A comb-shaped plasma actuator device for improving film cooling performance and its application

Abstract

A comb-shaped plasma actuator device and application for improving film cooling performance, belonging to the technical field of film cooling of gas turbine turbine blades; it includes a low-temperature plasma power supply, an exposed electrode, a buried electrode and an insulating medium; the low-temperature plasma power supply is connected to the exposed electrode and the buried electrode; the exposed electrode is in a comb shape, including a comb root and a comb tip, and is arranged on the upper surface of the first insulating medium, and there are film holes on the first insulating medium; the buried electrode is in a strip shape and is arranged on the lower surface of the first insulating medium; the exposed electrode and the buried electrode are asymmetrically arranged, and the distance along the flow direction is S; the bottom surface of the buried electrode is covered by the second insulating medium. The exposed electrode increases the distribution of the plasma in the spanwise direction, and the disturbance of the comb-shaped plasma to the flow field in the flow direction and the spanwise direction destroys the thermal boundary layer and the flow boundary layer of the wall surface, thereby strengthening the convective heat transfer performance of the wall surface.

Description

Technical Field

[0001] The present invention belongs to the technical field of film cooling for gas turbine blades, and particularly relates to a comb-shaped plasma actuator device for improving film cooling performance and its application. Background Art

[0002] At present, the gas temperature in front of the turbine of advanced aero-engines exceeds 2000K, far higher than the melting temperature of superalloys, and the growth rate of the gas temperature at the turbine inlet is much higher than the development rate of high-temperature resistant materials. When metal materials are in a high-temperature and high-load state for a long time, the crystals inside the materials will slip, resulting in creep phenomena. When running at high speed, the metal materials are subjected to a large centrifugal force, causing creep fracture. In addition, unburned molten particulate matter adheres to the surface of high-temperature blades, thus blocking the pores and seams on the blade surface. In order to avoid the thermal erosion of the main high-temperature gas on the turbine components, the film cooling technology is one of the most common and effective external cooling methods in advanced gas turbines. Although the film cooling has excellent cooling effect, on the one hand, the temperature reduction range of the film cooling is limited, and on the other hand, the cooling air comes from the compressor, reducing the air required for combustion, resulting in a decrease in the thermal performance of the gas turbine, a reduction in thrust, and an increase in aerodynamic losses.

[0003] Compared with passive flow control devices such as vortex generators and transverse grooves, plasma, as a new type of active flow control technology, has the advantages of simple structure, low power consumption, good robustness, and fast response. When the plasma actuator is turned on, the plasma generated by the actuator moves directionally under the action of the electric field and exchanges momentum with the surrounding air, thereby inducing the airflow to flow along the wall and accelerating the jet. By using this flow control effect of the plasma, plasma actuators can be arranged on the surface of the turbine blade to induce the cooling airflow to flow along the wall to improve the heat transfer performance on the surface of the turbine blade.

[0004] The prior art discloses a technique for generating different amounts of plasma according to different shock wave intensities. Its disadvantage is that the electrode shape of the plasma actuator is simple, and the effect of resisting the shock wave to destroy the supersonic film cooling boundary layer is limited. Summary of the Invention

[0005] Technical Problems to be Solved

[0006] In order to avoid the deficiencies of the prior art, the present invention provides a comb-shaped plasma actuator device for improving film cooling performance and its application. The special exposed electrodes of the comb-shaped plasma actuator increase the distribution of the plasma in the spanwise direction. The disturbance of the comb-shaped plasma to the flow field in the flow direction and the spanwise direction destroys the thermal boundary layer and the flow boundary layer of the wall surface, thereby strengthening the convective heat transfer performance of the wall surface.

[0007] The technical solution of the present invention is: a comb-shaped plasma actuator device for improving the film cooling performance, including a low-temperature plasma power supply, an exposed electrode, a buried electrode and an insulating medium; the discharge type of the low-temperature plasma power supply is surface dielectric barrier discharge, which is connected to the exposed electrode and the buried electrode;

[0008] The exposed electrode is in a comb shape, including a comb root and a comb tip, and is arranged on the upper surface of the first insulating medium, and air film holes are opened on the first insulating medium; the buried electrode is in a strip shape and is arranged on the lower surface of the first insulating medium; the exposed electrode and the buried electrode are asymmetrically arranged, and the distance along the flow direction is S;

[0009] The bottom surface of the buried electrode is covered by the second insulating medium to prevent discharge on this side.

