CN111503049A - Combined deformation large-inclination-angle blade - Google Patents

Abstract

The invention discloses a combined deformation large-inclination-angle blade which is provided with a recurved structure in the circumferential direction, has large-angle rotation inclination in the same direction as the rotation direction of an impeller from a blade root to a blade tip, is provided with a sweepback structure in the axial direction and is provided with a torsion structure in the radial direction. The invention effectively reduces the attack angle of the working medium which radially flows into the impeller near the inlet of the impeller and promotes partial working medium to do centripetal diagonal flow in the impeller by deforming the blades in the circumferential direction, the axial direction and the radial direction, can achieve the effects of improving the flow, the acting capability and the working efficiency of the impeller and reducing the noise, improves the comprehensive performance of the impeller, is not only suitable for open axial flow impellers of fans, propellers and the like, but also can be used for constructing novel centripetal diagonal flow impellers, and has greater application and popularization values.

Description

Combined deformation large-inclination-angle blade

Technical Field

The invention belongs to the field of fluid machinery, and relates to a blade of an impeller, in particular to a combined deformation blade with a large inclination angle.

Background

The impeller machine is a power machine which takes continuous rotating blades as a body and enables energy to be converted between fluid working media and shaft power. The fluid flow direction can be divided into axial flow, radial flow, mixed (diagonal flow), combined type and the like. The power generation system can be classified into a prime mover such as a steam turbine, a gas turbine, etc. (output power) according to functions; work machines such as water pumps, fans, compressors, propellers, etc. (power consumption).

The impeller is usually a wheel disc provided with blades, and is an important component of a mechanical rotor of the impeller. The structure shape and performance of the impeller are different under different application occasions, and the impeller can be divided into different types. For example, the flow direction of the working medium can be generally divided into axial flow, radial flow (centrifugal) flow and diagonal flow.

The conventional open axial flow impeller, such as a fan, a propeller and the like, is generally low in overall efficiency and high in noise, and particularly, the impeller with a large hub has high linear velocity near a blade tip and high work-doing capability, and is low in linear velocity near a blade root and low in work-doing capability, so that the total pressure at the outlet of the impeller is not uniformly distributed in the radial direction, and the flow and the work-doing capability of the impeller are limited. The blade is the key part of the impeller, whether the design of the blade is reasonable or not and whether the blade is suitable for the working medium flow or not directly influences the performance indexes of the impeller, such as flow, working efficiency, noise and the like, and the poor performance of the existing open axial flow impeller is mainly related to the design of the blade.

At present, the blade design of the axial flow impeller usually adopts analysis methods such as primitive level, plane blade cascade, blade profile and the like, and optimizes the blade design by methods such as fluid dynamics theoretical calculation, numerical simulation, experiments and the like. It has been found that in some application scenarios, the performance of the impeller may be improved by appropriate deformation of the blades, referred to as bending, in the circumferential direction and as sweeping, in the axial direction. Curved blades find wider application in stator blades, while swept blade designs have been generalized in moving blades, particularly fans.

Disclosure of Invention

The invention aims to provide a combined deformation large-inclination-angle blade aiming at the defects of the performance of the existing open axial-flow impeller, the blade has the deformations such as recurvation, inclined rotation, sweepback, torsion and the like in the circumferential dimension, the axial dimension and the radial dimension, and the deformation of more than two dimensions is carried out on the blade, so the combined deformation is called; the blades are deformed and inclined at a large angle in the circumferential direction, and thus are called high-pitch blades. Through carrying out reasonable combination deformation to the blade to set up reasonable parameter, can effectively improve the characteristic of blade, and then play effectively and reduce the angle of attack that radial inflow impeller working medium, improve the flow efficiency of radial inflow impeller working medium, impel partial working medium to do the effect of centripetal diagonal flow in the impeller inside, reach the purpose that promotes the flow, the acting ability, the work efficiency and the noise reduction of impeller, improve impeller comprehensive properties.

