A fan blade of a large flow and low speed fan

Abstract

A fan blade of a large-flow low-speed fan comprises a hub sleeve, a fan blade, a fixing rod and a fixing bolt; the fan blade is rigidly connected to the fixing rod through a front panel, a rear panel and a plurality of fixing screws; the fan blade uses a U-shaped hoop to connect the fixing rod to the hub sleeve; the fan blade has a straight shape, and the blade geometry of each section is the same, and is divided into three areas: a leading edge guide area, a middle supercharging area and a trailing edge straightening area; the leading edge guide area accounts for about 10% of the chord length, and can adapt to the relative airflow direction of the flow at different linear speeds; the middle supercharging area is 50% of the chord length after the leading edge guide area, and generates sufficient wind pressure rise through the difference in blade geometry, and has a relative thickness of not less than 15% so that the fixing rod can be installed inside; the trailing edge straightening area is about 40% of the chord length of the rear part of the blade, and adopts a small wedge angle and a small curvature geometry to reduce the static pressure difference and slow down the exhaust loss. The blade surface geometric coordinates of the three areas are generated by multiple polynomial functions.

Description

[Technical field]

[0001] The invention belongs to the field of fan application, and in particular relates to a fan blade of a large-flow low-speed fan, which is suitable for axial-flow ventilation machinery with a wind pressure lower than 300Pa. [Background technology]

[0002] The expired patent 201020161228 "A hollow blade for a fan" discloses a fan blade, the key point of which is the use of a hollow blade and the strengthening of the connection strength between the blade and the rotating shaft.

[0003] For fan blades, in addition to the above technologies, the shape and structure that determine the aerodynamic performance of the blades are more important, and are key design factors for fan performance and energy efficiency. Some companies also adopt reverse design to change their aerodynamic shape to circumvent Western patents, but they know the results but not the reasons. The changes made in this way usually cause serious performance degradation, and they cannot provide effective self-designed products according to user needs.

[0004] Traditionally, such large-flow, low-speed fans use blades with equal thickness. The blades must be twisted from the hub to the casing to adapt to the relative flow direction. There are many types of fans, and each fan has its own unique "personality" due to different users, so it is impossible to form a standard blade shape to expand the scope of application. At present, variable-thickness blades have been widely used in the field of axial-flow ventilation machinery. The present invention is based on long-term basic research, through repeated design optimization and practical tests, to form a standard blade shape suitable for wind pressures below 300Pa.

[0005] Our company has been engaged in fan design and manufacturing for more than 20 years and has accumulated rich manufacturing experience. We have also worked closely with colleges and universities to make significant improvements and breakthroughs in the blades of large-flow, low-speed fans. This case thus occurred. [Summary of the invention]

[0006] In order to improve the gas dynamics performance of the fan and solve the defects of poor applicability, complex manufacturing and high cost of large-flow low-speed fans on the market, the present invention provides a fan blade of a large-flow low-speed fan.

[0007] To achieve the above object, the technical solution adopted by the present invention is:

[0008] A fan blade of a large-flow low-speed fan comprises: a hub sleeve, a fan blade, a fixing rod and a fixing bolt; a plurality of fan blades are evenly arrayed on the hub sleeve in a radial shape through a fixing structure, the hub sleeve is rigidly fixed on the fan shaft, the number of fan blades can be selected to be 2-8 according to the needs of air volume and air pressure, the fan blade is a hollow structure, a reinforcing rib is arranged inside, and the fan blade is rigidly connected to the fixing rod through a front panel, a rear panel and a plurality of fixing screws; the fan blade fixing structure is a plurality of U-shaped hoops, and the fixing rod is connected to the hub sleeve by using the U-shaped hoops;

[0009] The fan blade has a straight shape, and the blade geometry of each cross section is exactly the same, and can be divided into three areas: a leading edge guide area, a middle pressure-boosting area, and a trailing edge straightening area; the leading edge guide area occupies 10% of the chord length and can adapt to the relative airflow direction of the flow at different linear speeds; the middle pressure-boosting area is 50% of the chord length following the leading edge guide area, and generates sufficient wind pressure rise through the difference in blade geometry, and has a relative thickness of not less than 15% so that a fixing rod can be installed inside it; the trailing edge straightening area is 40% of the chord length of the rear part of the blade, and adopts a small wedge angle and a small curvature geometry to reduce the static pressure difference and slow down exhaust loss.

