Active wind shadow film cooling structure for improving endwall cooling performance

Abstract

The application discloses an active wind shadow film cooling structure with improved turbine first-stage static blade end wall cooling performance, which comprises an active wind shadow cooling chamber and a plurality of active wind shadow cooling film holes arranged on the pressure surface side of the static blade. During operation, cooling air is introduced from the bottom of the chamber and enters the main flow area of the cascade channel through the film holes arranged near the root of the cascade pressure surface. Due to the proper compound angle and surface angle of the film holes, the cooling air flow is injected into the cascade channel from the junction of the horseshoe vortex and the corner vortex, and under the entrainment of the horseshoe vortex and the corner vortex, the cooling air flow can develop downstream along the end wall. Therefore, without increasing the cascade aerodynamic loss, the film cooling efficiency of the turbine near the pressure surface side end wall can be significantly improved and the end wall thermal load can be reduced by using the structure.

Description

Technical Field

[0001] This invention belongs to the field of turbine technology and relates to a film cooling structure, particularly an active wind-shadow film cooling structure that improves end-wall cooling performance. Background Technology

[0002] To improve gas turbine performance, the inlet temperature of high-pressure turbines has been continuously increased, far exceeding the metal creep temperature. Furthermore, in recent years, lean premixed combustors have been applied to gas turbines to improve engine compactness and reduce NOx emissions. These two factors force the turbine's first-stage stator endwall region to operate under high temperature, high pressure, and complex flow environments. Therefore, effective cooling technologies must be applied to protect the turbine guide vane endwalls from high-temperature corrosion and damage that could affect the overall engine's operational safety.

[0003] To reduce the heat load on the endwall region, current film cooling methods mainly include discrete film cooling, blade passage clearance cooling, and upstream slot cooling. However, it is difficult to achieve efficient cooling coverage of the pressure side endwall using traditional cooling methods. Studies have shown that the high-temperature combustion gas stream from upstream stagnates at the leading edge of the first-stage stator and forms a horseshoe vortex at the blade root. At the stagnation point, the horseshoe vortex splits into two branches, left and right, which enter the blade passage and develop downstream. The pressure side branch of the horseshoe vortex extends towards the suction side due to the lateral pressure gradient within the blade passage, entraining cooling gas away from the wall and preventing it from reaching the pressure side endwall region, thus severely affecting the film cooling efficiency of the pressure side endwall. Simultaneously, the strong swirling characteristics at the outlet of the lean premixed combustion chamber migrate downstream, directly affecting the gas-thermal characteristics of the first-stage turbine. Related research indicates that under swirling inlet conditions, the horseshoe vortex is further intensified, the endwall heat load worsens further, and the effectiveness of the endwall film cooling is significantly reduced. Under the long-term scouring of the horseshoe vortex pressure surface branch and without efficient film cooling coverage, the side wall of the blade pressure surface is easily subjected to high-temperature ablation, which seriously affects the safe operation and aerodynamic efficiency of the gas turbine.

[0004] Therefore, developing new and efficient cooling structures to protect the pressure surface endwall region of the blade from erosion by the mainstream high-temperature airflow, reduce the heat load in this region, and ensure the safe and stable operation of the first-stage stationary blade endwall region has significant engineering application value. Summary of the Invention

[0005] To address the problem of insufficient cooling in the pressure-side endwall region of the first-stage stator blades under conventional cooling methods, which subject the turbine blade endwall to extremely high thermal loads, this invention aims to provide an active wind-shadow film cooling structure that improves endwall cooling performance. Utilizing the entrainment effect of horseshoe vortex pressure surface branches and angular vortices, this structure allows cooling gas from the film cooling holes in the pressure surface of the blade cascade to smoothly reach the pressure-side endwall region without increasing aerodynamic losses in the blade cascade passages. This creates wind-shadow cooling (secondary cooling) at the endwall and expands the coverage area of ​​the cooling gas on the endwall, significantly improving the film cooling performance of the pressure-side endwall. This invention can fundamentally reduce the thermal load on the pressure-side endwall of the blade cascade, ensuring the safe and effective operation of the blade endwall and extending the service life of the gas turbine.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] An active wind-shadow film cooling structure for improving endwall cooling performance includes an active wind-shadow cooling chamber and several active wind-shadow cooling film holes. The active wind-shadow cooling chamber is located inside the first-stage stator blade of the turbine. The active wind-shadow cooling film holes are opened on the pressure surface side of the first-stage stator blade, connecting the active wind-shadow cooling chamber and the blade passage at a certain jet angle. During operation, the cooling airflow is introduced from the bottom of the active wind-shadow cooling chamber, enters the mainstream region of the blade passage from the junction of the horseshoe vortex and the corner vortex through the active wind-shadow cooling film holes, and under the entrainment effect of the horseshoe vortex and the corner vortex, the cooling airflow develops downstream close to the endwall surface. The horseshoe vortex and the corner vortex are vortices formed near the endwall by the stagnation of the mainstream gas flow at the leading edge of the first-stage stator blade.

