Impeller of a centrifugal machine

Abstract

This utility model pertains to compressor and pump engineering, specifically to centrifugal machine impellers. The technical result is optimization of the hydrodynamic flow parameters in the impeller region to minimize hydraulic losses, ensuring stable operation and high energy efficiency of centrifugal machines. This technical result is achieved through the use of an impeller comprising a coaxially arranged main disk and cover disk, as well as long blades located between them, and short blades located between them. The leading edge of each shortened blade is offset circumferentially in the direction of impeller rotation by an amount equal to 0.08-0.12 of the pitch of the main blades along the arc of a circle on which the leading edges of the shortened blades are located, while the trailing edges of the long and short blades are equidistant from each other.This offset arrangement of the short blades allows for effective control of the flow of the working fluid, preventing its separation from the rear surface of the main blade and suppressing the development of vortex structures, which leads to a reduction in hydraulic losses and an increase in efficiency.

Description

[0001] The utility model relates to the field of compressor and pump engineering, in particular to the designs of impellers of centrifugal machines such as compressors and pumps.

[0002] The impeller is the primary working element of a centrifugal machine, designed to transfer energy from the drive to the working fluid (gas or liquid) by compressing and moving it. An impeller typically consists of a set of blades mounted on a central disk. The blades capture and accelerate the gas within the impeller, direct the gas flow, and compress the gas as it moves along the blades toward the outer edge of the impeller. The impeller design, specifically the geometry and arrangement of its blades, determines the hydrodynamic characteristics and efficiency of the machine.

[0003] Technology Level

[0004] The design features of impellers are determined by the parameters of the flow path and the operating mode. Depending on the ratio of pressure and flow, flow paths are classified as low-speed (high-pressure), normal (universal), and high-speed (high-performance), which influences the blade geometry. Most standard technical solutions are designed for normal operating modes, but specialized designs exist for extreme pressure and flow values.

[0005] There are known designs of impellers of centrifugal machines in which, in order to improve the hydrodynamic characteristics, along with the main (long) blades, additional shortened (short) blades are used, installed in the inter-blade channels.

[0006] A centrifugal compressor impeller (Author's Certificate SU 1320524, June 30, 1987) is known. It features a main and cover disc, with extended and shortened blades positioned between them. The shortened blades are offset by 1 / 16th of the pitch of the extended blades from the centerline of the interblade channels in the direction of rotation, and their trailing edges are located on the centerline of these channels. This improves the uniformity of the velocity field and increases efficiency.

[0007] The centrifugal impeller of a gas turbine engine (Patent No. RU 191663, dated August 15, 2019) contains radial or slightly curved blades. The blades are arranged such that the distances from the trailing edges of the shortened, short, and main curved blades are equal to 1.18-1.22 times the distance between the shortened and adjacent main blades. The offset of the leading edges of the shortened and short blades is 0.4 and 0.54 times the impeller radius. This solution improves efficiency by reducing losses in the peripheral region, but its complexity and redundancy limit its practical application.

[0008] The design of the ECV8-25 borehole pump impeller with a flat pressure characteristic is well known, as described in the source (https: / / agrovodcom.ru / infos / protochnye-chasti-nasosov-ecv.php). It features a reduced blade angle at the outlet to 24°56', which reduces the stage pressure by 15%. To compensate, a tier of short blades with leading edge radii of 23.6 and 54 mm and a 24°56' angle is added. The width of the small blades is 2 mm. This design increases efficiency compared to single-row models, but has limitations associated with the formation of vortices and secondary flows in the interblade space.

[0009] A pump with an electric drive (patent US 10393121, dated August 27, 2019) is known. It features a centrifugal impeller with long and short blades. The leading and trailing edges are located on circles, with the distance between the trailing edge of the short blade and the trailing edge of the long blade being 0.35-0.5 times the distance between the trailing edges of the long blades, and the leading edge diameter of the short blades being 0.6-0.75 times the trailing edge diameter. This pump has limitations associated with the formation of vortices and secondary flows in the interblade space, which reduces efficiency; it is only suitable for certain types of machines, such as low-speed compressors.

[0010] A common drawback of analogs is the insufficiently efficient organization of flow in the inter-blade space, leading to hydraulic losses.

[0011] The closest analogue (prototype) of the claimed solution is the impeller of a centrifugal pump disclosed in patent CN 103953583 A (published July 30, 2014). This impeller comprises a main and cover disc, between which long and short blades are alternately arranged. According to this solution, the short blades are offset circumferentially by 0.55-0.65 pitches from the working (concave) surface of the long blade. This arrangement is aimed at improving the pump's suction capacity and increasing its resistance to cavitation.

