Turbine rotor double-groove tip structure based on scraping vortex control

Abstract

The application provides a turbine rotor double-groove tip structure based on scraping vortex control, which comprises three ribs, namely a pressure side rib, a suction side rib and a middle rib, and the three ribs are located at the top of a crownless turbine rotor blade; the pressure side rib and the suction side rib are connected at the front and tail edges, and a groove is formed in the middle of the top of the rotor blade; the middle rib divides the groove into two sub-grooves, one of which is a pressure side groove near the pressure side rib, and the other is a suction side groove near the suction side rib. The application makes full use of the tip groove structure, forms a double aerodynamic staggered tooth labyrinth seal structure, increases the included angle between the leakage flow and the top of the rib, enhances the separation bubble at the top of the rib, reduces the effective flow area of the leakage flow, thereby inhibits the tip leakage flow, reduces the flow rate and momentum of the tip leakage flow, reduces the mixing loss of the tip leakage flow and the main flow, reduces the aerodynamic loss of the turbine, and improves the aerodynamic performance of the turbine.

Description

Technical Field

[0001] This invention relates to a turbine rotor double-groove blade tip structure based on scraping vortex control, belonging to the field of turbine technology. Background Technology

[0002] As one of the three core components of a gas turbine, the turbine is used to convert the energy in the fluid working medium into mechanical energy. As a rotating impeller machine, considering safety and reliability, and to prevent the rotor blades from scraping against the casing, a gap, known as the blade tip clearance, is necessary between them. Furthermore, due to the characteristics of its flow field, there is a large pressure difference on both sides of the gap, making blade tip clearance leakage in the turbine rotor impossible to eliminate.

[0003] Turbine rotor tip leakage flow often has multiple impacts on work capacity, aerodynamic performance, and heat transfer performance. Increased tip leakage flow means less fluid participates in work, leading to a decrease in turbine work capacity. After exiting the gap on the suction side of the blade, the tip leakage flow forms tip leakage vortices, enhancing the three-dimensionality and unsteadiness of the flow field. Furthermore, the mixing of the leakage flow with the mainstream causes significant aerodynamic losses. In gas turbines, the tip leakage flow is a high-temperature gaseous working fluid, which can easily cause ablation at the turbine rotor blade tips, reducing blade life. Therefore, reducing turbine tip leakage flow and minimizing turbine tip leakage losses are crucial for improving the efficiency of modern gas turbine turbine components.

[0004] Different methods are used to suppress tip leakage flow for different types of turbines. Generally, for high-pressure turbines, a grooved blade tip structure is used to suppress tip leakage flow; for low-pressure turbines, a crowned rotor structure is used. In high-pressure turbine rotor structures, a traditional grooved blade tip refers to a blade with pressure-side and suction-side ribs at the tip, with the two ribs connected at the leading and trailing edges, and a concave cavity structure in the middle of the blade tip, forming a single-groove structure. Figure 1 As shown.

[0005] Studies have shown that the mechanism by which the grooved blade tip suppresses tip leakage flow is the aerodynamic staggered-tooth sealing effect. This effect is actually composed of the pressure-side ribs, the suction-side ribs, and the scraping vortex structure within the cavity, such as... Figure 2 As shown, the scraping vortex is the key flow structure that forms this effect, forming a staggered grate-like sealing structure with the side ribs. The sealing effect of this structure is closely related to the grate spacing and the number of ribs. Similarly, controlling the scraping vortex flow structure is crucial to the flow affecting tip leakage.

[0006] Currently, there is a lack of research on customized control of scraped vortex structure and enhancement of aerodynamic staggered tooth sealing effect, and it is difficult to find relevant results and theories. However, this is precisely the key to further enhancing the control of tip leakage flow. Therefore, it is necessary to propose a crownless turbine rotor tip structure that can further enhance the aerodynamic staggered tooth sealing effect. Summary of the Invention

[0007] To address the aforementioned problems, this invention aims to propose a crownless turbine rotor blade tip structure that can enhance the scraping vortex and the resulting aerodynamic staggered tooth sealing effect. This structure can be customized to improve the scraping vortex morphology, better suppress tip leakage flow, reduce the entry of high-temperature gas into the tip clearance, reduce aerodynamic losses caused by the mixing of leakage flow and mainstream flow, and improve turbine aerodynamic performance.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A double-groove blade tip structure based on scraping vortex control includes three ribs: a pressure-side rib, a suction-side rib, and a central rib. All three ribs are located at the tip of a crownless turbine rotor blade. The leading and trailing edges of the pressure-side rib and the suction-side rib are connected to form a groove in the middle of the blade tip. The central rib divides the groove into two sub-grooves: the one closer to the pressure-side rib is the pressure-side groove, and the one closer to the suction-side rib is the suction-side groove.

