CN216554519U

CN216554519U - Centrifugal fan impeller structure and centrifugal fan

Info

Publication number: CN216554519U
Application number: CN202122841229.6U
Authority: CN
Inventors: 田伶; 柳洲; 梁浩; 饶长健; 张驰
Original assignee: Gree Electric Appliances Inc of Zhuhai
Current assignee: Gree Electric Appliances Inc of Zhuhai
Priority date: 2021-11-18
Filing date: 2021-11-18
Publication date: 2022-05-17
Anticipated expiration: 2031-11-18

Abstract

The utility model provides a centrifugal fan impeller structure and a centrifugal fan, wherein the impeller structure comprises an impeller body, the impeller body comprises blades, the blades comprise a plane section close to the root parts of the blades and an arc-shaped section close to the tip parts of the blades, and the plane section and the arc-shaped section are in smooth transition. Based on the technical scheme of the utility model, on one hand, under the condition of not additionally increasing the size of the blade, the contact area between the blade and the airflow is increased by the cambered surface section, and the improvement of pressure and air volume is realized; on the other hand, the smooth transition of the plane section and the cambered surface section ensures that the noise generated when the blade is contacted with air is smaller, thereby realizing noise reduction; the improvements in both aspects improve the performance of the impeller structure and the corresponding centrifugal fan as a whole.

Description

Centrifugal fan impeller structure and centrifugal fan

Technical Field

The utility model relates to the technical field of centrifugal fan impellers, in particular to a centrifugal fan impeller structure and a centrifugal fan.

Background

The centrifugal fan accelerates gas by utilizing an impeller rotating at a high speed, and is widely applied in the household appliance industry. In the prior art, the blade structure inside the impeller is a linear or arc plate-shaped blade. When the impeller rotates, the moving air flow inside generates flow separation under the action of fluid viscous force, inverse pressure gradient and rotary Coriolis force, secondary vortex is formed, the working efficiency of the impeller is low, and the pneumatic performance and the working noise of the fan are influenced. Meanwhile, under the condition that the diameter of the impeller and the thickness of the blades are the same, the contact area between the blades and a medium is small, the energy loss is large in the conversion process, and the problems of low pressure, insufficient air volume and low motor efficiency exist at the same time.

Aiming at the problems, the blade structure of the impeller needs to be designed so as to reduce boundary layer separation and discrete noise of the centrifugal fan and meet the requirements of high pressure and large air quantity of the fan.

SUMMERY OF THE UTILITY MODEL

In order to solve the problem that work efficiency, aerodynamic performance that the fan wheel among the prior art exists are low and the noise is great, this application has proposed a centrifugal fan impeller structure and centrifugal fan.

In a first aspect, the utility model provides a centrifugal fan impeller structure, which comprises an impeller body, wherein the impeller body comprises a blade, the blade comprises a plane section close to the root of the blade and an arc section close to the tip of the blade, and the plane section and the arc section are in smooth transition.

In one embodiment, the blade is generally symmetrical, tapered with increasing width from root to tip. Through this embodiment, guaranteed that the area of blade tip part is enough big to do not additionally increase the width of root, alleviateed the blade dead weight, improved the performance of impeller structure.

In one embodiment, the impeller body further comprises an inner disk and an outer disk, a plurality of blades are uniformly distributed in an annular region between the inner disk and the outer disk along the circumferential direction, and the cambered surface sections of all the blades are same in circumferential direction. Through this embodiment, based on interior rim plate and foreign steamer dish, realize guaranteeing stability, the reliability of impeller structure to the fixed of blade both ends.

In one embodiment, the root of the blade is connected to the outer circumferential surface of the inner disk and forms a first connection point, and the blade inlet angle α between the tangent of the outer circumferential surface of the inner disk at the first connection point and the plane of the planar segment is 25 ° or more and 35 ° or less. Through the embodiment, the centrifugal fan is beneficial to reducing boundary layer separation, reducing vortex and reducing noise during operation of the centrifugal fan.

In one embodiment, the tips of the blades connect the inner circumference of the outer disc and form a second connection point, and an arc line of the outer disc inner circumference at the second connection point and a line corresponding to the arc segment at the second connection point have an exit angle β, β being 52 ° or more and 60 ° or less. Through the embodiment, the centrifugal fan is beneficial to reducing boundary layer separation, reducing vortex and reducing noise during operation of the centrifugal fan.

