CN105736426A - Axial flow fan comprising blade pressure surfaces with winglets and blade tops with blowing structures - Google Patents

Abstract

The invention discloses an axial flow fan comprising blade pressure surfaces with winglets and blade tops with blowing structures. The axial flow fan comprises a mesh enclosure, an impeller, guide blades, an inner cylinder, an outer cylinder and a motor, wherein the mesh enclosure formed by weaving of iron wires is fixed on the outer cylinder, and the impeller comprises a hub and blades. The blade top blowing structures are added on the blade tops, winglet structures are added at the tails of blade force suction surfaces, and the inner cylinder at the guide-blade-grade outer end is provided with rectangular holes, so that blade top flowing conditions can be improved, blade top leakage and vortex loss are reduced, noise generated in gaps is reduced, radially moving secondary flow is controlled, boundary layer thickness of blade surfaces is controlled, vortex noise caused by blade wakes is inhibited, vortex guide blade-grade vortex shedding frequency is decreased and outlet noise is reduced. Based on improvements on different positions of an existing axial flow fan, the axial flow fan is higher in efficiency, lower in noise and more energy saving and environment friendly.

Description

An axial flow fan with winglets on the pressure surface of the blade and an air blowing structure on the top of the blade

technical field

The invention belongs to the technical field of fans, and in particular relates to an axial flow fan with winglets on the pressure surface of the blade and an air blowing structure on the top of the blade.

Background technique

The axial flow fan is a machine that relies on the input mechanical energy to increase the gas pressure and discharge the gas. It is widely used in ventilation, dust extraction and cooling of factories, mines, tunnels, cooling towers, vehicles, ships and buildings; ventilation and induction of boilers and industrial furnaces; cooling and ventilation in air conditioning equipment and household appliances ; Grain drying and selection; wind tunnel wind source and hovercraft inflation propulsion, etc., have very important applications in various industries of the national economy. According to statistics, the power consumption of fans accounts for about 10% of the country's power generation, and the average power consumption of main coal mines accounts for about 16% of mine power consumption; the power consumption of fans in metal mines accounts for 30% of mining power; Electricity consumption accounts for 20% of its production electricity consumption; the electricity consumption of wind turbines in the coal industry accounts for 17% of the coal industry's electricity consumption. It can be seen that the status and role of fan energy saving in various sectors of the national economy is of great importance. Due to the high specific speed of the axial flow fan, it has the characteristics of large flow and low total pressure, and occupies an irreplaceable position in these industries.

Therefore, it is very important to design and optimize the axial fan with high efficiency, good performance, low noise and energy saving. However, the flow in the axial flow fan is very complicated, mainly reflected in: 1) the three-dimensionality of the flow; 2) the viscosity of the fluid; 3) the unsteadiness of the flow. It is difficult to consider the above three points in the traditional fan design. Even if CFD is used as an auxiliary design in the modern design method, the influence of the above three factors on the performance of the fan cannot be completely controlled. The most critical factor is the viscosity of the fluid. Viscosity does not only affect the blade wake vortices formed at the blade exit edge to satisfy the Kutta-Zhukovsky condition. Due to the viscosity, there will be a viscous boundary layer on the surface of the blade and the surface of the ring wall channel, and there will be a strong interaction between them and the main flow, resulting in the so-called "secondary flow" phenomenon. The secondary flow is the main source of the loss increase and efficiency decrease of the axial flow fan. At the same time, due to the influence of viscosity, there is aerodynamic noise in the axial flow fan. The aerodynamic noise of the axial flow fan is mainly composed of two parts: rotating noise and eddy current noise. If the fan outlet is directly discharged into the atmosphere, there will be exhaust noise.

To sum up, in order to design and optimize an axial flow fan with high efficiency, good performance, low noise and energy saving, it is necessary to control and reduce the secondary flow, control and reduce the thickness of the boundary layer, prevent eddy shedding, or is to control the formation of vortices.

