savonius wind turbine ratio

Abstract

In the past, a Savonius wind turbine has the ability to operate more efficiently than other drag-type vertical axis turbines when built to certain parameters. Previous literature has not considered the ratio of the shaft diameter to the available space for the wind to pass through the center as a determinative relationship upon which other improvements to this type of turbine can be built. Both the chord diameter and the overlap distance depend on the size of the central shaft and its ratio to the inner endpoints of the overlapping semicircular blades. This paper presents the ratios for maximum efficiency. These effective ratios also depend on their performance when the turbine is turning at the ideal tip speed ratio.

Description

[0001] This application is a continuation-in-part of International Application No. PCT / IL2019 / 051172, International Filing Date, October 30, 2019, entered into the National Stage in China on April 23, 2021, National Application No. 201980070040.4, having the title "Savonius Wind Turbine Proportions", which claims priority to U.S. Provisional Patent Application No. 62 / 840,929, filed April 30, 2019, entitled "Savonius Wind Turbine Proportions", and U.S. Provisional Patent Application No. 62 / 676,879, filed November 15, 2018, entitled "Savonius Wind Turbine Variations". BACKGROUND

[0002] The present invention relates to making Savonius type wind turbines more efficient.

[0003] First, identify the parts of a Savonius turbine.

[0004] In Figure 1 The conventional and simplest Savonius prior art is shown.

[0005] It has parallel and similar covers at the bottom (1) and top (2). Sometimes, (2) and (2) are complete circles. The blades (4) are perpendicular to the covers and are circular in shape, usually forming a hollow semi-cylinder. They all rotate around a central axis (3).

[0006] The axis (3) is not used for support, as the two covers (1 and 2) provide support. Therefore, the axis is usually small relative to the overall turbine diameter; in the example shown, it is approximately 5% of the turbine diameter. The blades do not necessarily have overlap around the axis. There are two blades, each with an inner edge (7) and an outer edge (8). Wind enters the space (5) between the inner edge of one blade and the outer edge of the other blade, and circulates in the turbine along path (6).

[0007] Figure 2 is a cross-sectional view. In Figure 2 Each blade (21 and its equivalent facing semicircle) has an inner edge (22) and an outer edge (23). The blade is characterized by a diameter, technically called a chord (29). There is a central axis (24) characterized by an axis diameter (25). (26) represents the distance between the two blades through the center of the axis. The free space within the center is (26) minus (25). The turbine diameter (30) is the distance from one outer edge (23) to the outer edge on the second blade.

[0008] (27) is the overlap or extension of the inner edge of the blade and is the line extending directly from the inner edge through the midpoint. In this case it is straight.

[0009] This patent relates to the novel relationship of the shaft, the space between the blades, the overlap and the chord diameter, which results in higher efficiency. The basic idea behind this is that the passage of the wind through the turbine needs to be under the right conditions to be most advantageous. The concept behind this application is that the free space in the center is the most important element, but it is not independent, because the relationship with the overlap and the chord length is related to this free space, so that the free space in the middle does not concentrate the airflow too much and create friction, while on the other hand it does not remain too open to lose the effect of wind recirculation.

[0010] A review of previous literature shows that these important relationships are ignored and that the free space in the middle is not defined, either correctly or at all.

[0011] Traditionally, the focus on overlap is on the overlap ratio, which is defined as (overlap minus shaft diameter) / blade diameter (in our application called chord or c; sd equals shaft diameter). A study (B.D. Altan, M. Atdgan, An experimental study on improvement of a Savonius rotor performance with curtaining, Experimental Thermal and Fluid Science 32 (2008) 1673-1678) has shown that the ideal overlap ratio is 0.15. (Note that this is not the same as the overlap ratio used in the description of this application, because our "overlap ratio" refers to the overlap distance divided by the shaft diameter, so for a turbine with a shaft of 100 mm, the prior art overlap ratio for our ideal parameter is (20-100) / 660, which is a negative number, because the prior art erroneously thought that the overlap in relation to the shaft diameter should be large.

