An air film cooling structure with a spiral structure

Abstract

The present invention discloses an air film cooling structure with a spiral structure, including a cold air cavity opened at the leading edge of a turbine blade, a plurality of jet holes opened on the side wall of the spiral structure cold air cavity, the spiral structure cold air cavity is connected to the outer surface of the spiral structure turbine blade through the spiral structure jet holes, and a spiral structure is opened on the inner side wall of the spiral structure jet hole. The present invention optimizes the traditional cylindrical air film hole. By changing the channel shape of the air film hole, the coolant at the outlet of the air film hole generates a combined vortex pair, inducing a swirl flow, so that the coolant adheres better to the wall surface, which is beneficial to the thermal protection of the wall surface. At the same time, it solves the problem that the special-shaped hole is difficult to process due to its complex structure, breaks the kidney-shaped vortex structure inherent in cylindrical air film cooling, greatly improves the air film cooling effect, and has good engineering application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of turbine blade cooling, and in particular relates to an air film cooling structure with a spiral structure. Background Art

[0002] In order to improve the thermal efficiency and output power of gas turbines, the turbine inlet temperature continues to increase, and the high-temperature materials of turbine components can no longer meet the above working conditions. Therefore, the development of efficient cooling technology has become the key. Film cooling is a commonly used cooling technology for high-temperature turbine components. Its advantage is that it has the dual functions of heat preservation and heat absorption, which can achieve maximum temperature drop. As a hot research topic, film cooling has made great progress. Cylindrical holes are the earliest and most widely used film hole configuration, which has a certain cooling effect. However, downstream of the cylindrical hole jet, the coolant easily forms kidney-shaped vortex pairs. This larger vortex structure limits the lateral coverage ability of the cooling film and entrains the mainstream to the wall, seriously affecting the cooling capacity of the film hole.

[0003] Changing the film hole shape is one way to mitigate kidney-shaped vortices. In recent years, film holes have evolved from cylindrical shapes to fan-shaped, conical, slotted, elliptical, crescent-shaped, and heart-shaped. These research focuses on eliminating the adverse effects of kidney-shaped vortices and offer unique advantages in heat transfer and aerodynamics. However, these film hole geometries all face a common challenge: processing.

[0004] Therefore, it is necessary to design an air film cooling structure with a spiral structure to solve the problems of poor cooling effect of traditional cylindrical air film holes and difficulty in processing special-shaped air film holes. Summary of the Invention

[0005] The purpose of the present invention is to provide an air film cooling structure with a spiral structure to solve the above problems, thereby achieving the purpose of improving the cooling effect of the air film hole and reducing the difficulty of air film hole processing.

[0006] To achieve the above-mentioned purpose, the present invention provides the following solution: an air film cooling structure with a spiral structure, comprising a cold air cavity opened at the leading edge of a turbine blade, a plurality of jet holes opened on the side wall of the cold air cavity, the cold air cavity is connected to the outer surface of the turbine blade through the jet holes, and a spiral structure is opened on the inner wall of the jet hole.

[0007] Preferably, the shape of the cold air cavity is adapted to the shape of the outer surface of the turbine blade, and the distance A between the side wall of the cold air cavity and the outer surface of the turbine blade is 3 mm to 7 mm.

[0008] Preferably, the angle θ between the jet hole axis and the outer surface of the turbine blade is 30°-40°.

[0009] Preferably, the tooth shape of the jet hole spiral structure is triangular.

[0010] Preferably, the inner diameter D of the jet hole is 1 mm-2 mm, the tooth height H of the spiral structure is 0.5D, and the pitch I is 1.3D.

[0011] Preferably, the jet hole spiral structure is a right-hand spiral.

[0012] Preferably, the plurality of jet holes are arranged at equal intervals along the span direction of the turbine blade.

