A secondary flow system for low Reynolds number wind tunnels

Abstract

A secondary flow system for a low Reynolds number wind tunnel relates to the technical field of turbine blade cascade aerothermal performance testing. The present invention solves the problem that existing secondary flow systems cannot simultaneously provide multiple secondary flows to the blade cascade for testing during the test process. The air compression assembly, dryer, pressure-surge tank, switch valve, regulating valve, flow meter and multi-nozzle pressure-surge tank of the present invention are connected in sequence from left to right and then connected to the test chamber, and the multi-nozzle pressure-surge tank provides simultaneous multiple secondary flows to multiple blade cascades in the test chamber; wherein, when the test piece inlet is throttled, the pressure of the test section is low. At this time, compressed air is provided to the pressure-surge tank through the suction unit in the wind tunnel system, thereby providing the air source required for the secondary flow test; when the pressure of the test section is high, compressed air is provided to the pressure-surge tank through the air compressor of the air compression assembly, thereby providing the air source required for the secondary flow test. The present invention is used for multi-path secondary flow turbine blade cascade testing.

Description

Technical Field

[0001] The present invention relates to the technical field of turbine blade cascade aerothermal performance testing, and in particular to a secondary flow system for a low Reynolds number wind tunnel, which is used for turbine blade cascade testing. Background Art

[0002] When an aircraft operates at high altitude (above 10,000 meters), the density of the atmosphere is significantly reduced compared to the density on the ground, and the Reynolds number, a key aerodynamic parameter affecting flow, becomes very low, which leads to low-Reynolds-number flow problems. Specifically, when turbine blades operate at low Reynolds numbers, the flow within the blade slots is often laminar or a laminar-turbulent mixed flow state, which can easily cause flow separation on the blade suction surface. In severe cases, this can cause flow blockage, affecting the matching between the compressor and turbine blade rows, resulting in reduced efficiency and performance of engine components, ultimately leading to reduced engine thrust, increased fuel consumption, and poor operating stability and reliability, significantly impacting the completion of flight missions.

[0003] Over the past few decades, numerous researchers have conducted extensive and in-depth research on the low-Reynolds number problems of low-pressure turbines. For example, the boundary layer on the suction side of the blade remains laminar over the front portion of the chord length. However, in the diffuser region at the rear of the blade, influenced by the adverse pressure gradient, separation is highly likely to occur. The separated boundary layer may develop into a "long" or "short" closed separation bubble, or even an open separation in certain environments. The mechanism of the separation bubble transition was first extensively and in-depth studied. The separation bubble size gradually increases with decreasing Reynolds number. At extremely low Reynolds numbers, the separated boundary layer no longer adheres to the blade surface, resulting in an open separation. Subsequent researchers conducted extensive experiments to investigate the effects of factors such as periodic wake flow and turbulence on the low-Reynolds number problems of low-pressure turbines. The study found that the periodic sweep of the upstream wake can influence the development of the boundary layer, thereby suppressing the size of the laminar separation bubble, and the suppression effect is related to the frequency of the wake's passage. Thanks to the continuous development of computational fluid dynamics (CFD) technology, researchers have also conducted a large number of numerical simulation studies on the low Reynolds number problem of low-pressure turbines and deeply analyzed the physical mechanism of boundary layer separation transition.

[0004] However, most of these experiments and numerical simulations were conducted under low-speed conditions (the exit Mach number is usually less than 0.3). Therefore, it is necessary to conduct experimental research on the aero-thermal performance of turbine cascades under low Reynolds number conditions and gradually establish and improve a database of turbine cascades under low Reynolds number conditions.

[0005] The turbine blades are part of the hot end of the engine and operate in a high-temperature, high-pressure airflow environment from the combustion chamber. This has a significant impact on the structure and strength of the turbine blades, as well as the performance of the engine. There are currently two solutions: one is to find stronger materials to increase the turbine inlet temperature, thereby improving turbine performance; the other is to design turbine cooling blades with better structures so that they can withstand higher combustion chamber inlet temperatures, thereby improving turbine performance. Both of these approaches have the problems of high cost and long design cycles. Therefore, it is necessary to conduct experimental research on the aero-thermal performance of turbine blades, and the secondary flow system is an indispensable and important component in conducting experimental research on the aero-thermal performance of turbine blades.

[0006] During the test process of the existing secondary flow system, in order to improve the test efficiency, multiple turbine blades are generally tested simultaneously. However, since the surge tank can only provide one secondary flow to the blades, it is impossible to provide multiple secondary flows to the blades at the same time for testing.

