A hydrofoil tip leakage flow vortex elimination device and impeller based on array cylindrical wake

Abstract

The present invention provides a hydrofoil tip leakage flow vortex elimination device and impeller based on an array of cylindrical wakes. The hydrofoil tip is provided with at least one semi-open groove near the leading edge. Within this semi-open groove are several arrays of cylindrical elements, with the axes of the cylindrical elements parallel to the chord length of the hydrofoil tip leading edge. This device can suppress or eliminate tip clearance leakage vortices and separation vortices caused by hydrofoil tip leakage flow, inhibit tip cavitation damage, extend the service life of the hydrofoil, and improve the operational efficiency and stability of the hydrofoil.

Description

Technical Field

[0001] The present invention relates to the technical field of fluid machinery, and in particular to a hydrofoil blade tip leakage flow vortex elimination device and an impeller based on array cylindrical wake flow. Background Art

[0002] Marine hydropower is one of the most stable and sustainable energy sources humanity can rely on in the future. The energy conversion efficiency of hydraulic machinery directly determines the social value that marine energy can provide to human society. In axial-flow hydraulic machinery (such as axial-flow pumps, waterjets, and tidal turbines), a gap between the blade tip and the casing is unavoidable. Although the tip gap is small, the pressure differential between the pressure and suction sides of the blade causes the fluid near the blade tip to move from the high-pressure side to the low-pressure side through the gap between the blade tip and the outer wall, forming a complex vortex system near the blade, including tip leakage vortices, tip separation vortices, and induced vortices. Typically, the pressure within the vortex core is much lower than the pressure in the surrounding flow field. When the vortex core pressure drops to the saturated steam pressure corresponding to that temperature, cavitation occurs at the vortex core, forming tip leakage vortex cavitation flow. The generation of tip leakage vortex cavitation in hydraulic machinery can cause changes in the local flow structure and significantly increase vibration, noise, and cavitation, leading to a decline in mechanical performance and ultimately reduced fluid machinery performance and energy conversion efficiency.

[0003] The existing research proposal is based on the hydrofoil tip leakage flow vortex elimination device of passive jet based on the working principle of Tesla valve. Although it can suppress the tip leakage vortex to a certain extent, according to the numerical simulation results, its ability to suppress the tip leakage vortex is limited, and it does not consider the suppression of the tip separation vortex. In addition, it will cause new hole separation vortex, which will increase the complexity of the vortex system in the tip area. Summary of the Invention

[0004] To address the shortcomings of the existing technology, the present invention provides a hydrofoil tip leakage flow vortex elimination device and impeller based on array cylindrical wakes. This device can suppress or eliminate tip clearance leakage vortices and separation vortices caused by hydrofoil tip leakage flow, thereby inhibiting tip cavitation damage, extending the service life of the hydrofoil, and improving the operating efficiency and stability of the hydrofoil. At the same time, it does not induce new hole separation vortices, and the suppression effect on tip separation vortices is more significant.

[0005] The present invention achieves the above technical objectives through the following technical means.

[0006] A hydrofoil blade tip leakage flow vortex elimination device based on array cylindrical wake flow, wherein the hydrofoil blade tip is provided with at least one semi-open groove near the leading edge, and a plurality of arrayed cylinders are provided in the semi-open groove, and the axis of the cylinders is parallel to the chord length of the leading edge of the hydrofoil blade tip.

[0007] Furthermore, the cross section of the semi-open groove is C-shaped, and a plurality of arrays of cylinders are provided between the end surfaces at both ends of the semi-open groove.

[0008] Furthermore, the semi-open groove includes an arc surface and an end surface; the arc surface extends from the top surface of the hydrofoil to the pressure surface of the hydrofoil; and end surfaces perpendicular to the chord length of the leading edge of the hydrofoil blade tip are provided at both ends of the arc surface.

[0009] Furthermore, the semi-open groove is located at 2%-30% of the chord length of the hydrofoil blade tip near the leading edge; the length of the semi-open groove is greater than the maximum thickness of the hydrofoil.

[0010] Furthermore, the cylinders in the plurality of arrays are staggeredly distributed along the flow direction of the C-shaped cross section of the semi-open groove.

