbines present a shaft parallel to the fluid flow, whereas in Vertical Turbines, the shaft is placed perpendicularly to the flow direction. Accordingly, wind turbines are categorized as Horizontal Axis Wind Turbine, HAWT, and

Vertical Axis Wind Turbine, VAWT.

While so-called Savonius type rotor blades take advantage of a differential pressure between the front and rear side of the blade, so-called

Darrieus type rotor blades works in function of the differential pressure generated by the shape of the blades. The same working principle occurs in a plane when pressure gradient is generated from the thick to the thin part of the wing.

Each type of turbine has its own advantages: while the Savonius type is capable of self-start spinning, the Darrieus type has 20% more efficiency. To sum up, a three-blade wind turbine has a maximum converted energy of 45%, a Savonius type has a maximum of 15% and a Darrieus Type has a maximum of 40%

That yield difference is the main reason why the wind market has been focused on HAWTs.

However, in April of 2021, the School of Engineering, Computing and Mathematics (ECM) at Oxford Brookes discovered that in windfarms, the HAWT converted around the 50% of the kinetic energy in the front line, while the back row of generators could convert between 25-30% of the kinetic energy because of the turbulence generated downstream.

This does not occur with Darrieus turbines, because blades speed does not achieve such high magnitude, and the most important thing, this kind of VAWTSs do not produce high intensity turbulence because of the open space between shaft and blades.

There are at least two reasons why turbines do not convert more than 45% percent of the kinetic energy. Firstly, the blade effectiveness depends on the shape, but there is always a portion of the energy lost, not transmitted as lift force, being exerted as dragging force instead, which neither Darrieus nor TBT can transform. Although, energy loss can be reduced by changing the blade shape. Secondly, the axis or shaft cannot convert the fluid kinetic energy into rotary force.

It is an object of the invention to counteract at least one of the disadvantages mentioned above. It is a further objection of the invention to provide a turbine having an increased efficiency.

Thereto, according to an aspect of the invention, a vertical axis turbine is provided, comprising a rigid structure having mutually opposite portions defining a turbine volume therebetween, a single or a multiple number of stators located in the turbine volume, and a rotor element located in the turbine volume and arranged for periodic movements relative to the single or multiple number of stators, the turbine further comprising a pre- tensioned tensioning structure suspending the rotor element between the opposite portions of the rigid structure so as to enable the rotor element to perform periodic movements relative to the single or multiple number of stators upon occurrence of a force having a component oriented mainly transverse to a body axis of the rotor element and induced by a flowing fluid surrounding the rotor.

By providing suspending the rotor element to the rigid structure using a pre-tensioned tensioning structure, the conventional rigid shaft is replaced by a more flexible shaft structure including the tensioning structure allowing the above-mentioned dragging force induced by the fluid impact to be converted into spinning energy contributing to the overall turbine efficiency.

Additionally, due to the orientation of the rotation axis, the vertical axis turbine according to the invention would have greater efficiencies than conventional wind farms.

Advantageously, a fundamental resonance frequency of the pre- tensioned tensioning structure is pre-selected to be associated with a periodicity of the periodic movements performed by the rotor element by setting a pre-tensioning level of the tensioning structure, so as to optimize the conversion into spinning or pendulum movements of the rotor element.

The periodic movements performed by the rotor element may include rotations around a line of symmetry coinciding with a longitudinal axis of the tensioning structure in an equilibrium state, thus realizing rotational pendulum movements.

Preferably, the rotor element is arranged to perform a superposition of rotations around the line of symmetry and rotations around its body axis, so that also rotations of the rotor element around its own body axis may contribute to the overall turbine efficiency.

The invention also relates to the use of a vertical axis turbine.

Other advantageous embodiments according to the inventions are described in the following claims.