[0012] Another study (V.J. Modi, N.J. Roth, M.S. Fernando, Optimum-configuration, studies and prototype design of a wind-energy-operated, irrigation system, Journal of Wind Engineering and Industrial Aerodynamics 16 (1984) 85-96.) shows the value to be 0.25. We believe that the difference in the above opinions and results indicates that there is another factor that determines the conditions for the ideal overlap ratio. These studies do not define its relationship with the blade shape nor mention the key component of free space. However, previous studies (see Arriving at the Optimum Overlap Ratio for an Elliptical-Bladed Savonius Rotor, Nur Alom and Ujjwal K. Saha, ASME Turbo Expo 2017: Turbomachinery Technical Conference and Exposition, Volume 9: Oil and Gas Applications; Supercritical CO2 Power Cycles; Wind Energy, Charlotte, North Carolina, USA, June 26-30, 2017 and Mahmoud, which gives an ideal overlap of 0) do not identify whether the amount of free space can make it work; in the ideal configuration, our condition for free space is 3.5 sd is a more basic observation that works better for other ratios.

[0013] A study (F. Mahamarakkalage, On the Performance and Wake Aerodynamics of the Savonius Wind Turbine, a Thesis of Doctoral of Philosophy, University of Peradenyia, Srilanka, 1980) showed that no spacing was most efficient and found an efficiency of 32%. As mentioned above, we simulated this condition without using the ideal aspect ratio and found a maximum efficiency of 27% in all simulations mentioned here where the outer shape was uniform and passed the range of 30% in all our simulations with spacing, all consistently performed by the same person using similar programs.

[0014] Another study of the Savonius rotor (Geometrical optimization of a swirling Savonius wind turbine using an open jet wind tunnel, Abdullah Al-Faruk ,Ahmad Sharifian, Computational Engineering and Science Research Centre (CESRC), University of Southern Queensland, Toowoomba, Queensland 4350, Australia, Received 19 March 2015; revised 19 June 2016; accepted 11 July 2016, available online 30 July 2016) states that "The results indicate that the blade overlap ratio, hot air inlet diameter, and tip-plate conditions have significant effects on the power and torque coefficients...". It is another example where the free space is neglected as a condition. Their summary in Table 1 does not mention the center free space at all. Their ideal turbine has a curved overlap.

[0015] An experimental study to improve the performance of Savonius rotor presented in N.H. Mahmoud a, A.A. El-Haroun a, E. Wahba a, M.H. Nasef b, Alexandria Engineering Journal, Received 15 July 2010; accepted 21 November 2010 only involves the overlap ratio and the length-width ratio (height-width ratio).

[0016] The conclusion obtained in Computational Fluid Dynamics Prediction of a Modified Savonius Wind Turbine with Novel Blade Shapes, Wenlong Tian, Baowei Song, James H. Van Zwieten and Parakram Pyakurel, Energies 2015, 8, 7915-7929; doi:10.3390 / en8087915 is that no air space is preferred and gives an efficiency (called Cp, coefficient of power) of 25%.

[0017] A design study for a two-step Savonius rotor for local power generation (J.-L Menet, Renewable Energy 29 (2004) 1843-1862) does not show a formula, not even any relation of the absolute size of the inner air space and the shaft size.

[0018] In Review of Savonius Wind Turbine Design and Performance by M. Zemamou, M. Aggour, and A. Toumi, Energy Procedia, 141 (2017), 383-388 the overlap ratio, the length-width ratio and the use of curtains are mentioned in relation to the performance of the Savonius, but no relation of the shaft-blade is mentioned.

[0019] In DESIGN AND DEVELOPMENT OF HYBRID VERTICAL AXIS TURBINE, Md. Jahangir Alam, M.T. Iqbal, Faculty of Engineering and Applied Science, Memorial University of Newfoundland, it is mentioned that tip speed ratio and overlap ratio are important factors. This is true, but they are not the only factors.

[0020] EPO application no. 86907045.8 (Alvin Benesh, WIND TURBINE SYSTEM USING A SAVONIUS-TYPE ROTOR) notes on page 7 that "Although the shaft 28 preferably has a diameter D3 = 0.1 Di, sufficient space needs to be left for larger size shafts if required. Applicant's tests have shown that similar rotors do not show a significant loss of efficiency due to the constriction of the wind through the rotor blades 21, 22 and 15 limiting the size of the shaft 28. However, Applicant notes that there is a significant loss of efficiency if the air passage near the shaft 28 is completely blocked. He only relates the shaft diameter to the diameter of the entire turbine. He concludes that there is no difference in efficiency regardless of the free air space, which is contrary to the current application.