In one embodiment, the root of the blade is connected with the outer circumferential surface of the inner wheel disc to form a first connecting point, an included angle between a straight line passing through the center of the inner wheel disc and the first connecting point and a tangent line of an arc line corresponding to the arc surface section passing through the center of the inner wheel disc is a blade wrap angle theta, and theta is larger than or equal to 26 degrees and smaller than or equal to 31 degrees. Through the embodiment, the centrifugal fan is beneficial to reducing boundary layer separation, reducing vortex and reducing noise during operation of the centrifugal fan.

In one embodiment, the root of each blade is connected with the outer circumferential surface of the inner wheel disc to form a first connecting point, and an included angle between two connecting lines, which are formed by connecting two corresponding first connecting points of two adjacent blades with the center of the inner wheel disc respectively, is a blade distribution angle γ, and γ is equal to 10 °. Through the embodiment, the centrifugal fan is beneficial to reducing boundary layer separation, reducing vortex and reducing noise during operation of the centrifugal fan.

In one embodiment, the projected trajectory of the portion of the outer contour of the blade between the root and the tip on the target plane matches one leg of a hyperbola; wherein the target plane is a plane passing through the axis of the inner disk and the corresponding connecting point of the root of the blade and the inner disk at the same time. Through this embodiment, can effectively reduce the degree that produces flow separation in the impeller runner, promote centrifugal impeller work efficiency, reduce the vortex noise.

In one embodiment, the blade root has a mounting opening at a central location for attachment to the inner disk, the mounting opening extending through the blade in a direction perpendicular to the plane of the planar section.

In one embodiment, the minimum vertical distance from the side wall surface of the assembly opening to the edge of the blade root is H, half of the maximum width of the blade tip is H, and H is greater than or equal to 0.1H and less than or equal to 0.15H. Through this embodiment, when guaranteeing the pressure of going out wind and amount of wind, strengthened structural strength, be favorable to improving impeller structure's reliability.

In one embodiment, the circumferential surface of the inner disk has a raised connecting portion for engaging with the assembly opening, and the connecting portion can be snapped into the assembly opening.

In one embodiment, the scroll housing the impeller body, the extension path of the scroll housing matches an archimedean spiral, the scroll housing has an extension starting point with a minimum distance from the impeller body and an extension ending point with a maximum distance from the impeller body, and an air outlet is arranged between the extension starting point and the extension ending point.

In one embodiment, a wind guiding structure is arranged at the wind outlet, the wind guiding structure comprises a wind guiding plate and a volute tongue, the wind guiding plate and the volute are tangent to the extension endpoint, and the volute tongue is arranged at the extension starting point. Through this embodiment, combine the spiral case ability structure of matcing the Archimedes spiral, the interior wind pressure of spiral case can be enough promoted in the tangential direction air-out, can overcome the air resistance in the air supply arrangement wind channel to can promote centrifugal fan's work efficiency.

In one embodiment, the minimum value of the distance between the volute and the impeller body is δ, δ being (0.05-0.1) D, where D is the outer diameter of the impeller body. By the adoption of the embodiment, the noise of the centrifugal fan during working can be reduced, so that the user experience is improved; meanwhile, air leakage of the volute is slowed down, and the air output of the centrifugal fan is improved, so that the working efficiency of the centrifugal fan is improved.

In one embodiment, an included angle between two connecting lines connecting the extending start point and the extending end point with the center of the impeller body respectively is 90 °. Through this embodiment, guaranteed the size in air-out wind channel to the at utmost, be favorable to improving the amount of wind.

In a second aspect, the present invention provides a centrifugal fan, which includes the above-mentioned impeller structure.

The features mentioned above can be combined in various suitable ways or replaced by equivalent features as long as the object of the utility model is achieved.

Compared with the prior art, the centrifugal fan impeller structure and the centrifugal fan provided by the utility model at least have the following beneficial effects:

the centrifugal fan impeller structure and the centrifugal fan are based on the blade structure that the plane section is combined with the cambered surface section; on one hand, under the condition that the size of the blade is not additionally increased, the contact area between the blade and airflow is increased by the cambered surface section, and the pressure and the air volume are improved; on the other hand, the smooth transition of the plane section and the cambered surface section ensures that the noise generated when the blade is contacted with air is smaller, thereby realizing noise reduction; through the improvement of above two aspects, the performance of impeller structure and corresponding centrifugal fan has wholly been improved.