The blade can be regarded as a three-dimensional entity formed by stacking a plurality of blade elementary sections from the blade root to the blade tip, the gravity centers of the blade elementary sections can be connected into a curve, which is called a stacking line, if the blade is not deformed, the stacking line is usually a radial straight line, that is, the gravity centers of all the blade elementary sections are overlapped in the radial direction. If the blade is deformed, the stacking line is also bent and deformed. For convenience of description, the stacking line is projected to the end face (a plane perpendicular to the impeller shaft) and the meridian plane of the impeller respectively, the projection line of the stacking line on the end face can clearly reflect the deformation condition of the blade in the circumferential direction, and similarly, the projection line of the stacking line on the meridian plane can clearly reflect the deformation condition of the blade in the axial direction.

The center of gravity of the blade element section is displaced in the circumferential direction and is called bending, and the displacement in the axial direction is called sweeping. At present, the curved and swept shapes are basically C-shaped arcs, and correspondingly, the projection lines of the blade stacking line on the end face and the meridian plane are C-shaped arc curves. For the bending, when the direction of the C-shaped projection line of the end surface of the blade stacking line is the same as the rotating direction of the impeller, the bending is called positive bending, and when the direction of the C-shaped projection line is opposite to the rotating direction of the impeller, the bending is called negative bending; for the sweep, when the direction of the projection line of the meridional plane of the blade stacking line is towards the inlet (incoming flow) direction of the impeller, the sweep is called backward sweep, and when the projection line of the meridional plane of the blade stacking line is towards the outlet direction of the impeller, the sweep is called forward sweep.

The technical solution adopted by the present invention is described in detail below:

a combined deformation high-inclination-angle blade is characterized in that on one hand, the blade is of a reverse-bending structure in the circumferential direction, namely a projection line of the end surface of a blade stacking line is a C-shaped arc curve, the protruding direction of the curve is opposite to the rotation direction of an impeller, and the blade is gradually inclined in a large-angle rotation manner from a blade root to a blade tip in the rotation direction of the impeller, and on the other hand, the blade is of a backswept structure in the axial direction, namely a meridian projection line of the blade stacking line is a C-shaped arc curve, and the protruding direction of the curve faces the inlet direction of the impeller.

In order to describe and measure the rotating inclination degree of the blade from the blade root to the blade tip to the rotating direction of the impeller, the concept of circumferential rotating angle is introduced, and the circumferential rotating angle is used for measuring the rotating inclination degree of the blade in the circumferential direction. The circumferential rotation angle is defined as: two end points of the plane projection line of the blade stacking end are connected into a straight line, an included angle between the straight line and a straight line passing through the radial direction of the impeller at the corresponding point of the blade root is called as a circumferential rotation angle, and the circumferential rotation angle usually needs to be larger than 30 degrees to obtain a better effect.

The invention also introduces the concept of circumferential inclination, which is defined as: the circumferential inclination angle reflects the circumferential inclination degree of the blades at different blade heights, and the circumferential inclination angle is larger and the inclination is more severe along the circumferential direction. In the invention, because the blade adopts the recurved shape in the circumferential direction and the blade rotates in an inclined way gradually towards the rotating direction of the impeller from the blade root to the blade tip, the circumferential inclination angle corresponding to the blade tip is larger and is required to be not less than 45 degrees, and the blade is called as a large-inclination-angle blade because the circumferential inclination angle is larger.

The characteristics of the combined deformation large-inclination-angle blade are described above, and the working state of the open axial-flow impeller is analyzed to find out the problems existing in the existing blade design, so that the design idea of the invention and the action mechanism for improving the performance of the impeller are explained.