Contents of the invention

The purpose of the present invention is to solve the shortcomings of the prior art that the boundary layer thickness, secondary flow and eddy current noise in the axial flow fan cannot be well controlled through the traditional design, and to provide a blade pressure surface with winglets and blade tip with air blowing The structure of the axial flow fan, the air blowing structure is added to the tip of the blade, the winglet structure is added to the tail of the suction surface of the blade, and the rectangular hole is processed on the inner cylinder at the outlet end of the guide vane stage, which can improve the flow of the tip of the blade; Top leakage loss, eddy current loss; reduce the noise generated by the gap; control the secondary flow of radial motion; control the thickness of the boundary layer on the blade surface; suppress the eddy current noise caused by the blade wake; Exit noise. Through the improvement of different positions of the axial flow fan, the efficiency of this type of axial flow fan is higher, the noise is lower, and it is more energy-saving and environmentally friendly.

The technical solution adopted in the present invention is: a kind of axial flow fan with winglets on the pressure surface of the blade and air blowing structure on the blade top, including a net cover, an impeller, guide vanes, an inner cylinder, an outer cylinder, and a motor; the net cover is It is braided with iron wire and fixed on the outer cylinder; the feature is that: the impeller includes a hub and blades, there is a winglet structure at the tail of the suction surface of the blade, and a blowing hole structure at the top of the blade; the blade is an isolated airfoil through isocircumference For the airfoil blade designed by the method, the torsion speed decreases with the increase of the variable diameter, the pressure is constant along the radial direction, the blade thickness distribution is the same as the NACA four-digit airfoil thickness distribution, and the relative thickness of the airfoil is 10%-15 %, the number of blades is 5-9, and the blade tip clearance is 1%-2% of the blade height; the blade suction surface winglets are evenly distributed on the blade, and the positions relative to the blade height are respectively 20% and 40% , 60% and 80% of the four positions, the tail end of the winglet is perpendicular to the blade surface, the leading edge is 30-60° from the blade surface, the middle passes through the spline curve, the chord length of each section of the winglet is equal, accounting for the average radius About 1/4-1/3 of the chord length, the thickness of the winglet is 4-8mm, the height of the winglet is 30%-60% of the chord length, and the trailing edge of the winglet is 5%-10% from the trailing edge of the blade The average chord length of the blade; the blowing structure of the blade top is to open holes from the pressure surface of the blade top, so that the high-pressure gas can flow through the blade top gap, and the blowing holes are evenly distributed on the middle arc of the blade top airfoil section. The diameter of the blade is 5-10% of the chord length, the distance between the small holes is 10%-20% of the chord length, and the small holes on the pressure surface are mainly evenly distributed in the area of 85%-90% of the blade height; the guide The blades are fixed on the inner cylinder and the outer cylinder, the guide vane blades are circular arc plate blades, there is no twist along the radial direction, the number of guide vanes is 7-17, and the axial gap between the guide vane impeller and the impeller is 5- 10mm, the thickness of the guide vane blades is 2-4mm; the inner cylinder is at the end of the air section, with a rectangular hole; the rectangular hole structure is evenly distributed on the entire circumference of the inner cylinder, and the length of the rectangular hole is the circumference of the inner cylinder 3%-5% of the length, the aspect ratio of the rectangular sawtooth is 2-4, and the number of rectangular holes is between 10-30; the motor is a three-phase asynchronous motor, and the motor is fixed on the web of the inner cylinder. The impeller is connected to the motor shaft through a shaft sleeve.

Beneficial effects of the present invention:

The present invention can blow the high-energy gas on the pressure surface into the boundary layer region of the blade tip gap by adding a blade top blowing structure to the top of the impeller blade, so that the thickness of the boundary layer can be well controlled, and the gas backflow and blade tip vortex can be prevented. Formation and shedding can effectively improve the leakage flow at the tip of the blade, reduce flow loss, and improve the problem of low-energy fluid accumulation and blockage of the flow channel caused by leakage flow at the tip of the blade, thereby reducing noise. At the same time, the axial flow fan evenly adds four small wings on the tail of the suction surface of the impeller blades. The small wings can guide the airflow to move along the chord direction, and can well control the flow caused by the imbalance of fluid pressure and centrifugal force. Radial flow can also control the size of a pair of channel vortexes in the blade flow channel and the creeping flow of the boundary layer on the blade surface, which also controls the secondary flow of radial motion, reduces the unevenness of the velocity, and reduces the The jet wake loss controls the thickness of the boundary layer, so that the separation point of the boundary layer on the suction surface of the blade moves backward, reduces energy loss, controls vortex shedding, and suppresses the vortex noise caused by the blade wake. The rear part of the inner cylinder of the guide vane stage is also designed in the shape of a rectangular hole, which can effectively control the thickness of the boundary layer and the shedding frequency of the vortex. The viscous airflow at the root of the fan blade is effectively separated and guided, resulting in an ideal airflow, reducing the fan wake loss and eddy current noise. Through the improvement of different positions of the axial flow fan, the efficiency of this type of axial flow fan is higher, the noise is lower, and it is more energy-saving and environmentally friendly.

