A flow control method for low-pressure turbine blades based on swept-frequency ejector

Abstract

The present invention discloses a method for controlling the flow of low-pressure turbine blades based on a sweeping ejector: the method is a method for passively controlling the unsteady flow of low-pressure turbine blades to control the boundary layer separation and end zone secondary flow of the blade suction surface of the low-pressure turbine blade. The method is implemented by the following steps: Step 1, installing a sweeping ejector on the low-pressure turbine blade, the inlet of the sweeping ejector being located at the blade pressure surface, the outlet of the sweeping ejector being located at the blade suction surface, and the outlet position of the sweeping ejector corresponding to the boundary layer accumulation on the blade pressure surface, so as to achieve the effect of diverting the jet from the blade pressure surface to the blade suction surface. Compared with other flow control methods, the present invention utilizes the pressure difference on both sides of the turbine blade to form passive unsteady flow control. The energy required is extremely small, and the operation is entirely based on the pressure difference. There is no need to arrange redundant control circuits, and there are no complex moving parts, making it easier to install.

Description

Technical Field

[0001] The present invention relates to a control method for low-pressure turbine blades in a turbofan engine, and in particular to a flow control method for low-pressure turbine blades based on a sweeping frequency ejector. Background Art

[0002] Turbofan engines are widely used in civil aviation due to their high efficiency, low fuel consumption, and long range. As the demand for economic benefits in civil aviation continues to increase, the demand for turbofan engine efficiency is also increasing. Improving the efficiency of the low-pressure turbine by reducing its weight—that is, by reducing the number of stages and blades—is one effective way to improve turbofan engine efficiency.

[0003] However, for the low-pressure turbine, the reduction in the number of stages and blades means that the blades bear higher loads. The high aerodynamic load will make the flow inside the low-pressure turbine more complicated, the flow separation will be serious, and the turbine performance will decline.

[0004] Boundary layer separation is one of the sources of turbine performance loss. If the adverse pressure gradient on the suction side of the blade is increased, the boundary layer on the end wall and the boundary layer on the blade will converge at the blade root under the combined effects of the lateral pressure gradient and the axial adverse pressure gradient, causing boundary layer accumulation. Since the Reynolds number of civil aircraft is low in cruise conditions, the blade surface is laminar, and the airflow's ability to resist separation is low, which makes boundary layer separation more likely to occur. It is mainly divided into closed separation bubbles and open separation bubbles. Figure 2 It is a closed separation bubble. The closed separation bubble has little effect on the aerodynamic performance of the turbine. If the transition point is far away from the separation point, it will form a closed separation bubble. Figure 3 The open separation bubble shown in the figure will greatly affect the pressure distribution on the suction surface of the blade, and may even block the blade channel and reduce turbine performance.

[0005] As another source of turbine performance loss, the secondary flow in the end area mainly affects the flow field in the end area in the form of channel vortex, causing the performance of the turbine to decline. Figure 4 As shown, the low-energy fluid in the boundary layer at the leading edge of the blade is affected by the radial pressure gradient, flowing toward the end wall and rolling up to form a vortex after hitting the end wall. This vortex continues to develop downstream from the leading edge of the blade to form a horseshoe vortex. After the horseshoe vortex enters the blade channel, it is affected by the lateral pressure gradient and continuously draws in the low-energy fluid in the boundary layer of the blade end wall, intersecting with the horseshoe vortex on the suction surface of the downstream blade to form a channel vortex. Under the combined influence of the horseshoe vortex and the channel vortex, a wall vortex is formed on the suction surface of the blade, which develops downstream to form a shedding vortex at the trailing edge of the blade. The presence of these vortices leads to a decline in the performance of the low-pressure turbine.

[0006] The impact of these complex flow phenomena on turbine efficiency cannot be ignored, so it is particularly important to control the flow of the turbine. Flow control methods are divided into steady flow control methods and unsteady flow control methods. The unsteady flow control method can use far less energy than the steady flow control method to achieve the same effect as the steady flow control method, so it is widely used.

[0007] Flow control methods can be categorized as active and passive. Compared to active flow control, passive flow control requires no active energy injection, avoids the need for complex energy excitation paths, and only requires certain component processing to achieve uninterrupted flow control. Therefore, passive unsteady flow control has become a preferred option. Currently studied passive flow control methods include ball and socket surface treatment and groove surface treatment. While these technologies can improve low-pressure turbine performance to a certain extent, they are significantly affected by the Reynolds number and are difficult to maintain at optimal operating conditions under actual operating conditions. However, compared to active flow control, passive flow control requires no active energy injection, avoids the need for complex energy excitation paths, and only requires certain component processing to achieve uninterrupted flow control. Therefore, passive unsteady flow control has become a preferred option.

