A backward centrifugal fan impeller

Abstract

The present invention discloses a backward centrifugal fan impeller, belonging to the field of fan impeller design. The impeller is composed of an impeller front disc, an impeller rear disc and blades. Among them, the blades have a high-efficiency blade form, and the blade profile is composed of a pressure surface, a suction surface, an upper surface, a lower surface and a trailing edge surface; the pressure surface is locally provided with a ridge-shaped surface structure. In the present invention, a row of continuous, equal-sized ridge-shaped structures with an isosceles triangle cross-section shape is arranged at a local position of the blade pressure surface from the blade height of 0% to the blade height of 100%. Through the design of 4 parameters, namely the starting position sl of the ridge-shaped surface on the pressure surface, the ridge height h, the ridge spacing s and the overall length l, the efficiency of the backward centrifugal fan can be effectively improved.

Description

Technical Field

[0001] The present invention belongs to the field of fan impeller design, and more specifically, relates to a backward centrifugal fan impeller. Background Art

[0002] Backward centrifugal fans are generally applied in various occasions such as factories, mines, tunnels, buildings, etc. At the same time, they are also widely used in air conditioning equipment and household electrical appliances. Due to the particularity and universality of their uses, the requirements for their high efficiency and energy conservation are getting higher and higher.

[0003] The impeller is the main work - doing component of a backward centrifugal fan, which plays an important role in improving the efficiency of the fan and improving the performance of the fan. However, when a backward centrifugal fan is working, various flow phenomena such as flow separation and secondary flow will occur on the blade surface, thereby causing flow losses inside the fan and reducing the operating efficiency of the fan. Summary of the Invention

[0004] In view of the above - mentioned defects or improvement requirements of the prior art, the present invention provides a backward centrifugal fan impeller to improve the aerodynamic performance of the backward centrifugal fan, effectively control the flow separation on the blade surface, and reduce the flow loss.

[0005] To achieve the above object, according to one aspect of the present invention, there is provided a backward centrifugal fan impeller, including: an impeller front disc, an impeller rear disc, and blades;

[0006] The blades include a pressure surface, a suction surface, an upper surface, a lower surface, and a trailing - edge surface; wherein, the upper surface and the lower surface coincide with the impeller front disc and the impeller rear disc respectively; the pressure surface intersects with the suction surface, and both intersect with the upper surface and the lower surface respectively;

[0007] A row of continuous, equal - sized ridge - like structures with an isosceles - triangle cross - section shape are arranged in a preset area of the pressure surface; the ridge height h, ridge spacing s, starting position sl, and length l of the ridge - like structure satisfy the following relationships with the length c of the pressure curve formed by the intersection of the cross - section of the blade and the pressure surface:

[0008]

[0009]

[0010] 0.1c ≤ sl ≤ 0.4c

[0011] 0.1c ≤ l ≤ 0.4c

[0012] 0.2c ≤ sl + l ≤ 0.5c

[0013] 0.5 ≤ s / h ≤ 4

[0014] Among them, h + and s + are dimensionless parameters, 1 ≤ h + ≤ 24, 1 ≤ s + ≤ 24; Re is the Reynolds number based on the oncoming flow of the blade, and its value is determined by the average velocity at the leading edge curve of the blade cross-section.

[0015] Preferably, the preset area is the first 10%-50% area near the leading edge curve; the leading edge curve is formed by the intersection of the pressure surface and the suction surface.

[0016] Preferably, the cross-section is perpendicular to the height direction of the blade.

[0017] Preferably, the upper surface, the lower surface and the cross-section are all airfoils.

[0018] Preferably, the upper surface, the lower surface and the cross-section are all NACA airfoils.

[0019] Preferably, the pressure surface intersects with the suction surface to form the leading edge curve;

[0020] The upper surface intersects with the pressure surface and the suction surface to form an upper curve;

[0021] The lower surface intersects with the pressure surface and the suction surface to obtain a lower curve.

[0022] Preferably, the cross-section of the blade intersects with the suction surface and the trailing edge surface to form a suction curve and a trailing edge curve.

[0023] Generally speaking, compared with the prior art by the above technical solution conceived by the present invention, the following beneficial effects can be achieved:

[0024] Aiming at the adverse effects of the separation vortex structure on the blade surface and the flow separation at the trailing edge of the blade on the aerodynamic performance of the backward centrifugal fan, the present invention proposes a backward centrifugal fan impeller with a locally ridged surface on the blade surface. By arranging a row of continuous, equal-sized, and isosceles triangle cross-section ridged structures at the local position of the blade pressure surface from the blade height of 0% to the blade height of 100%. Through the design of 4 parameters, namely the starting position sl of the ridged surface on the pressure surface, the ridge height h, the ridge spacing s, and the total length l, the flow separation on the blade surface can be effectively controlled, the flow loss can be reduced, the aerodynamic performance of the backward centrifugal fan can be improved, and thus the efficiency of the backward centrifugal fan can be effectively improved, so as to achieve the purpose of energy conservation and efficiency improvement. Description of the Drawings