[0010] A further technical solution of the present invention is: the exposed electrode is a comb-shaped electrode composed of a number of T-shaped units arranged periodically along the span direction, the horizontal direction of the T-shaped unit is the comb root, and the vertical direction is the comb tip; the comb root is perpendicular to the flow direction, and its leading edge is arranged at the trailing edge of the air film hole outlet; the comb tip is parallel to the flow direction and is located directly downstream of the air film hole.

[0011] A further technical solution of the present invention is: the flow direction distance S between the exposed electrode and the buried electrode is not greater than 0.5 mm.

[0012] A further technical solution of the present invention is: the exposed electrode is connected to the high-voltage end of the low-temperature plasma power supply, and the buried electrode is connected to the low-voltage end of the plasma power supply.

[0013] A further technical solution of the present invention is: the materials of the exposed electrode and the buried electrode are selected from copper foil or aluminum foil.

[0014] A further technical solution of the present invention is: the material of the insulating medium is polyimide, the thickness is 0.2 mm - 0.5 mm, and the width is the same as the width of the mainstream channel.

[0015] A further technical solution of the present invention is: the length of the exposed electrode along the flow direction is 8 mm, the amplitude is 5 mm, the wavelength is 12.7 mm, and the thickness is 0.1 mm; the width is the same as the width of the mainstream channel.

[0016] A further technical solution of the present invention is: the length of the buried electrode along the flow direction is 10 mm, the thickness is 0.1 mm, and the width is the same as the width of the mainstream channel.

[0017] A further technical solution of the present invention is: the working voltage of the low-temperature plasma power supply is 0 - 30 kV, and the working frequency is 6 - 30 kHz.

[0018] Application of a comb-shaped plasma actuator device for improving film cooling performance, wherein the comb-shaped plasma actuator device for improving film cooling performance is arranged on a turbine blade, and the turbine blade serves as a first-layer insulating medium, and the exposed electrode and the buried electrode are arranged on two side surfaces of the turbine blade in an asymmetric form; the exposed electrode is arranged downstream of the trailing edge of the film hole outlet of the turbine blade; the flow direction distance between the buried electrode and the exposed electrode is not greater than 0.5 mm.

[0019] Beneficial effects

[0020] The beneficial effects of the present invention are as follows: Compared with the prior art (without applying plasma excitation), by changing the shape of the exposed electrode of the plasma actuator, the distribution of the plasma along the gas flow direction and the expansion direction (spanwise direction) is changed; the tip of the comb-shaped actuator is aligned with the film hole outlet, and the body force of the actuator along the spanwise direction causes the cooling air flow to diffuse to both sides along the spanwise direction after spraying out from the film hole, significantly improving the spanwise film cooling performance; the body force of the comb tip actuator forward accelerates the flow velocity of the cooling air flow, greatly improving the flow direction film cooling efficiency; the aerodynamic excitation effect of the comb-shaped actuator destroys the thermal boundary layer near the wall surface, reduces the normal velocity of the cooling air flow, and the cooling air flow still adheres to the wall surface under a high blowing ratio (when the blowing ratio is greater than 1.0). The structure of the present invention is simple, small in size, low in power consumption, low in price and easy to install.