[0021] In Experimental investigations on single stage, two stage and three stage conventional Savonius rotor, M. A. Kamojil, S. B. Kedarel and S. V. Prabhu, Int. J. Energy Res. 2008; 32:877-895, the relationship of the shaft to the free space is not considered.

[0022] In Experimental investigations on single stage modified Savonius rotor, M. A. Kamoji a, S. B. Kedare a, S. V. Prabhu, Applied Energy 86 (2009) 1064-1073, it is also not mentioned. The parameters studied are overlap ratio, blade wrap angle, length to width ratio and Reynolds number. The modified Savonius rotor with overlap ratio of 0.0, blade wrap angle of 124 and length to width ratio of 0.7 has maximum power coefficient of 0.21 at Reynolds number 1,50,000, which is higher than that of conventional Savonius rotor (0.19). Correlations are developed for single stage modified Savonius rotor for the range of Reynolds number studied.

[0023] In A review on the performance of Savonius wind turbines by Joao Vicente Akwaa, Horacio Antonio Vielmo, Adriane Prisco Pety, Renewable and Sustainable Energy Reviews 16 (2012) 3054- 3064 confirms the prevailing view that the center shaft with air space is an interference that can be dispensed with.

[0024] Definition: A wind turbine has an angular velocity w or frequency domain

[0025]

[0026] The tip speed ratio (TSR shown as λ) is therefore

[0027]

[0028] That is, the ratio of the tangential velocity of the tip of the blade to the actual speed of the wind. This is an important factor in determining efficiency and varies with the diameter of the turbine and the design. SUMMARY

[0029] The present invention successfully addresses the shortcomings of the presently known configurations by providing an improved configuration of aerodynamic parameters of a Savonius type wind turbine.

[0030] It is now the first time that a vertical axis turbine is disclosed, comprising two similar blades, substantially semi-circular in a horizontal plane along any cross section of the height of said turbine, having a central axis in the vertical direction, concave sides of said two blades partially facing each other, each blade having a chord diameter of distance c, said chord diameter referring to the distance between inner surfaces of said two blades, said two blades being separated by a distance a, said distance a being the distance along a straight line from an inner end point of the semi-circle of the first blade, through said axis of diameter sd, to an inner end point of the semi-circle of the second blade, the position of said inner end points facing each other being located less than half of said chord distance from said inner end points to an outer end point of the opposite blade, said vertical axis turbine comprising:

[0031] Said distance a is substantially 3 to 4 times sd.

[0032] According to another embodiment, said distance a is about 3.5 times sd.

[0033] According to another embodiment, c is 6 to 7.2 times a.

[0034] According to another embodiment, c is about 6.6 times a.

[0035] In an embodiment, said system further comprises:

[0036] An overlap, referred to as b, is an extension at the end of said inner end points of said two blades, said extension being substantially perpendicular in a horizontal plane to a virtual line connecting said two inner end points and the center of said axis, said overlap comprising a substantially straight body extending from said inner end point of each blade, said overlap being 0 to 0.25 times a.

[0037] According to another embodiment, said overlap is about 0.2 times a.

[0038] According to another embodiment, said blades do not have an upper cap connected to said blade at the upper tip.

[0039] According to another embodiment, said blades do not have a lower connecting base.

[0040] In an embodiment, said turbine, further comprises:

[0041] Said semi-circular diameter varies less than 15% along most of the vertical height of said blade.

[0042] In an embodiment, said turbine, further comprises:

[0043] A tip speed ratio, for a turbine having a shaft diameter of 100 mm, the tip speed ratio ranges from 0.475 to 0.546 times the shaft diameter in mm, approximately doubling for each doubling of the shaft diameter, and approximately halving for each halving of the shaft diameter, proportionally for sizes in between, proportionally for other shaft diameters.

[0044] According to another embodiment, the two blades are shaped as hyperbolas.