[0010] The geometric coordinates of the blade surfaces of the three regions are generated by multiple polynomial functions:

[0011] First, the center arc line geometry that adapts to the aerodynamic effect is determined by the center arc line bevel angle. A fourth-order polynomial fitting curve is generated according to the designed center arc line bevel angle. The design formula is:

[0012] α=30.782c 4 -93.764c 3 +141.39c 2 -131.79c+33.3706

[0013] Where c is the percentage chord length, α is the mid-arc angle;

[0014] Secondly, the coordinates of the middle arc are calculated according to the middle arc angle to form a sixth-order polynomial curve. The design formula is:

[0015] y=-3.8117×10 -13 c 6 +3.6398×10 -10 c 5 -1.4459×10 -7 c 4 +3.4525

[0016] ×10 -5 c 3 -6.7509×10 -3 c 2 +6.7714×10 -1c-3.19373where c is the percentage chord length and y is the relative deflection of the mid-arc;

[0017] Finally, the geometric coordinates of the blade surface are generated by the thickness distribution that adapts to the aerodynamic laws of the leading edge guide, middle pressure boost and trailing edge straightening. The thickness distribution design formula is:

[0018] t=-0.56403m 6 +2.1175m 5 -3.3814m 4 +3.2549m 3 -2.0297m 2

[0019] +0.58494m+0.021270

[0020] Among them, m is the relative length of the mid-arc, and t is the relative half thickness.

[0021] As an optimization solution, a front panel and a rear panel are provided at both ends of the fan blade shell, and the peripheral contour lines of the front panel and the rear panel coincide with the peripheral contour line of the fan blade shell; a fixing rod through hole is provided on the front panel to accommodate the fixing rod passing through.

[0022] As an optimization solution, the fan blade fixing structure is composed of several U-shaped hoops and fixing rods; the fixing rods have several annular grooves on the side of the hub sleeve, and the diameter of the annular grooves is adapted to the U-shaped hoops; the fixing rods are fixed to the inside of the fan blade housing with screws.

[0023] As an optimization solution, the hub sleeve is provided with a plurality of semicircular grooves, the radius of which matches the fixing rod of the fan blade, so that the number of fan blades to be installed can be determined according to the use process.

[0024] As an optimization solution, the hub sleeve is also provided with a plurality of through holes, so that the U-shaped hoop can pass through the through holes to press the fixing rod onto the hub sleeve; a keyway is provided in the central shaft hole of the hub sleeve to facilitate fixing the hub sleeve onto the fan shaft (not shown).

[0025] As an optimization solution, the fan blades are made of aluminum alloy or fiberglass.

[0026] The present invention has the following beneficial effects:

[0027] 1. A blade shape that can adapt to a wide range of angles of attack is adopted, which greatly simplifies the geometric shape of the wind blade and has more advanced aerodynamic performance characteristics. The resulting standard wind blade will be conducive to high efficiency, low power consumption, low noise, corrosion resistance, high fatigue strength, and reduce manufacturing costs.

[0028] 2. The hub sleeve has various specifications, different sizes, and different numbers of semicircular grooves; the fan blades rigidly mounted on the hub sleeve are replaceable and also have various sizes and shapes; various combinations of hub sleeves and fan blades enable the implementation of multi-specification standardized serialization of fans, and provide a variety of fan flow requirements through changes in diameter, height difference, number of blades, and scaling of blade geometry, allowing users to freely choose the best fan diameter according to their application.

[0029] 3. The connection between the fan blade and the hub sleeve allows for partial adjustment of the fan blade angle, which is conducive to simple and convenient adjustment of dynamic balance.

[0030] 4. The fan blades have a fixed geometric shape and will not be twisted under extremely strong wind pressure.

Brief Description of the Drawings

[0031] Figure 1 This is a schematic diagram of the overall assembly of the fan blade of the present invention;

[0032] Figure 2 This is a schematic diagram of the back of the fan blade assembly;

[0033] Figure 3 It is a schematic diagram of the fan blade components;

[0034] Figure 4 This is an exploded view of the fan blade structure;

[0035] Figure 5 It is a schematic diagram of the cross-section of the new air blade (in the figure, H is the maximum thickness and C is the chord length).

