A turbine blade for suppressing break-up of a tip leakage vortex

Abstract

This invention provides a turbine blade for suppressing tip leakage vortex breakup. Based on a conventional turbine blade with a grooved tip, both the suction-side ribs and the pressure-side ribs are designed to be inclined. The two side walls of the suction-side ribs have different inclination directions: the outer wall inclines outward from the gap, while the inner wall inclines inward. The pressure-side ribs are all inclined outward from the gap, meaning both the inner and outer walls of the pressure-side ribs incline outward. The inclined sections of the ribs are all circular arcs, and their shape is determined by the inclination angle and the height of the inclined section. The inclination angle of the ribs varies at different cross-sectional positions, ensuring a smooth transition of the rib inclination. The advantage of this invention is that, through this turbine blade, tip leakage vortex breakup can be suppressed, reducing mixing losses caused by breakup; this structure can also further reduce tip leakage flow, thereby reducing mixing losses between the leakage flow and the mainstream, thus significantly improving the aerodynamic performance of the turbine.

Description

Technical Field

[0001] This invention belongs to the field of turbine technology, and specifically relates to a turbine blade for suppressing tip leakage vortex breakage. Background Technology

[0002] Turbine tip leakage loss is a significant component of turbine aerodynamic losses. High-pressure turbine shrouded rotor blades typically employ grooved tip structures to control tip leakage flow, aiming to reduce the flow rate and momentum of the leakage flow, thus contributing to reduced tip leakage loss and improved turbine aerodynamic performance. The traditional grooved tip structure primarily controls the evolution of vortex structures within the clearance, thereby controlling leakage flow, but its impact on the evolution of vortex structures within the passage is relatively small. However, the mechanism of leakage loss in the turbine tip region is extremely complex, involving not only the mixing of the leakage flow with the mainstream but also the breaking up of leakage vortices and the interaction between complex multi-scale vortex systems in the tip region. Therefore, tip leakage flow control and tip vortex evolution control in shrouded rotors remain hot and challenging issues in current turbine aerodynamic research.

[0003] Blade tip leakage losses can be broadly categorized spatially into internal and external gap losses. Internal gap losses are primarily caused by the mixing and dissipation between the leakage flow and the vortex structure within the gap. External gap losses have a more complex mechanism, including not only the mixing loss between the leakage flow and the mainstream, but also additional mixing losses caused by the breakup of leakage vortices generated by the leakage flow.

[0004] Current development trends in gas turbines and gas turbines favor high performance and high load. High-pressure turbines typically operate under transonic conditions, leading to the breakup of tip leakage vortices downstream of the throat due to strong adverse pressure gradients. This also signifies the prevalence of leakage vortex breakup. Currently, traditional grooved tip structures focus on reducing mixing losses between the leakage flow and the mainstream flow, achieving this reduction by decreasing leakage flow rate and momentum. However, this approach cannot directly affect leakage vortex breakup, let alone suppress it.

[0005] Furthermore, both the losses within the clearance and the mixing losses between the tip leakage flow and the mainstream outside the clearance are closely related to the flow rate and momentum of the leakage flow. As long as tip leakage flow exists, these losses will inevitably exist. In the pursuit of turbine components with higher performance, the blocking effect of current conventional grooved blade tip structures on tip leakage flow needs further improvement. Summary of the Invention

[0006] This invention aims to provide a turbine blade for suppressing tip leakage vortex breakup. By reducing the adverse pressure gradient experienced by the tip leakage vortex, the breakup of the tip leakage vortex is suppressed, thereby reducing the mixing loss caused by breakup. Furthermore, the inclined rib configuration provided in this invention can also reduce the tip leakage flow rate by enhancing the aerodynamic grating effect of the scraping vortex within the groove, thereby reducing the mixing loss between the leakage flow and the mainstream. The combined effect of these two effects significantly improves turbine stage efficiency. The effectiveness of this tip structure has been verified through numerical simulation. In the embodiments, the breakup of the leakage vortex was completely suppressed, and the leakage flow rate was also significantly reduced, resulting in a significant improvement in turbine aerodynamic performance.

[0007] The specific technical solution is as follows:

[0008] A turbine blade for suppressing tip leakage vortex breakage is based on a turbine blade with a conventional grooved tip structure. While keeping the tip clearance height τ and rib height H constant, the pressure side ribs and suction side ribs are designed to be inclined along a specific direction and line.

[0009] The inner and outer walls of the suction side ribs are inclined in different directions; the outer wall is inclined outward from the gap, while the inner wall is inclined inward from the gap.

[0010] The pressure-side ribs are all inclined outwards from the gap, that is, both the inner and outer walls of the pressure-side ribs are inclined outwards from the gap.