The method comprises the following steps of firstly analyzing the internal flow field of the existing open axial-flow impeller. In an open axial-flow impeller such as a fan or a propeller, the periphery of the impeller is not covered by a casing. When the impeller is in a working state, the rotating blades can push the fluid working medium to flow from the inlet to the outlet of the impeller, and the flow field distribution inside and around the impeller is usually complex, is in an uneven dynamic state, and still presents approximate regularity. The flow field inside the impeller is analyzed from the axial dimension, the radial dimension and the circumferential dimension, and the general distribution of the total pressure, the static pressure and the flow velocity of the working medium inside the impeller is mainly concerned. Viewed from the axial direction, the blades push the working medium to flow from the inlet to the outlet of the blades, the energy is transferred to the working medium, the energy of the working medium is gradually increased, the total pressure is gradually increased to be close to the outlet, the total pressure generally reaches the maximum value, the total pressure difference between the inlet and the outlet is positively correlated with the flow velocity, and the larger the flow velocity is, the larger the total pressure difference between the inlet and the outlet is. From the radial view, as the radius is increased, the linear speed of the blade in rotation motion is gradually increased along with the increase of the blade height, and the work-doing capability is gradually enhanced, so that for an open axial-flow impeller, particularly an impeller with a relatively large hub, the total pressure and the flow speed of the working medium at the outlet of the impeller are generally gradually increased along with the increase of the blade height (unless specially designed for isobaric output); viewed from the circumferential direction, the total pressure of the working medium is approximately distributed in a gradient manner from the pressure surface (leaf basin) of one leaf to the suction surface (leaf back) of the adjacent leaf, the total pressure near the pressure surface is higher, the total pressure near the suction surface is lower, the total pressure from the pressure surface to the suction surface is gradually reduced, the difference (pressure difference) between the total pressures of the pressure surface and the suction surface cannot exceed a certain limit, the working medium on one side of the suction surface (leaf back) is separated and swirled due to the too large pressure difference, and the flow efficiency is greatly reduced.

The flow field around the impeller inlet was analyzed as follows. Generally, before a working medium enters an impeller, the total pressure of the working medium at each position on the periphery of an inlet is equal, for an open axial-flow impeller, the impeller is surrounded by a fluid working medium, under the condition that the flow of the impeller is constant, the farther the impeller inlet is away from the inlet of the impeller, the lower the flow speed of the working medium is, the higher the static pressure is, the higher the flow speed is at the position close to the inlet of the impeller, the lower the static pressure is, the static pressure difference exists between the working medium at the inlet of the impeller and the working medium at the farther position, and the static pressure difference enables the working medium.

The working medium flow conditions near the blade tip are analyzed. Under the working state, the linear velocity near the blade tip is large, the acting capacity is strong, in order to fully excavate the acting potential of the impeller and increase the impeller flow, the acting capacity of the blade tip is usually fully utilized when the impeller is designed, and the flow velocity of the working medium near the blade tip is usually large. At the blade tip of the inlet of the impeller, because the blades do not work on the working medium, the working medium has high flow velocity, high dynamic pressure and low static pressure, and the working medium at the position far away from the inlet has low flow velocity, low dynamic pressure and high static pressure, and the static pressure difference not only enables the working medium at the position far away from the inlet of the impeller to flow to the inlet of the impeller, but also enables the working medium at the position far away from the inlet of the impeller in the radial direction to flow to the inlet of the impeller, namely near the blade tip of the inlet of the impeller, the working medium not only enters the impeller from. In the process that the blade tip enters the impeller and then flows out of the impeller, the blade acts on the working medium, so that the total pressure of the working medium is continuously increased, and the main increase of the total pressure is the static pressure of the working medium, therefore, the flow of the working medium entering the impeller from the radial direction of the blade tip is larger near the inlet of the impeller, and the static pressure is increased near the outlet of the impeller after the blade acts on the working medium, the static pressure difference between the working medium inside the impeller and the working medium outside the radial direction of the impeller is reduced, so that the radial flow is smaller, and if the static pressure of the working medium inside the impeller is higher than the static pressure.

For the working medium entering the impeller axially, the problem of flow efficiency is fully considered in the existing blade design, but the working medium entering the impeller radially is not considered and paid attention, so that the working medium flowing into the impeller radially from the blade tip near the impeller inlet has a large attack angle which can reach more than 60 degrees, the efficiency is seriously reduced due to the large attack angle flow, and large impact noise is also caused, which is the main reason that the overall performance of the existing open axial-flow impeller is poor.

