A tip clearance control skirt and method of designing the same

Abstract

The application discloses a kind of blade tip clearance control skirt and its design method, skirt is fixed with skirt in the top edge of blade, skirt is gradually increased in thickness from the starting point of blade inside O To blade tip point P Forming;Skirt is provided with periodically distributed protrusions on the side away from the surface of casing wall, the protrusions undulate in chord direction of skirt, and the profile curve of the protrusions is constructed by cosine function.The application can effectively interfere and weaken the strength of tip clearance leakage vortex, and inhibit the generation and development of tip clearance leakage vortex cavitation by fixing skirt in the top edge of blade, and providing periodically distributed protrusions on the side away from the surface of casing wall, which undulate in chord direction of skirt.

Description

Technical Field

[0001] This invention relates to the field of axial-flow hydraulic machinery blade technology, specifically to a blade tip clearance control skirt and its design method. Background Technology

[0002] In rotating machinery such as axial-flow turbines, axial-flow pumps, and fans, a certain gap exists between the blade tip and the pump casing wall. Due to the pressure difference between the pressure side and the suction side of the blade, fluid leaks from the pressure side through the blade tip gap to the suction side, forming a blade tip gap leakage flow. This leakage flow interacts with the mainstream, swirling near the blade suction side to form a blade tip gap leakage vortex. When the core pressure of the leakage vortex is lower than the saturated vapor pressure of the fluid, cavitation of the blade tip leakage vortex will occur, leading to cavitation damage to the blade tip and casing wall, vibration noise, and reduced efficiency. Existing technologies for suppressing blade tip gap leakage vortex cavitation mainly include: reducing the blade tip gap size, optimizing the blade tip shape, and using skirts and wall groove treatments.

[0003] Reducing clearance is limited by manufacturing precision; the effect of blade tip shape optimization is highly dependent on clearance size; traditional skirt design mainly relies on experience and lacks systematic design theory guidance; wall grooves are very sensitive to clearance size. The humpback whale's flipper leading edge has a unique wavy convex knot structure, which research shows can effectively delay flow separation, reduce stall angle of attack, and reduce turbulent noise. However, current research on humpback whale biomimetic technology focuses on the leading edge design of wind turbine blades, airfoils, etc., with the technical goal of delaying stall and improving efficiency. There is a lack of research on applying the humpback whale flipper leading edge convex knot structure to the blade tip skirt of rotating machinery to suppress vortex cavitation caused by blade tip clearance leakage. Therefore, transplanting the humpback whale biomimetic structure from the airfoil leading edge to the blade tip skirt requires solving the matching problem between the convex knot parameters and the clearance leakage flow field. Currently, there is a lack of systematic biomimetic blade tip skirt design methods both domestically and internationally. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a blade tip clearance control skirt and its design method. By introducing a biomimetic convex junction structure into the leading edge design of the blade tip skirt and establishing a systematic design method, the intensity of the blade tip clearance leakage vortex is effectively interfered with and weakened, and the generation and development of blade tip clearance leakage vortex cavitation are suppressed.

[0005] The objective of this invention is achieved as follows: In a first aspect, the present invention proposes a blade tip clearance control skirt, wherein a skirt is fixedly provided on the tip edge of the blade, and the skirt starts from the inner side of the blade. O To the tip of the blade P Gradually increase the thickness to form; The skirt has periodically distributed protrusions on the side away from the casing wall. The protrusions undulate in a wave-like manner along the chord of the skirt, and the profile curve of the protrusions is constructed by a cosine function, satisfying the following relationship: ; In the formula, y This represents the displacement of the convex joint in the longitudinal direction. x Let be the coordinate position along the chord. A For the amplitude of the convex junction, λ The wavelength is the convex junction wavelength.

[0006] The side surface is straight in cross-section.

[0007] The side surface has an inwardly concave curve in cross-section.

[0008] The side surface has an outwardly convex curve in cross-section.

[0009] The skirt and blade are either integrally cast or welded.

[0010] The peak position of the convex junction corresponds to the starting position of the leakage flow channel at the blade tip clearance, and the distribution range of the convex junction covers the peak position of the leakage flow velocity and the vortex concentration area.