[0011] The specific linear shape refers to a cross-section perpendicular to the mid-arc line of the blade tip, where the inclined sections of the inner and outer walls of both the suction-side and pressure-side ribs are circular arcs. The center O and radius r of these arcs are determined by the inclination angle θ and the height h of the circular arc of the inclined section. The lowest point of the inclined section remains tangent to the original shape, and the line connecting the center O and the lowest point of the inclined section is perpendicular to the blade. The radius can then be determined by the following formula:

[0012] r = h / sinθ

[0013] The height h of the inclined arc is taken as the larger of three times the tip clearance height τ and the rib height H, that is, h = max(3τ,H).

[0014] The angle θ of the rib's inclination varies in different cross-sectional positions. At the leading edge (5%–10% arc length) and trailing edge (90%–95% arc length), the angle θ of each rib's wall surface is 0°, meaning the rib is not inclined in these two surfaces. Within the range of 40%–60% arc length, the rib's inclination angle θ reaches its maximum value. max θ max The value ranges from 45° to 75°.

[0015] From the location of the leading edge surface to the maximum tilt angle θmax Location and maximum tilt angle θ max Within the two intervals from the location of the rib to the location of the trailing edge, the tilt angle θ changes monotonically increasing and monotonically decreasing, respectively, ensuring a smooth transition of the rib's tilt.

[0016] In the same cross-section perpendicular to the mid-curve of the blade tip, the inclination angles of the inner and outer walls of the suction-side rib can be different, with the inclination angle of the inner wall being θ. s1 The inclination angle of its outer wall is θ s2 The inner and outer walls of the pressure-side ribs have the same inclination angle, θ. p .

[0017] The advantages of this invention are as follows: Through a suitable inclined rib design, the breakup of the tip leakage vortex is effectively suppressed, and the aerodynamic grate sealing effect of the scraped vortex structure within the gap is further enhanced, reducing leakage flow and effectively controlling the tip leakage flow and the evolution of the tip leakage vortex, thus improving turbine aerodynamic performance. The inner wall of the suction-side rib is inclined inwards towards the gap, which reduces the distance between the scraped vortex and the suction-side rib, enhancing the aerodynamic grate sealing effect of the scraped vortex, effectively blocking leakage flow, and reducing leakage flow. The outer wall of the suction-side rib is inclined outwards towards the gap, which significantly reduces the trailing edge suction peak downstream of the blade's suction-side throat, i.e., reduces the adverse pressure gradient at this location. Since the breakup of the tip leakage vortex is mainly affected by the adverse pressure gradient, as the adverse pressure gradient decreases, the breakup of the tip leakage vortex is effectively suppressed, thereby significantly reducing the losses caused by the breakup of the leakage vortex. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the geometric structure of a turbine blade with a conventional grooved tip and its tip cross-section in the prior art.

[0019] Figure 2 This is a schematic diagram of a turbine blade with inclined ribs at the tip, as described in this invention.

[0020] Figure 3 This is a schematic diagram of the cross-sectional geometry and configuration parameters of the inclined rib blade tip structure in this invention;

[0021] Figure 4 This is a schematic diagram of the blade tip profile, mid-curve, and cross-section perpendicular to the mid-curve from a top-down view of a prototype turbine blade.

[0022] Figure 5 This is a schematic diagram showing the inclination angles of the ribs on the leading edge, trailing edge, and maximum inclination surfaces of the inclined rib blade tip structure in this invention.

[0023] Figure 6 This refers to the distribution of leakage per unit length at the gap outlet along the arc length direction between the inclined rib blade tip structure and the traditional groove blade tip structure in this invention.

[0024] Figure 7 This is a comparison of the internal streamline distribution of the tip leakage vortex in the inclined rib blade tip structure of this invention and the traditional grooved blade tip structure.

[0025] Explanation of reference numerals in the attached figures:

[0026] 1. Rotor blade; 2. Casing; 3. Pressure side rib; 4. Suction side rib; 5. Cross section perpendicular to the mid-curve of the blade tip airfoil; 11. Prototype turbine blade blade tip airfoil; 12. Mid-curve of the prototype turbine blade blade tip airfoil; 31. Inner wall surface of the pressure side rib; 32. Outer wall surface of the pressure side rib; 41. Inner wall surface of the suction side rib; 42. Outer wall surface of the suction side rib; 50. Leading edge surface; 51. Trailing edge surface; 52. Maximum inclination surface; h. Height of the rib inclination section; H. Height of the rib; O. Center of the arc of the rib inclination section; r. Radius of the arc of the rib inclination section; t p Thickness of the pressure-side ribs; t s The thickness of the suction ribs; α, the angle between the ribs and the groove bottom plate; θ, the inclination angle of the rib wall surface; θ p Specifically refers to the inclination angle of the inner and outer walls of the pressure-side rib; θ s1 Specifically refers to the inclination angle of the inner wall surface of the suction-side rib; θ s2 Specifically refers to the inclination angle of the outer wall surface of the suction-side rib; θ max τ refers to the maximum tilt angle of the rib wall surface; τ is the tip clearance height. Detailed Implementation