[0045] A method of manufacturing a vertical axis turbine comprising two similar blades, substantially semi-circular in a horizontal plane at any cross-section along the height of the turbine, having a central axis in the vertical direction, the concave sides of the two blades facing each other partially, each blade having a chord diameter of distance c, referring to the distance between the inner surfaces of the two blades, the two blades being separated by a distance a, the distance a being the distance along a straight line from an inner endpoint of the semi-circle of the first blade, through the shaft of diameter sd, to an inner endpoint of the semi-circle of the second blade, the position of the inner endpoints facing each other being located at less than half the chord distance from the inner endpoints to an outer endpoint of the opposite blade, the method comprising the steps of:

[0046] Selecting a shaft diameter;

[0047] The distance through the center of the shaft from the inner side of one blade to the inner side of the other blade is approximately 3.5 times the shaft diameter, in the range of 3 to 4 times;

[0048] The overlap is approximately 20% of the shaft diameter, in the range of 0% to 25%;

[0049] The chord length is approximately 6.6 times the shaft diameter, in the range of 6 to 7.2 times.

[0050] In an embodiment, the method further comprises the steps of:

[0051] The orientation of the blades is changed from semi-circular to quarter-circular on a proportional basis, and the distance between the blades is set to be approximately 3.5 to 4 times the shaft diameter, according to the degree of change, and the chord length is set to be approximately 6.6 to 30 times the shaft diameter, according to the degree of change, on a proportional basis. Figure 5 The lines shown set the overlap ratio to be 0 to 4 times the shaft diameter, on a proportional basis. Figure 6 The chart shown sets the chord diameter to be approximately 6.6 to 30 times the shaft diameter.

[0052] CLAIM

[0053] 1. A vertical axis turbine comprising two similar vanes, substantially semi-circular (21) in a horizontal plane at any cross-section along the height of the turbine, having a central axis (24) in the vertical direction, the concave sides of the two vanes partially facing each other, each vane having a chordal diameter of distance c, referring to the distance (29) between the inner surfaces of the two vanes, the two vanes being separated by a distance a (26), the distance a being the distance along a straight line from an inner end point (22) of the semi-circle of the first vane, through the axis of diameter sd (25) to an inner end point of the semi-circle of the second vane, the position of the inner end points facing the opposite vane being located less than half the chordal distance from the inner end point of the opposite vane to an outer end point (22 and 23) of the opposite vane, the vertical axis turbine comprising:

[0054] the distance a being substantially 3 to 4 times sd.

[0055] 2. The vertical axis turbine of claim 1, wherein the distance a is about 3.5 times sd.

[0056] 3. The vertical axis turbine of claim 1 or 2, wherein c is 6 to 7.2 times a.

[0057] 4. The vertical axis turbine of claim 1, 2 or 3, wherein c is about 6.6 times a.

[0058] 5. The vertical axis turbine of claim 1, 2, 3 or 4, further comprising:

[0059] an overlap, referred to as b (27), being an extension at the end of the inner end points of the two vanes, the extension being substantially perpendicular in a horizontal plane to a virtual line connecting the two inner end points and the center of the axis, the overlap comprising a substantially straight body extending from the inner end point of each vane, the overlap being 0 to 0.25 times a.

[0060] 6. The vertical axis turbine of claim 1, 2, 3, 4 or 5, wherein the overlap is about 0.2 times a.

[0061] 7. The vertical axis turbine of claim 1, 2, 3, 4, 5 or 6, wherein the vanes do not have an upper cap (2) connected to the upper tip of the vanes.

[0062] 8. The vertical axis turbine of claim 1, 2, 3, 4, 5, 6, or 7 wherein the blades have no lower connecting base.

[0063] 9. The vertical axis turbine of claim 1, 2, 3, 4, 5, 6, 7, or 8 further comprising:

[0064] the semi-circular diameter varies less than 15% along most of the vertical height of the blade.

[0065] 10. The vertical axis turbine of claim 1, 2, 3, 4, 5, 6, 7, 8, or 9 further comprising:

[0066] a tip speed ratio in the range of 0.475 to 0.546 times the shaft diameter in millimeters for a turbine having a shaft diameter of 100 millimeters, approximately doubling for each doubling of the shaft diameter, and proportionally increasing for sizes in between, approximately halving for each halving of the shaft diameter, proportionally halving for sizes in between, and proportionally for other shaft diameters.

[0067] 11. The vertical axis turbine of claim 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10 wherein the two blades are shaped as a hyperbola.

