Source: http://www.google.com.pe/patents/WO2010133584A1?cl=en
Timestamp: 2018-01-19 03:41:08
Document Index: 475583172

Matched Legal Cases: ['art. 3', 'art 34', 'art 436', 'art 441', 'art 443', 'art 441', 'art 443', 'arts 441', 'arts 441']

Patent WO2010133584A1 - Wind turbine blade with base part having non-positive camber - Google Patents
A blade for a rotor of a wind turbine having a substantially horizontal rotor shaft is described. The rotor comprises a hub, from which the blade extends substantially in a radial direction when mounted to the hub. The blade comprises a profiled contour comprising a pressure side and a suction side as...http://www.google.com.pe/patents/WO2010133584A1?cl=en&utm_source=gb-gplus-sharePatent WO2010133584A1 - Wind turbine blade with base part having non-positive camber
Publication number WO2010133584 A1
Application number PCT/EP2010/056799
Also published as CN102459880A, CN102459880B, EP2253835A1, EP2432994A1, US9057359, US20120057987
Publication number PCT/2010/56799, PCT/EP/10/056799, PCT/EP/10/56799, PCT/EP/2010/056799, PCT/EP/2010/56799, PCT/EP10/056799, PCT/EP10/56799, PCT/EP10056799, PCT/EP1056799, PCT/EP2010/056799, PCT/EP2010/56799, PCT/EP2010056799, PCT/EP201056799, WO 2010/133584 A1, WO 2010133584 A1, WO 2010133584A1, WO-A1-2010133584, WO2010/133584A1, WO2010133584 A1, WO2010133584A1
Wind turbine blade with base part having non-positive camber
WO 2010133584 A1
A blade for a rotor of a wind turbine having a substantially horizontal rotor shaft is described. The rotor comprises a hub, from which the blade extends substantially in a radial direction when mounted to the hub. The blade comprises a profiled contour comprising a pressure side and a suction side as well as a leading edge and a trailing edge with a chord extending between the leading edge and the trailing edge, the profiled contour generating a lift when being impacted by an incident airflow, the profiled contour in the radial direction being divided into a root region with a substantially circular or elliptical profile closest to the hub, an airfoil region with a lift generating profile furthest away from the hub, and preferably a transition region between the root region and the airfoil region, the transition region having a profile gradually changing in the radial direction from the circular or elliptical profile of the root region to the lift generating profile of the airfoil region, wherein the airfoil region comprises at least a first longitudinal segment extending along at least 20% of a longitudinal extent of the airfoil region, the first longitudinal segment comprising a first base part having a leading edge and a trailing edge with a chord extending between the leading edge and the trailing edge. The first base part has a cross-sectional profile, which when being impacted by an incident airflow at an angle of attack of 0 degrees has a lift coefficient, which is 0 or less.
- the airfoil region comprises at least a first longitudinal segment extending along at least 20% of a longitudinal extent of the airfoil region, the first longitudinal segment comprising a first base part having a leading edge and a trailing edge with a chord extending between the leading edge and the trailing edge, characterised in that - the first base part has a cross-sectional profile, which when being impacted by an incident airflow at an angle of attack of 0 degrees has a lift coefficient, which is 0 or less, a positive lift being defined as a lift coefficient having a lift component directed from the pressure side towards the suction side of the blade, and a negative lift coefficient being defined as a lift coefficient having a lift component directed from the suction side towards the pressure side of the blade.
2. A blade according to claim 1 , wherein the first base part has an inherent non-ideal twist and/or chordal length at a rotor design point, and wherein the cross-sectional profile is adapted to compensate for the non-ideal twist and/or chordal length by shifting an axial induction towards a target axial induction at the rotor design point.
3. A blade according to claim 1 or 2, wherein the first longitudinal segment is provided with a number of first flow altering devices arranged so as to adjust the aerodynamic properties of the first longitudinal segment to substantially meet a target axial in- duction factor at a rotor design point.