Fig. 1 shows a schematic side view of a vertical axis turbine according to the invention,

Fig. 2 shows a force diagram of the turbine shown in Fig. 1,

Fig. 3 shows a schematic perspective view of another vertical axis turbine according to the invention,

Fig. 4 shows a force diagram of the turbine shown in Fig. 3,

Fig. 5 shows a schematic top view of the turbine shown in Fig. 3 provided with radial flux type stator,

Fig. 6 shows a schematic perspective top partial view of the turbine shown in Fig. 3,

Fig. 7 shows a schematic top view of the turbine shown in Fig. 3 provided with axial flux type stator,

Fig. 8 shows a schematic view of rotor types applicable to the turbine shown in Fig. 3, and

Fig. 9 shows an array of turbines shown in Fig. 3.

In the figures identical or corresponding parts are represented with the same reference numerals. The drawings are only schematic representations of embodiments of the invention, which are given by manner of non-limited examples.

Figure 1 shows a schematic view of a side view of a vertical axis turbine 1 according to the invention, relative to an xyz coordinate system.

The turbine 1 has a rigid structure 2, shown in Fig. 1 in a simplified geometry, provided with mutually opposite portions 2a,b defining a turbine volume V therebetween. The turbine 1 also has two stators 3a,b positioned in the turbine volume V, and a rotor element 4 that is arranged for performing periodic movements relative to the two stators 3a,b also described in more detail below. The stators 3a,b can be mounted to the rigid structure 2 or can be arranged in the turbine volume V in another way, e.g. 5 vla an intermediate structure, for positioning the stators 3a,b in the turbine volume. The two stators 3a,b each extend in a plane that is mainly parallel to the x,y plane. The rotor element 4 has a body axis B that in the shown embodiment is oriented in a mainly vertical direction z.

The turbine 1 further has a pre-tensioned tensioning structure 5 suspending the rotor element 4 between the opposite portions 2a,b of the rigid structure 2 so as to enable the rotor element 4 to perform periodic movements relative to the single or multiple number of stators 3 upon occurrence of a driving fluid force Fy. Generally, the driving fluid force Fp is induced by a flowing fluid 6, such as air or water, surrounding the rotor 4.

Further, the driving fluid force F4 is oriented mainly transverse to the body axis B of the rotor element 4, or has at least a component mainly transverse to the body axis B of the pendulum 4.

The turbine 1 in Fig. 1 is shown in a rest state, when no driving fluid force Fy is exerted on the rotor 4. Then, the pre-tensioned tensioning structure 5 is stationary having a longitudinal axis forming an axis of symmetry S. In operation, the combination of the pre-tensioned tensioning structure 5 and the rotor element 4 act as pendulum as explained in more detail below. The movement of the rotor element 4 relative to the stators 3 induces electrical energy, the turbine 1 than acting as an electric power generator.

In Fig. 1, the pre-tensioned tensioning structure 5 includes a first string 5a connecting the rotor element 4 to the first opposite portion 2a of the rigid structure 2, and a second string 5b connecting the rotor element 4 to the second opposite portion 2b of the rigid structure 2. At least the first string 5a or the second string 5b is elastic. The first string 5a and/or the second string 5b may include a smooth or soft material for application in lower fluid speeds or a rough material for higher fluid speeds. As an example, the strings 5 may include stainless steel having the advantage that it can be electrically heated to avoid water crystallization. As another example, the strings 5 may include a polymer or polymers such as nylon having the advantage of being lighter and less sensible to temperatures, leading to less breakages and less fatigue cracking.

Preferably, the turbine 1 is provided with a tensioner element 7, see in more detail the description referring to Fig. 3 below, for setting a pre- tensioning level of the tensioning structure 5. By setting a pre-tensioning level of the tensioning structure 5, a fundamental resonance frequency of the pre-tensioned tensioning structure can be pre-selected or pre-set to be associated with a periodicity of the periodic movements performed by the rotor element 4.

In the shown embodiment, a first stator 3a is positioned vertically above the rotor element 4, offset along the z-axis, while a second stator 3b is positioned vertically below the rotor element 4, offset along the z-axis. It is noted that, in principle, the turbine 1 may include a single stator only, e.g. the first stator 3a only or the second stator 3b only, or a stator positioned at mainly the same vertical position as the rotor element 4. Further, the turbine 1 may include more than two stators, e.g. three or four stators, or even more than four stators.