[0027] The objectives, technical solutions, and advantages of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0028] For turbine blades employing a traditional grooved tip structure, their geometry is as follows: Figure 1 As shown, the rotor blade 1 has two ribs at its tip: a pressure-side rib 3 and a suction-side rib 4, which together form a closed groove at the tip. An enlarged view of the rotor blade's cross-section 5 shows the geometry of the tip profile. The distance between the casing 2 and the blade 1 is the tip clearance height τ, and the thickness of the pressure-side rib 3 is t. p The thickness of the suction side rib 4 is t. s Both sides of the ribs are perpendicular to the bottom plate of the groove (i.e., α = 90°), and the height of both sides of the ribs is H.

[0029] This invention provides a turbine blade for suppressing tip leakage vortex breakage. Based on the aforementioned turbine blade employing a conventional grooved tip structure, while maintaining the tip clearance height τ and rib height H constant, the suction-side rib 4 and pressure-side rib 3 of the rotor blade 1 are designed to be inclined along a specific direction and line shape, such as... Figure 2 As shown.

[0030] Figure 3 The tip geometry of the turbine blade at a cross section 5 perpendicular to the blade tip airfoil is shown in this invention. The inclination directions of the two side walls of different ribs are different. The inner wall 41 of the suction side rib is inclined towards the inside of the gap, and the outer wall 42 of the suction side rib is inclined outward. The pressure side rib 3 is inclined outward as a whole, that is, both the inner wall 31 and the outer wall 32 of the pressure side rib are inclined outward.

[0031] In addition, such as Figure 3 As shown, the line shape and configuration method of each inclined segment are consistent. The line shape of each inclined segment is a circular arc, with its center at point O and radius r, which can be determined by the rib inclination angle θ of the cross section and the height h of the circular arc of the inclined segment. First, the lowermost end of the inclined segment is kept tangent to the prototype, and the line connecting the center O and the lowermost end of the inclined segment is perpendicular to the blade. Then the radius can be determined by the following formula:

[0032] r = h / sinθ

[0033] The design parameters for the arc shape of the inclined segment are the inclination angle θ of the rib and the height h of the inclined part of the rib. Once these two parameters in the cross-section are determined, the arc of the inclined segment of the rib can be uniquely determined.

[0034] In this invention, the height h of the inclined arc segment is taken as the larger of three times the tip clearance height τ and the rib height H, that is, h = max(3τ,H).

[0035] In this invention, the rib inclination angle θ varies in cross-sections at different locations. To determine the value of the rib inclination angle θ at different locations, the location is first defined. The location is defined using the mid-arc line 12 of the prototype turbine blade tip profile 11, as follows: Figure 4 As shown. Each cross-section is perpendicular to the central arc 12, and the position of the cross-section is defined according to the percentage of the arc length of the central arc.

[0036] like Figure 5 As shown, in the leading edge surface 50 (5%–10% arc length position) and the trailing edge surface 51 (90%–95% arc length position), the tilt angle θ is 0°, meaning that neither the inner nor outer wall surfaces of the two side ribs are tilted; in the maximum tilt surface 52 within the range of 40%–60% arc length, the tilt angle θ reaches its maximum value. max θ max The value is 45°–75°. Within the two intervals from the leading edge surface 50 to the maximum inclined surface 52, and from the maximum inclined surface 52 to the trailing edge surface 51, the inclination angle θ changes monotonically increasing and monotonically decreasing, respectively, ensuring a smooth transition of the rib inclination.

[0037] In addition, such as Figure 3As shown, in this invention, the inclination angles θ of the inner wall surface 41 and the outer wall surface 42 of the suction-side rib within the same cross-section 5 can be different, namely θ1, θ2, θ3, θ4, θ5, θ6, θ7, θ8, θ9, θ10, θ11, θ2, θ9, θ10, θ2 ... s1 and θ s2 The inclination angle θ of the inner wall surface 31 and the outer wall surface 32 of the pressure side rib are the same, both being θ. p .