According to the invention, the blades are subjected to reverse bending deformation in the circumferential direction and are inclined from the blade root to the blade tip along the rotation direction of the impeller, so that the circumferential inclination angle near the blade tip is larger, the blades are subjected to sweepback deformation in the axial direction, and meanwhile, the blades are subjected to multi-dimensional deformation, so that the problem of overlarge attack angle of working media flowing into the impeller in the radial direction near the impeller inlet can be solved, and the flow field distribution in the impeller can be changed and optimized, and part of the working media in the impeller is promoted to perform centripetal oblique flow. After the deformation, when the circumferential inclination angle near the blade tip is 45 degrees, the attack angle of the working medium flowing into the impeller from the blade tip at the impeller inlet in the radial direction is usually within 20 degrees (the attack angle is an estimated value under a common condition, and specific data may have certain difference due to specific conditions), and compared with the attack angle of about 60 degrees of radial straight blades which are not subjected to circumferential inclined bending, the flow efficiency is obviously improved; when the circumferential inclination angle near the blade tip is about 65 degrees, the attack angle of the working medium flowing into the impeller in the radial direction is usually within 5 degrees, at the moment, the flowing efficiency of the working medium flowing into the impeller in the radial direction can usually reach an ideal state, so that the overall efficiency of the impeller can be improved, and the noise is reduced.

After the blades are subjected to the circumferential and axial combined deformation, the attack angle of the working medium which flows into the impeller in the radial direction near the inlet of the impeller is greatly reduced, the radial flow of the working medium can be maintained to a certain degree in the impeller, and the working medium which flows in the radial direction and the working medium which flows in the axial direction interact, influence and mix in the impeller, so that part of the working medium presents centripetal oblique flow to a certain degree in the impeller, namely the working medium flows obliquely from the blade tip to the axis direction. The oblique flow impeller is different from a common oblique flow impeller, the common oblique flow impeller is centrifugal oblique flow from an inlet to an outlet, and the impeller adopting the oblique flow impeller as the blades is centripetal oblique flow from the inlet to the outlet. Because more working media flow in from near the apex that the linear velocity is great, consequently than current open axial compressor impeller do work ability reinforce, the flow is bigger, and efficiency is higher, and the total pressure distribution of impeller export is also more even, and the comprehensive properties of impeller obtains obviously promoting.

According to the invention, the blade is further in a torsional shape in the radial direction, the blade profile mounting angles at different blade heights are unequal, the mounting angle near the blade root is smaller, and the mounting angle near the blade tip is larger. This twisting is the opposite of the conventional blade twisting. The difference between the maximum and minimum values of the profile setting angle is called the twist angle, and the twist angle can be used for measuring the magnitude of the radial twist amplitude of the blade. The impeller with the combined deformation large-inclination-angle blades is adopted, the flow direction of a considerable amount of working media entering the impeller is centripetal and oblique flow, the blade height at an inlet is large, the linear speed is large, the blade height at an outlet is small, the linear speed is also small, the difference between the linear speeds of the inlet and the outlet is large, if the mounting angles are the same, and the mounting angles are large, the turning angle of the working media is easy to be overlarge, so that the blade back is separated to cause efficiency reduction, therefore, the blades are deformed in a radial torsional mode, the blade profile mounting angle near the blade root is set to be small, and the problem can be effectively relieved and solved. The twist angle is typically greater than 3 ° and less than 10 °.

Therefore, the invention can better solve the problems of the existing open axial flow impeller by performing combined deformation on the blades in three dimensions of circumferential direction, axial direction and radial direction, so that the internal flow field of the impeller is more optimized, the comprehensive performance of the impeller is obviously improved, and the invention has great popularization and application values.

It should be noted that in determining the circumferential, axial and radial deformation parameters of the blade, the deformation amplitude in a single dimension should not be too large, otherwise negative effects may occur. For example, the circumferential rotation angle is usually not more than 60 °, and too large can not only affect the strength of the blade, but also cause the flow field distortion inside the impeller, and is unfavorable for improving the efficiency and the flow rate.