[0025] Figure 1 is a three-dimensional schematic diagram of the backward centrifugal fan impeller provided by the embodiment of the present invention;

[0026] Figure 2 Front view of the impeller provided by the embodiment of the present invention;

[0027] Figure 3A 、 3B 3C, 3D are three-dimensional schematic diagrams of the blade under different angles provided by the embodiment of the present invention;

[0028] Figure 4 Schematic diagram of the distribution of control points on the lower curved surface of the blade provided by the embodiment of the present invention;

[0029] Figure 5 Schematic diagram of the distribution of the friction coefficient of the blade cross-section provided by the embodiment of the present invention;

[0030] Figure 6 Schematic diagram of the ridge surface structure parameters of the blade provided by the embodiment of the present invention;

[0031] Figure 7 Front view of the pressure curved surface of the blade provided by the embodiment of the present invention;

[0032] Figure 8 Three-dimensional schematic diagram of the blade applied in the example of the present invention;

[0033] Figure 9 Schematic diagram of the ridge surface parameters applied in the example of the present invention;

[0034] Figure 10 Comparison of the experimental characteristic curve applied in the example of the present invention with the experimental pressure characteristic curve of a backward centrifugal fan with blades of the same smooth surface;

[0035] Figure 11 Comparison of the experimental characteristic curve applied in the example of the present invention with the experimental efficiency characteristic curve of a backward centrifugal fan with blades of the same smooth surface. Detailed implementation manners

[0036] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0037] The embodiment of the present invention provides a backward centrifugal fan impeller, as Figure 1 shown, including: an impeller front disc, an impeller rear disc and blades;

[0038] The blade includes a pressure surface, a suction surface, an upper surface, a lower surface and a trailing edge surface; wherein, the upper surface and the lower surface coincide with the front disc and the rear disc of the impeller respectively; the pressure surface intersects with the suction surface, and both intersect with the upper surface and the lower surface respectively.

[0039] Preferably, the cross-section is perpendicular to the height direction of the blade.

[0040] Preferably, the upper surface, the lower surface and the cross-section are all airfoils.

[0041] Preferably, the upper surface, the lower surface and the cross-section are all NACA airfoils.

[0042] Specifically, as Figure 1-2 shown, the impeller provided by the present invention is a backward centrifugal fan impeller with a locally ridged surface on the blade surface, which is composed of a front disc of the impeller, a rear disc of the impeller and blades. As Figure 3A 、 3B 、3C, 3D shown, the blade is a three-dimensional curved surface in space, including a pressure surface, a suction surface, an upper surface, a lower surface and a trailing edge surface. The upper surface coincides with the front disc of the impeller, and the lower surface coincides with the rear disc of the impeller. The shapes of the upper surface and the lower surface are airfoils. The upper curve is obtained by the intersection of the upper surface with the pressure surface and the suction surface; the lower curve is obtained by the intersection of the lower surface with the pressure surface and the suction surface. The pressure surface and the suction surface intersect to form a leading edge curve. At each blade height cross-section, the pressure surface, the suction surface and the trailing edge surface intersect with the cross-section to form a pressure curve, a suction curve and a trailing edge curve respectively; the leading edge curve intersects with the cross-section to form a leading edge point. Denote the length of the pressure curve of the airfoil at different blade height cross-sections as c.

[0043] A row of continuous, equal-sized, ridge-like structures with an isosceles triangle cross-section shape is arranged in a preset area of the pressure surface.

[0044] Preferably, the preset area is the first 10%-50% area close to the leading edge curve side; the leading edge curve is formed by the intersection of the pressure surface and the suction surface.

[0045] Specifically, 11 control points (respectively 0%, 10%, 20%, …, 90%, 100% away from the leading edge curve) are evenly obtained on the pressure curves of each blade cross-section of the backward centrifugal fan blade, and are respectively denoted as control point 1 - control point 11.

[0046] Figure 4It shows the distribution of control points on the lower camber of the blade of the present invention. Although the lengths of the pressure curves of the sectional airfoils vary at different blade heights, the relative positions of each control point on the pressure curve are fixed on each section and can be expressed as a percentage of the length of the pressure curve. Therefore, a unified rule can be used to describe the illustration.

[0047] On the pressure surface of the blade, within the local control point interval, ridge-shaped surface structures are arranged from the 0% blade height position to the 100% blade height position. In the ridge-shaped surface, the cross-sectional shape of each ridge-shaped structure is an isosceles triangle. As Figure 6 shown, the ridge-shaped surface is composed of a row of continuous, equal-sized ridge-shaped structures with an isosceles triangle cross-sectional shape, and includes 4 parameters: starting position sl, ridge height h, ridge spacing s, and overall length l.