[0008] Therefore, a low-pressure turbine blade flow control method based on a swept-frequency ejector must be proposed to solve the above technical problems. Summary of the Invention

[0009] The object of the present invention is to provide a low-pressure turbine blade flow control method based on a swept-frequency ejector to overcome the above-mentioned shortcomings and deficiencies of the prior art.

[0010] A low-pressure turbine blade flow control method based on a sweeping ejector, wherein the method is a passive unsteady flow control method for the low-pressure turbine blade to control the boundary layer separation and end zone secondary flow of the blade suction surface of the low-pressure turbine blade. The method is achieved by the following steps: Step 1, installing a sweeping ejector on the low-pressure turbine blade, wherein the inlet of the sweeping ejector is located at the blade pressure surface, and the outlet of the sweeping ejector is located at the blade suction surface. The outlet position of the sweeping ejector corresponds to the boundary layer accumulation area of ​​the blade pressure surface, so as to achieve the effect of diverting the jet from the blade pressure surface to the blade suction surface.

[0011] Furthermore, the method adjusts the height, inlet width, outlet width, jet angle and number of the sweeping ejector according to the boundary layer separation position of the blade suction surface.

[0012] Furthermore, the method adjusts the jet intensity and jet frequency by adjusting the jet angle, inlet width, outlet width and height of the sweeping jet;

[0013] The method adjusts the jet angle and moves the inlet position of the sweeping ejector so that the inlet corresponds to the higher pressure point on the blade pressure surface, thereby increasing the pressure difference between the inlet and outlet of the sweeping ejector and achieving the effect of increasing its jet frequency.

[0014] The method increases the inlet width, outlet width and height of the sweeping jet device, and increases the jet flow rate by increasing the inlet and outlet areas, thereby achieving the effect of increasing the jet intensity.

[0015] Furthermore, the method achieves a superposition effect for the boundary layer separation at different positions on the suction surface of the blade by arranging multiple swept-frequency ejectors on the low-pressure turbine blade.

[0016] Beneficial effects of the present invention:

[0017] Compared with other flow control methods, the present invention utilizes the pressure difference on both sides of the turbine blade to form passive unsteady flow control. The energy required is extremely small, and it operates entirely on the pressure difference. There is no need to arrange redundant control lines and no complicated moving parts, making it easier to install. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the installation of low-pressure turbine blades and swept-frequency ejectors.

[0019] Figure 2 It is a schematic diagram of a closed separation bubble.

[0020] Figure 3 This is a schematic diagram of an open separation bubble.

[0021] Figure 4 It is a schematic diagram of secondary flow in the end area.

[0022] Figure 5 This is a schematic diagram of a swept-frequency ejector.

[0023] Figure 6 This is a schematic diagram of the flow path of the swept-frequency ejector.

[0024] Figure 7 This is another flow path diagram of a swept-frequency ejector.

[0025] Figure 8 It is a schematic diagram of the installation parameters of the outlet width and the height of the sweeping ejector of the present invention.

[0026] Figure 9 It is a schematic diagram of the installation parameters of the jet angle of the present invention.

[0027] Figure 10It is a schematic diagram of the installation parameters of the entrance width of the present invention.

[0028] Figure 11 It is a structural schematic diagram of the present invention.

[0029] Figure 12 It is another structural schematic diagram of the present invention.

[0030] Figure 13 It is a schematic diagram of the installation of multiple sweep-frequency ejectors of the present invention.

[0031] Figure 14 This is a top view of the installation of multiple sweep-frequency ejectors of the present invention.

[0032] Reference numerals:

[0033] Low-pressure turbine blade 100, blade pressure surface 1, blade suction surface 2, open separation bubble 3, closed separation bubble 4, horseshoe vortex 5, channel vortex 6, swept ejector inlet 7, wall 8, outlet wall 9, feedback channel 10, ejector wall 11, height h, outlet width b, jet angle α, inlet width a.

[0034] Swept frequency ejector 110. DETAILED DESCRIPTION

[0035] The present invention will be further described below with reference to specific examples. It should be understood that the following examples are only used to illustrate the present invention and are not intended to limit the scope of the present invention.