[0008] In one embodiment, the active wind-cooling chamber is located near the bottom of the first stage stator blade and extends through the root of the first stage stator blade along the flow direction.

[0009] In one embodiment, the active wind-cooled film cooling holes are located near the root of the stationary blade pressure surface and are opened at a certain jet angle.

[0010] In one embodiment, the distance L = 0.1C between the active wind-cooled chamber and the leading edge of the stator blade in the axial direction of the blade. ax C ax The chord length along the axis of the stationary blade.

[0011] In one embodiment, the number of active wind-cooled film cooling holes is 2-4, the cross-section of each film cooling hole is circular, the diameter d of the film cooling hole ranges from 1 to 2 mm, and the distance between adjacent film cooling holes is 4d.

[0012] In one embodiment, the active wind-shadow cooling chamber is rectangular, with a height a ranging from 20d to 30d, a width b ranging from 3d to 5d, and a length c ranging from 10d to 15d. The distance between the bottom of the active wind-shadow cooling chamber and the wall surface of the end wall is 8d. Herein, the height refers to the direction along the height of the first stage stationary blade; the width refers to the direction along the circumference of the blade; the length refers to the direction along the axial direction of the blade; and the bottom refers to the lower surface of the active wind-shadow cooling chamber.

[0013] In one embodiment, the distance h between the outlet of the active wind-cooled film cooling air hole and the wall surface of the end wall ranges from 1%H to 10%H, where H is the height of the stationary blade.

[0014] In one embodiment, the angle between the outflow direction of the active wind-cooled film cooling hole and the turbine axis is defined as the composite angle α, and the angle between the outflow direction and the stationary blade pressure surface is defined as the surface angle β. The value of α ranges from 10 to 30 degrees, and the value of β ranges from 15 to 45 degrees.

[0015] In one embodiment, the outlet of the active wind-shadow cooling film vent is located at the junction of the horseshoe vortex and the angular vortex formed near the endwall by the main gas flow stopping at the leading edge of the first stage stator blade of the turbine.

[0016] The present invention also provides a turbine that employs the aforementioned active wind-shadow film cooling structure for improving end-wall cooling performance.

[0017] Compared with the prior art, the beneficial effects of the present invention are:

[0018] This invention provides an active wind-shadow film cooling structure that can effectively improve the film cooling efficiency of the turbine stator blade's endwall near the pressure surface. Its key feature is the creation of multiple film cooling holes near the leading edge root of the turbine stator blade's pressure surface. Cooling gas introduced from the compressor passes through the wind-shadow cooling chamber and enters the blade passage through the film cooling hole outlet. Because these film cooling holes have appropriate surface angles and compound angles, a portion of the cooling gas moves downstream along the pressure surface root with the angular vortex, while another portion is carried by the horseshoe vortex and develops close to the endwall surface towards the center of the passage. Therefore, this cooling method not only covers the blade passage pressure surface but also forms secondary cooling in the cooling dead zone near the pressure surface of the endwall, greatly improving the film cooling efficiency of the endwall and solving the problem of cooling gas not being able to cover the pressure surface endwall.

[0019] 1. The active wind-shadow film cooling structure, designed using the flow characteristics of horseshoe vortices and angular vortices, allows cooling gas to smoothly reach the endwall of the stator blades and form a cooling cover. Therefore, with almost no aerodynamic losses in the blade cascade, the effectiveness of the film cooling near the pressure side of the endwall can be significantly improved with less cooling gas, greatly avoiding cooling gas losses and improving the overall operating efficiency of the machine.