[0007] In summary, during the test process, the existing secondary flow system has the problem of being unable to simultaneously provide multiple secondary flows to the blade cascade for testing. Summary of the Invention

[0008] The present invention aims to solve the problem that existing secondary flow systems cannot simultaneously provide multiple secondary flows to the blade cascade during testing, and further provides a secondary flow system for low Reynolds number wind tunnels.

[0009] The technical solution of the present invention is:

[0010] A secondary flow system for a low Reynolds number wind tunnel includes an air compression component, which includes an air compressor and a suction unit. It also includes a dryer, a pressure-surge tank, an on-off valve, a regulating valve, a flow meter and a multi-nozzle pressure-surge tank. The air compression component, the dryer, the pressure-surge tank, the on-off valve, the regulating valve, the flow meter and the multi-nozzle pressure-surge tank are connected in sequence from left to right and then connected to a test chamber, and the multi-nozzle pressure-surge tank provides simultaneous multi-path secondary flows to multiple blade grids in the test chamber; wherein, when the test piece inlet is throttled, the pressure of the test section is low. At this time, compressed air is provided to the pressure-surge tank through the suction unit of the air compression component, thereby providing the air source required for the secondary flow test; when the pressure of the test section is high, compressed air is provided to the pressure-surge tank through the air compressor of the air compression component, thereby providing the air source required for the secondary flow test.

[0011] Furthermore, the multi-nozzle pressure-stabilizing tank includes a tank body, an air inlet pipe and two sets of nozzles. The tank body is a cylindrical tank body. The air inlet pipe is coaxially installed at the bottom of one side of the tank body and introduces gas into the tank body. The two sets of nozzles are symmetrically installed on the tank body with upper and lower axes.

[0012] Furthermore, each group of nozzles is multiple and is installed on the tank body at equal intervals.

[0013] Furthermore, the number of nozzles in each group is 8-16.

[0014] Preferably, the number of nozzles in each group is 12 or 14.

[0015] Furthermore, the axis of each nozzle is at 90 degrees to the axis of the tank body.

[0016] Furthermore, an axis of each nozzle forms an acute angle with the axis of the tank body.

[0017] Furthermore, the angle between the axis of each nozzle and the axis of the tank body is 25°-50°.

[0018] Preferably, the angle between the axis of each nozzle and the axis of the tank body is 30°.

[0019] Furthermore, it also includes a pipeline, one end of the pipeline is connected between the air compressor and the dryer, and the other end of the pipeline is connected to the exhaust system.

[0020] Compared with the prior art, the present invention has the following effects:

[0021] 1. The present invention provides a secondary flow system for the special environment of low-Reynolds-number wind tunnel turbine blade tests (this special environment refers to: when an aircraft operates at high altitude (above 10,000 meters), the density of the atmosphere is significantly reduced compared to the density on the ground, and the Reynolds number, a key aerodynamic parameter affecting the flow, becomes very low, which will bring about low-Reynolds-number flow problems. At the same time, the high-temperature environment in which the turbine operates may cause the aerodynamic and heat transfer performance of the turbine blades to degrade). When the inlet is throttled, the system effectively utilizes the lower pressure of the test section and compresses the gas into the surge tank 3 through the function of the suction unit, thereby enabling experimental research related to the secondary flow. Compared with conventional secondary flow systems, the present invention utilizes the device functions more reasonably (wherein, "more reasonably" is reflected in: during the low Reynolds number test, the present invention utilizes the wind tunnel's suction unit to provide a secondary flow air source. The suction unit not only exhausts the wind tunnel, but also provides an air source for the secondary flow, thereby realizing the rational use of the suction unit), is more economical, and reduces carbon emissions (by using the suction unit alone, it can reduce carbon emissions and meet the needs of tests under different conditions); turbine blade grid tests are generally aimed at multi-turbine blade grid deployment tests. This system is also designed with a multi-nozzle pressure-stabilizing tank to meet the secondary flow test requirements of multiple blades.

[0022] 2. In the structure of the multi-nozzle pressure-surge tank of the present invention, the various interfaces can not only be distributed on the tank body of the pressure-surge tank, but multiple interfaces can also be evenly distributed on the bottom surface of the pressure-surge tank opposite to the inlet, so as to adapt to and provide secondary flows at different angles, providing a more flexible test method for the secondary flow test of the blade grid, thereby improving the accuracy of the blade grid test and providing a more multi-dimensional test for in-depth research on engine blades.