[0011] Furthermore, the number of cylinders in the arrays distributed along the flow direction of the C-shaped cross section decreases.

[0012] Furthermore, in the cross section of the semi-open groove, the distance from the intersection of the cambered surface and the blade tip surface to the pressure surface is greater than the distance from the intersection of the cambered surface and the blade tip surface to the suction surface.

[0013] Furthermore, the distance from the intersection of the cambered surface and the blade top surface to the pressure surface is greater than 1 / 2 of the thickness of the hydrofoil cross section where the semi-open groove is located.

[0014] Furthermore, at least two semi-open grooves are provided at the blade tip of the hydrofoil near the leading edge, the numbers of cylinders distributed in adjacent semi-open grooves are different, and the number of semi-open grooves near the blade tip is the largest.

[0015] An impeller, the blades of which are provided with the hydrofoil blade tip leakage flow vortex elimination device based on array cylindrical wake flow.

[0016] The beneficial effects of the present invention are:

[0017] The hydrofoil blade tip leakage flow vortex elimination device based on the array cylinder wake of the present invention is provided with a semi-open groove at the hydrofoil blade tip and an array cylinder is arranged therein. When the hydrofoil blade tip leakage flow flows through the blade tip position, due to the large pressure difference on both sides of the hydrofoil, in addition to the original blade tip leakage flow, part of the fluid is drained through the semi-open groove and flows from the pressure surface to the blade tip gap. When flowing through the array cylinder, a complex vortex structure is formed in its wake. These complex vortex structures will impact the leakage flow in the blade tip gap and cause huge flow losses to it, thereby effectively suppressing the generation of separation vortices and blade tip leakage vortices at the hydrofoil blade tip. In addition, the blade tip leakage vortex and separation vortex caused by the hydrofoil blade tip leakage flow are suppressed or eliminated, the blade tip cavitation damage is suppressed, the service life of the hydrofoil is extended, and the operating efficiency and stability of the hydrofoil are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. The drawings described below are some embodiments of the present invention. For ordinary technicians in this field, it is obvious that other drawings can be obtained based on these drawings without paying any creative work.

[0019] Figure 1 This is a three-dimensional diagram of the hydrofoil blade tip leakage flow vortex elimination device based on the array cylindrical wake flow described in the present invention.

[0020] Figure 2 This is a partial enlarged view of the semi-open groove described in the present invention.

[0021] Figure 3 This is a cross-sectional view of the semi-open groove described in the present invention.

[0022] Figure 4 Schematic diagram of the Karman vortex street formed by the wake of flow around a cylinder.

[0023] Figure 5 Schematic diagram of a mixed complex vortex system formed by array cylinders.

[0024] Figure 6 It is a cross-sectional view of the semi-open groove of 9 cylinders in the embodiment.

[0025] Figure 7 Schematic diagram of the hydrofoil blade top elimination principle.

[0026] Figure 8 Simulation of vortex elimination of hydrofoil tip leakage flow in existing technology Figure 1 .

[0027] Figure 9 Simulation of vortex elimination of hydrofoil tip leakage flow in existing technology Figure 2 .

[0028] Figure 10 The vortex elimination simulation of the hydrofoil tip leakage flow of the present invention Figure 1 .

[0029] Figure 11 The vortex elimination simulation of the hydrofoil tip leakage flow of the present invention Figure 2 .

[0030] In the picture:

[0031] 1-cylinder; 2-semi-open groove; 2-1-arc surface; 2-2-end surface; 3-hydrofoil. DETAILED DESCRIPTION

[0032] The following describes embodiments of the present invention in detail, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present invention, and are not to be construed as limiting the present invention.

[0033] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "axial", "radial", "vertical", "horizontal", "inside", "outside" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first" and "second" are used for descriptive purposes only, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "multiple" means two or more, unless otherwise clearly and specifically defined.