[0021] The calculation results show that there is a pair of kidney-shaped vortex pairs at the film hole outlet without applying plasma excitation, which intensifies the entrainment and lifting effect of the mainstream on the cooling air flow. The comb-shaped actuator induces a pair of anti-kidney-shaped vortex pairs with a rotation direction opposite to that of the kidney-shaped vortex pairs, and their scales are much larger than those of the kidney-shaped vortex pairs, greatly weakening the effect of the kidney-shaped vortex pairs. Compared with the working condition without applying plasma excitation, the average film cooling efficiency of the wall surface with the comb-shaped plasma actuator at each blowing ratio (M = 0.25, 0.5, 0.75 and 1.0) is increased by 90.9%, 108.9%, 87.2% and 38.0% respectively. The film cooling performance of the present invention is also significantly improved in the spanwise direction. When the blowing ratio increases from 0.25 to 1.0, the spanwise cooling efficiency is increased by 62.3%, 103.4%, 164.6% and 150.5% on average respectively. Description of the drawings

[0022] Figure 1 Schematic diagram of the arrangement of the comb-shaped plasma actuator of the present invention on a three-dimensional flat plate;

[0023] Figure 2 Schematic diagram of the physical parameters of the embodiment of the present invention;

[0024] Figure 3 Schematic diagram of the body force distribution of the embodiment of the present invention;

[0025] Figure 4 Nondimensional temperature contour maps and streamline trajectories for different flow cross-sections (X / D = 2 and 20);

[0026] Figure 5a Film cooling efficiency distribution contour maps at different excitation voltages under a low blowing ratio (M ≤ 0.50);

[0027] Figure 5b Film cooling efficiency distribution contour maps at different excitation voltages under a high blowing ratio (M ≥ 0.50);

[0028] Figure 6 Spanwise film cooling efficiency at different blowing ratios for the flow cross-section (X / D = 4);

[0029] Figure 7 Comparison results of the wall-averaged film cooling efficiency at different blowing ratios;

[0030] Figure 8 Wall-averaged film cooling efficiency at different excitation voltages when the blowing ratio is 0.5;

[0031] Description of reference numerals: 1 - flat plate, 2 - film hole, 3 - comb-shaped plasma actuator, 31 - exposed electrode, 311 - comb root, 312 - comb tip, 32 - buried electrode, 33 - insulating medium, 34 - cryogenic plasma power supply, 341 - high-voltage terminal of the power supply, 342 - low-voltage terminal of the power supply. Detailed implementation manners

[0032] The embodiments described below by referring to the accompanying drawings are exemplary and are intended to explain the present invention, and should not be construed as limiting the present invention.

[0033] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc. indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as limiting the present invention.

[0034] As Figure 1As shown, this embodiment is unfolded with a three-dimensional flat plate model, on which a single film hole and a single T-shaped unit are provided. The numerical simulation calculation uses the commercial software ANSYS FLUENT, and the k-ε turbulence model is used for simulation. The comb-shaped plasma actuator device 3 of this embodiment includes a comb-shaped exposed electrode 31, a strip-shaped buried electrode 32, a flat plate 1, an insulating medium 33, and a low-temperature plasma power supply 34. Using the plasma phenomenological model established by Shyy et al., the electrokinetic body force of the comb-shaped plasma (see Figure 3 ) is loaded into the momentum conservation equation through a user-defined function (UDF) for solution, so as to realize the aerodynamic excitation effect of the plasma.

[0035] The exposed electrode 31 is a comb-shaped copper foil electrode or aluminum foil electrode, which is a comb-shaped electrode composed of several T-shaped units arranged periodically in the spanwise direction; the buried electrode 32 is a strip-shaped copper foil electrode or aluminum foil electrode, and the insulating medium 33 uses polyimide. The exposed electrode 31 is connected to the high-voltage end 341 of the low-temperature plasma power supply 34, and the buried electrode 32 is connected to the low-voltage end 342 of the low-temperature plasma power supply 34. The exposed electrode 31 includes a comb-shaped root and a comb-shaped tip; an air film hole is opened on the flat plate 1; the exposed electrode 31 is arranged downstream of the outlet of the air film hole 2 on the flat plate 1, and the comb-shaped tip 312 of the exposed electrode 31 is directly opposite to the outlet of the air film hole 2; the buried electrode 32 is covered with the insulating medium 33 to prevent discharge, and the insulating medium 33 is an insulating tape. The exposed electrode 31 and the buried electrode 32 are asymmetrically arranged on both sides of the flat plate 1, and the distance S between the two electrodes in the flow direction is not greater than 0.5 mm to ensure that plasma can be generated above the buried electrode 32.