[0023] 3. The present invention can directly use the suction unit to compress the gas in the surge tank. Compared with using a separate compressor 1 to compress the air in the surge tank 3, this technical solution can make the test more economical and reduce carbon emissions. The use of a multi-mouth surge tank can provide multiple secondary flows to meet the needs of multiple turbine blades. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a temperature-controlled open low-Reynolds number intelligent wind tunnel system diagram;

[0025] Figure 2 This is the main view of the multi-mouth surge tank;

[0026] Figure 3 yes Figure 2 Side view

[0027] In the figure: 1. Air compressor, 2. Dryer, 3. Pressure regulating tank, 4. On-off valve, 5. Control valve, 6. Flow meter, 7. Multi-nozzle pressure regulating tank, 7-1. Tank body, 7-2. Inlet pipe, 7-3. Two sets of nozzles, 8. Pipeline, C. Inlet system, A. Test chamber, A-1. Contraction section, A-2. Nozzle section, A-3. Test section, B. Exhaust system. DETAILED DESCRIPTION

[0028] Specific implementation method 1: Combination Figures 1 to 3 Describe this embodiment, this embodiment includes an air compression component, the air compression component is an air compressor 1 and a suction unit, it also includes a dryer 2, a pressure-surge tank 3, a switch valve 4, a regulating valve 5, a flow meter 6 and a multi-mouth pressure-surge tank 7, the air compression component, the dryer 2, the pressure-surge tank 3, the switch valve 4, the regulating valve 5, the flow meter 6 and the multi-mouth pressure-surge tank 7 are connected in sequence from left to right and then connected to the test chamber A, and the multi-mouth pressure-surge tank 7 provides simultaneous multi-path secondary flows to multiple blade grids in the test chamber A; wherein, when the test piece inlet is throttled, the pressure of the test section is low, at this time, compressed air is provided to the pressure-surge tank 3 through the suction unit of the air compression component, thereby providing the air source required for the secondary flow test; when the pressure of the test section is high, compressed air is provided to the pressure-surge tank 3 through the air compressor 1 of the air compression component, thereby providing the air source required for the secondary flow test.

[0029] The present invention is designed for a low Reynolds number test environment in a conventional secondary flow system, especially when the inlet is throttled and the pressure in the test section is low. At this time, the function of the suction machine can be directly used to compress the gas into the surge tank, and then carry out experimental research related to the secondary flow; at the same time, in the test related to the thermal performance of the turbine blade gas, multiple blades are usually used for testing, so multiple secondary flows are required to flow to each blade. Therefore, a multi-nozzle surge tank is designed to solve the situation where multiple secondary flows are required at the same time.

[0030] Specific implementation method 2: Combination Figures 2 to 3 To illustrate this embodiment, the multi-nozzle pressure-stabilizing tank 7 of this embodiment includes a tank body 7-1, an air inlet pipe 7-2 and two groups of nozzles 7-3. The tank body 7-1 is a cylindrical tank body. The air inlet pipe 7-2 is coaxially installed at the bottom of one side of the tank body 7-1 and introduces gas into the tank body 7-1. The two groups of nozzles 7-3 are symmetrically installed on the upper and lower axes on the tank body 7-1.

[0031] When this embodiment is actually used, a plurality of through holes are first opened on the tank body 7-1 according to the design requirements of the number of secondary flow paths in the actual test process. The through holes are used to install the nozzle 7-3, and the nozzle 7-3 is sealed and installed on the through holes. In addition, the installed nozzle 7-3 can withstand higher pressure to ensure the smooth completion of the entire secondary flow test.

[0032] This configuration can provide multiple secondary flows according to actual test requirements, and provides the necessary hardware equipment for testing multiple blade cascades to simultaneously implement multiple secondary flows. Other components and connection relationships are the same as any one of the specific embodiments 1 to 2.

[0033] Specific implementation method three: Combination Figures 2 to 3 To illustrate this embodiment, the number of each group of nozzles 7-3 in this embodiment is multiple and is installed on the tank body 7-1 at equal intervals.

[0034] In actual use, the number of nozzles 7-3 in each group is designed based on experimental requirements. However, to ensure the controllability of the secondary flow, the nozzles 7-3 are designed with equal spacing. This facilitates accurate calculation of the parameters of each secondary flow and ensures accurate testing. The other components and connections are the same as those in Specific Embodiments 1 or 2.