[0068] 12. A method of making a vertical axis turbine comprising two similar blades that are substantially semi-circular (21) in a horizontal plane at any cross-section along the height of the turbine, having a central axis (24) in the vertical direction, the concave sides of the two blades partially facing each other, each blade having a chordal diameter of distance c, referring to the distance (29) between the inner surfaces of the two blades, the two blades being separated by a distance a (26), the distance a being the distance along a straight line from an inner endpoint (22) of the semi-circle of the first blade, through the axis of diameter sd (25), to an inner endpoint of the semi-circle of the second blade, the positions of the inner endpoints facing the opposite blade being located less than half the chordal distance from the inner endpoint of the opposite blade to an outer endpoint (22 and 23) of the opposite blade, the method comprising the steps of:

[0069] selecting a shaft diameter;

[0070] the distance through the center of the shaft from the inner side of one blade to the inner side of the other blade being approximately 3.5 times the shaft diameter, in the range of 3 to 4 times;

[0071] The overlap is approximately 20% of the shaft diameter, within the range of 0% to 25%.

[0072] The chord length is approximately 6.6 times the diameter of the shaft, in the range of 6 to 7.2 times.

[0073] 13. The method of claim 12, further comprising the step of:

[0074] Based on a certain proportion, the orientation of the blades is changed from a semicircle to a quarter circle, and the distance between the blades is set to approximately 3.5 to 4 times the shaft diameter, depending on the degree of change. Figure 5 The lines shown have an overlap ratio set to 0 to 4 times the diameter of the axis, and according to... Figure 6 The diagram shown sets the chord diameter to approximately 6.6 to 30 times the shaft diameter. Attached Figure Description

[0075] This invention is described by way of example only, with reference to the accompanying drawings, wherein:

[0076] Figure 1 This is a schematic diagram of a traditional Savonius turbine.

[0077] Figure 2 This is a schematic diagram of the cross-section of a major component of a Savonius turbine.

[0078] Figure 3 This is a schematic diagram of airflow passing through a Savonius turbine.

[0079] Figure 4 It is a schematic diagram of Savonius, a quarter circle.

[0080] Figure 5 It is a curve showing the overlap ratio in a quarter circle of Savonius.

[0081] Figure 6 It is a curve of the chord proportions in Savonius, a quarter circle. Detailed Implementation

[0082] The principle and operation of the wind turbine according to the present invention can be better understood by referring to the accompanying drawings and description.

[0083] Please refer to the attached diagram now. Figure 1 and 2 The different parameters that have been identified are shown. Figure 2 In this design, the shaft occupies more than 10% of the turbine diameter. This improves strength and efficiency. (In the prior art...) Figure 1 In this case, the shaft will be approximately 5% of the turbine diameter.

[0084] Please note that the parameters in this application refer to the inner surfaces of the plurality of blades facing the shaft.

[0085] according to Figure 2 The ideal parameters are revealed and calculated as follows. They apply to all sizes; the shaft diameter is 100 mm for ease of understanding of the numbers. Reasonable expected variations for each object will be shown later. Assuming the diameter of the shaft (24) is 100 mm ( Figure 2 If the distance in the middle is 25), then it is called sd. Therefore: the distance from the inner edge to the inner edge ( Figure 2 Item 26) is ideally sd x 3.5 or 350 mm. The extension b ( Figure 2 Item 27) Ideally, it should be sd x 0.2 or 20 mm. The chord distance (blade diameter) c ( Figure 2 Item 29 (i.e., the distance from item 22 to item 23) is ideally sd x 6.6 or 660 mm. Then, for reference only, the diameter of the entire turbine is... Figure 2 Item 30 in the document is shown, and it is in the format of (sdx 6.6) + ((sd 6.6)-(sd 3.5)) is used for calculation.

[0086] A good performance configuration is defined as the distance from the inner edge of the semicircle of one blade to the inner edge of the semicircle of another blade (a definition that prevents confusion when an overlap occurs) being 3-4 times the shaft diameter, with an ideal value of 3.5 times.

[0087] The range of overlap for good performance is 5-25% of the shaft diameter, with an ideal value of 20%, but zero overlap to 40% overlap can also produce a highly efficient turbine.

[0088] When combined with a chord diameter that is 6-7 times the shaft diameter, ideally 6.6 times, the effect is optimal.