[0036] Figure 2 It is a schematic diagram of the physical parameters of the embodiment. Among them, the wavelength λ of the comb-shaped exposed electrode 31 is 12.7 mm, the amplitude is 5 mm, the flow direction length L1 is 8 mm, and the width is the same as the width of the mainstream channel. The flow direction length L2 of the strip-shaped buried electrode 32 is 10 mm, and the width is the same as the width of the mainstream channel; the thickness of both electrodes is 0.1 mm. The excitation frequency of the low-temperature plasma power supply 34 used in this embodiment is 2 kHz, and the excitation voltages are 6 kV, 12 kV, and 24 kV.

[0037] Figure 3 It is a schematic diagram of the body force distribution of the embodiment. There are body forces in the spanwise direction on both sides of the tip 312 of the comb-shaped plasma actuator, and there is a forward body force distributed at the front end of the tip 312. There is a forward body force distribution at the root 311 of the comb-shaped plasma actuator.

[0038] Figure 4Are the dimensionless temperature contour maps and streamline trajectories for cross-sections with different flow directions (X / D = 2 and 20). Without plasma excitation, the low-temperature region on the wall is concentrated in the spanwise range of -0.75 < Y / D < 0.75. The low-temperature region downstream of the wall decreases and the temperature increases. There is a pair of kidney-shaped vortex pairs in the cross-section. Under the action of this pair of vortex pairs, the cooling air flow is entrained by the high-temperature mainstream and lifted off the wall, greatly weakening the performance of the film cooling. Along the flow direction, the scale and the height of the vortex core of the kidney-shaped vortex pair increase, and the entrainment effect of the mainstream on the cooling air flow also enhances. When using the comb-shaped plasma actuator of this embodiment, the temperature of the low-temperature region downstream of the wall decreases as a whole, and the range of the low-temperature region increases. The comb-shaped actuator generates a pair of relatively large-scale anti-kidney-shaped vortex pairs on both sides of the spanwise wall, reducing the distribution of the middle kidney-shaped vortex pair, so that the cooling air flow is more widely distributed in the spanwise direction.

[0039] Figures 5(a) and 5(b) are the contour maps of the film cooling efficiency under different blowing ratios and excitation voltages. The spanwise-expanding body force generated by the comb-shaped plasma actuator spreads the cooling air flow over the entire flat plate surface. When the blowing ratio is 0.25, the film cooling efficiency on the wall is the most widely distributed at an excitation voltage of 12 kV. When the blowing ratio is 0.50, as the excitation voltage increases, the distribution of the film cooling efficiency on the wall increases, but the cooling efficiency distributions at 12 kV and 24 kV are relatively close. When the blowing ratio is 0.75 and the excitation voltage is 24 kV, the film cooling efficiency is distributed over the entire wall, which greatly improves the film cooling performance of the wall under high blowing ratios. As the excitation voltage increases, the distribution of the film cooling efficiency on the wall where the comb-shaped actuator is arranged gradually increases in the flow direction and the spanwise direction.

[0040] Figure 6 Is the spanwise film cooling efficiency at different blowing ratios for the cross-section in the flow direction (X / D = 4). At each blowing ratio, the spanwise film cooling efficiency using the comb-shaped plasma actuator is much higher than the spanwise cooling efficiency without plasma excitation, because the comb-shaped actuator has a body force that diffuses in the spanwise direction, making the cooling air flow more fully distributed in the spanwise direction. Especially when the blowing ratios are 0.5, 0.75, and 1.0, the average spanwise film cooling efficiencies of the comb-shaped actuator increase by 103%, 165%, and 151% respectively.

[0041] Figure 7 Is the comparison result of the average film cooling efficiency on the wall under different blowing ratios. When the blowing ratio increases from 0.25 to 1.0, the average cooling efficiency on the wall using the comb-shaped plasma actuator increases by 38.0% to 108.8% compared with that without plasma excitation. For various working conditions, the film cooling efficiency is the largest when the blowing ratio is 0.5.