Drawings

The utility model will be described in more detail hereinafter on the basis of embodiments and with reference to the accompanying drawings. Wherein:

FIG. 1 shows a schematic structural view of the impeller body of the impeller structure of the present invention;

FIG. 2 shows a schematic cross-sectional structural view of an impeller body of the impeller structure of the present invention;

FIG. 3 shows a schematic overall structure of the impeller structure of the present invention;

FIG. 4 shows an exploded view of the structure of the impeller structure of the present invention;

FIG. 5 shows a velocity cloud when a centrifugal fan operates in accordance with the impeller configuration of the present invention;

fig. 6 shows a speed cloud chart of a centrifugal fan corresponding to the prior impeller structure during operation.

In the drawings, like parts are provided with like reference numerals. The drawings are not to scale.

Reference numerals:

10-impeller body, 11-blade, 111-plane section, 112-arc section, 12-inner wheel disc, 121-connecting part, 13-outer wheel disc, 20-volute, 201-front shell, 202-rear shell, 21-extension starting point, 22-extension terminal point, 23-air outlet, 24-air inlet, 30-air guide structure, 31-volute tongue, 32-air guide plate and 40-base circle.

Detailed Description

The utility model will be further explained with reference to the drawings.

The embodiment of the utility model provides a centrifugal fan impeller structure, which comprises an impeller body 10, wherein the impeller body 10 comprises a blade 11, the blade 11 comprises a plane section 111 close to the root of the blade and an arc-shaped section 112 close to the tip of the blade, and the plane section 111 and the arc-shaped section 112 are in smooth transition.

Specifically, as shown in fig. 1 of the accompanying drawings, the impeller structure of the present invention is mainly an improvement on the structure of the blade 11, and the blade 11 adopts a structure in which a plane section 111 and an arc-shaped section 112 are combined. Under the condition that the size of the blade 11 is not increased, the contact area between the cambered surface section 112 at the tip of the blade 11 and the airflow is increased, the air outlet pressure and the air volume of the airflow can be improved, and then the corresponding use requirements are met. Meanwhile, the smooth transition of the plane section 111 and the cambered surface section 112 avoids the generation of overlarge resistance when contacting with the airflow, thereby being beneficial to reducing the noise.

In one embodiment, the blade 11 is generally symmetrical, tapered in shape with increasing width from root to tip.

Specifically, in the centrifugal fan corresponding to the impeller structure of the present invention, air is fed from one end of the root of the blade 11 and blown from the other end of the tip, so that the pressure and the air volume of the blown air mainly depend on the structure of the tip of the blade 11, and further, it is mainly necessary to ensure that the contact area between the tip of the blade 11 and the air flow is large enough.

As shown in fig. 2 of the drawings, in the present embodiment, the blade 11 is further configured to be a plane-symmetric conical structure with a small root width and a large tip width, that is, the width of the arc-shaped section 112 is greater than the width of the straight section, so as to ensure that the area of the tip portion of the blade 11 is sufficiently large, and the width of the root is not additionally increased, thereby reducing the self weight of the blade 11 and improving the performance of the impeller structure.

In one embodiment, the impeller body 10 further includes an inner disk 12 and an outer disk 13, a plurality of blades 11 are uniformly distributed in an annular region between the inner disk 12 and the outer disk 13 along a circumferential direction, and the cambered surface sections 112 of all the blades 11 are oriented in the same direction in the circumferential direction.

Specifically, as shown in fig. 1 of the drawings, the blades 11 are fixed to an annular region between an inner disk 12 and an outer disk 13, and the root portions thereof are fixedly connected to the inner disk 12. The tip is fixedly connected with the outer wheel disc 13. The blades 11 are arranged obliquely, i.e. the overall extension direction of the blades 11 is not in the radial direction of the inner disc 12, but at an angle with the radial direction of the inner disc 12. Also, the cambered surface sections 112 of the plurality of blades 11 are oriented in the same direction in the circumferential direction, that is, the cambered surface sections 112 of all the blades 11 are oriented in the same direction with respect to the recessed side surface, and are oriented in the direction corresponding to the rotation direction of the inner disk 12.