[0036] Figure 6 This is a cross-sectional view of an old wind blade in the prior art;

[0037] Figure 7 A comparison diagram of the blade cross-sections of the new fan blade and the old fan blade of the present invention;

[0038] Figure 8 The calculation result of the full pressure characteristic curve of Example 2;

[0039] Fig. 9 The calculation result of the static pressure rise characteristic curve of Example 2;

[0040] Fig.10 The calculation result of the efficiency characteristic curve of Example 2;

[0041] Fig.11 The power characteristic curve calculation result of Example 2;

[0042] Fig.12 The calculation result of the full pressure characteristic curve of Example 3;

[0043] Fig.13 The calculation result of the static pressure rise characteristic curve of Example 3;

[0044] Fig.14 The calculation result of the efficiency characteristic curve of Example 3;

[0045] Fig.15 The power characteristic curve calculation result of Example 3;

[0046] Fig.16 The total pressure characteristic curves at different height differences in Example 3;

[0047] Fig.17 This is the efficiency characteristic curve of Example 3 at different height differences.

[0048] Reference numerals:

[0049] 1. Hub sleeve; 1.1 semicircular groove, 1.2 shaft hole, 1.3 through hole.

[0050] 2. Blades; 2.1 Blade shell, 2.1.1 Reinforcement ribs, 2.2 Hub end panel, 2.2.1 Fixing rod through hole, 2.3 Blade top panel, 2.3.1 Leading edge, 2.3.2 Leading edge guide area, 2.3.3 Middle pressurization area, 2.3.4 Suction surface, 2.3.5 Fixing rod position, 2.3.6 Trailing edge, 2.3.7 Pressure surface, 2.3.8 Trailing edge fairing area.

[0051] 3.Fixed rod, 3.1 Ring groove.

[0052] 4. U-shaped hoop.

[0053] 5. Screw parts.

[0054] 6. New fan blades.

[0055] 7. Old wind blades. [Specific implementation method]

[0056] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments.

[0057] A blade for a large flow rate, low speed fan mainly includes two parts: a standard blade blade and a fan assembly. Since a certain blade geometry is required to adapt to the relative flow field of fans with different blade heights, different flow rates, and different wind pressures, the blade must adapt to a large angle of attack range. At the same time, in order to ensure that the pull rods that tighten and fix the blades have sufficient strength, the blade geometry adopts an aerodynamic design that is different from the previous geometric shapes. Its design features include: the leading edge guide area 2.3.2, the middle boost area 2.3.3, and the trailing edge straightening area 2.3.8 are generated by three polynomial function curves. The leading edge guide area 2.3.2 not only uses the leading edge 2.3.1 to adapt to the direction of the incoming flow, but also adapts to a wide range of angles of attack through a leading edge guide area of ​​about 10% of the chord length, increases the range of low-loss angles of attack, and expands the adaptability to the direction of the incoming flow; the gentle pressure surface 2.3.7 slowly decelerates the airflow entering the fan, causing its surface static pressure to rise uniformly, while the suction surface 2.3.4 accelerates sharply at the front, causing the surface static pressure to reach the maximum in the maximum thickness H area, thereby forming the pressure surface 2.3.7 and the suction surface 2.3.4. The huge pressure difference on the pressure surface 2.3.4 forms a middle boost zone with front loading characteristics. The static pressure potential energy conversion of the impeller energy input is mainly completed in this area, and sufficient wind pressure rise is generated through the difference in the geometric shape of the blade profile; about 40% of the chord length of the rear of the blade profile is the trailing edge fairing area 2.3.8. The function of this area is to slow down the static pressure rise on the pressure surface 2.3.7, while the static pressure on the suction surface 2.3.4 still increases linearly, so that the airflow has a balanced static pressure when it reaches the trailing edge 2.3.6 to reduce the wake of the blade profile outlet. Due to the effective use of the aerodynamic structural characteristics of the small wedge angle and small curvature of the trailing edge fairing area 2.3.8, the trailing edge 2.3.6 can adopt a square or triangular geometric shape, which effectively reduces the requirements for the manufacturing accuracy of the trailing edge; since the pressure surface 2.3.7 has a relatively low flow velocity, its friction loss does not play a decisive role in efficiency, and the manufacturing accuracy can be reduced.