[0035] Specific implementation method four: Combination Figures 2 to 3 In this embodiment, each group of nozzles 7-3 has 8 to 16 nozzles. If a large number of blades are being tested simultaneously, a larger number of nozzles 7-3 can be selected, and each nozzle 7-3 can be independently controlled for start / stop and jet volume. The other components and connections are the same as in any one of the first to third embodiments.

[0036] Specific implementation method five: Combination Figures 2 to 3 To illustrate this embodiment, the number of nozzles 7 - 3 in each group is 12 or 14.

[0037] In actual use, the preferred number of nozzles 7-3 is 12. This number of nozzles 7-3 is suitable for most test situations. Furthermore, the number of nozzles 7-3 selected is not only related to the number of test blades, but also to the size and structural parameters of the blades. The other structures and components are the same as those of any one of the first to fourth embodiments.

[0038] Specific implementation method six: combination Figures 2 to 3 To illustrate this embodiment, the axis of each nozzle 7-3 of this embodiment is 90 degrees to the axis of the tank body 7-1.

[0039] This configuration is suitable for the case where the secondary flow ejected directly from the nozzle 7-3 directly acts on the blades, which is more consistent with the actual working conditions of the engine turbine blades and is also the most commonly used test condition. The other components and connection relationships are the same as any one of the specific embodiments 1 to 3.

[0040] Specific implementation method seven: combination Figures 2 to 3 To illustrate this embodiment, the axis of each nozzle 7-3 of this embodiment forms an acute angle with the axis of the tank body 7-1.

[0041] This configuration is suitable for research and development of blade-to-secondary flow systems, primarily for studying the impact of secondary flow on blade impact at varying angles and parameters. This provides a broader research space for testing new blade structural parameters and blades made of different materials. This eliminates the need to redesign the secondary flow system, saving R&D costs and providing additional research opportunities. The remaining components and connections are identical to those in any of the first through sixth embodiments.

[0042] Specific implementation method eight: combination Figures 2 to 3 To illustrate this embodiment, the angle between the axis of each nozzle 7-3 and the axis of the tank body 7-1 is 25°-50°.

[0043] This configuration is applicable to the secondary flow test performed by rotating the blade clamping angle during the blade test. The other components and connection relationships are the same as any one of the specific embodiments 1 to 7.

[0044] Specific implementation method nine: Combination Figures 2 to 3 To illustrate this embodiment, the angle between the axis of each nozzle 7-3 and the axis of the tank body 7-1 is 30°.

[0045] This arrangement is suitable for most secondary flow tests, especially multi-path secondary flow tests performed after conventional blades are rotated a certain angle after being clamped. Other components and connection relationships are the same as any one of the specific embodiments 1 to 8.

[0046] Specific implementation method ten: Combination Figure 1 To illustrate this embodiment, this embodiment further includes a pipeline 8 , one end of which is connected between the air compressor 1 and the dryer 2 , and the other end of which is connected to the exhaust system B.

[0047] This arrangement facilitates connection with an external exhaust system, thereby forming a more complete secondary flow test. Other components and connection relationships are the same as any one of the specific embodiments 1 to 9.

[0048] Combine Figures 1 to 3 The working principle of the present invention is described:

[0049] like Figure 1 As shown in the figure, it is a temperature-controllable open low-Reynolds number intelligent wind tunnel system. Its working principle is: under the suction action of the exhaust unit (the exhaust unit adopts variable frequency control, which can reduce energy consumption in the test project and improve the efficiency of test parameter adjustment), it works in a suction manner; its inlet condition is the atmospheric environment, and the airflow at the outlet of the test section passes through the heat exchanger (because the exhaust unit cannot withstand high temperatures, the airflow must be cooled) and then connected to the exhaust unit, and finally discharged into the atmosphere;

[0050] After the test is started, the suction unit creates a low back pressure at the outlet of the test section to meet the low Reynolds number requirement. The air passes through the air intake duct and is heated (oil or electric heating is possible) by the heater (the heater is installed at the front end of the wind tunnel body and is used to heat the air). The main and auxiliary pressure regulating valves in the air intake system C are adjusted, and the air flows from the diffusion section into the stable section, and then into the nozzle section through the contraction section, forming an airflow at a certain speed that enters the test section to carry out a blowing test on the model test piece. The secondary flow system is an indispensable and important component in conducting experimental research on the thermal performance of turbine blades.