Description of drawings

Fig. 1 is a three-dimensional view of the axial flow fan of the present invention.

Fig. 2 is a structure diagram of the impeller of the present invention.

Fig. 3 is a schematic diagram of the pressure surface of the impeller blade of the present invention.

Fig. 4 is a schematic diagram of the suction surface of the impeller blade of the present invention.

Figure 5 is a sectional view of the winglet of the present invention.

Fig. 6 is a structure diagram of the guide vane stage impeller of the present invention.

Fig. 7 is a schematic diagram of the section design of the blade airfoil of the present invention.

detailed description

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

As shown in Figure 1, the axial flow fan consists of 6 parts, including 1, impeller 2, inner cylinder 3, motor 4, guide vane 5, outer cylinder 6, net cover; outer cylinder 5, guide vane 4 and inner The barrel 2 is fixed together by welding, and the motor 3 is fixed on the web of the inner barrel 2. The working parameters of the motor 3 are 720r/min, and the power is 4KW; the impeller 1 is fixed on the shaft of the motor 3 through a bushing, and the impeller 1 The gap between the wheel hub and the inner cylinder 3 is 10mm; the net cover 6 is installed on the outer cylinder 5, which has the functions of rectifying and preventing foreign matter from entering.

As shown in Figures 1, 2, 3, and 5, the impeller 1 is driven by the motor 3 to do work for the gas, increasing the dynamic pressure and static pressure of the gas. The blades 1-1 on the impeller 1 are designed by the isocircumference isolated airfoil method For the airfoil blade, the twisting speed decreases with the increase of the variable diameter, the pressure is constant along the radial direction, the relative thickness of the blade is 10%, the number of blades is 6, and the blade tip clearance is 2% of the blade height. The specific method of impeller blade design is as follows:

The simple radial balance equation of the fluid inside the axial flow fan:

Among them, P represents the pressure on the fluid microcluster, Cu is the speed of the fluid microcluster rotating around the axis, and r is the radius of rotation of the fluid microcluster. The formula indicates that assuming that there is no radial flow inside the axial flow fan, the pressure P received by the fluid cluster at any position in the radial direction is balanced with the centrifugal force generated by the rotational movement of the fluid cluster.

In formulas (2)-(3), Pt is the total pressure of the gas, ρ is the density of the gas, C is the total velocity of the gas, Cu, Ca, and Cr are the circumferential velocity, circumferential velocity, and radial velocity of the gas, respectively. Speed, but with the above assumptions, it can be seen that Cr=0, the total pressure of the gas is equal to the dynamic pressure plus the static pressure.

From the formulas (2)-(3), the differential relations of Pt, P, Cu, and Ca can be obtained as the formula (4). Substituting the formula (4) back into the formula (1) can get another more general and simple The radial balance equation (5).

The equal circulation design method assumes that the total pressure Pt is constant along the radial direction, and the axial velocity Ca is also constant along the radial direction. Substituting it into formula (5), we can know:

It can be seen from the above formula that the equal circulation design method assumes that Cr=0 inside the fan, and the total pressure Pt is constant along the radial direction, the axial velocity Ca is also constant along the radial direction, and the circumferential velocity decreases with the increase of the radius. Small.

Equation (7) is derived from the cascade theory, a , blade twist speed , cascade lift coefficient , and the average relative velocity in the cascade The relationship between.

The isolated airfoil design method assumes that the lift coefficient of the cascade No interference from the blades between the cascades, which is the lift coefficient of the cascades lift coefficient of an isolated airfoil same.