[0013] The present invention has the following technical effects:

[0014] The air film cooling structure of the present invention is located at the leading edge of the turbine blade, and the ejected coolant is rotated through the jet hole, inducing a swirl to achieve thermal protection for the turbine blade. In the jet hole, the flow field separation area is small, there are small-scale vortices, and the streamlines are vortex-shaped. The momentum of the coolant at the jet hole outlet in the vertical direction is small and uniform, which can better protect the wall surface. At the same time, the outlet has a larger lateral velocity area, which makes the coolant produce a larger spanwise distribution range, and has a strong inhibitory effect on the high-temperature mainstream invading the cooling jet below. Due to the influence of rotation, a vortex pair consisting of a large-scale vortex and a small-scale vortex is generated in the vertical direction downstream of the coolant outlet, and finally merged into a new vortex, whose rotation direction is completely different from the kidney-shaped vortex, breaking the kidney-shaped vortex structure inherent in ordinary air film holes, so that the coolant is better attached to the surface of the turbine blade, the cooling efficiency is greatly improved, and it is of great significance to improve the air film cooling effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] 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. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0016] Figure 1 This is an axonometric drawing of the present invention;

[0017] Figure 2 This is an axonometric view from another angle of the present invention;

[0018] Figure 3 It is a cross-sectional view of the present invention;

[0019] Figure 4 Schematic diagram of the jet hole of the present invention;

[0020] Figure 5 This is a diagram showing the cooling effect of the cylindrical hole on the flat plate under different blowing ratios;

[0021] Figure 6 This is a diagram showing the cooling effect of the spiral structure holes on the flat plate under different blowing ratios;

[0022] Figure 7 is the comparison curve of the average cooling efficiency along the flow direction under different blowing ratios;

[0023] Figure 8 This is a smooth structure diagram downstream of the spiral structure hole.

[0024] Among them, 1. Turbine blades; 2. Cold air cavity; 3. Jet hole. DETAILED DESCRIPTION

[0025] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0026] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0027] Reference Figure 1-3 The present invention discloses an air film cooling structure with a spiral structure, comprising a cold air cavity 2 opened at the leading edge of a turbine blade 1, a plurality of jet holes 3 opened on the side wall of the cold air cavity 2, the cold air cavity 2 is connected to the outer surface of the turbine blade 1 through the jet holes 3, and a spiral structure is opened on the inner wall of the jet hole 3.

[0028] The cold air cavity 2 can be located at the leading edge of the turbine blade 1 or inside the turbine end wall, and the spiral structure can be obtained by additive manufacturing or directly tapping the turbine blade 1.

[0029] According to a further optimization scheme, the shape of the cold air cavity 2 is adapted to the shape of the outer surface of the turbine blade 1, and the distance A between the side wall of the cold air cavity 2 and the outer surface of the turbine blade 1 is 3 mm to 7 mm.

[0030] According to a further optimized solution, the angle θ between the axis of the jet hole 3 and the outer surface of the turbine blade 1 is 30°-40°.

[0031] The angle direction is along the incoming flow direction.

[0032] According to a further optimization scheme, the tooth shape of the spiral structure of the jet hole 3 is triangular.

[0033] According to a further optimization scheme, the inner diameter D of the jet hole 3 is 1 mm to 2 mm, the tooth height H of the spiral structure is 0.5D, and the pitch I is 1.3D.

[0034] Furthermore, the length of the jet hole 3 is L, where L=A / sinθ.

[0035] The number of cycles of the spiral structure is determined according to the specific length of the jet hole 3 .

[0036] According to the further optimized solution, the spiral structure of the jet hole 3 is a right spiral.

[0037] Under the action of the spiral structure, the Coanda effect is reduced due to the change of outlet momentum and hole shape, thereby improving the cooling performance.

[0038] In a further optimized solution, a plurality of jet holes 3 are arranged at equal intervals along the span of the turbine blade 1 to form a cooling film hole array.

[0039] The selected distance between the sidewall of the cooling cavity 2 and the outer surface of the turbine blade 1, and the inner diameter of the jet hole 3, provide the optimal cooling effect for the spiral channel hole configuration. Under the same conditions, the vertical vortex pairs generated by the spiral channel hole with these parameters are the strongest and most stable. The vertical vortex pair structure consists of a large-scale vortex at the top and a small-scale vortex at the bottom. Under these parameters, the large vortex has the strongest suppressive effect on the smaller vortex below, resulting in a higher lateral velocity and lower normal velocity for the cooling film. The higher lateral velocity ensures stronger spanwise coverage of the cooling film generated by the spiral channel hole. It also provides strong resistance to the high-temperature mainstream flowing laterally below the film, preventing it from intruding beneath it. The lower normal velocity, however, reduces the coolant's ability to penetrate the high-temperature mainstream, weakening mixing between the coolant and the high-temperature mainstream. At this point, the mixed airflow is relatively cool, and this cooler airflow adheres to the blade surface, forming a cooling film and ultimately improving cooling performance.