Figure 2 shows a force diagram of the turbine shown in Fig. 1 provided that a single coil stator 3 is applied instead of two stators above and below the rotor element 4. The coil stator 3 is located at the same height as the rotor element 4.

Operation of the turbine 1 is based on a so-called vortex induced effect associated with a correlation called Strouhal Number St, discovered by the physicist Vincent Strouhal (1850-1922). This correlation describes the oscillating flow mechanisms experimented by bodies, originally wires.

The non-dimensional number Strouhal Number St can be defined for cylinders as follows:

Strouhal Number for cylinders

SE Je where Vis the fluid velocity (m/s), f the oscillating frequency, perpendicular to the fluid direction, and d the cylinder diameter.

The vortex induced vibration (VIV) phenomena generally occurs for

St = 0.2 and this phenomenon appears when the velocity of the fluid reaches the natural harmonic frequency, ’f = fv’, depends on the diameter of the body, strength (in case of rigid cylinders) or tension (in case of strings), length, material density, the body surface rugosity.

In the case of generators or turbines described here, the key magnitude is the fundamental frequency of a pendulum formed by the rotor element 4 and the pre-tensioned tensioning structure, modulated by controlling the tension of the string, like the strings of a musical instrument, as well as by choosing the adequate diameter of the rotor element 4, material and shape depending on the fluid dynamic conditions.

The fundamental structure of these generators is based on a conic rotor element with a couple of add-ins: a string attached to two surfaces, a rigid cylindrical, spherical shape or conical shaped module shape attached to the string, permanent magnets attached to the rotor element, and at least one stator with a single or a multiple numbers of coils, where the induced current 1s produced.

As indicated above, the tensor regulator 7 may be used to set a pre- tensioning level in a range of magnitudes of tension, e.g. depending on a fluid velocity of fluid surrounding the rotor element 4.

As can be seen in Fig. 2, a dragging force Fw generated by the fluid forces the rotor element 4 to follow a closed contour path that is mainly circular around the line of symmetry S, in a plane generally transverse to the line of symmetry S. Here, r is a radius of the circular path while h is the distance to the first opposite portion 2a of the rigid structure 2. Further, T is tension generated by a tensor regulator 7, A an amplitude, Fc a centrifugal force generated by the circular trajectory followed by the rotor element 4, and “Fv” a force generated by the Vortex Induced Vibration. This vibration force Fv is just a direct effect of a vibration frequency, however it is not an external force, but it is described here to clarify the concepts.

As described above, the periodic movements performed by the rotor element 4 include rotations around the line of symmetry S coinciding with a longitudinal axis of the tensioning structure 5 in an equilibrium state. The rotor element 4 and the tensioning structure 5 act as a pendulum performing periodic circular movements with a periodicity associated with a vibration frequency. The periodic circular movements performed by the rotor element 4 are also referred to as translational, oscillation or pendular movements.

Figure 3 shows a schematic perspective view of another vertical axis turbine 1 according to the invention. Here, the rotor element 4 is not formed as a rigid cylindrical, spherical shape or conical shaped module, but is formed as a rotor having Savonius type rotor blades 4a converting the kinetic force of the fluid into a drag force. Then, the rotor element 4 does not only follow a pendular path PP as described referring to Fig. 2 but also a rotational path RP by rotating around a body axis B of the rotor element 4.

Induced by a force exerted by fluid flowing along the rotor element 4, the rotor element 4a performs a superposition of pendular path PP rotations around the line of symmetry S and rotational path RP rotations around its own body axis B.

It 1s noted that, generally, other rotor blades can be applied instead of the Savonius type rotor blades, such as helicoidal type blades, Darrieus type blades, Helix-shaped blades or H-type Darrieus blades or Darrieus-

Savonius type blades.

Further, the turbine 1 includes a tensioner element 7 having a manual crank for manual operation for adjusting a pre-tensioned level of the tensioning structure 5. Alternative, the tensioner element 7 may be mechanically or electrically actuated.