[0020] 2. Preliminary numerical simulations demonstrate that even under the influence of strong swirling at the outlet of a real lean premixed combustion chamber, this film cooling structure still exhibits good robustness. Using only cooling gas with a mass flow rate (MFR) of 0.5%, the average film effectiveness at the end wall can be increased by approximately 50%. Therefore, this structure performs well in practical applications and has broad application prospects. Attached Figure Description

[0021] Figure 1 This is a cross-sectional view of a typical traditional lean premixed combustion chamber and the meridional section of the first-stage turbine blades.

[0022] Figure 2 This is a schematic diagram of the first-stage stator blades and conventional endwall film cooling layout of a turbine.

[0023] Figure 3 This is a cross-sectional view of the meridional plane of the first stage of a turbine with an active wind-shadow film cooling structure.

[0024] Figure 4 This is a schematic diagram of the air film cooling layout for the first stage stationary blades of a turbine with an active wind-shadow air film cooling structure.

[0025] Figure 5 This is a three-dimensional flow diagram of an active wind-induced film cooling jet and a typical end-wall secondary flow.

[0026] Figure 6 This is a schematic diagram of the axial cross-section of an active wind-shrink film cooling jet cooling method.

[0027] Figure 7 This is a diagram of the active wind-shrink film cooling structure of the present invention.

[0028] Figure 8 This is a schematic diagram of the meridional surface of the turbine stationary blade with an active wind-shadow film cooling structure.

[0029] Figure 9 A top view of the turbine stator blades with an active wind-shadow film cooling structure.

[0030] Figure 10 The diagram shows the distribution of the effective air film on the end wall of the active wind-shadow air film cooling structure. (a) is a traditional air film cooling structure without active wind-shadow, (b) is Example 1, (c) is Example 2, and (d) is Example 3.

[0031] Figure 11 This is a distribution diagram of the average circumferential air film effectiveness of the end wall with an active wind-shadow air film cooling structure.

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

[0033] 1-Cooling structure of the inner wall of the combustion chamber; 2-Combustion chamber; 3-Dispersion cooling structure of the combustion chamber; 4-First stage stationary blade; 5-First stage moving blade; 6-Film cooling structure inside the first stage stationary blade passage; 7-Film cooling structure upstream of the first stage stationary blade; 8-Swirl generator of the combustion chamber; 9-End wall; 10-Active wind shadow cooling chamber; 11-Active wind shadow cooling film hole; 12-Leading edge of the first stage stationary blade; 13-Tail edge of the first stage stationary blade. Detailed Implementation

[0034] The present invention will be further described in detail below with reference to the accompanying drawings and technical principles.

[0035] For the conventional combustion chamber and first-stage turbine stator blades and their associated film cooling structure, please refer to the appendix. Figure 1 and attached Figure 2 The turbine first-stage stator blade with the active wind-shadow film cooling structure of this invention is shown in the appendix. Figure 3 and attached Figure 4 The design concept of the active wind-shadow film cooling structure of this invention is detailed in the appendix. Figure 5 and attached Figure 6 For its specific structural parameters and installation location, please refer to the appendix. Figure 7-9 The film cooling effect of the embodiment is shown in the appendix. Figure 10 and attached Figure 11 .

[0036] See Figure 1 and Figure 2 In a typical lean premixed combustion chamber, a swirl generator 8 is usually employed to ensure sufficient premixing of fuel and air and stable combustion. Furthermore, a low-temperature cooling airflow is ejected from the combustion chamber inner wall cooling structure 1 and the combustion chamber divergent cooling structure 3 to protect the inner wall of the combustion chamber 2. Therefore, the downstream development of the main gas flow is often accompanied by strong swirl and uneven temperature distribution, directly affecting the secondary flow development of the turbine's first-stage stator blade 4 and first-stage moving blade 5, and severely damaging the cooling protection of the end wall 9 of the turbine's first-stage stator blade. Traditional film cooling structure designs, including the film cooling structure 6 within the first-stage stator blade passage and the upstream film cooling structure 7 of the first-stage stator blade, cannot achieve adequate end wall film cooling coverage. See Appendix. Figure 10 Numerical simulation results show that when using a traditional film cooling structure, a large area of ​​the end wall region lacks cooling protection, and the cooling airflow can hardly reach the near-pressure side of the end wall 9. Therefore, in order to improve the effectiveness of the film cooling system on the near-pressure side of the end wall 9 and ensure the safe and stable operation of the engine, this invention is designed using the following technical approach:

[0037] See Figure 3 and Figure 4The present invention provides an active wind-shadow film cooling structure for improving the effectiveness of film cooling on the near-pressure sidewall of the first-stage turbine stator blade, comprising an active wind-shadow cooling chamber 10 and a plurality of active wind-shadow cooling film holes 11. The active wind-shadow cooling chamber 10 is disposed inside the first-stage turbine stator blade 4, more specifically near the bottom of the first-stage stator blade 4, and penetrates the root of the first-stage stator blade 4 along the flow direction of the cooling jet. The active wind-shadow cooling film holes 11 are opened on the pressure side of the first-stage stator blade 4, more specifically at the root of the pressure side of the stator blade, and are opened at a certain jet angle, that is, connecting the active wind-shadow cooling chamber 10 and the blade passage at a certain jet angle.

[0038] In this embodiment of the invention, the active wind-shadow cooling film cooling hole 11 adopts a conventional circular cross-section film cooling hole with a diameter d ranging from 1 to 2 mm. The spacing between adjacent film cooling holes is 4d. The distance between the outlet of the active wind-shadow cooling film cooling hole 11 and the wall surface of the end wall 9, i.e., the outlet height of the film cooling hole, is h. h is determined based on the stator blade height H, and generally ranges from 1%H to 10%H. h should not be too large or too small. If it is too large, it will reduce the film cooling effect of the end wall; if it is too small, it will cause the heat transfer coefficient in the local area of ​​the end wall to be too large. The distance L between the active wind-shadow cooling chamber 10 and the leading edge of the stator blade in the axial direction of the blade is 0.1°C. ax At this location, the cooling coverage of the endwall near the pressure surface is extremely poor, where C ax The axial chord length of the stator blade is given. Each film cooling orifice has a compound angle α and a surface angle β designed according to the specific blade. The compound angle α is defined as the angle between the outflow direction of the active wind-shadow cooling film cooling orifice 11 and the turbine axis, and the surface angle β is the angle between the outflow direction of the active wind-shadow cooling film cooling orifice 11 and the pressure surface of the stator blade. The value of α ranges from 10 to 30 degrees, and the value of β ranges from 15 to 45 degrees. Too large or too small a values ​​of α and β will reduce the endwall cooling coverage area, thus reducing the wind-shadow cooling gain effect. The number of active wind-shadow cooling film cooling orifices 11 is adjusted according to the cooling effect, ranging from 2 to 4. Too few or too few or too many or too few or too few or too many will result in a waste of cooling gas.

[0039] More specifically, in an embodiment of the present invention, the active wind-shadow cooling chamber 10, after being individually processed, is installed inside the blade from the bottom of the first-stage stator blade 4, and connects with the active wind-shadow cooling film holes 11 processed on the blade to form a complete flow channel. The size of the active wind-shadow cooling chamber 10 must be designed according to the blade geometry and should not be too small, ensuring that the cooling gas can be introduced from its bottom and uniformly enter the blade channel through the active wind-shadow cooling chamber 10. The active wind-shadow cooling chamber 10 can be rectangular, and the recommended size is: height a range of 20d-30d, width b range of 3d-5d, and length c range of 10d-15d. The distance between the bottom of the active wind-shadow cooling chamber 10 and the wall surface of the end wall 9 is 8d to ensure that the cooling airflow can fully develop after being introduced from the bottom. In this invention, the height is defined here as along the blade height direction of the first-stage stator blade 4; the width is along the circumferential direction of the blade; the length is along the axial direction of the blade; and the bottom is the lower surface of the active wind-shadow cooling chamber 10.

