RU2697001C1 - Connecting element for connection of blade to hub of industrial axial fan and blade device containing said connecting element - Google Patents

Abstract

FIELD: machine building.

SUBSTANCE: present invention relates to connecting element for connection of blade or airfoil to industrial axial fan hub, and also relates to a vane device comprising said connecting element, and to an industrial axial fan comprising such a vane device. According to this invention, connecting element (1) for connection of blade (10) to hub (20) of industrial axial fan is made in form of a single L-shaped element comprising first part (1a), having a substantially rectilinear configuration, and second part (1b), having a substantially rectilinear configuration, wherein first part (1a) and second part (1b) are connected by binding part (1c), having a radius of curvature, and lie in substantially perpendicular planes.

EFFECT: connecting element according to this invention provides a number of advantages relative to the prior art, one of which is that this element has a very simple shape and is very easy to manufacture, which makes it preferable from an economic point of view.

9 cl, 16 dwg

Description

FIELD OF TECHNOLOGY

This invention relates to a connecting element for attaching a blade or aerodynamic profile to the hub of an industrial axial fan, and also relates to a blade device containing the specified connecting element, and to an industrial axial fan containing such a blade device.

Axial fans for industrial use, as a rule, contain a hub and aerodynamic profiles.

The blade usually has two parts, namely the aerodynamic profile, which performs the function of moving air, and the connecting element or mount serving (serving) to ensure communication of the aerodynamic profile with the hub.

The subject of this invention is a connecting element for attaching an aerodynamic profile to a hub and a blade device comprising a blade, a hub and a connecting element according to this invention.

Another subject of this invention is an industrial axial fan comprising such a blade device.

BACKGROUND

In the field of axial fans, various technical solutions are known for connecting an aerodynamic profile to a fan hub.

For a brief discussion of the prior art, it is important to recall the static and dynamic forces acting on the blades of an industrial axial fan during its operation, in particular, regarding the influence of centrifugal forces.

Next, a description will be given of various solutions that are essentially known in the art and the purpose of which is to reduce the stationary and, ultimately, unsteady loads on the element connecting the aerodynamic profile with the hub of the axial fan.

The forces acting on the axial fan blades during its operation can be divided into stationary forces A) and unsteady forces B).

A) To the stationary forces noted in the attached FIG. 4a include the following:

- aerodynamic or lifting forces (L),

- force (D) of drag,

- centrifugal force (C) and

- weight (W) of the blade.

If the axis of the blade is inclined at an angle a to the suction side of the air relative to the ideal plane of rotation, the centrifugal force creates a bending moment in the axial plane, the direction of which is opposite to the direction of the moment created by the lifting force and weight, as shown in FIG. 4b.

Therefore, the resulting bending moment in stationary mode transmitted to the hub is reduced according to the following formula:

Where:

Oxy - a coordinate system in which the origin is in the fixed part of the supporting element for the blade, while the x axis passes in the radial direction, and the y axis is parallel to the rotation axis,

M - the resulting bending moment in stationary mode,

X _sa - the radial position of the center of aerodynamic force,

X _cg is the radial position of the center of gravity,

Y _cg is the vertical position of the center of gravity.

C) Non-stationary forces are forces formed as a result of:

взаимодействия между аэродинамическим полем, созданным вокруг лопасти, и конструкцией, поддерживающей вентилятор или корпус, в котором он находится, причем данные силы пропорциональны аэродинамическим силам в стационарном режиме,

the interaction between the aerodynamic field created around the blade and the structure supporting the fan or the housing in which it is located, and these forces are proportional to the aerodynamic forces in stationary mode,

работы в критических условиях, таких как резонанс лопасти или резонанс конструкции, при этом амплитуда данных сил зависит от пассивных и активных демпфирующих свойств лопасти,

work in critical conditions, such as blade resonance or structure resonance, while the amplitude of these forces depends on the passive and active damping properties of the blade,

взаимодействия с окружающей средой, например с потоком ветра или с другим оборудованием,

environmental interactions, such as wind flow or other equipment,

вихревых следов, созданных профилем лопасти, так что данные силы являются самоиндуцированными.

vortex traces created by the profile of the blade, so that these forces are self-induced.