[0010] Within the two grooves mentioned above, the relative motion of the casing causes the leakage flow to generate strong scraping vortices, resulting in a pneumatic staggered-tooth grate sealing effect in each groove, and ultimately creating a multi-layered pneumatic staggered-tooth grate sealing effect. The presence of scraping vortices also alters the angle at which the leakage flow exits. The stronger the scraping vortex, the larger the angle between the leakage flow and the blade tip, and the stronger the separation bubble at the rib top. This reduces the flow area of ​​the leakage flow and significantly lowers the leakage rate. Especially after scraping vortices form in the two grooves, the leakage flow is blocked by the central rib and the suction-side rib, respectively, making the leakage flow control effect even more pronounced.

[0011] In a preferred embodiment of the present invention, the ribs include at least one pressure-side rib, one suction-side rib, and one central rib.

[0012] In a preferred embodiment of the present invention, the pressure-side ribs and suction-side ribs should be connected at both the front and rear edges, that is, the two ribs should be continuous, and are collectively referred to as the outer ribs in the present invention.

[0013] In a preferred embodiment of the present invention, the centerline of the central rib should be substantially along the direction of the central arc of the blade tip shape, that is, the direction of the central rib is substantially along the mainstream flow direction.

[0014] In a preferred embodiment of the present invention, the starting point and the ending point of the middle rib should be on the outer rib, so the middle rib must be connected to the outer rib, and there must be two grooves on the blade tip, located on the pressure side and the suction side respectively. The starting point and the ending point of the middle rib determine the relative size of the grooves on both sides, as well as the length-to-width ratio of each groove.

[0015] In a preferred embodiment of the present invention, under the premise of ensuring the processing limit and the strength of the blade tip structure, the thickness of the pressure side rib, the suction side rib and the middle rib should be as small as possible. It is recommended that the rib thickness be 1-2 times the hot blade tip clearance height.

[0016] In a preferred embodiment of the invention, the height of the rib, i.e. the height of the groove, should be 2.5–3.5 times the height of the hot blade tip clearance.

[0017] In a preferred embodiment of the present invention, the maximum width of each of the two sub-grooves should be more than 7.5 times the height of the hot blade tip clearance. The maximum width of the groove is defined as the distance between the intersection of the straight line perpendicular to the arc in the groove profile and the two sides of the groove profile.

[0018] In a preferred embodiment of the present invention, limited by the maximum blade thickness, in order to maximize the maximum width of the two sub-grooves, the pressure-side ribs and suction-side ribs can be configured as inclined structures, that is, the angle between the ribs and the groove bottom plate is obtuse. If, even with this inclined structure, it is still impossible to guarantee that the maximum width of both grooves is above 7.5 times the hot blade tip clearance height, the double-grooved blade tip structure proposed in this invention is not recommended.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects:

[0020] In the structure of this invention, the central ribs are oriented basically along the flow direction, which will not destroy the original scraping vortex structure in the groove blade tip, and will help reduce the distance between the scraping vortex and the ribs on both sides of the groove, enhance the aerodynamic staggered tooth sealing effect, more effectively suppress blade tip leakage flow, and effectively reduce leakage flow.

[0021] In the structure of this invention, since there are two sub-grooves at the blade tip, and each has a sufficient maximum width, an effective scraping vortex structure is formed within both sub-grooves, and an aerodynamic staggered-tooth grate sealing effect is achieved within both sub-grooves. Because most of the blade tip leakage flow will flow through the two sub-grooves, under the action of the scraping vortices, the angle between the leakage flow and the blade tip increases, the leakage flow area decreases, and the leakage flow rate and leakage volume decrease. This effectively reduces the mixing loss between the leakage flow and the mainstream, improving the turbine aerodynamic performance. Attached Figure Description

[0022] Figure 1This is a schematic diagram of a traditional single-groove blade tip structure;

[0023] Figure 2 This is a schematic diagram of the flow topology inside the tip gap of a traditional single-groove blade.