4. A blade according to any of the preceding claims, wherein the flow altering devices comprises devices chosen from the group of:
5. A blade according to claim 4, wherein the flow altering devices in addition comprises boundary layer control means, such as holes or a slot for ventilation, vortex gen- erators and a Gurney flap.
6. A blade according to any of the preceding claims, wherein the first base part has a cross-sectional profile having a camber line and a chord line with a chord length, and wherein the average difference between the chord line and a camber line of the cross- sectional profile is negative over the entire chord length so that the camber on average, when seen over the entire length of the chord, is closer to the pressure side of the blade than to the suction side of the blade.
7. A blade according to claim 6, wherein the camber line is closer to the pressure side than the suction side over the entire length of the chord.
8. A blade according to any of claims 1-6, wherein the first base part has a cross- sectional profile having a camber line and a chord line with a chord length, and wherein the camber line and the chord line are coinciding over the entire length of the chord.
9. A blade according to any of the preceding claims, wherein the first base part has a twist being linearly dependent on a radial position.
10. A blade according to any of the preceding claims, wherein the length of the chord of the first base part varies linearly in the radial direction of the blade.
1 1. A blade according to any of the preceding claims, wherein the first base part has a thickness, and wherein the thickness of the base part varies linearly in the radial direction of the blade.
12. A blade according to any of the preceding claims, wherein the target axial induction factor is close to the aerodynamic optimum target axial induction factor.
13. A blade according to any of the preceding claims, wherein the target axial induc- tion factor lies in the interval between 0.25 and 0.4, or between 0.28 and 0.38, or between 0.3 and 0.33
14. A blade according to any of the preceding claims, wherein the induction factor of the first base part without flow altering devices at the design point deviates at least 5%, or 10%, or 20% or 30% from the target axial induction factor.
15. A blade according to any of the preceding claims, wherein the first base part without flow altering devices at the design point further deviates from a target loading, and wherein the first flow altering devices are further arranged so as to adjust the aerody- namic properties of the first longitudinal segment to substantially meet the target loading at the design point.
16. A blade according to claim 15, wherein the loading of the first base part without flow altering devices at the design point deviates at least 5%, or 10%, or 20% or 30% from the target loading.
17. A blade for a rotor of a wind turbine having a substantially horizontal rotor shaft, the rotor comprising a hub, from which the blade extends substantially in a radial direction when mounted to the hub, the blade having a predetermined target axial induction factor at a rotor design point, the blade comprising:
- a profiled contour comprising a pressure side and a suction side as well as a leading edge and a trailing edge with a chord extending between the leading edge and the trailing edge, the profiled contour generating a lift when being impacted by an incident airflow, - the profiled contour in the radial direction being divided into a root region with a substantially circular or elliptical profile closest to the hub, an airfoil region with a lift generating profile furthest away from the hub, and preferably a transition region between the root region and the airfoil region, the transition region having a profile gradually changing in the radial direction from the circular or elliptical profile of the root region to the lift generating profile of the airfoil region, characterised in that - the airfoil region is divided into a number of base sections, a first one of said base sections extending along at least 20% of a longitudinal extent of the airfoil region, the first base section having a leading edge and a trailing edge with a chord extending between the leading edge and the trailing edge, - the first base section being formed with a cross-sectional profile, which when being impacted by an incident airflow at an angle of attack of 0 degrees has a lift coefficient, which is 0 or less, a positive lift being defined as a lift coefficient having a lift component directed from the pressure side towards the suction side of the blade, and a negative lift coefficient being defined as a lift coefficient having a lift component di- rected from the suction side towards the pressure side of the blade.