The amplitude of the indicated forces is repeated in a cyclical manner, and for this reason they are also often called periodic forces.

The indicated forces give rise to the phenomenon of fatigue and therefore pose an increased danger in terms of the resource of the blade compared to stationary forces. In addition, these forces cause vibration to the structure supporting the fan.

Currently, to reduce the above forces, various solutions are applied regarding the attachment of the blade and providing improvement of the finished product design with a reduction in the loads acting on it and a decrease in its cost.

In addition, the purpose of this invention is the creation of a new mount for the blades of industrial axial fans, capable of reducing the influence of both stationary and non-stationary loads, and reduce the cost of this mount.

In the attached FIG. Figures 2a, 2b, 2c, 2d and 2e show the connecting elements, which are essentially known in the field of industrial axial fans and are used on the market to reduce stationary and / or unsteady loads created by forces acting on the blades during operation, and a brief description of these elements.

The first connecting element comprises a rigid connection as shown in FIG. 2a and 2b: in this case, a rigid connecting part or element is used whose stiffness (of which) in the radial direction exceeds the stiffness of the profile.

The support of the connecting element on the hub is made so that the axis of the aerodynamic profile is inclined in the vertical plane and has a fixed angle a relative to the ideal plane of rotation. This configuration, in which the centrifugal force is directed opposite to the lifting force, provides the possibility of reducing stationary loads according to the above formula (1), but does not affect unsteady loads.

Another connector known in the art is the swivel shown in FIG. 2c: a hinge having a horizontal axis acts as a connection between the profile and the hub. In this case, the profile can freely rotate perpendicular to the plane of rotation of the fan, so when the fan is in operating mode, it tends to hold a position in which the traction force is balanced by centrifugal force, minimizing stationary loads.

Another connecting element known in the art is a flexible connection containing only one element, as shown in FIG. 2d, while one element connecting the profile to the hub has such high flexibility that it can bend in the vertical plane without being subjected to overvoltage, which ensures a decrease in both stationary and non-stationary loads.

As in the previous example, the next connecting element is a flexible connection containing two superimposed elements, as shown in FIG. 2e, while the two elements connecting the profile to the hub, interacting with each other, bend in a controlled manner in a vertical plane, without experiencing overvoltage. Stationary and non-stationary loads are reduced.

Another connecting device known in the art comprises the connecting element shown in FIG. 2f The specified connecting element has variable stiffness, corresponding elongation and additional weight near the top of the blade, which causes the blade to vibrate according to the second mode of vibration, thereby reducing both stationary and non-stationary forces.

It should be emphasized that during operation, forces acting in a stationary mode tend to deform the blade so that it acquires a shape corresponding to the first mode of oscillation of the cantilever beam.

At the same time, the centrifugal force tends to counteract the deformation of the blade. Thus, the longer the connecting element of the blade, the greater the displacement of the center of gravity and the greater the decrease in the resulting bending moment in a stationary state.

The effect of centrifugal force in a linear manner depends on the displacement of the center of gravity, which also linearly depends on the length of the blade attachment.

The dynamic response of the blade to variable loads depends on its modal characteristics.

The fan blade can be schematically represented as a cantilever beam (mount), mounted on one end and containing a suspended rigid mass (profile) on the free end. Regardless of the discussion, if we assume that the mount has an unchanged cross section, the natural frequencies of the blade are inversely proportional to the square of the length of the mount according to the following expression:

Where:

ω _i -i-th natural frequency,

L is the length of the mount,

E is Young's modulus,

J is the moment of inertia during bending,

m = reduced mass per unit length.

Taking into account the same radial length of the fastening, the invention provides an increase in length due to the curvature of the profile compared to known devices, which means that for an identical fan blade, the natural frequencies of the blade will be significantly lower.

If we consider the axial fan blade as a system with an interdependence of mass, attenuation, and stiffness, and assume that it is similar to a system with several degrees of freedom (MDoF system), then when dynamic oscillations are excited in the system under the action of forces that are a function of time f (t) , the equation of motion is as follows:

Where:

M is the mass matrix of the blade,

C is the attenuation coefficient matrix,

K is the stiffness matrix of the blade,

x (t) is the reaction vector of the system,

f (t) is the vector of the force function.