[0034] In the present invention, unless otherwise expressly specified or limited, the terms "mounted," "connected," "connect," "fixed," etc. should be understood broadly. For example, they may refer to fixed, detachable, or integral connections; mechanical or electrical connections; direct or indirect connections through an intermediary; or internal communication between two components. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0035] like Figure 1 and Figure 2 As shown, the hydrofoil tip leakage flow vortex elimination device based on the array cylinder wake of the present invention has at least one semi-open groove 2 provided at the tip of the hydrofoil 3 near the leading edge, and a plurality of array cylinders 1 are provided in the semi-open groove 2, and the axis of the cylinder 1 is parallel to the chord length of the leading edge of the hydrofoil tip. When the hydrofoil tip leakage flow flows through the tip position, due to the large pressure difference on both sides of the hydrofoil, in addition to the original tip leakage flow, part of the fluid is drained through the semi-open groove and flows from the pressure surface to the tip gap. When flowing through the array cylinder, a complex vortex structure is formed in its wake. These complex vortex structures will impact the leakage flow in the tip gap and cause huge flow losses to it, thereby effectively suppressing the generation of separation vortices and tip leakage vortices at the hydrofoil tip.

[0036] like Figure 2 and Figure 3As shown, the cross section of the semi-open groove 2 is C-shaped, and a plurality of arrays of cylinders 1 are provided between the end surfaces at both ends of the semi-open groove 2. The semi-open groove 2 includes a cambered surface 2-1 and an end surface 2-2; the cambered surface 2-1 extends from the top surface of the hydrofoil 3 to the pressure surface of the hydrofoil 3; and the ends of the cambered surface 2-1 are provided with end surfaces 2-2 perpendicular to the chord length of the leading edge of the hydrofoil tip. In the cross section of the semi-open groove 2, the distance from the intersection of the cambered surface 2-1 and the top surface to the pressure surface is greater than the distance from the intersection of the cambered surface 2-1 and the top surface to the suction surface. The distance from the intersection of the cambered surface 2-1 and the top surface to the pressure surface is greater than 1 / 2 of the cross-sectional thickness of the hydrofoil 2 where the semi-open groove 2 is located.

[0037] In the embodiment, the semi-open groove 2 is located at the top surface of the hydrofoil blade near the leading edge. The specific position is related to the angle of attack of the hydrofoil 3 and the size of the blade tip clearance. Generally, when the angle of attack of the hydrofoil 3 is in the range of 8 to 12°, the blade tip clearance is 1 to 5 mm, and the incoming flow velocity is 7.5 to 12.5 m / s, the semi-open groove 2 can be arranged at the top wall of the hydrofoil blade near the leading edge at a chord length of 2% to 30%. The length and radius of the semi-open groove 2 depend on the installation and working conditions of the hydrofoil. Generally, the length of the semi-open groove 2 is greater than the maximum thickness of the hydrofoil 2. Figure 3 As shown, on the cross section of the semi-open groove 2, the intersection point of the arc surface 2-1 with the pressure surface of the hydrofoil is B, the intersection point with the blade top surface is A, and the intersection point with the intersection line of the blade top surface and the pressure surface is O. It is necessary to ensure that the lengths of OB and OA are basically the same and are greater than 1 / 2 times the thickness of the hydrofoil where the semi-open groove 2 is located.

[0038] The number, arrangement and distance between the cylinders 1 in the array are determined according to the working conditions faced by the hydrofoil. Figure 3 As shown, from the cross section of the semi-open groove 2, the number of cylinders 1 in the arrays decreases along the flow direction of the C-shaped cross section, and along the flow direction of the C-shaped groove section, the rear row of cylinders and the front row of cylinders are staggered. Specifically, in Example 1, as shown Figure 3 As shown in the figure, three cylinders 1 are distributed in the semi-open groove 2. When viewed from the direction of the incoming flow when the hydrofoil is working, the array cylinders in the C-shaped groove on the cross section are arranged in an L-shaped manner, with two cylinders 1 arranged side by side near the pressure surface and one cylinder 1 provided near the blade tip surface. Figure 6 As shown in the figure, 9 cylinders 1 are distributed in the semi-open groove 2. On the C-shaped groove cross section, 3 cylinders 1 are arranged side by side at the inlet of the flow direction (i.e., close to the pressure surface side), 1 cylinder 1 is provided near the top surface side of the blade, and there are 5 cylinders 1 distributed staggered in the middle.