[0040] The technical principles of this invention are described in [reference needed]. Figure 5 and Figure 6 The main gas flow stagnates at the leading edge 12 of the first-stage stator blade of the turbine and forms vortices, namely horseshoe vortices and angular vortices, near the endwall 9. These vortices develop downstream along the pressure and suction surfaces of the first-stage stator blade 4, forming pressure-side and suction-side branches. The pressure-side branches of the horseshoe vortex entrain the near-endwall airflow, causing it to leave the wall and develop downstream in the blade passage. Therefore, conventional endwall film cooling airflow cannot enter the horseshoe vortex and angular vortex control area. Using this invention, the cooling airflow is introduced from the bottom of the active wind-shadow cooling chamber 10 and enters the blade passage through the active wind-shadow cooling film orifice 11. Since the outlet height of the active wind-shadow cooling film orifice 11 is precisely at the junction of the horseshoe vortex and angular vortex, and the film orifice has appropriate compound angle α and surface angle β, the cooling jet is injected into the main flow from the junction of the horseshoe vortex and angular vortex, entering the main flow area of ​​the blade passage. Under the entrainment effect of the horseshoe vortex and angular vortex, the cooling airflow develops downstream close to the endwall. Specifically, because the horseshoe vortex and the angular vortex have opposite rotation directions, the cooling jet is accelerated and carried towards the end wall 9: on the one hand, it is guided by the horseshoe vortex to the end wall 9 in the channel (i.e., cooling line 1 in the figure), and on the other hand, it is drawn in by the angular vortex to the junction of the stator blade and the end wall (i.e., cooling line 2 in the figure). Therefore, this cooling structure can greatly improve the effectiveness of film cooling on the turbine near-pressure side end wall and reduce the end wall thermal load without increasing the aerodynamic losses of the blade cascade.

[0041] See Figures 7-11 The installation location and usage method of the present invention will be described in detail below with reference to the following three embodiments and numerical simulation results. The three embodiments are identical to the first-stage stationary blade 4 and the traditional film cooling structure, except that the distance h between the active wind-cooled film cooling hole outlet and the end wall is changed.

[0042] This embodiment first considers the axial chord length C of the first-stage stator blade. ax It is defined as the axial distance between the leading edge 12 and the trailing edge 13 of the first-stage stator blade, and the distance L between the active wind-shadow cooling and the leading edge of the stator blade in the axial direction of the blade is determined to be 0.1C. ax .

[0043] The active wind-cooled film cooling system uses 3 holes 11, with a hole diameter d of 1.5 mm, and the spacing between adjacent film cooling holes is 6 mm.

[0044] The height a of the active airflow cooling chamber 10 is 25d, which is 37.5 mm. The width b of the active airflow cooling chamber is 4d, which is 6 mm. The length c of the active airflow cooling chamber is 13d, which is 19.5 mm. The distance between the bottom of the active airflow cooling chamber 10 and the wall surface of the end wall 9 is 8d, which is 12 mm.

[0045] After numerical simulation calculations, the migration paths of horseshoe vortices and angular vortices were determined, and the optimal active wind-shadow cooling film hole composite angle α in this blade cascade channel was determined to be 20 degrees, and the optimal active wind-shadow cooling film hole surface angle β was determined to be 30 degrees.

[0046] Based on the parameters determined above, three embodiments were obtained by changing the ratio of the distance h between the outlet of the active wind-cooled film cooling air hole and the end wall to the height H of the first stage stationary blade: Embodiment 1 uses a distance h of 1.5%H between the outlet of the active wind-cooled film cooling air hole and the end wall, which is 2mm; Embodiment 2 uses a distance h of 4.0%H between the outlet of the active wind-cooled film cooling air hole and the end wall, which is 5mm; Embodiment 3 uses a distance h of 6.5%H between the outlet of the active wind-cooled film cooling air hole and the end wall, which is 8mm.

[0047] When verifying the effectiveness of this design through numerical simulation, the mass flow rate ratio (MFR) of the active wind-cooled jet and the main gas flow remained unchanged at 0.5%.