[0024] Figure 3 This is a schematic diagram of the double-groove blade tip structure in this invention;

[0025] Figure 4 This is a top view of the double-groove blade tip structure in this invention;

[0026] Figure 5 This is a cross-sectional schematic diagram of the double-groove blade tip structure in this invention;

[0027] Figure 6 This is a schematic cross-sectional view of the double-groove blade tip structure in the form of inclined ribs in this invention;

[0028] Figure 7 This is a schematic diagram of the flow structure inside the gap of the double-groove blade tip structure in this invention;

[0029] Figure 8 This is a schematic diagram of the flow topology inside the gap of the double-groove blade tip structure in this invention;

[0030] Figure 9 This is a comparison diagram of the leakage flow distribution per unit length between the double-groove blade tip structure and the traditional single-groove blade tip structure in this invention;

[0031] Figure 10 This is a diagram showing the distribution of the total pressure loss coefficient in the tip region of the double-groove blade tip structure and the traditional single-groove blade tip structure in this invention.

[0032] Explanation of reference numerals in the attached figures:

[0033] 1. Rotor blade; 2. Groove; 3. Pressure side rib; 4. Suction side rib; 5. Rotor blade pressure surface; 6. Rotor blade suction surface; 7. Casing; 11. Scraping vortex in the groove; 12. Leakage; 13. Scraping vortex in the pressure side groove; 14. Scraping vortex in the suction side groove; 15. Pressure side rib angular vortex; 16. Middle rib angular vortex; 17. Blade tip leakage vortex; 18. Rib top separation bubble; 21. Pressure side groove; 22. Suction side groove; 23. Middle rib; 41. Rotor blade tip airfoil; 42. Pressure side groove profile; 43. Suction side groove profile; 44. Mid-curve; 45. Centerline; 46. Perpendicular to the mid-curve 4. Auxiliary straight line, used to determine the positions of the front end connection point A and the rear end connection point B of the middle rib 23; 51. Leakage distribution curve per unit length of single-groove blade tip; 52. Leakage distribution curve per unit length of double-groove blade tip; 53. Total pressure loss coefficient distribution curve of the blade tip region of single-groove blade tip; 54. Total pressure loss coefficient distribution curve of the blade tip region of double-groove blade tip; A. Front end connection point of the middle rib 23 and the outer rib; B. Rear end connection point of the middle rib 23 and the outer rib; C. The foot of the perpendicular on the middle arc line 44 corresponding to the front end connection point A or the rear end connection point B of the middle rib 23, that is, the intersection of auxiliary straight line 46 and the middle arc line 44; t p Thickness of the pressure-side ribs; t s Thickness of the suction side ribs; t m The thickness of the central rib; W p , Maximum width of the pressure side groove; W s 1. Maximum width of the suction side groove; τ: height of the rotor blade tip clearance; H: rib height; α: angle between the inclined rib and the bottom plate of the groove. Detailed Implementation

[0034] The objectives, technical solutions, and advantages of the present invention will be described in detail below with reference to the accompanying drawings and embodiments.

[0035] Tip leakage flow control in crownless turbines typically employs a single-groove tip structure, as shown in the diagram. Figure 1 As shown. The rotor blade 1 has pressure-side ribs 3 and suction-side ribs 4. The pressure-side ribs 3 and suction-side ribs 4 are outer ribs, and the two outer ribs are connected at the leading and trailing edges, forming a groove 2 at the center of the blade tip. The flow structure topology inside its gap is as follows. Figure 2 As shown, the scraping vortex 11 in the groove, together with the pressure-side ribs 3, suction-side ribs 4, and casing 7, constitutes a pneumatic staggered-tooth grate sealing structure, which blocks the leakage flow 12, reduces the leakage amount and leakage flow, and thus reduces aerodynamic losses.

[0036] To enhance the sealing effect of the pneumatic staggered tooth comb, this invention constructs as follows: Figure 3The double-groove blade tip structure is shown. Based on the single-groove blade tip, a central rib 23 is added along the flow direction. The central rib 23 is connected to the pressure-side rib 3 and the suction-side rib 4, dividing the single groove into two sub-grooves: the pressure-side groove 21 and the suction-side groove 22.