The invention is not only suitable for the open axial flow impeller, but also can be used for reforming the existing closed axial flow impeller into a novel closed centripetal diagonal flow impeller. The transformation method is that the existing blades are changed into combined deformation large-inclination-angle blades, the chord length of the blades is greatly increased, a casing which wraps an impeller near an inlet of the impeller is axially retracted by a section (the axial length of the retracted casing is determined by calculation), so that the blades near the inlet are partially exposed in an inlet flow field, a working medium can simultaneously enter the impeller from the radial direction and the axial direction, the working medium performs centripetal oblique flow after entering the impeller, the radial size of the impeller is gradually reduced so as to be adapted to the centripetal oblique flow of the working medium, of course, in order to obtain better performance, the ratio of the radial sizes of the inlet and the outlet of the impeller cannot exceed a certain limit, otherwise, the efficiency is reduced due to the fact that the turning angle is too large in the working medium flowing process. The centripetal diagonal flow impeller has the characteristic of small radial size of an outlet, is convenient to butt with an output pipeline with a smaller size, part of working media enter the impeller from the position close to the blade tip, the linear velocity of the blade tip is higher, the acting capacity is strong, the flow and the acting capacity of the impeller can be improved, and the novel centripetal diagonal flow impeller is believed to have a wide application prospect.

Compared with the prior art, the invention has the beneficial effects that:

1. the efficiency of the radial flowing working medium of the open axial flow impeller can be obviously improved. The invention better solves the problem that the attack angle is too large when the working medium which flows radially near the blade tip of the impeller inlet enters the impeller, and can obviously improve the efficiency of the impeller and reduce the noise.

2. The internal flow field of the open axial flow impeller can be further optimized. After the invention is applied, more working media can enter the impeller from the position near the blade tip of the impeller inlet, so that part of the working media do centripetal diagonal flow in the impeller, the problem of weak acting capability of a common axial-flow impeller caused by low blade root linear velocity is solved, the total pressure distribution of the impeller outlet is more uniform, the impeller flow is increased, and the integral acting capability of the impeller is favorably improved.

3. Can be used for constructing a novel closed centripetal oblique flow impeller. The invention can be used for reconstructing the existing closed axial flow impeller and constructing a novel closed centripetal diagonal flow impeller, and the impeller has the advantages of small radial size of an outlet, strong work-doing capability, high efficiency and the like, and has wide application prospect.

The following describes the problems of designing the circumferential inclination deformation parameters and the strength of the blade according to the present invention. The combined deformation high-inclination-angle blade generally puts higher requirements on the strength of the blade material due to the change of the shape of the blade, the problem is usually not obvious in a medium-low speed impeller, but the strength problem of the material can be more prominent in a high-speed impeller, and the relationship of various factors such as the bending and backswept amplitude of the blade, the strength of the material and the like should be comprehensively considered in specific application to realize the optimal balance.

The foregoing description is directed primarily to single stage impellers, and the present invention is applicable to multi-stage impellers, but the parameters therein need to be adjusted appropriately to suit the specific requirements of the design conditions.

Drawings

Fig. 1 is an axial view of an impeller employing the present invention as a vane.

Fig. 2 is a radial view of an impeller employing the present invention as a vane.

Figure 3 is a line-end projection view of the present invention.

Figure 4 is a view of the meridian plane projection of the present invention.

Wherein: 1. a blade; 2. a blade root; 3. a blade tip; 4. a wheel disc; 5. the direction of rotation of the impeller; 6. stacking lines; 7. a blade leading edge; 8. a blade trailing edge; 9. stacking line end surface projection lines; 10. stacking meridian plane projection lines; 11. a circumferential inclination angle; 12. the flow direction of the working medium; 13. circumferential rotation angle.

Detailed Description

The present invention will be further described with reference to the following drawings and examples, but the embodiments of the present invention are not limited thereto.

The application of the present invention in a fan impeller is specifically explained as an embodiment, fig. 1 is an axial view of an impeller adopting the embodiment of the present invention as blades, fig. 2 is a radial view of the impeller adopting the embodiment of the present invention as blades, the blades 1 are installed on a wheel disc 4 of the impeller, and the wheel disc 4 of the impeller is provided with the blades 1 with three same dimensional parameters. The direction of rotation 5 of the impeller means that the direction of rotation is counter-clockwise when the impeller is in operation.