[0012] A drawback of the prototype is that the proposed offset range (0.55-0.65 pitch) places the short blade too close to the high-pressure zone of the next long blade in the direction of rotation. This does not result in optimal flow distribution in the interblade channel and does not fully address the problem of secondary flow formation and flow separation from the rear (convex) surface of the preceding blade, which is a significant source of hydraulic losses and limits efficiency gains.

[0013] The prototype discloses the following set of features, common with the claimed solution:

[0014] Centrifugal machine impeller;

[0015] The presence of the main and cover discs (standard design);

[0016] The presence of long (main) blades;

[0017] The presence of short blades installed between the main ones;

[0018] Presence of circumferential displacement of shortened blades.

[0019] Disclosure of Utility Model

[0020] The claimed utility model is aimed at improving the design of the impeller of a centrifugal machine.

[0021] The technical problem of the claimed utility model is the expansion of the arsenal of technical means that ensure an increase in the performance and efficiency of the impeller of a centrifugal machine.

[0022] The technical result of the utility model is an increase in the efficiency of the impeller by optimizing the hydrodynamic parameters, minimizing hydraulic losses and preventing secondary flows and vortex formation in the inter-blade channels.

[0023] The specified technical result is achieved due to the fact that in the impeller of a centrifugal machine, containing a main disk, a cover disk and long blades placed between them along the circumference, uniformly placed on the disk at an equal distance from each other, forming inter-blade channels, in each of which at least one short blade is installed, the leading edge of which is shifted in the circumferential direction in the direction of rotation of the impeller, according to the invention, the value of the specified shift is from 0.08 to 0.12 pitch (preferably 1 / 10 pitch) of the main blades along the arc of the circle on which the leading edges of the short blades are located.

[0024] This significantly smaller offset of the short blade's leading edge in the direction of rotation (i.e., toward the rear, convex surface of the preceding long main blade) compared to the prototype is optimal for solving the problem. It allows the shortened blade to be positioned in the portion of the interblade channel where it most effectively impacts the boundary layer, preventing its separation from the rear surface of the main blade and suppressing the development of vortex structures. Unlike the prototype, this does not create excessive flow compression at the working surface of the following blade, but ensures a more uniform velocity distribution across the entire channel cross-section, which leads to a significant reduction in hydraulic losses and, consequently, increased efficiency.

[0025] In particular embodiments of the utility model, which additionally contribute to the achievement of the technical result:

[0026] The exit angle of the blades from the impeller is 25° to 35° (preferably 30°);

[0027] the radius of the circle of the location of the leading edges of the long blades is from 0.28 to 0.32 of the radius (preferably 0.3 of the radius) of the main disk, and the radius of the circle of the location of the leading edges of the short blades is from 0.64 to 0.68 of the radius (preferably 0.66 of the radius) of the main disk;

[0028] The length of the long blades is 0.4 to 0.7 times the diameter of the main disk, and the length of the short blades is 0.3 to 0.5 times the diameter of the main disk.

[0029] The essence of the utility model is explained by drawings, where:

[0030] Fig. 1 - schematically shows a meridional section of the impeller;

[0031] Fig. 2 - schematically shows a cross-section of the impeller;

[0032] in Fig. 3 - the result of CFD modeling illustrating the distribution of the flow lines of the working medium in the impeller of the claimed design;

[0033] Fig. 4 is the result of CFD modeling illustrating the distribution of the flow lines of the working medium in the impeller without shortened blades.

[0034] Implementation of a utility model

[0035] The impeller of a centrifugal machine (Fig. 1, 2) comprises a main disk (1) and a cover disk (2) mounted coaxially with it, forming the base of the wheel. Long main blades (3) are located between the disks, forming interblade channels, in each of which at least one short blade (4) is installed. The blades (3, 4) are uniformly distributed around the circumference of the main disk (1).

[0036] The long blades (3) are uniformly arranged on the main disk (1) at an equal distance from each other. The leading edges (3.1) of the long blades (3) are located on a circle with a radius of 0.28 to 0.32 times the radius (preferably 0.3 times the radius) of the main disk (1). The length of the long blades (3) is from 0.4 to 0.7 times the diameter of the main disk (1).

[0037] The radius of the arrangement of the leading edges (5) of the short blades (4) is from 0.64 to 0.68 of the radius (preferably 0.66 of the radius) of the main disk. The leading edges (5) of the short blades (4) are shifted relative to the center line (6) of the inter-blade channel by 0.08-0.12 of the pitch (preferably 1 / 10 of the pitch) of the long blades (the distance between the long blades) in the direction of rotation of the wheel (indicated by arrows in Fig. 2). The length of the short blades (4) is from 0.3 to 0.5 of the diameter of the main disk (1).

[0038] The trailing edges of the long and short blades are equally spaced. The blade exit angle is 25 to 35° (preferably 30°).