Further, as shown in fig. 1, the inner disk 12 and the outer disk 13 are both ring-shaped structures, and the radial thickness of the inner disk 12 is greater than that of the outer disk 13. Because the inner disc 12 serves to transmit torque, its thickness is increased to reinforce its structural strength and prevent fracture deformation.

In one embodiment, as shown in FIG. 1 of the drawings, the root of the blade 11 is connected with the outer circumferential surface of the inner disk 12 and forms a first connecting point, and the inlet angle α of the blade 11 between the tangent line of the outer circumferential surface of the inner disk 12 at the first connecting point and the plane of the plane segment 111 is 25 DEG-35 deg.

Further, as shown in fig. 1, the tips of the blades 11 are connected with the inner circumferential surface of the outer disk 13 and form a second connection point, and an outlet angle β is formed between a tangent of the inner circumferential surface of the outer disk 13 at the second connection point and a tangent of the arc surface section 112 at the second connection point, wherein β is greater than or equal to 52 ° and less than or equal to 60 °.

Further, as shown in fig. 1, the root of the blade 11 is connected to the outer circumferential surface of the inner disk 12 and forms a first connection point, an included angle between a straight line passing through the center of the inner disk 12 and the first connection point and a tangent line of an arc line corresponding to the arc surface segment 112 passing through the center of the inner disk 12 is a wrap angle θ of the blade 11, and θ is greater than or equal to 26 ° and less than or equal to 31 °.

Further, as shown in fig. 1, the root of each blade 11 is connected to the outer circumferential surface of the inner disk 12 and forms a first connection point, and an included angle between two connection lines, where two first connection points corresponding to two adjacent blades 11 are respectively connected to the center of the inner disk 12, is a distribution angle γ of the blade 11, where γ is 10 °.

In particular, the above design of the blades 11 with respect to each angle is advantageous for reducing boundary layer separation, reducing vortex and reducing noise when the centrifugal fan is operated.

In one embodiment, the projected trajectory of the portion of the outer contour of the blade 11 between the root and the tip on the target plane matches one leg of the hyperbola;

wherein the target plane is a plane passing through both the axis of the inner disk 12 and the connection point of the root of the respective blade 11 to the inner disk 12.

Specifically, as shown in fig. 2, in a cross section where the axis of the inner wheel disc 12 is located in the target plane, that is, the axis passing through the connection point of the root of the blade 11 and the inner wheel disc 12, the projection locus of the outer contour line of the blade 11 extending from the root to the tip on the cross section matches one branch of a hyperbola, and in the case of two blades 11 on both sides of the inner wheel disc 12 and in the same cross section as the connection point of the inner wheel disc 12, the projection locus of the outer contour line on the corresponding cross section matches a hyperbola. The structure can effectively reduce the degree of flow separation generated in the impeller flow channel, improve the working efficiency of the centrifugal impeller and reduce the vortex noise.

In one embodiment, the middle position of the root of the blade 11 has a fitting opening for connecting the inner disk 12, which extends through the blade 11 in a direction perpendicular to the plane of the planar section 111.

Preferably, the minimum vertical distance from one side wall surface of the assembling opening to the edge of the root of the blade 11 is H, half of the maximum width of the tip of the blade 11 is H, and H is more than or equal to 0.1H and less than or equal to 0.15H.

Specifically, as shown in fig. 1 and 2 of the drawings, the root of the blade 11 has a fitting opening, two remaining portions of the same width of the root of the blade 11 are arranged on two sides of the fitting opening, the width of a single remaining portion needs to be ensured to a certain value to ensure the strength of the root of the blade 11, and the strength of the root of the blade 11 is related to the resistance to the airflow, i.e. the width of the tip portion of the blade 11. The larger the width of the tip portion of the blade 11 is, the better the theoretical air-out performance is, but the larger the requirement on the strength of the root portion is, and further, a balance needs to be found between the strength and the working performance.

Experiments show that when H is more than or equal to 0.1H and less than or equal to 0.15H, the balance between the strength of the blade and the working performance of the blade is optimal.

In one embodiment, the inner hub 12 has a raised coupling portion 121 on its circumferential surface for engaging a mounting opening, the coupling portion 121 being capable of snapping into the mounting opening.