[0038] In this invention, the tilting method, tilting segment line shape, and configuration of the suction-side rib 4 are key to suppressing leakage vortex breakup and reducing leakage flow. The tilting direction of the outer wall surface 42 of the suction-side rib must face outward from the gap. In the cross-section perpendicular to the mid-arc line, the line shape of its tilting segment should be a circular arc, the main purpose of which is to suppress leakage vortex breakup. The tilting direction of the inner wall surface 41 of the suction-side rib should face inward from the gap. Its function is to reduce the distance between the scraping vortex and the inner wall surface 41 of the suction-side rib, thereby enhancing the aerodynamic grate sealing effect of the scraping vortex, enhancing the blocking effect on the tip leakage flow, and reducing the leakage flow.

[0039] Based on the numerical simulation results of a certain type of high-pressure turbine, the flow field parameters and characteristics of the traditional grooved blade tip structure and the inclined rib blade tip structure in this invention were analyzed. Figure 6 A comparison of the leakage per unit length at the gap outlet along the arc length direction between the inclined rib blade tip structure of this invention and the traditional grooved blade tip structure is presented. Using the blade tip structure of this invention, leakage flow can be blocked more effectively at the 30%–80% arc length position, reducing leakage flow rate.

[0040] Figure 7 A comparison of the streamline distribution within the tip leakage vortex of the inclined ribbed blade tip structure in this invention and the traditional grooved blade tip structure is presented. With the traditional single-groove blade tip, significant backflow is observed in the streamlines within the tip leakage vortex, indicating that the tip leakage vortex has broken up. However, with the inclined ribbed blade tip structure of this invention, no backflow is observed in the streamlines within the tip leakage vortex, indicating that the breaking up of the tip leakage vortex is suppressed.

[0041] Table 1 Comparison of numerical simulation results for high-pressure turbines

[0042]

[0043] Table 1 compares the vortex evolution characteristics, leakage flow aerodynamic parameters, and overall aerodynamic performance changes of high-pressure turbines using a traditional grooved blade tip structure and the inclined rib blade tip structure of this invention. The dimensionless leakage rate is the ratio of the tip leakage flow rate to the mainstream flow rate. Based on the traditional grooved blade tip structure, the tip leakage vortex breakup phenomenon disappears in this invention, the tip leakage rate is relatively reduced by 6.6%, and the turbine stage efficiency is improved by 0.24%, resulting in significant aerodynamic performance changes.

Claims

1. A turbine blade for suppressing tip leakage vortex breakage, characterized in that, Based on the turbine blade with a traditional grooved blade tip structure, with the blade tip clearance height τ and rib height H remaining unchanged, both the suction side rib (4) and the pressure side rib (3) are designed as inclined ribs. The characteristic is that the line shape of the inclined section of the rib is an arc, and the rib inclination direction is as follows: The two sides of the suction side rib (4) have different inclination directions. The inner wall (41) of the suction side rib is inclined towards the gap, while the outer wall (42) of the suction side rib is inclined towards the gap. The pressure side ribs (3) are all inclined outwards towards the gap, that is, the inner wall surface (31) and the outer wall surface (32) of the pressure side ribs are both inclined outwards towards the gap. In the cross section (5) perpendicular to the blade tip arc (12), the inclined sections of the inner and outer walls of the suction side rib (4) are all circular arcs, and their center O and radius r are determined by the inclination angle θ and the height h of the circular arc of the inclined section. The lowest end of the inclined section is tangent to the prototype, and the line connecting the center O and the lowest end of the inclined section is perpendicular to the blade. The radius is determined by the formula r=h / sinθ. The line shape and shaping method of the pressure side rib (3) are the same as those of the suction side rib (4). The inclination angle θ of the ribs varies in different cross sections; the leading edge (50) is at 5%–10% of the arc length, and the trailing edge (51) is at 90%–95% of the arc length. The inclination angle θ of the rib wall in both the leading edge (50) and trailing edge (51) is 0°, that is, the ribs in the leading edge (50) and trailing edge (51) are not inclined; the rib inclination angle θ reaches its maximum value in the maximum inclination surface (52) within the range of 40%–60% of the arc length. max θ max The value is 45°–75°; in the two intervals from the leading edge (50) to the maximum inclined surface (52) and from the maximum inclined surface (52) to the trailing edge (51), the inclination angle θ changes monotonically increasing and monotonically decreasing respectively, ensuring a smooth transition of the rib inclination.

2. A turbine blade for suppressing tip leakage vortex breakage according to claim 1, characterized in that, The height h of the inclined arc is taken as the larger of three times the tip clearance height τ and the rib height H, that is, h = max(3τ,H).

3. A turbine blade for suppressing tip leakage vortex breakage according to claim 1, characterized in that, In the same cross section (5), the inclination angles θ of the inner wall surface (41) and the outer wall surface (42) of the suction side rib are different, respectively θ s1 and θ s2 The inclination angle θ of the inner wall surface (31) and the outer wall surface (32) of the pressure side rib are the same, both being θ. p .

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