The design method of isocircumference isolated airfoil is as mentioned above, through the above method, the chord length and installation angle of each section of the blade can be calculated, and the blade inlet airflow machine and the blade outlet airflow machine can be calculated from the above parameters plus some experience The shape of the mid-arc can be calculated by the formula, and the relative thickness of the airfoil is taken as 10%. Then, the NACA four-digit airfoil thickness distribution is superimposed on the mid-arc of each section to obtain each airfoil section. NACA airfoil is an airfoil series published by the National Advisory Committee for Aeronautics. The four-digit airfoil is its commonly used airfoil series. The design method is as follows:

The NACA four-digit airfoil thickness distribution function equation is:

Where: t represents the relative thickness, , b is the chord length, the airfoil black line is the X axis, and the coordinate origin is placed on the leading edge point of the airfoil blade, .

The method is as follows, first, take the relative thickness as 10%, and obtain N discrete points of the thickness distribution function of different sections of the blade , and then, at the same time, the arcs in each section are equally divided to obtain N discrete points , and calculate the slope of the normal line at each point by difference method, and then calculate the inclination angle , so that the coordinate points of the upper and lower surfaces of the transformed airfoil can be obtained Then use the smooth connection of the curve to get the required airfoil of the section, as shown in Figure 7, a1 is the thickness distribution function, a4 is the blade mid-arc, a2 and a3 are the normal and tangent of any point on the mid-arc .

As shown in Figures 2 and 3, the trailing edge of the suction surface of the blade 1-1 on the impeller 1 is evenly distributed with four small wings 1-2, B1, B2, B3, B4, and Figure 4 shows the airfoil blade 1-2 at B2. 1 and winglet 1-2, the positions relative to the leaf height are 20%, 40%, 60% and 80% respectively, the distance d4 between winglet 1-2 is 56mm, and winglet 1 The tail end of -2 is perpendicular to the surface of blade 1-1, and the angle between the leading edge and the normal direction of the surface of blade 1-1 is 30°, the middle passes through the spline curve, the chord lengths of the winglets 1-2 in each section are equal, accounting for about 1/3 of the chord length d6 of the average radius of the blade 1-1, and the thickness d3 of the winglet 1-1 is 5mm. The height d5 of the winglet 1-2 is 40% of its chord length, and the distance d7 from the trailing edge of the winglet 1-2 to the trailing edge of the blade is 5% of the average chord length of the blade 1-1.

As shown in Figures 2, 3, and 5, the top of the blade 1-1 on the impeller 1 has a top blowing structure 1-3, and the blade top blowing structure 1-3 is to open holes from the pressure surface of the blade top to make the high pressure The gas can flow through the tip gap, and the blowing holes are evenly distributed on the middle arc A of the blade top airfoil section. The diameter d2 of the hole is 5% of the chord length, and the size is 8mm. The distance between the small holes d1 is the chord length 15% of the leaf height, the size is 30mm, and the small holes on the pressure surface are mainly evenly distributed in the area of 85%-90% of the leaf height.

As shown in Figures 1 and 6, the guide vanes 4 are fixed on the inner cylinder 2 and the outer cylinder 5. The guide vanes 4 are arc plate-shaped blades, and the number of guide vanes without twisting along the radial direction is 9. The guide vanes 4 impeller and The size of the axial clearance of the impeller 1 is 10mm, and the thickness of the guide vane 4 is 4mm; the inner cylinder 2 has a rectangular hole 2-1 at the tail of the gas outlet; the rectangular hole structure 2-1 is evenly distributed in the inner cylinder On the entire circumference, the length of the rectangular hole is 3% of the circumference of the inner cylinder, the size is 60mm, the aspect ratio of the rectangular sawtooth is 2, and the number of rectangular holes is 14.