[0048] Existing research shows that the ridge-shaped surface can only play a role in reducing flow resistance and improving flow structure in turbulent flow. Therefore, the present invention arranges the ridge-shaped surface in the turbulent flow region of the blade surface of the backward centrifugal fan.

[0049] According to the operating conditions and flow rate range of the backward centrifugal fan, the wind speed at the leading edge curve of the blade under different operating conditions of the backward centrifugal fan can be obtained. By intercepting the blade cross-sectional shapes at different blade heights, the present invention converts the three-dimensional complex flow on the blade surface into two-dimensional flow based on the blade cross-section to find the turbulent flow region on the blade surface and determine the arrangement position of the ridge-shaped surface.

[0050] The cross-sectional form of the blade of the backward centrifugal fan of the present invention is an airfoil, and the flow pattern on the airfoil surface can be determined by the distribution of the friction drag coefficient. As Figure 5 shown, when the flow on the airfoil surface changes from laminar flow to turbulent flow, the friction drag coefficient will show a sharp increase. And when the flow on the airfoil surface further develops from turbulent flow to chaotic state, the friction drag coefficient will show obvious fluctuations. According to the change of the friction drag coefficient, the flow transition on the upper surface of the airfoil becomes turbulent near 0.038c, and further develops to the chaotic state near 0.075c. Therefore, by comprehensively considering the distribution of the friction drag coefficient of the airfoil at different cross-sectional heights of the blade, the present invention arranges the ridge-shaped surface between 0.1c and 0.5c on the pressure surface of the blade.

[0051] The ridge height h and ridge spacing s of the ridge-shaped surface at different cross-sectional heights are jointly determined by the length of the pressure curve, the air flow velocity, and the dimensionless parameters h + and s + at this cross-sectional height. Specifically, it can be expressed as:

[0052]

[0053]

[0054] The simulation and experimental results show that the dimensionless parameters h + and s + of the ridged surface respectively satisfy 1 ≤ h + ≤ 24 and 1 ≤ s + ≤ 24, which has a certain effect on reducing the air resistance in the two-dimensional flow based on the blade section. Therefore, the specific arrangement form of the ridged surface is: arrange the ridged surface in the interval from control point 2 to control point 6 from blade height 0% to blade height 100% on the suction surface. For each section, where:

[0055] The starting position of the ridged surface 0.1c ≤ sl ≤ 0.4c;

[0056] The overall length 0.1c ≤ l ≤ 0.4c;

[0057] The starting position sl of the ridged surface and the overall length l satisfy the relationship:

[0058] 0.2c ≤ sl + l ≤ 0.5c

[0059] The ridge height 5×10 -4 c ≤ h ≤ 7×10 -3 c;

[0060] The ridge pitch 5×10 -4 c ≤ s ≤ 7×10 -3 c;

[0061] The ridge height h and the ridge pitch s satisfy the relationship:

[0062] 0.5 ≤ s / h ≤ 4

[0063] At different blade heights, the absolute values of the structural parameters of the ridged surface change uniformly with the change of the blade pressure curve length at the height of this section. That is: from blade height 0% to blade height 100% position, the absolute values of each structural parameter of the ridged surface uniformly become smaller; the absolute values of each structural parameter of the ridged surface on the upper surface of the blade are the smallest. As the blade height decreases and the blade pressure curve length increases, the structural parameters of the ridged surface at each section uniformly increase and reach the maximum at the lower surface of the blade. The formed blade structure is as Figure 7 shown.

[0064] Applying the ridged surface with the above parameters to the blades of a backward centrifugal fan can effectively enhance the work capacity of the backward centrifugal fan and improve its operating efficiency.

[0065] The following gives specific implementation cases.

[0066] Example 1:

[0067] In this example, the cross-sectional shape of the blade is a NACA airfoil. The length of the pressure curve on the upper surface of the blade is 90 mm, the length of the pressure curve on the lower surface of the blade is 175 mm, and the axial height of the blade is 164 mm. The formed blade shape is as shown in Figure 8 shown. In the interval between control point 2 and control point 3 on the pressure surface of the blade, that is, within the position from 10% of the distance from the leading edge curve of the blade to 20% of the distance from the leading edge curve of the blade, a ridged surface is arranged. As shown in Figure 9 shown, the starting position sl of the ridged surface is 0.1c, the overall length l is 0.1c, and both the ridge height h and the ridge spacing s are 2.86×10 -3 c. Among them, the ridge height h and the ridge spacing s of the ridged surface on the upper surface of the blade are both 0.26 mm, and the ridge height h and the ridge spacing s of the ridged surface on the lower surface of the blade are both 0.5 mm. When the blade cross-section moves from 0% to 100% of the blade height, the ridge height h and the ridge spacing s of the ridged surface uniformly decrease from 0.5 mm to 0.26 mm.