[0058] Example 1

[0059] As attached Figure 1 To Attachment Figure 5 As shown, a fan blade of a large flow rate low speed fan comprises: a hub sleeve 1, a fan blade 2; in this embodiment, there are 4 fan blades 2 arranged evenly in a radial shape on the hub sleeve 1, and the hub sleeve 1 is fixed on the fan shaft; the fan blade shell 2.1 is hollow, and there is a reinforcing rib 2.1.1 in the middle. The fan blade shell 2.1 has a straight shape and the cross-sectional dimensions are the same at all places; the fan blade shell 2.1 is rigidly connected to the fixing rod through the front panel, the rear panel, and a number of screw components 5, and the fixing rod 3 is connected to the hub sleeve 1 using a U-shaped hoop 4; the maximum thickness H area is at the 20-30% chord length position of the blade profile, and the thickness is greater than 116% of the diameter of the fixing rod to ensure that there is enough space inside the blade profile to place the fixing rod, and it has clear front loading aerodynamic geometric characteristics.

[0060] In this embodiment, the fan blade is made of aluminum alloy. The two ends of the fan blade housing 2.1 are provided with a front panel 2.2 and a rear panel 2.3, and the peripheral contours of the front panel 2.2 and the rear panel 2.3 coincide with the peripheral contours of the fan blade housing 2.1. The fixing rod 3 has two annular grooves 3.1 on the side close to the hub sleeve 1, and the diameter of the annular grooves 3.1 matches the diameter of the U-shaped hoop 4.

[0061] In this embodiment, the hub sleeve 1 is provided with 8 semicircular grooves 1.1, whose radius matches the radius of the fixing rod 3 of the fan blade 2; the number of the semicircular grooves 1.1 exceeds the number of the fan blades 2, so as to facilitate the installation of 2, 4 or 8 fan blades according to the use process without having to replace the hub sleeve. Similarly, if 6 semicircular grooves 1.1 are evenly arranged, the same hub sleeve 1 can be installed with either 3 or 6 fan blades 2.

[0062] The hub sleeve 1 is also provided with a plurality of through holes 1.3, so that the U-shaped hoop 4 can pass through the through holes 1.3 to press the fixing rod onto the hub sleeve 1; a keyway is provided in the central shaft hole 1.2, so that the hub sleeve 1 can be fixed onto the fan shaft (not shown).

[0063] See the attached old wind blade of the prior art Figure 6 , defined as: blade chord length 231.85mm, maximum thickness 37.55mm, maximum relative thickness 16.2%. Figure 7 Comparison of the new blade shape shows that the old blade is a typical modern aircraft airfoil with a lift-increasing feature of trailing edge loading, while the present invention is a typical turbine blade with a pressure-increasing feature of controlled diffusion. There are clear differences between the two from aerodynamic principles to structural forms.

[0064] Another advantage of the new blade of the present invention is that the maximum thickness is placed in front, which is also a common feature of modern subsonic blades. This feature enables the blade to have a wider flow adaptability. It is precisely because of this ability that the blades can be stacked along a straight line with equal geometric blades to form a low-speed impeller that can adapt to changes in angle of attack at different radii, thereby forming a universal standard blade that can adapt to a larger flow range and reduce manufacturing costs.

[0065] By highlighting its advantages and avoiding its defects, a more modern front-loaded blade shape is formed without reducing the scope of application and saving manufacturing costs, so that the "new blade shape" has the characteristics of independent intellectual property rights in the true sense. Figure 5, its maximum thickness and its relative position are changed, which can ensure that the size of the fixing rod for fixing the wind blade remains unchanged. In addition to the curvature of the middle arc line, the new blade shape retains the advantageous characteristics of the original blade shape before the maximum thickness, and strengthens the curvature of the blade shape after the maximum thickness, so that the effective aerodynamic load is placed in front, and the blade shape is kept straight and with a small wedge angle in the trailing edge finishing area, which is conducive to the pressure balance of the suction pressure surface to reduce the influence range of the wake. The trailing edge geometry of the present invention is no longer a key parameter, which reduces the molding difficulty and precision requirements of thin-walled parts.

[0066] Example 2

[0067] The impeller parameters of Example 2 of the present invention are:

[0068] Volume flow: 74300m 3 / h;

[0069] Speed: 480rpm;

[0070] Diameter: 1800mm;

[0071] Blade chord length: 231.5mm;

[0072] Number of blades: 6;

[0073] Tip clearance: 9mm;

[0074] Atmospheric temperature: 293.15K (20°C);

[0075] Atmospheric pressure: 100813.7Pa.