In the present invention, at first, the top of the blade 1-1 of the axial flow fan is provided with a blade top air blowing structure 1-2, which can well control the thickness of the boundary layer and prevent the formation and shedding of gas backflow and blade tip vortex, thereby It can effectively improve the leakage flow at the tip of the blade, reduce the flow loss, and improve the low-energy fluid accumulation and blockage of the flow channel caused by the leakage flow at the tip of the blade, thereby reducing noise. At the same time, four small wings 1-2 are evenly added to the tail of the suction surface of the impeller 1 blade 1-1 in the axial flow fan. The reason is that the boundary layer of the suction surface is much thicker than the boundary layer of the pressure surface, resulting in The flow is quite complicated, and as the fluid moves from the leading edge to the trailing edge, the reverse pressure gradient on the suction surface increases continuously, resulting in the continuous thickening of the boundary layer on the suction surface. Performance is critical. The function of the winglet 1-2 is to guide the airflow along the chord direction, which can well control the radial flow caused by the imbalance of fluid pressure and centrifugal force, and at the same time control the flow of the blade 1-1. The size of a pair of channel vortexes in the channel, and the surface boundary layer of the blade 1-1 can control the secondary flow of radial motion, reduce the unevenness of velocity, reduce the loss of jet wake, and control the boundary layer Thickness, so that the separation point of the boundary layer of the suction surface of the blade moves backward, reduces energy loss, controls vortex shedding, and suppresses the eddy current noise caused by the wake of the blade 1-1. Finally, the rear part of the inner tube 2 of the guide vane 4 stage is also designed as a rectangular hole shape 2-1. After optimization design, it is found that this structure can effectively reduce the wake noise of the guide vane 4, because the guide vane 4 is behind the moving vane Due to the superposition of the wake of the blade 1-1 and the boundary layer of the guide vane 4, the flow in the guide vane 4 stage channel is very complicated, and the airflow boundary layer near the hub and the inner cylinder 2 will further increase, that is, in the guide vane 4 There is a large vortex area in the outlet airflow near the inner cylinder 2 side of the stage. Therefore, the rectangular hole 2-1 is processed at the outlet of the inner cylinder 2, which can effectively control the thickness of the boundary layer and the shedding frequency of the vortex. The viscous airflow of the root is effectively separated and guided, resulting in an ideal airflow, which reduces the fan wake loss and eddy current noise. Through the improvement of different positions of the axial flow fan, the efficiency of this type of axial flow fan is higher, the noise is lower, and it is more energy-saving and environmentally friendly.

Claims (1)

1. An axial flow fan with winglets on the blade pressure surface and a blowing structure on the blade top, comprising a net cover, an impeller, guide vanes, an inner cylinder, an outer cylinder, and a motor; the net cover is woven with iron wire, It is fixed on the outer cylinder; it is characterized in that: the impeller includes a hub and blades, there is a winglet structure at the tail of the suction surface of the blade, and there is a blowing hole structure at the top of the blade; the blade is an airfoil blade designed by the isocyclic airfoil method , the torsion speed decreases with the increase of the variable diameter, the pressure is constant along the radial direction, the blade thickness distribution is the same as the NACA four-digit airfoil thickness distribution, the relative thickness of the airfoil is 10%-15%, and the number of blades is 5 -9 pieces, the blade tip clearance is 1%-2% of the blade height; the suction surface winglets of the blade are evenly distributed on the blade, and the positions relative to the blade height are respectively 20%, 40%, 60% and 80% Four positions, the tail end of the winglet is perpendicular to the blade surface, the leading edge is 30-60° to the blade surface, the middle passes through the spline curve, the chord length of each section of the winglet is equal, accounting for 1/ of the average radius out of the chord length About 4-1/3, the thickness of the winglet is 4-8mm, the height of the winglet is 30%-60% of its chord length, and the trailing edge of the winglet is 5%-10% of the average chord length of the blade from the trailing edge of the blade; The air blowing structure on the blade top is to open holes from the pressure surface of the blade top so that the high-pressure gas can flow through the gap of the blade top. 5-10%, the distance between the small holes is 10%-20% of the chord length, and the small holes on the pressure surface are mainly evenly distributed in the area of 85%-90% of the blade height; the guide vanes are fixed on the inner cylinder and On the outer cylinder, the guide vane blades are circular arc plate blades, without twisting along the radial direction, the number of guide vanes is 7-17, the axial gap between the guide vane impeller and the impeller is 5-10mm, the guide vane blade The thickness is 2-4mm; the inner cylinder has a rectangular hole at the end of the gas section; the rectangular hole structure is evenly distributed on the entire circumference of the inner cylinder, and the length of the rectangular hole is 3%-5% of the circumference of the inner cylinder %, the aspect ratio of the rectangular sawtooth is 2-4, and the number of rectangular holes is between 10-30; the motor is a three-phase asynchronous motor, the motor is fixed on the web of the inner cylinder, and the impeller is connected to the motor through the bushing Axes are connected.