Within this disclosure, a turbine wherein the rotor element 4 is arranged to follow only a pendular path PP is referred to as a Vortex

Induced Pendulum VIP generator, while a turbine wherein the rotor element 4 is arranged to follow both a pendular path PP and a rotational path RP is referred to as a Vortex Induced Rotary Pendulum VIRP generator. Generally, the VIRP combines advantages of the VIP generator with the efficiency of a regular Rotary Permanent Magnet Generator

RPMG wherein the rotor has a fixed rotation axle that is known for renewable energy production. In Fig. 3, magnet, coils and stators have not been depicted, for comprehensibility reasons.

Compared to RPMGs, VIRPGs have an advantage of amplified rotation motion due to the oscillation or translation movement produced by the dragging force exerted by the fluid when this impacts against the rotor element 4. This amplification is an effect well known in ballistic and in sports physics, called Magnus Effect.

According to the theory of the Magnus Effect a body (sphere or cylinder) is described rotating to generate a translational parallel movement to a fluid motion, although in the opposite orientation.

Due to a different path length, a fluid mass to which the body moves is flowing faster than the fluid on the opposite side of the body thanks to the drag force as quantified as follows: 2)

Kutta-Joukowsky equation applied to a cylinder shape.

Fam = pVGL = Zul pV L wherein © 1s the rotary frequency, p fluid density, d cylinder diameter, V fluid velocity and L the length of the body.

Figure 4 shows a force diagram of the turbine 1 shown in Fig. 3.

Looking into the fluid dynamics of the Vortex Induced Rotary Pendulum

VIRP generator, the kinetic power from the fluid is transformed into three different motion forces.

Here Fw is the drag force with two components, not defined here,

Fm the Magnus effect force an Fv the oscillating starting force, as a result of the St number conditions. Although, Fv may only become relevant when it is attempted to either increase or decrease the pendular velocity by adjusting the pre-tensioning level or tensioning value of the tensioning structure 5.

Considering all three forces, the drag force is defined as follows: 3)

Dragging force

Fu = L dcuv? = Liev? wherein d: diameter, L: length of the pendulum, cw: dragging coeficient, which depends on the shape of the pendulum and V: fluid velocity. (4)

VIRP forces equation

Evs Fuh + | Fm + vlg wherein the symbols “| y” and “|x” denote component along they axis and the x axis, respectively.

In principle, the turbine may include any stator type cooperating with coils or magnets provided in or on the rotor element 4a.

Figure 5 shows a schematic top view of the turbine shown in Fig. 3 provided with a radial flux type stator. Here, the stator includes a circular shaped yoke 1 provided with stator teeth 12 protruding radially mwardly and having stator coils 13 wound around said teeth 12. The rotor element 4 is provided with magnets 14 facing radially outwardly through a gap 15 towards the stator teeth 12.

Radial flux type stators are generally easy to build in a relatively compact design.

Figure 6 shows a schematic perspective top partial view of the turbine shown in Fig. 3 provided with the radial flux type stator shown in

Fig. 5.

Figure 7 shows a schematic top view of the turbine shown in Fig. 3 provided with axial flux type stators. Here, the stator 3 is provided with coils 23 wound around an annular shaped structure. Further, the rotor element 4 is provided with permanent magnets 24 oriented along a radial direction.

Axial flux type stators are generally more efficient than radial flux stators because the magnets 24 can be located closer to the coils, and they may experience less heating in the coils 23 due to the induction currents.

Figure 8 shows a schematic view of rotor types applicable to the turbine shown in Fig. 3. On the left hand side, the rotor 4 is provided with

Savonius-type rotor blades 4a for forming an axial flux pendulum. In the central portion of the figure, the rotor 4 is provided with Helicoidal-type rotor blades 4b for forming an axial flux pendulum. Further, on the right hand side, the rotor 4 is provided with Darrieus-Savonius-type rotor blades 4c for forming a radial flux pendulum.

Figure 9 shows an array of turbines 30, 31 shown in Fig. 3 arranged in a frame structure 28 containing multiple turbine for parallel power generation. As an alternative, a turbine park with multiple turbine can be provided wherein the individual turbines are offset from each other with a mutual distance minimizing fluid flow interference.