[0089] The table below (Table 1) shows some simulation options: (The turbine diameter is the chord diameter plus the chord diameter minus the inner edge distance)

[0090]

[0091] Case 8 exhibits the highest efficiency and represents the ideal set of proportions described above. It can be seen that other similar parameter sets also perform well. This is the first time the theoretical efficiency value of the Savonius-type turbine has consistently been above 30%, because the free space requirements of the inner shaft have been considered, followed by the relationship with the chord distance. The overlap is important but relatively less so. The tip velocity ratio is crucial and will be shown in more detail below.

[0092] Figure 3 The circulation of the wind in a Savonius turbine is shown, and why the proportions of the invention are important. In Figure 3 In the middle, the wind is coming from the left and hits the first blade (32) as shown by line (31). Then, the wind circulates around the shaft along lines (33) and (34). When the proportions are ideal, as calculated above, there is a region of wind circulation in the turbine that accelerates in the region of arrow (35) to higher than the prevailing outside wind, and then hits the second blade. This reveals the importance of the free space that is focused on the center of the turbine. It should not be too large or too small for the wind to be concentrated in the right way. The overlap, also called the extension from the semicircle, prevents the divergence of the wind by the lateral movement of the air inside the turbine.

[0093] An additional innovative approach is to skip the upper cap, instead making 2 blades without the upper cap, and additionally, the shape of the two blades is a hyperbola (a curve that is not too steep in the vertical direction) instead of a simple semicircle along their vertical dimension. This allows better capture of the wind and makes it more streamlined. This approach requires a higher efficiency with the right proportions to be balanced over the entire vertical span of the turbine. A reasonable compromise is to allow 15% variation in each blade shape and semicircle diameter from the ideal parameters in any horizontal plane. This is new when combined with other changes.

[0094] Not using the cap requires a thicker shaft, as it will be used for support. The review above did not find cases where the shaft size and the free space between the blades have been defined, and at the same time, once the conditions for the free space are met, the conditions are for a suitable overlap.

[0095] Based on the above, the original claims are proposed, whose efficiency is largely related to the amount of air that is made to pass through the free space in the middle, and the proportion of the shaft size to the total space between the blades is also important. This advantage can be enhanced in combination with other proportions and parameters discussed in this application.

[0096] The above Table 1 shows that the conditions for the highest efficiency are multi-factorial, but each thing is based on the shaft diameter, which determines the free space and all other proportions. The tip speed ratio (TSR) is known in the art and is

[0097]

[0098] That is, the ratio of the tangential velocity of the tip of the blade to the actual velocity of the wind. This has a great deal to do with the efficiency of all turbines. In these cases, a tip speed ratio of about 0.511 is best. Below.475, the efficiency becomes substantially lower for the sizes shown above. Therefore,.511 plus or minus.035 is a good range for this size of turbine. If the turbine diameter is doubled, the tip speed ratio (TSR) increases approximately by a factor of two. Here, case 8 has a turbine diameter of 970 mm. For this type of turbine, this section is independent of the shaft diameter. Therefore, a turbine with the proportions of case 8 but a shaft diameter of 200 mm will have a tip speed ratio (TSR) of approximately 1.22 plus or minus 0.07.

[0099] In general, Cp is a function of Reynolds number and the tip speed ratio (TSR). In general, the dependence on Reynolds number is small, so the pressure coefficient is mainly dependent on the tip speed ratio (TSR). To achieve the highest efficiency, the tip speed ratio (TSR) and the rotational speed (RPM) need to be set correctly. Note that if this ratio is not attended to, it can result in a wind turbine that is very inefficient.

[0100] In the mid-20s, previous literature claims that the Cp of a Savonius turbine does not need to concern itself with the primacy of the free space in the middle. Simulations include, case 8, a 0.34 Cp configuration that shows that the current method is not only innovative but also significant.

[0101] Therefore, in the subsequent claims, the calculation of the free space is considered a key innovation in the independent claims.

[0102] Once this is satisfied, other key innovations, such as the relationship of the overlap ratio to the blade size based on the blade arc, will be more effective.

[0103] Other changes to the Savonius semicircle can be to approach a quarter circle with different blade shapes. These configurations are slightly less efficient, but can be useful in some cases, such as in different cost-benefit situations. Figure 4 (41) and (42) are the blades. (43) is the shaft. (44) and (45) are the overlap or the extension of the quarter circle. This configuration is called 5e.