[0036] Figure 1 This is a schematic diagram of the installation of low-pressure turbine blades and swept-frequency ejectors. Figure 2 It is a schematic diagram of a closed separation bubble. Figure 3 This is a schematic diagram of an open separation bubble. Figure 4 It is a schematic diagram of secondary flow in the end area. Figure 5 This is a schematic diagram of a swept-frequency ejector. Figure 6 This is a schematic diagram of the flow path of the swept-frequency ejector. Figure 7 This is another flow path diagram of a swept-frequency ejector. Figure 8 It is a schematic diagram of the installation parameters of the outlet width and the height of the sweeping ejector of the present invention. Figure 9 It is a schematic diagram of the installation parameters of the jet angle of the present invention. Figure 10 It is a schematic diagram of the installation parameters of the entrance width of the present invention. Figure 11 Schematic diagram of the structure of the present invention. Figure 12 It is another structural schematic diagram of the present invention. Figure 13 It is a schematic diagram of the installation of multiple sweep-frequency ejectors of the present invention. Figure 14 This is a top view of the installation of multiple sweep-frequency ejectors of the present invention.

[0037] Example 1

[0038] like Figure 1-14 As shown, a low-pressure turbine blade flow control method based on a sweeping ejector is provided, wherein the method is a passive unsteady flow control method for a low-pressure turbine blade 100, so as to control the boundary layer separation and the end zone secondary flow of the blade suction surface 2 of the low-pressure turbine blade 100. The method is implemented by the following steps: Step 1, installing a sweeping ejector 110 on the low-pressure turbine blade 100, the inlet of the sweeping ejector 110 being located at the blade pressure surface 1, and the outlet of the sweeping ejector 110 being located at the blade suction surface 2, and the outlet position of the sweeping ejector 110 corresponding to the boundary layer accumulation position of the blade pressure surface 1, so as to achieve the effect of diverting the jet from the blade pressure surface 1 to the blade suction surface 2.

[0039] The method adjusts the height h of the sweeping ejector 110, the inlet width a of the sweeping ejector 110, the outlet width b of the sweeping ejector 110, the jet angle α of the sweeping ejector 110, and the number n of the sweeping ejector 110 according to the boundary layer separation position of the blade suction surface 2.

[0040] The method adjusts the jet intensity and jet frequency by adjusting the jet angle α, inlet width a, outlet width b and height h of the sweeping jet device 110;

[0041] The method adjusts the jet angle α and moves the inlet position of the sweeping ejector 110 so that the inlet corresponds to the higher pressure position of the blade pressure surface 1, thereby increasing the pressure difference between the inlet and outlet of the sweeping ejector 110, thereby achieving the effect of increasing its jet frequency.

[0042] The method increases the inlet width a, outlet width b and height h of the sweeping jet 110, and by increasing the inlet and outlet areas, increases the flow rate of the jet, thereby achieving the effect of increasing the jet intensity.

[0043] The method achieves a superposition effect for boundary layer separation at different positions of the blade suction surface 2 by arranging multiple swept-frequency ejectors 110 on the low-pressure turbine blade.

[0044] like Figure 1-5 As shown, in the existing turbofan engine with a large bypass ratio, the effect of reducing the turbine weight and improving the turbine efficiency can be achieved by reducing the number of low-pressure turbine stages and the number of blades, but this will lead to an increase in the blade load and the adverse pressure gradient, which will easily cause boundary layer separation, resulting in an open separation bubble 3 and a closed separation bubble 4. At the same time, secondary flow in the end area will be generated, forming a horseshoe vortex 5 and a channel vortex 6, all of which will cause serious aerodynamic losses.

[0045] like Figure 11-12As shown, the present invention proposes a device for installing a swept-frequency ejector on a low-pressure turbine blade, which utilizes the pressure difference on both sides of the blade channel and suppresses the boundary layer separation and the secondary flow in the end area at the blade through a passive unsteady flow control method, thereby improving the working efficiency of the turbine.

[0046] like Figure 6-7 As shown, in order to effectively improve the performance of the low-pressure turbine, the outlet of the swept-frequency ejector 110 in the present invention needs to be aligned as closely as possible with the separation bubble and channel vortex 6 on the blade suction surface 2, and the inlet is selected to be in the area with higher pressure on the blade pressure surface 1. Due to the pressure difference between the two blades, part of the airflow on the blade pressure surface 1 will flow into the swept-frequency ejector 110. Fluid flows into the swept-frequency ejector inlet 7. Due to the Coanda effect, when the curvature of an object is not large, the fluid tends to flow along the wall of the object. Therefore, the fluid flows along the ejector wall 8, passes through the throat and is ejected along the outlet wall 9. Part of the fluid flows into the feedback channel 10, forming a feedback flow that affects the upstream flow, causing the fluid at the swept-frequency ejector inlet 7 to change its flow direction and flow along the ejector wall 11. After passing through the throat, it forms a jet along the outlet wall 9. Part of the fluid enters the feedback channel 10 and affects the fluid at the swept-frequency ejector inlet 7. This cycle continues, forming a jet that sweeps up and down on the blade suction surface 2. The jet has the characteristics of large sweeping area and periodic sweeping, which can effectively suppress boundary layer separation and end zone secondary flow.