The system of coupled differential equations (3) can be transformed from a geometric coordinate system to a system of N unrelated differential equations in modal coordinates using the well-known modal analysis method:

Where:

m _i is the mass corresponding to the i-th mode,

c _i - attenuation corresponding to the i-th mode,

k _i - stiffness corresponding to the i-th mode,

p _i (t) is the load corresponding to the iu mode,

q _i (t) is the coordinate corresponding to the i-th mode,

i = 1, 2, ... N.

Equation (4) can be rewritten in terms of dynamic variables: ω _i , which is the frequency of the system, and δ _i , which is the mode attenuation coefficient, while these variables are determined as follows:

The Rayleigh formula for the mode attenuation coefficient is a good approximation of the nonlinear attenuation typical of an assembly of several elements:

Substituting equation (7) into equation (6), the mode attenuation can be rewritten in terms of the natural frequency:

where a ₀ and a ₁ are constant coefficients depending on the mass and stiffness parameters of the system.

Function (8) is shown in FIG. ten.

The reaction of the blade in the system of geometric coordinates can be obtained as a result of a superposition of the shifts corresponding to each individual mode.

Obviously, a decrease in the contribution made by the shift for each individual mode leads to a decrease in the overall reaction of the blade and, therefore, to a decrease in the effect of the load on the blade.

The contribution of an individual mode strictly depends on two main modal parameters indicated above: frequency and mode attenuation. As shown in FIG. 10, a decrease in the frequency of the blade results in more attenuation, which means a decrease in the response of the blade and, as indicated above, the loads on the blade.

Thus, in the art there is a need to create a connecting element, which at the same radial size and under the influence of the same loads provides the possibility of obtaining a greater shear and, therefore, a greater counteracting effect compared with the known blade units.

SUMMARY OF THE INVENTION

The aim of this invention, respectively, is to create a connecting element for industrial axial fans, which can provide a forced change in the modal parameters of the blade, namely the frequencies and types of deformation, when exposed to unsteady loads. Within the framework of this goal, the object of the present invention is to provide a connecting element for attaching an aerodynamic profile to the hub of an axial industrial fan and able to minimize the effect of unsteady loads on the blade device.

More specifically, an object of the present invention is also to provide a connecting element that can provide a reduction in the reaction of the blade to variable loads in general and to the resonance mode in particular.

Another objective of the present invention is to provide a connecting element that makes it possible to minimize the eigenfrequencies of the device with respect to known devices, while for the first modes, the corresponding attenuation is higher compared to the known solutions, and for higher modes, the corresponding attenuation is lower.

To achieve this goal, as well as these and other tasks that will become clearer from the following detailed description of a preferred embodiment, which is solely illustrative and not limiting of the invention, the invention proposes a connecting element having a rectangular cross section and an L-shaped longitudinal section, moreover, the short side of the letter “L” is connected to the hub, and its long side to the profile, with a typical ratio between the two sides indicated yaet 0.1.

The natural frequencies of the blade device containing the connecting element according to this invention are lower than the natural frequencies of known devices, while for the first modes, the corresponding attenuation is higher than in known solutions, and for higher modes, the corresponding attenuation is lower. Due to the distribution of the exciting forces, only the first three modes make a significant contribution to the reaction of the blade, thus, the reaction of the blade to cyclic loads is greatly weakened. In addition, exciting cyclic loads have a spatial (radial) distribution, the amplitude of which is a function of time according to the following formula:

Where:

g (x) is a function of only the radial position,

h (t) is a periodic function.

This means that after half the period the power function has exactly the same amplitude, but with the opposite sign. The deformed shape of the device has a different symmetry, since the fastening is not symmetrical, as is best seen in FIG. 3a and 3b. The first main consequence of this particular type of deformation is the fact that the reaction of the blade is more weakened. The second consequence is that the natural frequency of the blade is not constant and, therefore, there is virtually no resonance state.

Thus, in comparison with the known blade device, which due to the intensification of the reaction, as a rule, cannot work in a wide range of speeds close to the critical, in the blade device according to this invention, which contains a connecting element according to this invention and is also part of this invention , the specified range of speeds is significantly reduced, and in many cases there is no restriction on the range of operating speeds.