[0037] To ensure that both sub-grooves can effectively seal the teeth using a pneumatic staggered tooth design, the design of the central rib 23 is as follows: Figure 4 As shown, the centerline 45 of the central rib 23 is basically along the direction of the central arc line 44 of the rotor blade tip profile 41.

[0038] The connection point A at the front end of the middle rib 23 and the pressure-side rib 3 and the suction-side rib 4 or the connection point B at the rear end can be located on the pressure-side rib 3 or the suction-side rib 4. The specific location is the intersection of the auxiliary line 46 perpendicular to the middle arc line 44 and the pressure-side rib 3 and the suction-side rib 4. The foot of the perpendicular between the auxiliary line 46 and the middle arc line 44 is point C. The position of point C is determined according to the percentage of the arc length of the middle arc line 44, and the corresponding point A or point B is also determined accordingly.

[0039] The front connection point A corresponds to the perpendicular foot C at the position of the arc length of the mid-arc line, which is between 0% and 20%. Figure 4 In the embodiment, the front connection point A corresponds to the perpendicular foot C at the position of 0% of the arc length of the middle arc line. Therefore, A and C coincide.

[0040] The tail connection point B corresponds to the vertical foot C at the position of 50%–100% of the arc length of the middle arc. When the vertical foot C is at the position of 100% of the arc length of the middle arc, the center line 45 of the middle rib coincides with the middle arc 44, and the tail connection point B will be located at the tail edge point of the blade.

[0041] The thicknesses of the central rib 23, the pressure-side rib 3, and the suction-side rib 4 are respectively t m , t p and t s All three are taken as 1–2 times the tip clearance height τ of the hot rotor blades.

[0042] Maximum width W of the pressure side groove p The maximum width of the pressure-side groove profile 42 along the direction perpendicular to the mid-arc line 44 is defined as follows; similarly, the maximum width W of the suction-side groove is defined as follows. s Defined as the maximum width of the suction-side groove profile 43 along the direction of the vertical mid-arc line 44.

[0043] Maximum width W of the pressure side groove p and the maximum width W of the suction side groove s Both grooves should be greater than 7.5 times the hot tip clearance height τ, which is the key to ensuring that both grooves can form an aerodynamic staggered tooth sealing effect.

[0044] like Figure 5As shown, the height of the middle rib 23, the pressure side rib 3, and the suction side rib 4 of the double groove blade tip structure is H, which is 2.5–3.5 times the hot rotor blade tip clearance height τ.

[0045] When the maximum width of the pressure-side groove 21 or the suction-side groove 22 does not meet 7.5 times the hot tip clearance height τ, the pressure-side rib 3 and the suction-side rib 4 can be designed as inclined ribs with an inclination angle of α, ranging from 90° to 120°. Figure 6 As shown. If, even with this inclined structure, it is still impossible to guarantee that the maximum width of both grooves is above 7.5 times the hot tip clearance height τ, then it is not recommended to use the double-groove tip structure of this invention for leakage flow control.

[0046] Numerical simulation was used to analyze the flow field of the double-groove blade tip structure in this invention, demonstrating its aerodynamic advantages over the traditional single-groove blade tip structure. The double-groove blade tip structure in this invention successfully achieves a multi-layered aerodynamic staggered-tooth sealing effect, effectively suppressing tip leakage flow and reducing the mixing loss between the tip leakage flow and the mainstream, thereby reducing turbine aerodynamic losses and improving turbine aerodynamic performance.

[0047] Figure 7 This is a flow structure diagram of the double-groove blade tip structure in this invention. The leakage flow 12 flows into the gap from near the pressure surface 5 of the rotor blade, passing through the pressure-side rib 3 and the middle rib 23 respectively, forming pressure-side rib corner vortices 15 and middle rib corner vortices 16 respectively. These two vortex structures are relatively small. The more prominent vortex structures are the scraping vortex 13 within the pressure-side groove 21 and the scraping vortex 14 within the suction-side groove 22. In the pressure-side groove 21, the casing 7, pressure-side rib 3, scraping vortex 13 within the pressure-side groove, and middle rib 23 together form a pneumatic staggered-tooth grate sealing structure, which significantly obstructs the leakage flow 12. In the suction-side groove 22, the casing 7, middle rib 23, scraping vortex 14 within the suction-side groove, and suction-side rib 4 together form a second pneumatic staggered-tooth grate sealing structure, further obstructing the leakage flow 12. After being sealed twice, the leakage flow 12 flows out of the gap and forms a tip leakage vortex 17 near the tip of the rotor blade suction surface 6.