The turbine may include a single or a multiple number of sensors to determine a fluid velocity, a mechanical tension of the tensioning structure, a periodicity of the rotor and/or a temperature, for controlling operation of the turbine.

According to any aspect of the invention, the described turbine can be used for electric power generation. Also, the described turbine can be used as a sensor or instrument for fluid dynamics studies, especially if the turbine is constructed on small scale.

The flowing fluid driving the turbine 1 may include a gas, such as air, or a liquid, such as water.

The invention is not restricted to the embodiments described herein. It will be understood that many variants are possible.

It is noted that the turbine may be used for a variety of green power production applications including field, bridges, offshore, skyscrapers for wind energy; river shores or dam for hydraulic energy production; down sea offshore or coast for tidal energy, or even for energy production from rain droplets.

The turbine described above is of the so-called vertical axis type as a rotation axis of the rotor element is mainly perpendicular to a flowing direction of the fluid. As an example, for wind energy production, the vertical axis type turbine can have a compact design allowing application in urban areas, e.g. on roofs.

It is noted, however, that the z direction may be different from a height direction. As an example, the z direction may be a horizontal direction, e.g. if a fluid is flowing downwardly.

It is further noted that the turbine may include bearings connected to the tensioning structure for bearing the rotor element.

These and other embodiments will be apparent for the person skilled in the art and are considered to fall within the scope of the invention as defined in the following claims. For the purpose of clarity and a concise description features are described herein as part of the same or separate embodiments. However, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described.

Claims

Conclusions

A vertical axis turbine comprising: - a rigid structure having mutually opposed members defining a turbine space therebetween, - a single or multiple number of stators located in the turbine space, and - a rotor element located in the turbine space and is arranged to perform periodic motions relative to the single or multiple plurality of stators, the turbine further comprising a biased tension structure for suspending the rotor element between opposing portions of the rigid structure to allow the rotor element to to perform periodic movements relative to the single or multiple number of stators upon the occurrence of a force which has a component oriented substantially transverse to a body axis of the rotor element and induced by a fluid flow around the rotor element.

The turbine of claim 1, wherein a fundamental resonant frequency of the biased voltage structure is pre-selected to be associated with a periodicity of the periodic motions performed by the rotor element by setting a bias level of the voltage structure.

3. Turbine as claimed in any of the foregoing claims, further comprising a tension element for setting the bias level of the tension structure, in particular wherein the tension element can be operated manually, mechanically or electrically.

A turbine according to any one of the preceding claims, wherein the periodic movements performed by the rotor element include rotations about a line of symmetry that coincides with a longitudinal axis of the stress structure in a state of equilibrium.

5. Turbine according to claim 4, wherein the rotor element is adapted to perform a superposition of rotations about the line of symmetry and rotations about its body axis.

6. A turbine according to any one of the preceding claims, wherein the rotor element comprises rotor blades for causing the rotor element to perform rotations relative to its body axis.

A turbine according to claim 6, wherein the rotor blades are of a spiral, Darrieus, Savonius or Darrieus-Savonius type.

A turbine according to any one of the preceding claims, wherein the flowing fluid is a gas, such as air, or a liquid.

A turbine according to any one of the preceding claims, wherein the type of the single or multiple number of stators is a radial flux generator stator type and/or an axial flux generator stator type.

Turbine according to any one of the preceding claims, further comprising a single or multiple number of sensors to determine a fluid velocity, mechanical stress of the stress structure, a periodicity of the rotor element and/or a temperature.

11. Turbine as claimed in any of the foregoing claims, further comprising a bearing connected to the tension structure for bearing the rotor element.

Turbine according to any one of the preceding claims, for use in hydraulic, tidal and/or wind-based energy generation, in particular at multiple locations.

A turbine farm comprising a plurality of vertical axis turbines according to any one of the preceding claims.

Use of a turbine or group of turbines according to any one of the preceding claims 1-12 for generating electrical energy.

Use of a turbine or group of turbines according to any one of claims 1 to 12 as sensors or instruments for fluid dynamics investigations.