[0040] Swirl flow with a high radial pressure gradient can thin the thermal boundary layer and improve heat transfer, making it a promising cooling technology. Using swirl cooling within blades can improve the heat transfer coefficient within the internal channels, increasing the heat transfer capacity of the swirl cooling chamber walls by more than eight times. Based on this information, the present invention proposes a cooling structure that utilizes a combination of swirl flow and film hole cooling.

[0041] Reference Figure 4-5The minimum blowing ratio of 0.5 resulted in the largest cooling film coverage area. As the blowing ratio increased, the cooling film coverage area of ​​the cylindrical hole gradually decreased. When the blowing ratio exceeded 1.0, the cooling efficiency of the entire wall dropped below 0.5, nearly losing cooling capacity. The increase in blowing ratio can be attributed to the increase in coolant momentum, which enhanced the coolant's ability to penetrate the main flow after exiting the film hole. Subsequently, the coolant separated from the wall and failed to form a cooling film on the turbine blade surface. For all spiral holes, the cooling film coverage area was greater than that of the cylindrical hole. The spanwise dimension of the cooling film coverage area of ​​the spiral hole exceeded 1.5 times the hole diameter, demonstrating excellent cooling effectiveness. After passing through the spiral structure, the coolant achieved good wall adhesion. Furthermore, due to the influence of the spiral jet, the cooling film coverage area of ​​the spiral hole shifted toward the negative Z-axis, unlike the cooling film coverage area of ​​the cylindrical hole, which was essentially symmetric about the X-axis.

[0042] Reference Figure 6 As the mainstream develops along the incoming flow direction, the lateral average cooling efficiency gradually decreases and eventually tends to be flat. The coolant can adhere better to the wall surface at a low blowing ratio. Therefore, for both types of film holes, their lateral average cooling efficiency at a blowing ratio of 0.5 is higher than that at 1.0. From the data of the blowing ratio of 0.5, it can be seen that the lateral average cooling efficiency of the spiral structure hole at X / D=0 is 0.364, which is 1.56 times that of the cylindrical hole. After the curve stabilizes, the cooling efficiency value of the spiral structure hole is 79% higher than that of the cylindrical hole. In general, the average film cooling efficiency of the entire flat plate is increased by 97%. Downstream of the spiral structure hole, when the blowing ratio is 1.0, the average film cooling efficiency is increased by 66.7%. In particular, the value of each point on the curve of the spiral structure hole at a blowing ratio of 1.0 is higher than that on the cylindrical hole curve, proving that the former only needs half the coolant amount to achieve a better cooling effect than the latter. This difference mainly comes from two parts: (1) The spiral structure hole has a wider cooling film coverage area. Especially in the downstream region, the cooling film coverage area of ​​the spiral hole is significantly larger than that of the cylindrical hole. (2) The core high cooling efficiency region of the spiral hole (cooling efficiency > 0.85) is more obvious, occupying the region of X / D = 0-17. The core high cooling efficiency region of the cylindrical hole only appears in the region of X / D = 0-10.

[0043] The absolute value of the lateral velocity at the exit of the spiral structure hole is very large, which is mainly due to the vortex flow formed by the flow rotating in the air film hole channel. In addition, when approaching the hole exit, the vortex tends to develop in the positive direction of the Z axis, so that the injected coolant has a larger lateral velocity. In addition, when the blowing ratio increases, the swirling motion of the coolant is still greatly enhanced, and the area of ​​the high-speed zone also increases. The lateral velocity determines the lateral expansion capability of the cooling air film, that is, the spanwise coverage capability. This larger lateral velocity distribution brings about a different flow structure, so that after the coolant is ejected from the spiral structure hole, the spanwise range of the cooling air film distribution is larger.