[0076] The original blade type and the new blade type were compared through numerical simulation. Figures 8 to 11 These are the characteristic curves of total pressure, static pressure, efficiency and power changing with flow rate. For comparability, the two use the same inlet metal angle, that is, the original blade type (height difference 82.7) and the new blade type (height difference 91.7) have the same inlet metal angle, and the original blade type (height difference 97.4) and the new blade type (height difference 106.3) have the same inlet metal angle.

[0077] The simulation results show that the new blade shape maintains such a feature that the total and static pressures are improved compared with the original blade shape, and the new blade shape has a stronger high pressure boost capability under different height differences, which is consistent with the front load design. Therefore, the new blade shape is easier to meet the pressure rise requirements during application.

[0078] Regardless of the original blade type or the new blade type, the efficiency is on the left side of the peak efficiency, indicating that this type of fan blade has better large flow characteristics. The new blade type has relatively low efficiency in the low flow section, and has higher efficiency in the high flow area, indicating that the new blade type is more suitable for low-load applications with small height differences, and has better negative angle of attack characteristics, which is consistent with the general characteristics of the front-loaded blade type. The smoothness and consistency of the power characteristics provide convenience for motor selection, and the motor has almost equal power characteristics during the height difference debugging process.

[0079] Example 3

[0080] The impeller parameters of Example 3 of the present invention are:

[0081] Volume flow: 50000m 3 / h;

[0082] Pressure rise: 205Pa

[0083] Speed: 750rpm;

[0084] Diameter: 1200mm;

[0085] Blade chord length: 231.5mm;

[0086] Number of blades: 4;

[0087] Tip clearance: 10mm;

[0088] Atmospheric temperature: 293.15K (20°C);

[0089] Atmospheric pressure: 101325Pa.

[0090] The original blade type and the new blade type were also compared through numerical simulation. Figures 12 to 15 The characteristic curves of total pressure, static pressure, efficiency and power with flow rate are shown respectively. For comparability, the two use the same inlet metal angle, that is, the original blade type (height difference 110mm) and the new blade type (height difference 118.5mm) in the figure have the same inlet metal angle. The simulation results also have the characteristics of Example 2, that is, the new blade type maintains a higher total and static pressure lifting capacity ( Fig.12 , 13 ), and the new blade has higher efficiency under large flow conditions ( Fig.14 ). For design flow rate 50000m 3 / h, the total pressure achieved by the original blade type is 204.5Pa, while the new blade type is 249Pa, which is much higher than the design requirement of 205Pa. 3 / h and below all meet the pressure rise requirement of 205Pa, which means that even if the fan diameter is reduced to a certain extent, the desired flow rate and pressure rise can be achieved, which undoubtedly makes the fan more compact and efficient, and is conducive to reducing power and saving material costs.

[0091] The new blade height difference of Example 3 is changed, and the total pressure and efficiency obtained by numerical simulation vary with flow rate as shown in this paper Fig.16 and Fig.17 As shown in the figure (in the figure, pt110 is the original blade type with a height difference of 110mm; m is the new blade type with a height difference ranging from 110mm to 130mm). The results show that the new blade type with a height difference of 130mm (m130) is less than 50000m 3 / h flow rate, stall occurs, which is the maximum height difference of the blade profile of the present invention in Example 3. The height difference from 118mm to 130mm is available, and the efficiency shows an upward trend ( Fig.17 ). This shows that the new blade type has a wide range of height adjustment, which is closely related to the invention of the blade type.

[0092] At the same time, by adjusting the height difference, the fan No. 12 in Example 3 can be improved to the fan No. 11, while keeping the flow rate and pressure rise unchanged, and the significant increase in efficiency can further reduce the power demand. These advantageous features are derived from the aerodynamic shape of the fan blades that the present invention needs to protect.

[0093] By changing the loading method, a new blade shape of a certain type of low-speed and low-load impeller was designed, and the performance characteristics of the new and old blades were calculated and compared under two operating conditions with different height differences. The results of three-dimensional numerical simulation show that the new blades have better application advantages.

[0094] The new blade shape is suitable for impellers with a diameter of more than 1000mm. Impellers with smaller diameters can be reduced according to the chord length. This depends on whether the application requirements are worth improving, but the geometric integrity of the blade contour line should not be easily changed.