[0039] At least two semi-open grooves 2 are provided at the blade tip near the leading edge of the hydrofoil 3 . The numbers of cylinders 1 distributed in adjacent semi-open grooves 2 are different, and the number of semi-open grooves 2 near the blade tip is the largest.

[0040] like Figure 1 As shown in the figure, in the vortex-eliminating design of the hydrofoil tip, the processing of the semi-open groove 2 and the array cylinder only changes the structure of the hydrofoil tip near the leading edge. The processing can be done by traditional machining based on the prototype hydrofoil, or by 3D printing and fine grinding.

[0041] like Figure 4 and Figure 5 As shown, in the present invention, when a fluid flows through cylinder 1, a pair of regularly arranged linear vortices with opposite rotational directions periodically shed from both sides of the cylinder 1. Through nonlinear interaction, this creates a Karman vortex street. The formation of a Karman vortex street significantly depletes the kinetic energy of the fluid in the flow field. In the alternating arrangement of cylinders 1, a complex vortex system of mixed flow is generated at the tail of the cylinder 1, thereby increasing the kinetic energy loss of the wake fluid and decelerating the wake fluid.

[0042] For existing hydrofoils, the fluid near the tip area leaks from the pressure side to the suction side through the tip gap, forming a separation vortex in the gap and a tip leakage vortex and an induced vortex on the suction side of the hydrofoil. Figure 7 As shown, a semi-open groove 2 and an array cylinder 1 are arranged at the tip of the hydrofoil. Based on the principle that the wake of the array cylinder will generate a complex vortex system, the high-pressure fluid on the pressure side can be guided and laterally impacted against the tip leakage flow through the semi-open groove 2, and a complex vortex system is generated when passing through the array cylinder. These complex vortex systems will hinder the leakage flow and greatly increase the flow loss of the tip leakage flow, thereby effectively suppressing the generation of the hydrofoil tip separation vortex and the tip leakage vortex. The complex vortex system wake of the array cylinder guided by the C-shaped groove of the present invention can effectively suppress or eliminate the tip gap leakage vortex and separation vortex caused by the hydrofoil tip leakage flow, suppress the tip cavitation damage, extend the service life of the hydrofoil, and improve the operating efficiency and stability of the hydrofoil.

[0043] The blade tip leakage flow vortex elimination device of the prior art and the blade tip leakage flow vortex elimination device of the present invention are simulated and compared. Figure 8 and Figure 9 As shown in the figure, under the working conditions of speed 10m / s, blade tip clearance 2mm, and hydrofoil attack angle 10°, the vortex isosurface distribution (Q = 7×10 6 s -2) and pressure isosurface distribution (P=3574Pa). Among them, the vortex isosurface distribution can reflect the size of the tip leakage vortex, tip separation vortex and induced vortex generated by each scheme in the tip clearance area. The smaller the distribution volume of the vortex isosurface, the smaller the vortex generated in the tip area, the more stable the flow state of the local fluid, and the better the mechanical properties of the hydrofoil. The pressure isosurface represents the theoretical cavitation area, that is, under actual conditions, cavitation will occur in these areas. The smaller the pressure isosurface volume distribution, the milder the vortex cavitation caused by the vortex in the tip area, and the smaller the impact on the mechanical properties of the hydrofoil. Therefore, by comparing the size of the vortex isosurface and pressure isosurface distribution in the tip area of ​​each scheme, the vortex elimination ability of each technical scheme can be reflected. The smaller the vortex isosurface and pressure isosurface distribution in the tip area, the better the vortex elimination effect of the scheme. As Figure 8 and Figure 9 As shown in the figure, while existing technologies effectively suppress tip leakage vortices and the theoretical tip cavitation region, they fail to address the suppression of tip leakage vortices. Furthermore, due to the presence of Tesla jet holes, existing technologies also generate new hole separation vortices within the tip clearance region. This increases the complexity of the fluid flow pattern in the tip clearance region, negatively impacting hydrofoil performance.