[0048] Figure 8 This is a flow topology diagram of the double-groove blade tip structure in this invention. The leakage flow 12 forms a scraping vortex 13 in the pressure side groove and a scraping vortex 14 in the suction side groove within the two grooves. The two scraping vortices are closer to the ribs, causing the leakage flow 12 to flow out of the grooves at a larger angle and form a stronger rib-top separation bubble 18 at the top of the ribs, thereby reducing the effective flow area of ​​the leakage flow and forming a better blocking effect.

[0049] Figure 9 The leakage per unit length of the double-groove blade tip structure and the traditional single-groove blade tip structure are distributed along the axial chord length. At the middle chord length position, the leakage per unit length distribution curve 52 of the double-groove blade tip is significantly lower than that of the single-groove blade tip. This indicates that the double-groove blade tip effectively blocks the tip leakage flow in this region, and this region is precisely where the tip leakage vortex develops rapidly.

[0050] Figure 10 The distribution curves of the total pressure loss coefficient in the tip region of a single-groove blade tip (53) and a double-groove blade tip (54) are presented. Obviously, the total pressure loss coefficient of the double-groove blade tip structure is significantly lower. This reflects that the double-groove blade tip structure effectively suppresses the tip leakage vortex and tip leakage loss, reduces the aerodynamic loss of the turbine, and improves the aerodynamic performance of the turbine.

Claims

1. A turbine rotor double-groove blade tip structure based on scraping vortex control, characterized in that: The structure includes three ribs: a pressure-side rib (3), a suction-side rib (4), and a middle rib (23). The pressure-side rib (3) and the suction-side rib (4) are connected at their leading and trailing edges, forming a groove (2) at the middle of the blade tip of the rotor blade (1). The middle rib (23) divides the groove (2) into two sub-grooves: the one closer to the pressure-side rib (3) is the pressure-side groove (21), and the one closer to the suction-side rib (4) is the suction-side groove (22). Thickness of pressure side rib (3) t p Thickness of suction side rib (4) t s and the thickness of the central rib (23) t m It is 1–2 times the hot rotor blade tip clearance height. τ The height of the three rib sections should be 2.5–3.5 times the height of the hot rotor blade tip clearance. τ ; The maximum width of the two sub-grooves obtained by dividing the rotor into three rib sections is 7.5 times the height of the hot rotor blade tip clearance. τ The above refers to the maximum width of the two sub-grooves. W p , W s These are defined as the maximum width of the pressure-side groove line (42) and the suction-side groove line (43) along the direction of the vertical middle arc line (44), respectively.

2. The turbine rotor double-groove blade tip structure based on scraping vortex control according to claim 1, characterized in that: The centerline (45) of the middle rib (23) is along the direction of the middle arc line (44) of the rotor blade tip. The middle rib (23) is connected to the pressure side rib (3) or the suction side rib (4). The front end connection point is point A, and the tail end connection point is point B.

3. The turbine rotor double-groove blade tip structure based on scraping vortex control according to claim 2, characterized in that: The positions of the front connection point A and the tail connection point B are defined according to the position of the perpendicular foot (C) of the two points on the middle arc (44). The position of the perpendicular foot (C) is defined based on the percentage of the arc length of the middle arc (44). The position of the front connection point A is the position corresponding to 0%–20% of the arc length, and the position of the tail connection point B is the position corresponding to 50%–100% of the arc length.

4. The turbine rotor double-groove blade tip structure based on scraping vortex control according to claim 1, characterized in that: When the maximum width of the pressure-side groove (21) or suction-side groove (22) does not meet 7.5 times the hot rotor blade tip clearance height τ At this time, the pressure-side rib (3) or suction-side rib (4) is designed as a rib that is inclined towards the inside of the channel, that is, the angle between the rib and the bottom plate of the groove (2) is... α It is an obtuse angle. α The value should be in the range of 90°–120°.

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