[0095] The above specific implementation methods are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements or modifications made within the design principles of the present invention, such as trailing edge cutting, thickness changes, geometric shape changes, changing the fixing rod from a circular shape to a sheet shape, material replacement, etc., are regarded as technical derivatives of the blade type of the present invention and are all covered by the protection scope of the present invention.

Claims

1. A fan blade of a large flow rate low speed fan, comprising a hub sleeve and a fan blade, wherein a plurality of fan blades are evenly arrayed on the hub sleeve in a radial shape through a fixing structure, the hub sleeve is fixed on the fan shaft, the number of the fan blades is 2-8, the fan blade housing is hollow, and there is a reinforcing rib in the middle, and the characteristics are: The fan blade has a straight shape and the cross-sectional dimensions are the same at all locations; the fan blade is rigidly connected to the fixing rod through a front panel, a rear panel, and a plurality of screw components; the fan blade fixing structure is a plurality of U-shaped hoops, and the fixing rod is connected to the hub sleeve using the U-shaped hoops; The fan blade has a straight shape, and the blade geometry of each cross section is exactly the same, and can be divided into three areas: a leading edge guide area, a middle pressure zone, and a trailing edge straightening area; the leading edge guide area occupies 10% of the chord length, and can adapt to the relative airflow direction of the flow at different linear speeds; the middle pressure zone is 50% of the chord length following the leading edge guide area, and generates sufficient wind pressure rise through the difference in blade geometry, and has a relative thickness of not less than 15% so that a fixing rod can be installed inside it; the trailing edge straightening area is 40% of the chord length of the rear part of the blade, and adopts a small wedge angle and a small curvature geometry to reduce the static pressure difference and slow down the exhaust loss; The geometric coordinates of the blade surface of the three regions are generated by multiple polynomial functions. First, the mid-arc line geometry that adapts to the aerodynamic effect is determined by the mid-arc line oblique angle. A fourth-order polynomial fitting curve is generated according to the designed mid-arc line oblique angle. The design formula is: α = 30.782c 4 -93.764c 3 +141.39c 2 -131.79c+33.3706, where c is the percentage chord length and α is the mid-arc angle; Secondly, the coordinates of the middle arc are calculated according to the middle arc angle to form a sixth-order polynomial curve. The design formula is: y=-3.8117×10 -13 c 6 +3.6398×10 -10 c 5 -1.4459×10 -7 c 4 +3.4525×10 -5 c 3 -6.7509×10 - 3 c 2 +6.7714×10 -1 c-3.19373 Among them, c is the percentage chord length, y is the relative deflection of the mid-arc; Finally, the geometric coordinates of the blade surface are generated by the thickness distribution that adapts to the aerodynamic laws of the leading edge guide, middle pressure boost and trailing edge straightening. The thickness distribution design formula is: t=-0.56403m 6 +2.1175m 5 -3.3814m 4 +3.2549m 3 -2.0297m 2 +0.58494m+0.021270 Among them, m is the relative length of the mid-arc, and t is the relative half thickness.

2. The fan blade of a large flow rate low speed fan as claimed in claim 1, characterized in that: The two ends of the fan housing are provided with a front panel and a rear panel, and the peripheral contour lines of the front panel and the rear panel coincide with the peripheral contour line of the fan housing; the front panel is provided with a fixing rod through hole to accommodate the fixing rod passing through.

3. The fan blade of a large flow rate low speed fan as claimed in claim 1, characterized in that: The fan blade fixing structure comprises a plurality of U-shaped hoops and fixing rods; the fixing rods are provided with a plurality of annular grooves on one side close to the hub sleeve, and the diameter of the annular grooves is adapted to the U-shaped hoops.

4. The fan blade of a large flow rate low speed fan as claimed in claim 1, characterized in that: The hub sleeve is provided with a plurality of semicircular grooves, the radius of which is adapted to the fixed axis of the fan blade.

5. The fan blade of a large flow rate low speed fan as claimed in claim 1, characterized in that: The hub sleeve is also provided with a plurality of through holes; a keyway is provided in the central rotating shaft hole.

6. The fan blade of a large flow rate low speed fan as claimed in claim 1, characterized in that: The fan blades are made of aluminum alloy or glass fiber reinforced plastics.

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