[0044] like Figure 10 and Figure 11 As shown, under the same operating conditions, the present invention has a very significant effect on suppressing the tip leakage vortex isosurface and pressure isosurface. The vortex isosurface distribution and the pressure isosurface distribution are significantly reduced compared to the prior art, indicating that the tip leakage vortex, the tip separation vortex, and the theoretical cavitation area are all greatly suppressed, and no new hole separation vortex is generated. Only a small amount of separation vortex exists on the cylindrical surface inside the C-shaped groove and at the boundary of the C-shaped groove, but its impact is almost negligible. Therefore, the device of the present invention has a good suppressive effect on the hydrofoil tip clearance leakage vortex (TLV) and separation vortex.

[0045] An impeller, the blades of which are provided with the hydrofoil blade tip leakage flow vortex elimination device based on array cylindrical wake flow.

[0046] It should be understood that although this specification is described according to various embodiments, not every embodiment contains only one independent technical solution. This narrative method of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment can also be appropriately combined to form other implementation methods that can be understood by those skilled in the art.

[0047] The series of detailed descriptions listed above are only specific descriptions of feasible embodiments of the present invention. They are not intended to limit the scope of protection of the present invention. Any equivalent embodiments or changes that do not deviate from the technical spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A hydrofoil tip leakage flow vortex elimination device based on array cylindrical wake, characterized in that: At least one semi-open groove (2) is provided at a position near the leading edge of the blade tip of the hydrofoil (3); a plurality of arrays of cylinders (1) are provided in the semi-open groove (2); and the axes of the cylinders (1) are parallel to the chord length of the leading edge of the blade tip of the hydrofoil; The cross section of the semi-open groove (2) is C-shaped, and a plurality of arrays of cylinders (1) are provided between the end faces at both ends of the semi-open groove (2); the number of the plurality of arrays of cylinders (1) is distributed in decreasing order along the flow direction of the C-shaped cross section.

2. The hydrofoil tip leakage flow vortex elimination device based on array cylindrical wake according to claim 1 is characterized in that: The semi-open groove (2) comprises a cambered surface (2-1) and an end surface (2-2); the cambered surface (2-1) extends from the top surface of the hydrofoil (3) to the pressure surface of the hydrofoil (3); and end surfaces (2-2) perpendicular to the chord length of the leading edge of the hydrofoil blade tip are provided at both ends of the cambered surface (2-1).

3. The hydrofoil tip leakage flow vortex elimination device based on array cylindrical wake according to claim 1 is characterized in that: The semi-open groove (2) is located at a position of 2%-30% of the chord length of the hydrofoil blade tip close to the leading edge; the length of the semi-open groove (2) is greater than the maximum thickness of the hydrofoil (3).

4. The hydrofoil tip leakage flow vortex elimination device based on array cylindrical wake according to claim 1, characterized in that: Several arrays of cylinders (1) are staggeredly distributed along the flow direction of the C-shaped cross section of the semi-open groove (2).

5. The hydrofoil tip leakage flow vortex elimination device based on array cylindrical wake according to claim 2, characterized in that: In the cross section of the semi-open groove (2), the distance from the intersection of the cambered surface (2-1) and the blade top surface to the pressure surface is greater than the distance from the intersection of the cambered surface (2-1) and the blade top surface to the suction surface.

6. The hydrofoil tip leakage flow vortex elimination device based on array cylindrical wake according to claim 5, characterized in that: The distance from the intersection of the cambered surface (2-1) and the blade top surface to the pressure surface is greater than 1 / 2 of the cross-sectional thickness of the hydrofoil (3) where the semi-open groove (2) is located.

7. The hydrofoil tip leakage flow vortex elimination device based on array cylindrical wake according to claim 1, characterized in that: At least two semi-open grooves (2) are provided at the tip of the hydrofoil (3) near the leading edge, and the number of cylinders (1) distributed in adjacent semi-open grooves (2) is different.

8. An impeller, characterized in that: The impeller blades are provided with a hydrofoil tip leakage flow vortex elimination device based on array cylindrical wake flow as described in any one of claims 1 to 7.

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