Title: Wind turbine blade with base part having non-positive camber
According to one aspect of the invention, this is obtained by the first base part having a cross-sectional profile, which when being impacted by an incident airflow at an angle of attack of 0 degrees has a lift coefficient, which is 0 or less. A positive lift is defined as a lift coefficient having a lift component directed from the pressure side (or upwind/windward side) towards the suction side (or downwind/leeward side) of the blade. A negative lift is defined as a lift coefficient having a lift component directed from the suction side (or downwind/leeward side) towards the pressure side (or up- wind/windward side) of the blade.
In other words, the invention provides a blade for a rotor of a wind turbine having a substantially horizontal rotor shaft, the rotor comprising a hub, from which the blade extends substantially in a radial direction when mounted to the hub, the blade having a predetermined target axial induction factor at a rotor design point, the blade comprising: a profiled contour comprising a pressure side and a suction side as well as a leading edge and a trailing edge with a chord extending between the leading edge and the trailing edge, the profiled contour generating a lift when being impacted by an incident airflow, the profiled contour in the radial direction being divided into a root region with a substantially circular or elliptical profile closest to the hub, an airfoil region with a lift generating profile furthest away from the hub, and preferably a transition region between the root region and the airfoil region, the transition region having a profile gradually changing in the radial direction from the circular or elliptical profile of the root region to the lift generating profile of the airfoil region. The airfoil region may be divided into a number of base sections, a first one of said base sections extending along at least 20% of a longitudinal extent of the airfoil region, the first base section having a leading edge and a trailing edge with a chord extending between the leading edge and the trailing edge, and the first base section being formed with a cross-sectional profile, which when being impacted by an incident airflow at an angle of attack of 0 degrees has a lift coef- ficient, which is 0 or less. Thus, the base part or base section has a cross-sectional profile having an aerodynamic relationship between the lift coefficient and the angle attack, which when being plotted in a coordinate system with the lift coefficient as a function of the angle of attack crosses the origin of the coordinate system or crosses the lift coefficient axis at a nega- tive value. In other words, the lift coefficient changes sign at a positive angle of attack or at an angle of zero degrees, i.e. at a non-negative angle of attack.
Thus, the blade comprises at least one longitudinal segment extending along a sub- stantial part of the airfoil region of the blade. According to a first embodiment, the airfoil region includes a blade tip region of the blade. According to a second embodiment, the blade further comprises a blade tip region abutting the airfoil region. Thus, the blade tip region may be seen as either part of the airfoil region or as a separate part. Typically, the tip region covers the outer 5-10% of the longitudinal extent of the airfoil region.
In an example, where the first longitudinal segment has a zero twist or a twist being lower than the near-optimum twist, the novel profile (with the above-mentioned relationship between lift coefficient and angle of attack) compensates for the "lack" of twist, since the angle of attack has to be higher than a conventional profile in order to obtain the right target characteristics, e.g. with respect to the necessary lift coefficient in order to obtain the correct axial induction. The use of the novel profile makes it feasible to achieve a modular blade design, in which the base part can be used for several different blade types and blade lengths. Thus, it is possible to reuse the base part of an existing blade further outboard on a larger/longer blade, or alternatively reuse the base part of an existing blade further inboard on a smaller/shorter blade. All in all, it is possible to make a blade design in such a way that the blade design of the airfoil region is put together from pre-designed sections and that blades of different lengths can be composed partly from sections already existing from previous blades.
In the following additional advantageous embodiments are described. According to an advantageous embodiment, the first base part has an axial induction factor, which without flow altering devices deviates at least 5% from a target axial induction factor at a design point, and the first longitudinal segment is provided with a number of first flow altering devices arranged so as to adjust the aerodynamic properties of the first longitudinal segment to substantially meet the target axial induction factor at the design point.
Advantageously, the loading of the first longitudinal segment with flow altering devices deviates no more than 2% from the target loading at the design point. Advantageously, the deviation is no more than 1 % from the target loading at the design point. According to an advantageous embodiment, the first base part has an inherent non- ideal twist, such as no twist, or a reduced twist compared to a target blade twist. Such a base part is further simplified compared to conventional blade shapes.