[0048] Appendix Figure 10 and attached Figure 11The paper presents a comparison of the film cooling effectiveness of the endwall 9 in three embodiments with that in a conventional film cooling structure. In the conventional structure without active wind shadow cooling, the effective coverage area of ​​the film cooling system is small, and the endwall near the pressure surface receives almost no effective film cooling protection, resulting in an average film cooling effectiveness of only 0.195. In Embodiment 1, the distance h between the outlet of the active wind shadow cooling film cooling orifice and the endwall is small, allowing more cooling gas to flow into the blade passage along cooling path 1, resulting in a higher peak film cooling efficiency. The average film cooling effectiveness increases to 0.300, an improvement of 53.8%. In Embodiment 3, the distance h between the outlet of the active wind shadow cooling film cooling orifice and the endwall is large, allowing the cooling gas to develop better downstream of the blade passage. This results in more uniform film cooling coverage within the blade passage, increasing the average film cooling effectiveness to 0.297, an improvement of 52.3%.

[0049] In summary, numerical simulation results show that applying this invention can significantly improve the effectiveness of the air film cooling system on the endwall of the first-stage turbine stator without increasing aerodynamic losses in the blade passage, and the cooling coverage of the near-pressure side endwall is also significantly improved. This is of great significance for reducing the thermal load on the endwall of the first-stage turbine stator and ensuring the safe and stable operation of the engine. Based on the above-mentioned active wind-shadow air film cooling structure, a corresponding turbine can be obtained.

Claims

1. An active wind-shrink film cooling structure for improving end-wall cooling performance, characterized in that, It includes an active wind-shadow cooling chamber (10) and several active wind-shadow cooling film holes (11). The active wind-shadow cooling chamber (10) is located inside the first stage stator (4) of the turbine. The active wind-shadow cooling film holes (11) are opened on the pressure surface side of the first stage stator (4) and connect the active wind-shadow cooling chamber (10) and the blade passage at a certain jet angle. When working, the cooling airflow is introduced from the bottom of the active wind-shadow cooling chamber (10) and enters the mainstream area of ​​the blade passage from the junction of the horseshoe vortex and the corner vortex through the active wind-shadow cooling film holes (11). Under the entrainment effect of the horseshoe vortex and the corner vortex, the cooling airflow closely adheres to the end wall and develops downstream. The horseshoe vortex and the corner vortex are the vortices formed by the main gas flow at the leading edge (12) of the first stage stator of the turbine and near the end wall (9). The active wind-shadow cooling chamber (10) is located near the bottom of the first stage stationary blade (4) and penetrates the root of the first stage stationary blade (4) along the flow direction. The active wind-shadow cooling air film hole (11) is located near the root of the stationary blade pressure surface and is opened along a certain jet angle. The active wind-shadow cooling chamber (10) is rectangular, with a height a ranging from 20d to 30d, a width b ranging from 3d to 5d, and a length c ranging from 10d to 15d. The distance between the bottom of the active wind-shadow cooling chamber (10) and the wall surface of the end wall (9) is 8d. The height refers to the direction along the blade height of the first stage stator blade (4); the width refers to the circumferential direction of the blade; the length refers to the axial direction of the blade; and the bottom refers to the lower surface of the active wind-shadow cooling chamber (10). The range of the distance h between the outlet of the active wind-cooled film air hole (11) and the wall surface of the end wall (9) is 1%H-10%H, where H is the height of the stationary blade; The angle between the outflow direction of the active wind-cooled film cooling hole (11) and the turbine axis is defined as the composite angle. The angle between the outflow direction and the pressure surface of the stationary blade is defined as the surface angle. , The value range is 10-30 degrees. The value range is 15-45 degrees; The outlet of the active wind-shadow cooling film hole (11) is located at the junction of the horseshoe vortex and the angular vortex formed at the leading edge (12) of the turbine first stage stator blade where the main gas flow stops.

2. The active wind-shrouded film cooling structure for improving end-wall cooling performance according to claim 1, characterized in that, The distance L between the active wind-cooled chamber (10) and the leading edge of the stationary blade in the axial direction of the blade is = ,in The chord length along the axis of the stationary blade.

3. The active wind-shrouded film cooling structure for improving end-wall cooling performance according to claim 1, characterized in that, The number of active wind-cooled air film holes (11) is 2-4, the cross-section of the air film holes is circular, the diameter d of the air film holes ranges from 1 to 2 mm, and the distance between adjacent air film holes is 4d.

4. A turbine employing the active wind-shadow film cooling structure for improving end-wall cooling performance as described in any one of claims 1 to 3.

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