Fig. 3 is an end-of-line projection view of the stack according to the embodiment of the present invention, which can reflect the deformation of the blade 1 in the circumferential direction. In fig. 3, it can be seen that the line of line 9 is a curved line in the shape of a "C", which projects in the opposite direction to the direction of rotation 5 of the impeller and is therefore curved in a negative direction, while the line of line is inclined in the direction of rotation of the impeller by a circumferential angle 13 of about 48 °. The circumferential inclination angle 11 increases gradually with the increase of the radius of the blade 1, reaches a maximum value of about 60 degrees near the blade tip 3, and belongs to a large-inclination-angle blade.

Fig. 4 is a view of the stacked meridian plane projection line according to the embodiment of the present invention, and the stacked meridian plane projection line 10 can more clearly reflect the axial deformation of the blade 1. As can be seen from the figure, the meridian plane projection line 10 of the superimposed line is a "C" shaped arc curve, and the convex direction of the curve is opposite to the flowing direction 12 of the working medium, i.e. the convex direction of the curve is towards the inlet direction of the impeller, thus being sweepback deformation.

From the above, the blades in the embodiment are subjected to reverse bending deformation in the circumferential direction, are subjected to rotating inclination in the same direction as the rotating direction of the impeller, are subjected to sweepback deformation in the axial direction, and belong to combined deformation blades. The circumferential inclination angle of the blade reaches 60 degrees at the maximum, so that the blade in the embodiment belongs to a combined deformation large-inclination-angle blade.

In order to prevent the excessively large turning angle of the working medium in the process of centripetal diagonal flow, the blade 1 is in a twisting form in the radial direction, specifically, the installation angle of the blade profile of the blade root 2 is 23 degrees, the corresponding blade profile installation angle is gradually increased along with the increase of the blade height, and the maximum value is reached to 27 degrees near the blade tip 3, so that the blade 1 is in the twisting form in the radial direction. The difference between the maximum mounting angle and the minimum mounting angle is called a twist angle, which can be used to measure the radial twist degree of the blade 1, in this embodiment, the maximum mounting angle of the blade profile near the blade tip 3 is 27 °, the mounting angle of the blade profile at the blade root 2 is 23 °, and the twist angle is 4 °.

Experiments show that the fan adopting the design has the characteristics of large air quantity, high efficiency and low noise, and the feasibility and the advancement of the invention are verified.

The above is only a preferred embodiment of the present invention under a certain specific working condition, and since the determination of the blade parameters is closely related to the working condition, and various parameters are mutually restricted and influenced, the parameters of the blade deformation can be determined only after being comprehensively considered according to the actual conditions and requirements; in addition, there may be differences in the parameter settings of the blades for open and closed impellers. For those skilled in the art, without departing from the technical principle of the present invention, several improvements and modifications may be made, for example, to improve efficiency and reduce noise, on the basis of the present invention, the blade tip may be turned over to deform, the front edge and the rear edge of the blade may be partially cut and shaped, the rear edge of the blade may be provided with saw teeth or notches, the suction surface may be provided with turbulence protrusions, and the like, and these improvements and modifications should also be considered as being within the protection scope of the present invention.

The protection scope of the present invention should be subject to the definition of the claims.

Claims (2)

1. A combined deformation large-inclination-angle blade is characterized in that: the blades are of a reverse-bending structure in the circumferential direction, namely the projection line of the end surface of the blade stacking line is a C-shaped arc curve, and the protruding direction of the curve is opposite to the rotating direction of the impeller; the blades rotate and incline towards the rotating direction of the impeller from the blade root to the blade tip gradually, and the circumferential rotating angle is not less than 30 degrees; the maximum value of the circumferential inclination angle of the blade is not less than 45 degrees; the axial direction is a sweepback structure, namely the meridian plane projection line of the blade stacking line is a C-shaped arc curve, and the convex direction of the curve faces to the inlet direction of the impeller.

2. The combined morphing high incidence blade of claim 1, wherein: the blade has different blade profile installation angles at different blade heights, the blade profile installation angle from the blade root to the blade tip is changed from small to large, the blade is in a torsional form in the radial direction, and the torsional angle is larger than 3 degrees.

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