According to yet another advantageous embodiment, the first base part has a twist, which is non-ideal along substantially the entire longitudinal extent of the first longitudi- nal segment. Accordingly, the inherent twist differs from the ideal twist along substantially the entire longitudinal extent of the segment, but the inherent twist may at various radial positions be identical to the optimum twist. Thus, graphs representing the ideal twist and the inherent twist may at certain point cross each other.
The invention is particularly suited for optimising the performance of blades having substantially no twist, i.e. blades which have not inherently been designed to compensate for the local inflow velocity due to the local varying velocity of the blade. Accordingly, the flow altering devices can be utilised to vary the shift angle in the longitudinal direction of the blade, so that the shift angle corresponds to a virtual twist of the blade in order to compensate for the local inflow velocity due to the local varying velocity of the blade. However, the invention can also be utilised with other types of blades and particularly on blades having a reduced overall twist angle compared to the optimum. Therefore, the blade according to one embodiment of the invention has an airfoil region with a twist of less than 8 degrees. In other words, the orientation of the chord plane changes less than 8 degrees in the radial direction of the blade. However, the blade may still be pre-bent and/or tapered in the radial direction of the blade. According to an alternative embodiment the twist is less than 5 degrees, or 3 degrees, or even less than 2 degrees. Thereby, it is possible to provide a wind turbine blade with a much less complex profile than a conventional wind turbine blade, which typically has an airfoil section with a maximum twist between 10 and 12 degrees, sometimes even 15 de- grees, and providing the blade with flow altering devices in order to compensate for the "missing" twist or providing the "remaining" twist.
According to a particularly advantageous embodiment, the first base part has a substantially constant twist, e.g. substantially no twist, meaning that the chord of the first base part is substantially arranged in the same direction. Thus, the first base part may be substantially straight. According to another advantageous embodiment, the first base part has a twist being linearly dependent on a radial position. That is, the twist angle or the chord angle varies linearly in the spanwise or longitudinal direction of the first longitudinal segment. Such a blade segment may be fitted to follow the ideal twist as closely as possible, but has a number of advantages with respect to obtaining a feasible modular design, where the first base part is reused on another blade type or where it is "connected" to a second base part of a second longitudinal segment and having another dependency on the radial position, optionally via an intermediate, transitional blade segment. In other words, such a blade segment has a number of advantages with respect to obtaining a modular design of the blade.
According to an advantageous embodiment, the first base part has an inner dimension that varies linearly in the radial direction of the blade in such a way that an induction factor of the first base part without flow altering devices at a rotor design point deviates from a target induction factor. Such a base part simplifies the design even further com- pared to the design of conventional blade designs.
According to yet another advantageous embodiment, the first base part has a constant relative thickness. That is, the ratio between the thickness and the chord is constant along the entire longitudinal extent of the first longitudinally extending section of the blade. In principle the relative profile may be varying in the longitudinal direction of the blade; however, according to an advantageous embodiment the first base part com- prises a constant relative profile. In one embodiment, the first base part comprises a constant relative profile along the entire extent of the first longitudinally extending section. That is, every cross-section of the first base part has the same relative airfoil profile or overall shape.
According to an advantageous embodiment, the first base part is a pultruded or extruded profile. Such base parts are feasible to manufacture due to the linearly varying inner dimensions and simplify the manufacturing process significantly. All in all, a first base part comprising: a linear chord, a linear thickness, and a twist, which varies linearly or is constant in the radial direction of the blade, has a number of advantages when designing a modular assembled blade and in respect to manufacturing such blades.