[0011] Secondly, the present invention also proposes a design method for implementing the blade tip clearance control skirt, comprising the following steps: Step 1: Parameter Extraction; Obtain the geometric contour of the leading edge of the humpback whale's flipper, and use a sine or cosine curve for fitting to determine the amplitude of the convex knot. A With wavelength λ The range of values ​​for ; Step 2: Skirt control curve design; based on blade tip clearance height δ The control curve for the skirt is designed and determined by the following set of equations: ; In the formula, m、n To control the parameters of the skirt hem shape, z The coordinates are along the span direction; Step 3: Distribution Determination; Based on the development intensity of the leakage flow in the tip clearance of the target axial-flow hydraulic machinery blade, obtain the velocity field distribution and vorticity field distribution of the leakage flow, and determine the distribution range of the convex junction on the skirt; The distribution range of the convex junction covers the peak position of the leakage flow velocity and the vorticity concentration area, and the peak position of the convex junction corresponds to the starting position of the leakage flow in the tip clearance of the blade.

[0012] In step one, the geometric contour of the leading edge of the humpback whale's flipper is obtained through image processing methods, and the convex knot contour curve is processed by denoising, smoothing and parametric fitting. In step two, the skirt control curve It is a straight line.

[0013] In step three, the velocity field distribution and vorticity field distribution of the leakage flow are obtained through CFD numerical simulation or PIV experimental measurement. Compared with the prior art, the above-conceptual technical solution conceived in this application has the following beneficial effects: 1. This invention introduces biomimetic principles into the control of tip clearance leakage flow. A skirt is fixed at the tip edge of the blade, and periodically distributed convex knots are provided on the side of the skirt away from the casing wall. The convex knots undulate in a wave-like manner along the chord of the skirt, thereby effectively interfering with and weakening the intensity of tip clearance leakage vortices when the blade rotates, and suppressing the generation and development of tip clearance leakage vortex cavitation. The wavy leading edge of the convex knot causes periodic geometric disturbance to the leakage flow as it flows through the skirt, exciting pairs of opposing rotating vortices arranged alternately along the chord at the clearance inlet. These pairs of vortices interact with the tip clearance leakage vortex, breaking the originally concentrated large-scale leakage vortex into multiple small-scale, low-intensity dispersed vortex systems, significantly increasing the minimum pressure of the vortex core and making it difficult to drop below the saturated vapor pressure. At the same time, the crest region of the convex knot divides the continuous leakage flow into multiple independent small-flow leakage flows, reducing the velocity and intensity of individual leakage flows, weakening the driving force for leakage vortex formation from the source, thereby suppressing the generation and development of tip clearance leakage vortex cavitation.

[0014] 2. This invention improves the efficiency of axial-flow hydraulic machinery by fixing a skirt to the tip edge of the blade and periodically distributing protrusions on the side of the skirt away from the casing wall. The skirt itself increases the flow resistance and flow path length of the leakage channel, while the crest region of the protrusions further acts as a micro-throttling element. Together, they reduce the leakage flow in the tip clearance that does not participate in work, allowing more fluid to participate in the mainstream work. At the same time, the biomimetic protrusions break high-intensity concentrated leakage vortices into multiple low-intensity small-scale vortices, significantly reducing the mixing loss in the leakage vortex region and allowing more fluid kinetic energy to be effectively utilized. In addition, the protrusions allow the leakage flow to merge into the mainstream in a more dispersed manner, reducing the damage of the leakage flow to the ordered flow structure of the mainstream in the tip region, improving the blade load distribution and work efficiency, thereby achieving an overall efficiency improvement. 3. This invention can improve the applicable operating conditions of axial-flow hydraulic machinery. The vortex control mechanism of this invention mainly relies on the disturbance effect of the geometric parameters of the convex junction itself on the leakage flow, rather than on the absolute value of the gap size. Therefore, it can still maintain a stable and effective control effect when the gap size fluctuates due to manufacturing tolerances, thermal expansion, or wear, significantly improving the tolerance of hydraulic machinery to manufacturing and operational deviations. In addition, by breaking up large-scale leakage vortices and blocking the continuous expansion of cavitation regions, the convex junction effectively suppresses the flow instability caused by the periodic oscillation of leakage vortices and the unstable evolution of leakage vortex cavitation under non-design conditions, enabling hydraulic machinery to maintain safe and stable operation under a wider range of operating conditions. Attached Figure Description

[0015] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only for this invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0016] Figure 1 This is a schematic diagram of adding a skirt to a blade.

[0017] Figure 2 This is a magnified view of the raised knot at the front edge of the skirt hem.

[0018] Figure 3 This is a cross-sectional schematic diagram of the skirt structure.

[0019] Figure 4 This is a top view of the skirt structure.

[0020] Figure 5 This is a schematic diagram of a blade example.

[0021] Figure 6 A comparison diagram of the original blade and the tip clearance leakage vortex structure in this invention is shown; wherein... Figure 6 a represents the original leaf. Figure 6 b represents the blade of this invention.