Specifically, as shown in fig. 1 and 2, the connecting portion 121 protrudes from the outer circumferential surface of the inner wheel 12, and the structure thereof can be configured adaptively. In view of convenience in manufacturing and assembly, the connection portion 121 is provided as an annular plate-shaped structure that extends continuously one turn in the circumferential direction.

In one embodiment, the volute 20 is further included for accommodating the impeller body 10, the extending path of the volute 20 matches the archimedean spiral, the volute 20 has an extending starting point 21 with the smallest distance from the impeller body 10 and an extending end point 22 with the largest distance from the impeller body 10, and an air outlet 23 is arranged between the extending starting point 21 and the extending end point 22.

Specifically, as shown in fig. 3, the impeller structure further includes a volute 20 accommodating the impeller body 10, and a cavity inside the volute 20 is used for not only mounting the impeller body 10, but also guiding the air flow out. The volute 20 adopts a continuous extension structure matched with an Archimedes spiral line, and is beneficial to guiding air flow out.

In one embodiment, the air guiding structure 30 is disposed at the air outlet 23, the air guiding structure 30 includes an air guiding plate 32 and a volute tongue 31, the air guiding plate 32 is tangential to the volute 20 at the extension terminal 22, and the volute tongue 31 is disposed at the extension starting point 21.

Specifically, as shown in fig. 3, the air guiding structure 30 includes an arc-shaped volute tongue 31 and a straight plate-shaped air guiding plate 32, and an air outlet flow channel is formed between the two air guiding plates, and an extending direction of the air outlet flow channel is along a tangential direction of the volute 20 at the extending terminal 22. The spiral case 20 that combines to match the Archimedes spiral can the structure, and the air-out of tangential direction can promote the interior wind pressure of spiral case 20, can overcome the air resistance in the air supply arrangement wind channel to can promote centrifugal fan's work efficiency.

Preferably, the angle between two connecting lines connecting the center of the impeller body 10 with the extension starting point 21 and the extension ending point 22 is 90 °.

Further, the volute casing 20 is formed by buckling a front casing 201 and a rear casing 202, an air inlet 24 is formed in the center of the front casing 201, air flows enter from the center along the axial direction of the impeller body 10, and air flows out along the tangential direction of the impeller body 10 along the air outlet 23.

In one embodiment, the minimum distance between the volute 20 and the impeller body 10 is δ, δ being (0.05-0.1) D, where D is the outer diameter of the impeller body 10.

Specifically, the position where the distance between the volute 20 and the impeller body 10 is the minimum corresponds to the position of the volute tongue 31, so that the noise generated when the centrifugal fan works can be reduced, and the user experience is improved; meanwhile, air leakage of the volute 20 is slowed down, and the air output of the centrifugal fan is increased, so that the working efficiency of the centrifugal fan is improved.

Further, as shown in fig. 3, the starting point of the archimedean spiral corresponding to the volute 20, i.e. the position of the start point 21 of the extension of the volute 20, is determined with reference to the base circle 40, i.e. the start point 21 of the extension is located on the circumference of the base circle 40. The size of the base circle 40 is determined by the size of the impeller body 10, that is, the radius of the base circle 40 is equal to the radius + δ of the impeller body 10, δ is equal to (0.05 to 0.1) D, and D is the outer diameter of the impeller body 10.

In practical applications, the impeller structure of the present invention obtained based on the above improvement has a greater performance improvement compared to the existing impeller structure, and refer to the speed cloud charts of the centrifugal fans corresponding to the impeller structures shown in fig. 5 and 6. Comparison of the performance parameters at 3500rpm between the two is shown in the following table:

as can be seen from the speed cloud charts shown in fig. 5 and 6, the centrifugal fans corresponding to the impeller structure of the present invention have uniform speed distribution, and compared with the existing general centrifugal fan with arc blades, the impeller structure and the corresponding centrifugal fan of the present invention have greater improvement in two performance indexes of noise and air volume.

The embodiment of the utility model also provides a centrifugal fan which comprises the impeller structure and further has all the technical effects of the centrifugal fan.

In the description of the present invention, it is to be understood that the terms "upper", "lower", "bottom", "top", "front", "rear", "inner", "outer", "left", "right", and the like, indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, are only for convenience in describing the present invention and simplifying the description, and do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed in a particular orientation, and be operated, and thus, should not be construed as limiting the present invention.