According to an advantageous embodiment, the blade and in particular the first base part comprise a shell structure made of a composite material. The composite material may be a resin matrix reinforced with fibres. In most cases the polymer applied is thermosetting resin, such as polyester, vinylester or epoxy. The resin may also be a ther- moplastic, such as nylon, PVC, ABS, polypropylene or polyethylene. Yet again the resin may be another thermosetting thermoplastic, such as cyclic PBT or PET. The fibre reinforcement is most often based on glass fibres or carbon fibres, but may also be plastic fibres, plant fibres or metal fibres. The composite material often comprises a sandwich structure including a core material, such as foamed polymer or balsawood.
According to an advantageous embodiment, the first longitudinal segment extends along at least 25%, or 30%, or 40%, or 50%, of the airfoil region. The first longitudinal segment may even extend along at least 60%, 70% or 75% of the airfoil region. The extent of the first longitudinal segment may even be up to 100%, when the tip region is considered not being part of the airfoil region. However, the first longitudinal segment may as such be restricted to being part of the airfoil region, in which a near-optimum theoretical aerodynamic performance at the design point may be achieved. This excludes the tip part, the root section, and the transitional section, which due to load and structural considerations always will differ significantly from the near-optimum theoreti- cal aerodynamic performance. Advantageously, the airfoil region may further comprise a longitudinally extending transitional segment. The transitional segment - not to be confused with the transition region of the blade - may extend radially along 5-10% of the airfoil region, and is utilised in the airfoil region to obtain a gradual transition between two longitudinally extending segments according to the invention. Thus, it is recognised that the blade may comprise a number of longitudinally extending sections extending along a substantial part of the blade and a number of transitional segments. As an example, the outer part of the blade may comprise a first longitudinally extending blade segment extending along approximately 40% of the airfoil region, a transitional segment extending along ap- proximately 10% of the airfoil region, a second longitudinally extending blade segment extending along approximately 40% of the airfoil region, and finally a blade tip section extending along approximately 10% of the airfoil region.
According to yet another aspect, the invention provides a wind turbine comprising a rotor including a number of blades, preferably two or three, according to any of the aforementioned embodiments. Advantageously, the wind turbine comprises a substantially horizontal axis rotor shaft. Preferably, the wind turbine is operated in an upwind configuration, e.g. according to the "Danish concept".
Fig. 11 shows a third embodiment of a blade according to the invention, Figs. 12a-c and Figs. 13a-c illustrate compensatory measures for correcting non- optimum twist,
Fig. 23b shows a graph of the shift angle as a function of the radial distance from a hub, Fig. 23c shows graphs of the relationship between the drag coefficient and the lift coefficient and the relationship between the angle of attack and the lift coefficient for an outer part of a blade according to the invention, and
Fig. 36 illustrates the principle of adjusting blade characteristics to a target value, Fig. 37 shows an example of a chord length distribution,
The airfoil region 34 (also called the profiled region) has an ideal or almost ideal blade shape with respect to generating lift, whereas the root region 30 due to structural considerations has a substantially circular or elliptical cross-section, which for instance makes it easier and safer to mount the blade 10 to the hub. The diameter (or the chord) of the root region 30 is typically constant along the entire root area 30. The transition region 32 has a transitional profile 42 gradually changing from the circular or elliptical shape 40 of the root region 30 to the airfoil profile 50 of the airfoil region 34. The chord length of the transition region 32 typically increases substantially linearly with increas- ing distance rfrom the hub.
When the airfoil profile 50 is impacted by an incident airflow, a lift 66 is generated perpendicular to the resultant velocity vr. At the same time, the airfoil is affected by a drag 68 oriented in the direction of the resultant velocity vr. Knowing the lift and drag for each radial position makes it possible to calculate the distribution of resultant aerodynamic forces 70 along the entire length of the blade. These aerodynamic forces 70 are typically divided into two components, viz. a tangential force 74 distribution (in the rotational plane of the rotor) and a thrust 72 oriented in a right angle to the tangential force 74. Further, the airfoil is affected by a moment coefficient 75. The driving torque of the rotor can be calculated by integrating the tangential force 74 over the entire radial length of the blade. The driving torque together with the rotational velocity of the rotor provides the overall rotor power for the wind turbine. Integrating the local thrust 72 over the entire length of the blade yields the total rotor thrust, e.g. in re- lation to the tower.