[0022] Figure 7 This is a comparison diagram of the original blade and the vortex core pressure in this invention; wherein, Figure 7 a represents the original leaf. Figure 7 b represents the blade of this invention.

[0023] Figure 8 This is a flowchart of the design method of the present invention.

[0024] In the picture: 1. Blade; 2. Skirt; 3. Casing wall. Detailed Implementation

[0025] To more clearly illustrate the purpose, technical solution, and beneficial effects of this application, a further detailed description of this application is provided below in conjunction with illustrations and specific embodiments. It should be specifically noted that the specific embodiments described below are only for illustrating the technical content of this application and do not constitute a limitation on the scope of protection of this application.

[0026] In the accompanying drawings of the embodiments of the present invention, the same or similar reference numerals correspond to the same or similar components. In the description of the present invention, it should be understood that if terms such as "upper," "lower," "left," "right," "inner," and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting the present application. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0027] In the description of this invention, unless otherwise explicitly specified and limited, the term "connection" or similar designation indicating a connection between components should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral part; it can be a direct connection or an indirect connection via an intermediate medium; it can refer to the internal communication between two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0028] Example 1: Combination Figure 1-4 A blade tip clearance control skirt, wherein a skirt 2 is fixedly provided on the tip edge of the blade 1, and the skirt 2 starts from the inner side of the blade 1. O To the tip of the blade P It is formed by gradually increasing the thickness.

[0029] The skirt 2 has periodically distributed protrusions on its side away from the casing wall 3. The protrusions undulate in a wave-like manner along the chord direction of the skirt 2, and the contour curve of the protrusions is constructed by a cosine function, satisfying the following relationship: ; In the formula, y This represents the displacement of the convex joint in the longitudinal direction. x Let be the coordinate position along the chord. A For the amplitude of the convex junction, λ The wavelength is the convex junction wavelength.

[0030] In this embodiment, the side of the skirt 2 away from the casing wall 3 is straight in cross-section.

[0031] This invention utilizes a skirt 2 fixed to the top edge of the blade 1, with periodically distributed protrusions on the side of the skirt 2 away from the casing wall 3. These protrusions undulate chordally along the skirt 2, effectively interfering with and weakening the intensity of the tip clearance leakage vortex when the blade 1 rotates, thus suppressing the generation and development of tip clearance leakage vortex cavitation. The wavy leading edge of the protrusions causes periodic geometric disturbances to the leakage flow as it passes through the skirt, exciting alternating pairs of counter-rotating vortices along the chordal direction at the clearance inlet. These pairs of vortices interact with the tip clearance leakage vortex, breaking the originally concentrated large-scale leakage vortex into multiple small-scale, low-intensity dispersed vortex systems. This significantly increases the minimum pressure of the vortex core, making it difficult to drop below the saturated vapor pressure. Simultaneously, the crest region of the protrusions divides the continuous leakage flow into multiple independent small-flow leakage flows, reducing the velocity and intensity of each individual leakage flow, weakening the driving force for leakage vortex formation at its source, thereby suppressing the generation and development of tip clearance leakage vortex cavitation.

[0032] The skirt 2 and the blade 1 can be a single cast structure or a welded structure. The skirt 2 is a double-sided skirt configuration, that is, the skirt 2 is provided on both the suction side and the pressure side of the blade tip of the blade 1.

[0033] Furthermore, the crest position of the convex junction corresponds to the starting position of the leakage flow channel in the blade tip clearance, and the distribution range of the convex junction covers the peak position of the leakage flow velocity and the vortex concentration region. By setting the crest position of the convex junction to correspond to the starting position of the leakage flow channel in the blade tip clearance, the convex junction can apply the maximum local flow resistance to the leakage flow in the initial stage of entering the clearance, thereby limiting and segmenting the initial flow rate and kinetic energy of the leakage flow at the source, effectively weakening the driving force for the formation of the leakage flow. At the same time, by covering the peak position of the leakage flow velocity and the vortex concentration region with the periodic distribution range of the convex junction, the counter-rotating vortex pairs induced by the convex junction can precisely act on the core region where the leakage flow intensity is the greatest and the vortex core pressure is the lowest, thereby most effectively weakening the intensity of the leakage flow and disrupting the low-pressure conditions required for cavitation initiation. The above spatial matching setting achieves precise suppression of cavitation vortexes in the blade tip clearance leakage, that is, achieving the best cavitation suppression and vortex control effect with minimal structural modification.