[0047] like Figure 8-10 As shown, to further enhance control effectiveness, the present invention can modify the ejector parameters—h, outlet width b, jet angle α, and the number n of sweeping ejectors—according to the size and position of the separation bubble and channel vortex 6 to accurately suppress them. The inlet and outlet areas can also be adjusted by increasing the inlet width a, outlet width b, and height h, thereby increasing the intensity of the sweep. Furthermore, because pressure varies at different locations on the low-pressure turbine blades during operation, the jet angle α can be adjusted to increase the inlet and outlet pressure difference, thereby increasing the frequency of the sweep. Therefore, to achieve optimal control effectiveness, it is necessary to set each parameter to favorably suppress boundary layer separation and end zone secondary flow, based on actual conditions.

[0048] In this example, CFX simulations were performed using the SSTk-ω turbulence model with Gamma Theta transitions and second-order accuracy. This model has been extensively validated in separated flows. For unsteady calculations, the CFX "high-resolution" format and the second-order backward Euler transient format were employed. A constant time step of 5.0 × 10⁻⁶ s was used, with a maximum number of iterations per time step set to 5. Calculations show that the present invention achieves optimal results when the ejector height is 13.28 mm, the outlet width is 13.1 mm, the inlet width is 4.28 mm, and the ejection angle is 90°.

[0049] For the case where the suction surface 2 of the low-pressure turbine blade produces a large boundary layer separation, the present invention can be achieved by installing multiple sweeping ejectors on the low-pressure turbine blade, such as Figure 13-14 , achieving the effect of large-area flow control. In this embodiment, there is 1.

[0050] Compared with other flow control methods, the present invention utilizes the pressure difference on both sides of the turbine blade to form passive unsteady flow control. The energy required is extremely small, and it operates entirely on the pressure difference. There is no need to arrange redundant control lines and no complicated moving parts, making it easier to install.

[0051] The above describes the specific embodiments of the present invention, but the present invention is not limited thereto. The present invention can be modified in various ways without departing from the spirit of the present invention.

Claims

1. A low-pressure turbine blade flow control method based on a swept-frequency ejector, characterized by: The method is to perform a passive unsteady flow control method on a low-pressure turbine blade (100) to control the boundary layer separation and end zone secondary flow of the blade suction surface (2) of the low-pressure turbine blade (100). The method is achieved by the following steps: Step 1, installing a sweeping ejector (110) on the low-pressure turbine blade (100), wherein the inlet of the sweeping ejector (110) is located at the blade pressure surface (1), and the outlet of the sweeping ejector (110) is located at the blade suction surface (2). The outlet position of the sweeping ejector (110) corresponds to the boundary layer accumulation position of the blade pressure surface (1), so as to achieve the effect of diverting the jet from the blade pressure surface (1) to the blade suction surface (2).

2. The low-pressure turbine blade flow control method based on a swept-frequency ejector according to claim 1, characterized in that: The method adjusts the height (h) of the sweeping jet (110), the inlet width (a) of the sweeping jet (110), the outlet width (b) of the sweeping jet (110), the jet angle (α) of the sweeping jet (110), and the number n of the sweeping jets (110) according to the boundary layer separation position of the blade suction surface (2).

3. The low-pressure turbine blade flow control method based on a swept-frequency ejector according to claim 1, characterized in that: The method adjusts the jet intensity and jet frequency by adjusting the jet angle (α), inlet width (a), outlet width (b) and height (h) of a sweeping jet device (110); The method adjusts the jet angle (α) to move the inlet position of the sweeping-frequency ejector (110) so that the inlet corresponds to a higher pressure position on the blade pressure surface (1), thereby increasing the pressure difference between the inlet and outlet of the sweeping-frequency ejector (110) and achieving the effect of increasing the jet frequency. The method increases the inlet width (a), outlet width (b) and height (h) of the sweeping-frequency ejector (110), thereby increasing the inlet and outlet areas, improving the jet flow rate, and achieving the effect of increasing the jet intensity.

4. The low-pressure turbine blade flow control method based on a swept-frequency ejector according to claim 1, characterized in that: The method achieves a superposition effect for boundary layer separation at different positions on the blade suction surface (2) by arranging multiple sweeping ejectors (110) on the low-pressure turbine blade.

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