[0044] In the traditional film cooling hole flow field, as the flow develops, the counter-rotating kidney-shaped vortex pairs gradually move away from the wall, and the distance between the two opposite vortices gradually increases. The counter-rotating vortex pairs have separated from each other into two vortices. In addition, the temperature below the vortex core also gradually increases, indicating that the effectiveness of film cooling is gradually decreasing. For film cooling, the adverse effects of the counter-rotating vortex pairs are twofold: (1) In the vertical direction, the cooling film is completely separated from the wall. The further downstream it develops, the more obvious this lifting effect is. This lifting of the film is extremely detrimental to the coolant's protection of the wall. (2) When the flow develops downstream, the vortex is already a certain distance away from the wall. At the same time, the two independent vortices will suck the high-temperature mainstream into the coolant below it, further reducing the cooling effect. When the spiral film hole is applied, due to the influence of the vortex, a small-scale vortex is generated at the outlet of the spiral structure hole. As the flow develops, a vertical vortex structure can be clearly observed. The size of the vortex at the upper position is larger, and the size of the vortex at the lower position is smaller. The vortex at the bottom is developed from the small-scale vortex at the hole outlet. The temperature below the small-scale vortex is lower, indicating a more effective cooling effect there. Downstream at x = 10D, the two vortices gradually merge into a new vortex structure, which gradually moves toward the wall. The flow field structure reaches a stable state downstream, and the resulting vortex moves away from the wall. This vortex rotates in the opposite direction to the kidney-shaped vortex formed by the cylindrical hole, thus providing a different effect.

[0045] In the spiral structure hole, the flow separation zone is small and small-scale vortices exist. Due to the effect of the spiral structure, the streamlines are spiral-shaped and deviate significantly. The vertical momentum of the coolant at the outlet of the spiral channel is small and uniform, which can better protect the wall surface. At the same time, the outlet has a large lateral velocity area, which makes the coolant have a larger spanwise distribution range and has a strong inhibitory effect on the high-temperature mainstream invading the bottom of the cooling jet. The coolant flowing through the spiral structure hole can be divided into two parts. Fluid I is a fluid similar to that passing through a cylindrical hole, which interacts with the mainstream to form large-scale vortices. Fluid II rotates along the spiral wall, wrapping around fluid I, and eventually forming small-scale vortices. In the vertical direction, small-scale vortices are suppressed by large-scale vortices. Small-scale vortices can retain coolant attached to the wall surface, which is beneficial to the thermal protection of the wall surface. This swirl structure destroys the kidney-shaped vortex and is of great significance to improving the film cooling effect.

[0046] In the description of the present invention, it should be understood that the terms "longitudinal", "transverse", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside" and "outside" and the like to indicate orientations or positional relationships are based on the orientations or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention, 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 should not be understood as limiting the present invention.

[0047] The embodiments described above are merely descriptions of preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by persons skilled in the art should fall within the scope of protection defined by the claims of the present invention.

Claims

1. An air film cooling structure with a spiral structure, characterized in that: The invention comprises a cold air cavity (2) provided at the leading edge of a turbine blade (1), a plurality of jet holes (3) provided on the side wall of the cold air cavity (2), the cold air cavity (2) being connected to the outer surface of the turbine blade (1) through the jet holes (3), and a spiral structure provided on the inner side wall of the jet hole (3); The shape of the cold air cavity (2) is adapted to the shape of the outer surface of the turbine blade (1), and the distance A between the side wall of the cold air cavity (2) and the outer surface of the turbine blade (1) is 3 mm to 7 mm; The angle θ between the axis of the jet hole (3) and the outer surface of the turbine blade (1) is 30°-40°; The angle direction is along the incoming flow direction; The tooth shape of the spiral structure of the jet hole (3) is triangular; The inner diameter D of the jet hole (3) is 1 mm to 2 mm, the tooth height H of the spiral structure is 0.5D, and the pitch I is 1.3D; The spiral structure of the jet hole (3) is a right spiral; The length of the jet hole (3) is L, L = A / sinθ; The vertical vortex generated by the spiral structure jet hole (3) includes a large-scale vortex at the top and a small-scale vortex at the bottom. The large-scale vortex suppresses the small-scale vortex, so that the cooling air film obtains a larger lateral velocity and a smaller normal velocity. The larger lateral velocity enables the cooling air film to have a spanwise covering ability to resist the high-temperature mainstream flowing laterally at the bottom, and the smaller normal velocity suppresses the coolant from entering the high-temperature mainstream, weakens the mixing effect of the coolant and the high-temperature mainstream, and reduces the temperature of the mixed air flow and adheres to the surface of the turbine blade (1).

2. The air film cooling structure with a spiral structure according to claim 1, characterized in that: The plurality of jet holes (3) are arranged at equal intervals along the span direction of the turbine blade (1).

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