[0034] Example 2: The difference between this embodiment and Embodiment 1 is that the side of the skirt 2 away from the casing wall 3 has either an inwardly concave curve or an outwardly convex curve in cross-section. By setting the side of the skirt away from the casing wall with an inwardly concave or outwardly convex curve shape, the lateral oblique edge of the skirt has a flow control function similar to that of a convex junction. Specifically, when the side is in an inwardly concave curve, the concave surface can converge and guide the leakage flow on the side of the skirt, causing the leakage flow to locally accelerate along the concave surface and change its flow direction, thereby causing the leakage flow to adhere to the skirt wall, reducing the mixing loss between the leakage flow and the mainstream. At the same time, the secondary vortices induced by the concave surface can further break up the large-scale leakage vortex structure. When the side is in an outwardly convex curve, the outwardly convex surface can diffuse and decelerate the leakage flow, increase the local flow resistance of the leakage flow, weaken the kinetic energy of the leakage flow, and at the same time, the reverse rotating vortices generated by the outwardly convex surface can effectively disperse the concentrated vorticity of the leakage vortex, destroy the low-pressure conditions of the vortex core, thereby suppressing the initiation and development of leakage vortex cavitation. The aforementioned concave or convex curve shape works in synergy with the biomimetic convex knot on the blade tip to exert flow control on the leakage flow in the blade tip gap from multiple directions and dimensions, further enhancing the suppression effect on leakage vortex cavitation and the adaptability to operating conditions.

[0035] Example 3: This embodiment proposes a design method for implementing the blade tip clearance control skirt described in Embodiment 1, including the following steps: Step 1: Parameter Extraction; Obtain the geometric contour of the leading edge of the humpback whale's flipper, and use a sine or cosine curve for fitting to determine the amplitude of the convex knot. A With wavelength λ The range of values ​​for .

[0036] The geometric contour of the leading edge of the humpback whale's flipper was obtained through image processing methods, and the convex knot contour curve was processed by denoising, smoothing, and parametric fitting. Specifically, humpback whale flipper images were imported into MATLAB software, converted to grayscale, and then subjected to threshold segmentation. Precise edge points were obtained through structuring element closing operations and Canny edge detection. The edge points were then imported into CAD software to draw spline curves, and cosine curve fitting was performed using the curve fitting tool to obtain the expression for the convex knot contour curve.

[0037] Step 2: Skirt 2 control curve design; based on blade tip clearance height δ Design the control curve for skirt 2. The control curve is determined by the following set of equations: ; In the formula, m、n To control the parameters of the skirt hem shape, z The coordinates are along the span direction.

[0038] Skirt 2 control curve It is a straight line.

[0039] Specifically, based on the tip clearance height δ Design the skirt control curve. Obtain the control parameters. m , n and control curve f ( z )= y The skirt edge 2 starts from the inner side of the leaf 1. O To the tip of the blade P The thickness is gradually increased to form the skirt structure. The skirt structure is symmetrically distributed along both sides of the cross-section, with the blade tip point... P The distance between the blade tip clearance and the casing wall 3 is the blade tip clearance. δ .

[0040] Step 3: Distribution Determination; Based on the development intensity of the leakage flow at the blade tip clearance of the target axial-flow hydraulic machinery blade 1, the velocity field distribution and vorticity field distribution of the leakage flow are obtained to determine the distribution range of the convex junction on the skirt 2. The distribution range of the convex junction covers the peak position of the leakage flow velocity and the vorticity concentration area, and the peak position of the convex junction corresponds to the starting position of the leakage flow at the blade tip clearance. The velocity field distribution and vorticity field distribution of the leakage flow are obtained through CFD numerical simulation or PIV experimental measurement. Specifically, CFD numerical simulation methods, such as ANSYS CFX or OpenFOAM, were used to calculate the tip clearance leakage flow of the target blade under rated operating conditions. The computational domain included the blade (1), the tip clearance, and the casing wall (3). Post-processing was used to extract the leakage flow velocity and vorticity field distributions, identifying the peak velocity locations and vorticity concentration regions. Based on the flow field analysis results, the distribution range of the convex junction was determined to be the region covering the most intense leakage flow, and the peak position of the convex junction corresponded to the starting position of the tip clearance leakage flow.

[0041] During machining, a five-axis CNC milling method can be used to machine the protruding structure on the skirt 2 blank. The machining tool is a ball end mill, and polishing is performed after machining.