Although the utility model herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims. It should be understood that features described in different dependent claims and herein may be combined in ways different from those described in the original claims. It is also to be understood that features described in connection with individual embodiments may be used in other described embodiments.

Claims

1. The utility model provides a centrifugal fan impeller structure, includes the impeller body, its characterized in that, the impeller body includes the blade, the blade includes the plane section that is close to its root and the cambered surface section that is close to its tip, the plane section with smooth transition between the cambered surface section.

2. The centrifugal fan impeller structure of claim 1 wherein the entirety of the blades is a symmetrical conical structure that gradually increases in width from root to tip.

3. The centrifugal fan impeller structure of claim 2, wherein the impeller body further comprises an inner disk and an outer disk, a plurality of blades are uniformly distributed in an annular region between the inner disk and the outer disk along the circumferential direction, and the cambered surface sections of all the blades are in the same orientation in the circumferential direction.

4. The centrifugal fan impeller structure of claim 3 wherein the root portion of the blade connects the outer circumferential surface of the inner disk and forms a first connection point, the outer circumferential surface of the inner disk having a blade inlet angle α between a tangent to the first connection point and a plane of the planar segment, 25 ° ≦ α ≦ 35 °.

5. The centrifugal fan impeller structure of claim 3 wherein the tips of the blades connect to the inner circumferential surface of the outer disk and form a second connection point, and wherein an arc corresponding to the arc segment at the second connection point of the outer disk inner circumferential surface has an exit angle β between a tangent to the second connection point, wherein β is 52 ° or more and 60 ° or less.

6. The centrifugal fan impeller structure of claim 3, wherein the root of the blade is connected with the outer circumferential surface of the inner disk and forms a first connection point, and an included angle between a straight line passing through the center of the inner disk and the first connection point and a tangent line of an arc line corresponding to the arc surface section passing through the center of the inner disk is a blade wrap angle theta which is greater than or equal to 26 degrees and less than or equal to 31 degrees.

7. The impeller structure of the centrifugal fan as claimed in claim 3, wherein the root of each blade is connected with the outer circumferential surface of the inner disk to form a first connecting point, and an included angle between two connecting lines, which are respectively connected with the center of the inner disk, of two first connecting points corresponding to two adjacent blades is a blade distribution angle γ, and γ is 10 °.

8. The centrifugal fan impeller structure according to any one of claims 3 to 7, wherein a projection locus of a portion of an outer contour of the blade between the root and the tip on the target plane matches one branch of a hyperbola;

wherein the target plane is a plane passing through the axis of the inner disk and the corresponding connecting point of the root of the blade and the inner disk at the same time.

9. The centrifugal fan impeller structure according to any one of claims 3 to 7, wherein a middle position of the blade root has a fitting opening for connecting the inner disk, the fitting opening penetrating the blade in a direction perpendicular to a plane of the planar section.

10. The impeller structure of the centrifugal fan as claimed in claim 9, wherein a minimum vertical distance from a side wall surface of the assembling port to an edge of the root of the blade is H, a half of a maximum width of the tip of the blade is H, and H is 0.1H ≦ 0.15H.

11. The centrifugal fan impeller structure according to claim 9, wherein the circumferential surface of the inner disk has a protruding connecting portion for fitting the fitting opening, and the connecting portion can be snapped into the fitting opening.

12. The centrifugal fan impeller structure of claim 1 further comprising a volute housing the impeller body, the volute having an extension path matching an archimedean spiral, the volute having an extension starting point at a minimum distance from the impeller body and an extension ending point at a maximum distance from the impeller body, the extension starting point and the extension ending point having an air outlet therebetween.

13. The impeller structure of the centrifugal fan as claimed in claim 12, wherein an air guiding structure is disposed at the air outlet, the air guiding structure includes an air guiding plate and a volute tongue, the air guiding plate and the volute tongue are tangent to the extension end point, and the volute tongue is disposed at the extension starting point.

14. The centrifugal fan impeller structure according to claim 12 or 13, wherein a minimum value of a distance between the volute and the impeller body is δ, δ being (0.05-0.1) D, where D is an outer diameter of the impeller body.

15. The centrifugal fan impeller structure according to claim 12 or 13, wherein an angle between two connecting lines connecting the extending start point and the extending end point with the center of the impeller body respectively is 90 °.

16. A centrifugal fan characterised in that it comprises an impeller structure according to any one of claims 1 to 15.