[0051] It should be noted that the test chamber A in the present invention comprises a contraction section A-1, a nozzle section A-2, and a test section A-3. These sections are connected in sequence from left to right, and a pipeline connects the test section A-3 to the multi-nozzle surge tank 7. Multiple nozzles 7-3 in the multi-nozzle surge tank 7 simultaneously provide multiple secondary flows to the blades in the test section A-3 for testing.

[0052] Conventional secondary flow uses a separate air compressor to compress the air in the surge tank to provide a secondary flow air source of a certain pressure; however, due to the special test environment of low Reynolds number, when throttling occurs at the test piece inlet, the pressure in the test section is relatively low. At this time, the suction unit function can be directly used to compress the air in the surge tank, which can also meet the requirements of the secondary flow test; this technical solution more reasonably utilizes the equipment of the low Reynolds number wind tunnel test bench, making the wind tunnel more economical and reducing carbon emissions.

[0053] In the gas thermal performance test of turbine blade cascade, multiple blades are usually studied, such as Figure 2 and Figure 3 As shown, a multi-nozzle pressure-surge tank structure is adopted, in which air flow interfaces are evenly opened on both sides of the pressure-surge tank (or the bottom corresponding to the inlet). When needed, the pipeline is directly connected and it is directly sealed with bolts when not in use. This structure effectively divides the secondary flow into multiple airflows to meet the needs of the test.

[0054] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A secondary flow system for a low Reynolds number wind tunnel, comprising an air compression assembly, the air compression assembly being an air compressor (1) and a suction unit, characterized in that: It also includes a dryer (2), a pressure stabilizing tank (3), a switch valve (4), a regulating valve (5), a flow meter (6) and a multi-mouth pressure stabilizing tank (7). The air compressor (1), dryer (2), pressure stabilizing tank (3), switch valve (4), regulating valve (5), flow meter (6) and multi-mouth pressure stabilizing tank (7) are connected in sequence from left to right and then connected to the test chamber (A), and the multi-mouth pressure stabilizing tank (7) provides multiple secondary flows to multiple blade grids in the test chamber (A) at the same time; wherein, when the test piece inlet is throttled, the pressure of the test section is low, at this time, the suction unit of the air compression component is used to provide compressed air to the pressure stabilizing tank (3), thereby providing the air source required for the secondary flow test; when the pressure of the test section is high, the air compressor (1) of the air compression component is used to provide compressed air to the pressure stabilizing tank (3), thereby providing the air source required for the secondary flow test; The multi-nozzle pressure-stabilizing tank (7) comprises a tank body (7-1), an air inlet pipe (7-2) and two groups of nozzles (7-3). The tank body (7-1) is a cylindrical tank body. The air inlet pipe (7-2) is coaxially installed at the bottom of one side of the tank body (7-1) and introduces gas into the tank body (7-1). The two groups of nozzles (7-3) are symmetrically installed on the tank body (7-1) with respect to the upper and lower axes.

2. The secondary flow system for a low Reynolds number wind tunnel according to claim 1, characterized in that: Each group of nozzles (7-3) is multiple in number and is installed on the tank body (7-1) at equal intervals.

3. The secondary flow system for a low Reynolds number wind tunnel according to claim 2, characterized in that: The number of nozzles in each group (7-3) is 8-16.

4. The secondary flow system for a low Reynolds number wind tunnel according to claim 3, characterized in that: The number of nozzles in each group (7-3) is 12 or 14.

5. The secondary flow system for a low Reynolds number wind tunnel according to claim 4, characterized in that: The axis of each nozzle (7-3) is 90 degrees to the axis of the tank (7-1).

6. The secondary flow system for a low Reynolds number wind tunnel according to claim 5, characterized in that: The axis of each nozzle (7-3) forms an acute angle with the axis of the tank body (7-1).

7. The secondary flow system for a low Reynolds number wind tunnel according to claim 6, characterized in that: The included angle between the axis of each nozzle (7-3) and the axis of the tank body (7-1) is 25°-50°.

8. The secondary flow system for a low Reynolds number wind tunnel according to claim 7, characterized in that: The included angle between the axis of each nozzle (7-3) and the axis of the tank body (7-1) is 30 degrees.

9. The secondary flow system for a low Reynolds number wind tunnel according to claim 8, characterized in that: It also includes a pipeline (8), one end of which is connected between the air compressor (1) and the dryer (2), and the other end of which is connected to the exhaust system (B).

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