Compared with the prior art, the connecting element according to this invention makes it possible to reduce the reaction of the blade device to variable loads in general and to the resonant mode in particular.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional features and advantages of the present invention will become more apparent from the following detailed description of a preferred embodiment, which is purely illustrative and not limiting, and is shown in the accompanying drawings, in which:

FIG. 1a, 1b, 2a, 2b, 2c, 2d, 2e and 2f depict various examples of blade units of axial fans according to the prior art,

FIG. 3a and 3b depict two deformation states of a blade device comprising a connecting member according to the invention,

FIG. 4a and 4b show forces acting on a blade device comprising a connecting member according to the invention,

FIG. 5 is a side view of a blade attached to a hub by means of a connecting element according to this invention,

FIG. 6 is a plan view of a connecting member according to one embodiment of the present invention,

FIG. 7 is a perspective view of the connecting member shown in FIG. 6, after bending,

FIG. 8 depicts a connecting member according to a second embodiment of the present invention obtained by transverse extrusion or pultrusion,

FIG. 9 is a side view of the connecting member shown in FIG. 8, in which a variable cross section obtained by extrusion or pultrusion can be seen, and an increase in thickness in the critical region itself,

FIG. 10 is a graph of vibration damping as a function of the natural frequency of a blade device,

FIG. 11a and 11b depict various possible configurations of a connecting element according to this invention, rotated up and down, respectively

FIG. 12 illustrates an example installation of an industrial axial fan comprising a blade device with a connecting member according to the invention,

FIG. 13 shows a connecting element according to the invention, bolted to the hub,

FIG. 14 shows a connecting element according to a third embodiment of the present invention, in which the angle between the two parts of the connecting element is the taper angle of the blade,

FIG. 15 and 16 depict a connecting element according to a third embodiment of the present invention, in which the taper angle is obtained in various but simple ways.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the above drawings, the main objective of this invention is to provide a connecting element for attaching an aerodynamic profile to the hub of an industrial axial fan.

As indicated above, this invention relates to a connecting element 1, which consists of a very simple element (see, for example, Fig. 5-7) having a substantially rectangular cross section and an L-shaped longitudinal section having a first part 1a extending in a substantially rectilinear manner, and a second portion 1b extending in a rectilinear manner, wherein the first portion 1a and the second portion 1b are connected by a connecting portion 1c having a radius of curvature so that said portions 1a and 1b lie in substantially perpendicular planes.

The first part 1a of the L-shaped profile, which is the shorter part, is intended to be attached to the hub 20, while the second part 1b, which is the longer part, is intended to be connected to the aerodynamic profile 10, while the connecting part 1c connects the short part 1a and the long part 1b.

A paddle device 100 comprising a connector 1 according to the invention is also part of the invention.

The blade device 100 for industrial axial fans is characterized in that under the influence of unsteady loads the blade is forced to change its modal characteristics, namely the frequencies and types of deformation, as described above.

The inventors carried out functional tests to compare the blade device 100, made according to this invention and containing the connecting element 1 according to the invention, with devices known from the prior art. The results confirmed that when using the connecting element 1 according to this invention, the eigenfrequencies of the device are 20% lower compared to the prior art, and the attenuation coefficients of the first three vibration modes are 24%, 15% and 3% respectively higher than the same coefficients for the known blade device, while only the attenuation of the fourth mode is 4% lower.

For the usual load mode of the blade device, the relative participation coefficient of the first four modes is 0.43, 0.24, 0.14, and 0.09, respectively. Thus, the reaction of the device blade to this load system is completely determined by the superposition of the reactions of these four modes.

Due to differences in attenuation coefficient, the maximum reaction of the blade device 100 according to this invention containing the proposed connecting element 1 is 22% lower compared to the reaction of the blade device known in the art. Given that the loads on the blade are proportional to its reaction, the invention provides a significant reduction in the loads acting on the blade.

In addition, the connecting element 1 according to this invention has an additional, very important characteristic, namely, it is asymmetrical.

The influence of these factors on the behavior of the device is explained below with reference to FIG. 3a and 3b.

During operation, stationary static forces (weight W and lifting force L) tend to deform the blade 10 so that it acquires a shape corresponding to the first vibration mode of the cantilever beam.