1.1 Blade design parameters The aerodynamic design of new blade for a rotor directly involves the following overall rotor radius, R, and the number of blades, B.
One important key element in state of the art aerodynamic rotor design methods is the use of pre-designed airfoils. Airfoils are selected for blade stations along the blade ra- dius. The parameters describing each airfoil section are shown in Fig. 4: The lift coefficient 66, C/, the drag coefficient 68, cd, the moment coefficient 75, cm. For individual blade stations, these airfoil characteristics are all described versus the angle of attack, α, which is then determined by the overall blade inflow angle for every section.
Figs. 6b and 6c show the control parameters that govern the wind turbine blade design: Fig. 6b shows the rotor speed, Ω, versus wind speed and Fig 6c shows the blade tip pitch angle, Θ. The rotor speed has a minimum value at low wind speeds and when optimum power is tracked until rated power this corresponds to a linear increase in rotor speed with wind speed. When reaching a given maximum value for the rotor speed, this is then kept constant during power control. The blade pitch is typically kept con- stant during power optimization and is then increasing with wind speed during power control to prevent the power from exceeding the rated value.
The rotor design point may be seen as an average over the entire longitudinal extent of the first longitudinal segment, or it may be seen as an individual target for a plurality of smaller radial segments within the first longitudinal segment. Yet again, it may be seen as an individual target for each cross-section of the first longitudinal segment of the blade. When the rotor design target point is determined and the turbine control strategy is settled, airfoils are selected and the rotor radius and number of blades are decided upon. The parameters that are left are then the local chord, twist and thickness versus blade radius plus the local section design target point. These are then found by optimizing the rotor design target point performance taking into account loads and cost of energy. The rotor power coefficient at the design target point is therefore not necessarily the optimum achievable value, but for a given rotor there will always exist one design target point.
Vice versa, if deciding on the target induction factor it is possible to derive the local chord and twist when knowing the airfoil section. In the event of designing the local section for optimum aerodynamic performance, it can be shown that the optimum axial induction factor approaches 1/3 for high values of the tip speed ratio, whereas the tangential induction factor approaches zero. A simple method exists for determining the exact optimum induction and thereafter local chord and twist for optimum aerodynamic performance. An example of such a method is the method by Glauert published with the BEM method (Glauert, H. Airplane propellers in Aerodynamic Theory ed. Durand, W. F. Dower Publications, Inc. New York).
where as previously mentioned, x=Ω r/V is the tip speed ratio, V is the design point wind speed, X is the tip speed based on R and Φ is the local inflow angle, and a is the axial induction.
Next, selecting the airfoils for the individual blade sections and knowing the flow angle makes it possible to decide the blade twist. This is commonly chosen so that the airfoil lift-to-drag ratio is optimal on as large a part of the blade as possible to maximize the rotor power coefficient. The blade operating lift coefficient c,;O is then typically the airfoil design lift coefficient cid and the chord can then be derived from the target loading. However on parts of the blade there will be a difference between the blade operating lift coefficient c,o versus the airfoil design lift coefficient cld due to considerations on loads, manufacture, etc. When there is a difference, the operating lift coefficient will not lead to optimum lift-to-drag as indicated in Fig. 16 and the operating angle of attack, α0 will not be equal to the airfoil design angle of attack, αd. The blade thickness is chosen as a compromise between structural and aerodynamic considerations, since higher thickness favours the blade structure at the expense of degeneration of the airfoil lift-drag ratio.