[0039] The utility model operates as follows. When the impeller rotates, the flow of the working medium enters the impeller inlet and is distributed into the inter-blade channels formed by long blades (3). The impeller is driven around the central axis and, due to mechanical movement, the working medium flows through the inter-blade channels in the direction of the impeller outlet. The edge of the short blade (4) divides the flow of the working medium in the inter-blade channel into two approximately equal parts, while the displacement of the edge of the short blade (4) along the radius of the placement of the leading edges (5) of the short blades (4) allows for the flow to be divided in the inter-blade space, which in turn optimizes the distribution of kinetic energy across the channel cross-section within the inter-blade space and prevents the occurrence of vortex phenomena in the flows of the working medium and secondary currents within the inter-blade space.Short blades (4) create an additional guiding effect, stabilizing the main flow. The design also ensures uniform flow deceleration from the working fluid inlet to the outlet, and the working fluid velocity at the impeller outlet is uniform across the entire impeller perimeter. At sharper blade exit angles, the smoothness of the working fluid flow is disrupted during the impeller's operating cycle, and the influence of vortex phenomena increases. At more obtuse exit angles, the influence of short blades on the flow is weakened, and the pressure decreases. Blade lengths below the specified ranges have an insufficient effect on the working fluid flow, resulting in low pressure and vortex formation in the flow. Blade lengths above the specified ranges increase the risk of cavitation, and hydraulic friction losses increase.

[0040] CFD modeling was conducted to confirm the industrial applicability of the utility model. The modeling results are schematically presented in Fig. 3 and Fig. 4. The modeling results (Fig. 3) in the ANSYS environment demonstrate a uniform flow of the working fluid in the interblade space with a uniform decrease in flow velocity and a uniform flow velocity field in the area of ​​the working fluid outlet from the impeller, without the formation of vortices and clearly distinguishable secondary flows in the interblade space.

[0041] The results of mathematical modeling demonstrate that the utility model achieves a gradual and significant reduction in the flow velocity in the inter-blade space with the absence of secondary flows and turbulence, which leads to a reduction in hydraulic losses in the impeller and a corresponding increase in efficiency by 7-12%.

[0042] Furthermore, based on the simulation results, it was concluded that the current solution works optimally for blades with an impeller exit angle of 25° to 35°. At smaller exit angles, flow smoothness will be disrupted and vortex growth will occur; at exit angles greater than 35°, the effect of short blades and a reduction in pressure are minimized. The optimal long blade lengths range from 0.4 to 0.7 times the impeller's main disk diameter, while the short blade lengths range from 0.3 to 0.5 times the impeller's main disk diameter. If the long and short blade lengths are less than 0.4 and 0.3, respectively, the blades have an insufficient effect on fluid flow, vortex formation occurs, and pressure is reduced. If the long and short blade lengths are greater than 0.7 and 0.5, respectively, there is a high risk of cavitation and increased hydraulic friction losses.

[0043] The impeller design without short blades exhibits a sharp reduction in the working fluid flow velocity in the interblade space and the active formation of secondary flows in the interblade space. Local flow velocity is reduced by 50-55% compared to 10-15% for the claimed utility model. Recirculation zones occupy up to 55% of the channel volume. These effects indicate that the working fluid passes through the impeller more slowly than with the claimed utility model, resulting in hydraulic losses that reduce impeller efficiency.

[0044] Thus, the implementation of this utility model optimizes the flow of the working fluid in the impeller by reducing hydraulic losses and ensuring uninterrupted flow of the fluid around the blades. This ensures a uniform decrease in fluid velocity and increases the efficiency of the centrifugal machine.

Claims

1. An impeller of a centrifugal machine comprising a main disk, a cover disk installed coaxially with it, long blades secured to the main disk, placed evenly around the circumference between the disks at an equal distance from each other, forming inter-blade channels, in each of which at least one shortened blade is installed, the leading edge of which is shifted in the circumferential direction in the direction of rotation of the impeller, characterized in that the value of said shift is from 0.08 to 0.12 of the pitch of the main blades along the arc of the circle on which the leading edges of the shortened blades are located, while the trailing edges of the long and short blades are at the same distance from each other.

2. The impeller according to paragraph 1, characterized in that the angle of exit of the long and short blades from the impeller is from 25 to 35°.

3. The impeller according to paragraph 1, characterized in that the length of the long blades is from 0.4 to 0.7 of the diameter of the main disk, and the length of the short blades is from 0.3 to 0.5 of the diameter of the main disk.

4. The impeller according to paragraph 1, characterized in that the radius of the circle of the location of the leading edges of the long blades is from 0.28 to 0.32 of the radius of the main disk, and the radius of the circle of the location of the leading edges of the short blades is from 0.64 to 0.68 of the radius of the main disk.

5. The impeller according to paragraph 1, characterized in that the value of said offset is 0.1 of the pitch of the main blades along the arc of the circle on which the leading edges of the shortened blades are located.

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