At the same time, the centrifugal force C tends to counteract the deformation of the blade.

The effect of centrifugal force C linearly depends on the displacement of the center of gravity, which also linearly depends on the length of the blade attachment.

For the same radial size and under the same loads, the blade device according to this invention, containing a connecting element, the length of which is longer than the length of the known connecting elements, can provide a greater displacement of the blade and, therefore, a greater counteracting effect compared to a blade known from the level technicians.

As clearly seen from FIG. 5-7, the structure and profile of the connecting element 1 according to this invention are very simple to manufacture. The connecting element 1 can be performed while maintaining its individual characteristics in several different ways, which makes it possible to achieve very low production costs compared to the costs of the connecting elements currently available on the market.

Other advantages provided by the paddle device according to this invention due to the connecting element according to the invention are as follows:

- the connecting element 1 can be obtained as a result of a simple manufacturing process, including the first cutting step and the second drilling step, starting from the blank of a sheet of aluminum, steel or other appropriate material and in accordance with the desired shape, and the final bending step (see Fig. 5-7)

- the connecting element 1 can be obtained as a result of the manufacturing process, including the first stage of cutting and the second stage of drilling, starting with the workpiece obtained by extrusion or pultrusion (reference is made to Fig. 8 and 9), it should be understood that this extrusion provides the possibility of simple implementation of various forms that can provide additional important advantages: for example, increased thickness can be provided where higher mechanical stresses are expected, i.e. in the zone of connection with the hub (see Fig. 9),

- the connecting element 1 can be obtained as a result of the manufacturing process, including the first cutting step and the second drilling step, starting from the element obtained by pultrusion or molding of plastic or fiberglass material,

- the connecting element 1 can be obtained as a result of the manufacturing process, including the first cutting step and the second drilling step, starting with a simple L-shaped profile.

The L-shaped connector according to this invention can ultimately be combined with a known device to enhance its beneficial effects.

Another advantage provided by the connecting element according to this invention is its asymmetric shape: due to the L-shaped asymmetric profile, the element 1 can be assembled so that the connecting part 1c is turned either up or down (Figs. 5a and 5b), while it is asymmetric the shape of the connecting element makes it possible to raise or lower the plane of rotation of the blade in accordance with the requirements of the installation (see Fig. 12).

Of course, the connecting element can be attached to the hub 20 with one or more bolts depending on the operating conditions (see Fig. 13).

Claims (19)

1. Channel industrial axial fan containing a blade device (100), and each blade device (100) contains: - blade (10), - hub (20), - a connecting element (1) for attaching the blade (10) to the hub (20), made in the form of a single L-shaped element containing the first, shorter part (1a) having a substantially rectilinear configuration, and the second, longer part ( 1b) having a substantially rectilinear configuration, wherein said first part (1a) and second part (1b) are connected by a connecting part (1c) having a radius of curvature and lie in substantially perpendicular planes, and wherein said connecting element (1) is attached to the hub (20) with one or more bolts. 2. The axial fan according to claim 1, characterized in that said first part (1a) and said second part (lb) lie in planes inclined at an angle forming a constructive taper angle of the blade directly on the connecting element, and not on the hub. 3. Axial fan according to claim 1, characterized in that the connecting element (1) has a quadrangular cross section. 4. Axial fan according to claim 1, characterized in that the connecting element (1) has a rectangular cross section. 5. Axial fan according to any one of the preceding paragraphs, characterized in that the connecting element (1) is made of metal material. 6. Axial fan according to any one of the preceding paragraphs, characterized in that the connecting element (1) is made of plastic material. 7. Axial fan according to any one of the preceding paragraphs, characterized in that the connecting element (1) is made of fiberglass material. 8. An axial fan according to any one of the preceding paragraphs, characterized in that the connecting element (1) is obtained as a result of a manufacturing process comprising the following steps: the use of a sheet of metal, plastic or fiberglass material, cutting and drilling said metal sheet, bending the cut and drilled sheet to obtain a finished L-shaped element. 9. Axial fan according to any one of the preceding paragraphs, characterized in that the connecting element (1) is obtained as a result of a manufacturing process comprising the following steps: the use of billets obtained by extrusion or pultrusion, cutting and drilling said workpiece, bending of cut and drilled workpiece.

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