[0042] Example 4: In this embodiment, the finite volume method is used to discretize the governing equations; a high-quality hexahedral core mesh is used to spatially discretize the computational domain. Figure 5 The computational domain and boundary settings of this invention are illustrated, wherein velocity inlet and pressure outlet boundary conditions are used, and the computational domain walls are configured with no-slip and slip boundary conditions. The calculation employs the PISO algorithm for pressure-velocity coupling, and a dynamic time step is used to ensure that the maximum Courland number is less than 0.8. Figure 6Figure a shows the development of the tip clearance leakage vortex structure in the original blade, and Figure b shows the development of the tip clearance leakage vortex structure in the present invention. By comparing the development of the tip clearance leakage vortex structure in the original blade and the present invention, it can be seen that the tip clearance control skirt proposed in the present invention can effectively suppress the development of tip clearance leakage vortex, which demonstrates the reliability of the present invention in controlling the vortex structure.

[0043] in addition, Figure 7 Figure a shows the pressure distribution in the tip gap region of the original blade, and Figure b shows the pressure distribution in the tip gap region of the present invention. By comparing the pressure distribution in the tip gap region of the original blade and the present invention, it is found that the low-pressure distribution range and intensity obtained by the present invention are significantly smaller than those of the original blade. This indicates that the present invention effectively hinders the axial extension and radial diffusion of the low-pressure region, which is beneficial to suppressing the development of tip gap leakage vortex cavitation.

[0044] In summary, this invention provides a tip clearance control skirt that can effectively weaken the strength of the tip clearance leakage vortex structure, suppress the expansion of the low-pressure region at the vortex core, and thus achieve the goal of suppressing cavitation development. This invention provides a new technical approach for the design of structural schemes to suppress cavitation.

[0045] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no reference numerals in the claims should be construed as limiting the scope of the claims. Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A blade tip clearance control skirt, characterized in that: A skirt (2) is fixed to the top edge of the blade (1), and the skirt (2) starts from the inner side of the blade (1). O To the tip of the blade P Gradually increase the thickness to form; The skirt (2) has periodically distributed protrusions on the side away from the casing wall (3). The protrusions undulate in a wave-like manner along the chord direction of the skirt (2). The contour curve of the protrusions is constructed by a cosine function and satisfies the following relationship: ； In the formula, y This represents the displacement of the convex joint in the longitudinal direction. x Let be the coordinate position along the chord. A For the amplitude of the convex junction, λ The wavelength is the convex junction wavelength.

2. The blade tip clearance control skirt according to claim 1, characterized in that, The side surface is straight in cross-section.

3. The blade tip clearance control skirt according to claim 1, characterized in that, The side surface has an inwardly concave curve in cross-section.

4. The blade tip clearance control skirt according to claim 1, characterized in that, The side surface has an outwardly convex curve in cross-section.

5. The blade tip clearance control skirt according to claim 1, characterized in that, The skirt (2) and the blade (1) are integrally cast or welded fixed structures.

6. The blade tip clearance control skirt according to claim 1, characterized in that, The peak position of the convex junction corresponds to the starting position of the leakage flow channel at the blade tip clearance, and the distribution range of the convex junction covers the peak position of the leakage flow velocity and the vortex concentration area.

7. A design method for implementing the blade tip clearance control skirt as described in claim 2, characterized in that, Includes the following steps: Step 1: Parameter Extraction; Obtain the geometric contour of the leading edge of the humpback whale's flipper, and use a sine or cosine curve for fitting to determine the amplitude of the convex knot. A With wavelength λ The range of values ​​for ; Step 2, Skirt (2) Control Curve Design; Based on Blade Tip Clearance Height δ The control curve for the skirt (2) is designed and determined by the following set of equations: ； In the formula, m、n To control the parameters of the skirt hem shape, z The coordinates are along the span direction; Step 3: Determine the distribution; Based on the development intensity of the leakage flow in the tip gap of the target axial-flow hydraulic machinery blade (1), obtain the velocity field distribution and vorticity field distribution of the leakage flow, and determine the distribution range of the convex junction on the skirt (2); The distribution range of the convex junction covers the peak position of the leakage flow velocity and the vorticity concentration area, and the peak position of the convex junction corresponds to the starting position of the leakage flow in the tip gap of the blade.

8. The design method according to claim 4, characterized in that, In step one, the geometric contour of the leading edge of the humpback whale's flipper is obtained through image processing methods, and the convex knot contour curve is processed by denoising, smoothing and parametric fitting.

9. The design method according to claim 4, characterized in that, In step two, the skirt (2) control curve It is a straight line.

10. The design method according to claim 4, characterized in that, In step three, the velocity field distribution and vorticity field distribution of the leakage flow are obtained through CFD numerical simulation or PIV experimental measurement.

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