[0104] When the blades are quarter circles, the ideal overlap ratio varies from 0.2 times the shaft diameter to 4 times the shaft diameter, where the distance between the blades is 4 times the shaft diameter, ranging from 3 to 5 times, and the chord diameter is 5 times the shaft diameter, ranging from 4 to 6 times.

[0105] The following Table 2 shows some Cp (efficiency) simulation data for a configuration we call 5e, for various tip speed ratios and rotational speeds:

[0106]

[0107] This shows an ideal tip speed ratio for a chord diameter of about 3 meters.

[0108] Figure 5 The overlap is shown to vary with the shape of the circle. By using Figure 5 , the ideal overlap can be approximated as a function of the degree of circularity. (51) is a ratio of 0.2 times the diameter of the axis of a semicircle, while (52) is a ratio of 4 times the diameter of the axis of a quarter circle.

[0109] Figure 6 The chord diameter is shown to vary with the shape of the circle. By using Figure 6 , the ideal chord diameter can be approximated as a function of the degree of circularity. (61) is a ratio of 6.6 times the diameter of the axis of a semicircle, while (62) is a ratio of 28 times the diameter of the axis of a quarter circle.

Claims

1. A vertical axis wind turbine comprising two identical blades, substantially semi-circular in a horizontal plane of any cross section along the height of the turbine, having a central axis in a vertical direction, the concave sides of the two blades facing each other, each blade having a chord diameter at a distance c, the chord diameter referring to the distance between the inner and outer endpoints of each blade; The two blades are separated by a distance a, which is a straight distance from the inner end of the semicircle of the first blade through the central axis with an axial diameter of sd to the inner end of the semicircle of the second opposite blade; the position of the inner end of the first blade facing the second opposite blade is less than half the distance of the chord diameter from the inner end of the second opposite blade to the outer end of the second opposite blade. Its features are, Each blade has an overlap b, which is an extension at the end of the inner end point of each blade, the extension being substantially perpendicular in a horizontal plane to a virtual line connecting the inner end point of the first blade and the inner end point of the second opposing blade to the center of the central axis, the overlap comprising a substantially straight body extending from the inner end point of each blade. The distance a is in the range of 3 to 4 times the diameter sd of the shaft; The distance c is in the range of 6 to 7.2 times the diameter sd of the shaft.

2. The turbine as claimed in claim 1, characterized in that, The shaft diameter sd is 100mm.

3. The turbine as claimed in claim 1, characterized in that, The overlap b is approximately 0.2 times the shaft diameter sd.

4. The turbine as claimed in claim 1, characterized in that, The blade does not have a cap that is connected to the upper tip of the blade.

5. The turbine as claimed in claim 1, characterized in that, The blade does not have a lower connecting base.

6. The turbine as claimed in claim 1, characterized in that, Also includes: The value c of the semicircular diameter varies by less than 15% along the vertical height of the blade.

7. The turbine as claimed in claim 1, characterized in that, The distance c is approximately 6.6 times the shaft diameter sd.

8. A method of manufacturing a vertical axis wind turbine as claimed in any one of claims 1-2 and 4-6, the vertical axis wind turbine comprising two identical blades, substantially semi-circular in a horizontal plane of any cross-section along the height of the turbine, having a central axis in a vertical direction, the concave sides of the two blades facing each other, each blade having a chord diameter of distance c, the chord diameter referring to the distance between the inner and outer endpoints of each blade; the two blades being separated by a distance a, the distance a being a straight distance from an inner endpoint of the semicircle of a first blade through the central axis of axial diameter sd to an inner endpoint of the semicircle of a second opposing blade; the position of the inner endpoint of the first blade facing the second opposing blade being less than half the distance of the chord diameter from the inner endpoint of the second opposing blade to an outer endpoint of the second opposing blade; characterized in that... The method includes: Select the shaft diameter sd; The distance 'a' along a straight line from the inner end of one blade through the center of the central axis to the inner end of another blade is in the range of 3 to 4 times the diameter of the axis; and The distance c of the chord diameter is in the range of 6 to 7.2 times the shaft diameter sd.

9. The method as described in claim 8, characterized in that, Also includes: The overlap is made to be approximately 0% to 40% of the shaft diameter sd.

10. The method as described in claim 8, characterized in that, The distance 'a' is approximately 3.5 times the diameter of the shaft.

11. The method as described in claim 8, characterized in that, The distance c of the chord diameter is approximately 6.6 times the shaft diameter sd.

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