[0042] Figure 8It is the average film cooling efficiency of the wall surface under different excitation voltages when the blowing ratio is 0.5. After using the comb-shaped plasma actuator, with the increase of the excitation voltage, the average film cooling efficiency of the wall surface increases. When the excitation voltages are 6 kV, 12 kV and 24 kV, the cooling efficiencies are increased by 58.7%, 108.8% and 115.0% respectively compared with the case without plasma excitation. The cooling efficiency at 12 kV is increased by 31.6% compared with that at 6 kV, while the cooling efficiency at 24 kV is only increased by 2.9% compared with that at 12 kV. This shows that too high excitation voltage cannot significantly improve the film cooling performance. Generally speaking, the film cooling performance of the flat plate surface is the best when the optimal blowing ratio is 0.5 and the optimal excitation voltage is 12 kV.

[0043] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Without departing from the principles and spirit of the present invention, those of ordinary skill in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A comb-shaped plasma actuator device for improving film cooling performance, characterized in that: It includes a low-temperature plasma power supply, an exposed electrode, a buried electrode, and an insulating medium; the discharge type of the low-temperature plasma power supply is surface dielectric barrier discharge, which is connected to the exposed electrode and the buried electrode; The exposed electrode is in a comb shape, including a comb root and a comb tip, and is arranged on the upper surface of the first-layer insulating medium. There are air film holes opened on the first-layer insulating medium; the buried electrode is in a strip shape and is arranged on the lower surface of the first-layer insulating medium; the exposed electrode and the buried electrode are asymmetrically arranged, and the distance along the flow direction is S; The bottom surface of the buried electrode is covered by the second-layer insulating medium to prevent discharge on this side; The exposed electrode is a comb-shaped electrode composed of a number of T-shaped units arranged periodically along the span direction. The horizontal part of the T-shaped unit is the comb root, and the vertical part is the comb tip; the comb root is perpendicular to the flow direction, and its leading edge is arranged at the trailing edge of the air film hole outlet; the comb tip is parallel to the flow direction and is located directly downstream of the air film hole; The flow direction distance S between the exposed electrode and the buried electrode is not greater than 0.5 mm.

2. The comb-shaped plasma actuator device for improving film cooling performance according to claim 1, characterized in that: The exposed electrode is connected to the high-voltage end of the low-temperature plasma power supply, and the buried electrode is connected to the low-voltage end of the plasma power supply.

3. The comb-shaped plasma actuator device for improving the film cooling performance according to claim 1, wherein: The materials of the exposed electrode and the buried electrode are selected as copper foil or aluminum foil.

4. The comb-shaped plasma actuator device for improving the film cooling performance according to claim 1, wherein: The material of the insulating medium is polyimide, with a thickness of 0.2 mm - 0.5 mm, and the width is the same as the width of the mainstream channel.

5. The comb-shaped plasma actuator device for improving the film cooling performance according to claim 1, wherein: The length of the exposed electrode along the flow direction is 8 mm, the amplitude is 5 mm, the wavelength is 12.7 mm, and the thickness is 0.1 mm; the width is the same as the width of the mainstream channel.

6. The comb-shaped plasma actuator device for improving film cooling performance according to claim 1, characterized in that: The length of the buried electrode along the flow direction is 10 mm, the thickness is 0.1 mm, and the width is the same as the width of the mainstream channel.

7. The comb-shaped plasma actuator device for improving the film cooling performance according to claim 1, characterized in that: The working voltage of the low-temperature plasma power supply is 0 - 30 kV, and the working frequency is 6 - 30 kHz.

8. Application of the comb-shaped plasma actuator device for improving film cooling performance according to any one of claims 1-7, characterized in that: The comb-shaped plasma actuator device for improving the air film cooling performance is arranged on the turbine blade. The turbine blade serves as the first-layer insulating medium, and the exposed electrode and the buried electrode are arranged on both sides of the turbine blade in an asymmetric form; the exposed electrode is arranged downstream of the trailing edge of the air film hole outlet of the turbine blade; The flow direction distance between the buried electrode and the exposed electrode is not greater than 0.5 mm.

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