In Figs. 8a and 8b the ideal values (dashed lines) for loading (c- C,) and inflow angle, Φ, are shown together with the real target values (full drawn lines) for inflow and load- ing of a typical wind turbine blade. It can be seen that there is a nearby match between the two curves over a large part of the blade but that there are also discrepancies. It is seen that the target value especially deviates from the ideal values for low values of r, i.e. near the blade root. This is mainly due to structural considerations as explained in relation to Figs. 2 and 5. Furthermore, it appears clearly from Fig. 8a and Fig. 8b that since loading and inflow angle varies non-linearly with blade radius, this will also be the case for both the chord and twist - not only for the ideal blade but also for a typical commercial blade.
2. The transition region 32 between the blade root region and the remaining blade part. 3. An airfoil shaped part 34', which is the main part of the blade. Typically the airfoil shaped part extends from the area of the blade with maximum chord and towards the blade tip part.
This compensation may be exploited even further by providing at least a part of the longitudinal section with a profile 450 as shown in Fig. 32 having a "negative camber", i.e. a blade where the camber 462 is located closer to the pressure side 452 of the blade than the suction side 454 of the blade (or equivalently, where the camber 462 is located below the chord 460). A blade section has a negative lift coefficient for an incident airflow at an angle of attack of 0 degrees, i.e. the graph illustrating the relationship between lift coefficient and angle of attack is shifted even further towards larger inflow angles. This in turn means that a particular lift coefficient may be obtained at an even higher angle of attack. The use of profiles having a negative camber may be advantageous especially for blades having a very low twist or no twist, since such blades have blade sections, in which the operational angle of attack at the rotor design point is very high. This is particularly relevant for the inboard part of the airfoil region and the transition region. However, the camber 462 need not locally be located nearer the pressure side of the blade than the suction side of the blade along the entire chord of the profile as shown in Fig. 32. As shown in Fig. 33, it is also possible to provide a blade section with profile 550 having a negative camber 562, in which a part of the camber is closer to the suc- tion side 554 of the blade than the pressure side of the blade 552 (or above the chord 560) as long as the camber 562 on average is closer to the pressure side 552 than the suction side of the blade 554.
Fig. 34 illustrates this principle. A wind turbine blade 410 is divided into a root region 430, a transition region 432, and an airfoil region 434. The airfoil region 434 comprises a blade tip part 436, a first longitudinal section 440, and a second longitudinal section 442. The first longitudinal section 440 of the blade is divided into a first base part 441 and a number of first flow altering devices 446. The second longitudinal section 442 of the blade is divided into a second base part 443 and a number of second flow altering devices 448. The first base part 441 and the second base part 443 have profiles, which have a simplified structure with respect to for instance modularity of blade parts and/or manufacturing of the base parts 441 , 443, and which at the rotor design point in itself deviate significantly from the target axial induction factor and/or the target loading. The base parts 441 are here depicted as having linearly dependent chord lengths, but advantageously, the sections also have a linearly dependent thickness and linearly dependent twist or no twist. Therefore, the longitudinal sections are provided with the flow altering devices, which are here depicted as a first slat 446 and a first flap 448, however; the flow altering devices are not restricted to such flow altering devices only. The first longitudinal section 440 and the second longitudinal section 442 both extend along at least 20% of the longitudinal length of the airfoil region 434. The first longitudinal section or base part is located in a first radial distance r?.
In principle, a first blade may be reused entirely for a second blade, for instance by providing the first blade with a hub extender as shown in Fig. 35. In this situation, substantially the entire hatched part of the second blade be encumbered with off-design conditions and a majority of this section will need the use of flow altering devices, ad- vantageously both the airfoil region and the transition region of the second blade.
US20070217917 * 17 Mar 2006 20 Sep 2007 Sarbuland Khan Rotary fluid dynamic utility structure
CN105253295A * 30 Oct 2015 20 Jan 2016 深圳市道通智能航空技术有限公司 Screw propeller and aerocraft
Cooperative Classification F05B2240/301, F05B2240/32, F03D1/0641, Y02E10/721, F03D1/0675
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