[0068] Example 2:

[0069] In this example, the cross-sectional shape of the blade is a NACA airfoil. The length of the pressure curve on the upper surface of the blade is 90 mm, the length of the pressure curve on the lower surface of the blade is 175 mm, and the axial height of the blade is 164 mm. In a local position in the interval between control point 2 and control point 4 on the pressure surface of the blade, that is, within the position from 10% of the distance from the leading edge curve of the blade to 35% of the distance from the leading edge curve of the blade, a ridged surface is arranged. The starting position sl of the ridged surface is 0.1c, the overall length l is 0.25c, and both the ridge height h and the ridge spacing s are 1.14×10 -3 c. Among them, the ridge height h and the ridge spacing s of the ridged surface on the upper surface of the blade are both 0.1 mm, and the ridge height h and the ridge spacing s of the ridged surface on the lower surface of the blade are both 0.2 mm. When the blade cross-section moves from 0% to 100% of the blade height, the ridge height h and the ridge spacing s of the ridged surface uniformly decrease from 0.2 mm to 0.1 mm.

[0070] Example 3:

[0071] In this example, the cross-sectional shape of the blade is a NACA airfoil. The length of the pressure curve on the upper surface of the blade is 90 mm, the length of the pressure curve on the lower surface of the blade is 175 mm, and the axial height of the blade is 164 mm. In a local position in the interval between control point 3 and control point 6 on the pressure surface of the blade, that is, within the position from 20% of the distance from the leading edge curve of the blade to 50% of the distance from the leading edge curve of the blade, a ridged surface is arranged. The starting position sl of the ridged surface is 0.2c, the overall length l is 0.3c, and both the ridge height h and the ridge spacing s are 1.43×10 - 3c. Among them, the ridge height h and ridge spacing s of the ridged surface on the upper curved surface of the blade are both 0.13 mm, and the ridge height h and ridge spacing s of the ridged surface on the lower curved surface of the blade are both 0.25 mm. When the blade cross-section moves from 0% to 100% of the blade height, the ridge height h and ridge spacing s of the ridged surface uniformly decrease from 0.25 mm to 0.13 mm.

[0072] Figure 10 and Figure 11 The figure shows the measured performance curves of a fan with blades having a banded surface structure and a fan with the same smooth blades. It can be seen that the total fan pressure ratio of the fan of the present invention is greater than that of the fan with the same smooth blades under the same air volume, and the efficiency is also significantly improved, especially the performance of the fan under small flow conditions is improved.

[0073] Those skilled in the art can easily understand that the above are only the preferred embodiments of the present invention, and are not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principle of the present invention should be included within the protection scope of the present invention.

Claims

1. A backward centrifugal fan impeller, characterized in that, Comprising: The front disc of the impeller, the rear disc of the impeller and the blades; The blades include a pressure surface, a suction surface, an upper surface, a lower surface and a trailing edge surface; wherein, the upper surface and the lower surface coincide with the front disc and the rear disc of the impeller respectively; the pressure surface intersects with the suction surface, and both intersect with the upper surface and the lower surface respectively; A row of continuous, equal-sized, ridge-like structures with an isosceles triangle cross-section is provided in a preset area of the pressure surface; the ridge height h, ridge spacing s, starting position sl, length l of the ridge-like structure and the length c of the pressure curve formed by the intersection of the cross-section of the blade and the pressure surface satisfy the following relational expressions: 0.1c ≤ sl ≤ 0.4c 0.1c ≤ l ≤ 0.4c 0.2c ≤ sl + l ≤ 0.5c 0.5 ≤ s / h ≤ 4 where h + and s + are dimensionless parameters, 1 ≤ h + ≤ 24, 1 ≤ s + ≤ 24; Re is the Reynolds number based on the oncoming flow of the blade; the preset region is the first 10%-50% region near the leading edge curve side; the cross-section is perpendicular to the height direction of the blade.

2. The impeller according to claim 1, wherein, The leading edge curve is formed by the intersection of the pressure surface and the suction surface.

3. The impeller according to any one of claims 1-2, characterized in that, The upper surface, the lower surface and the cross-section are all airfoil-shaped.

4. The impeller according to claim 3, characterized in that, The upper surface, the lower surface and the cross-section are all NACA airfoils.

5. The impeller according to claim 1, characterized in that, The upper surface intersects with the pressure surface and the suction surface to form an upper curve; The lower surface intersects with the pressure surface and the suction surface to obtain a lower curve.

6. The impeller according to claim 1, characterized in that, The cross-section of the blade intersects with the suction surface and the trailing edge surface to form a suction curve and a trailing edge curve.

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