Secondary flow system for wind tunnel with low Reynolds number

Abstract

The invention discloses a secondary flow system for a low-Reynolds-number wind tunnel, and relates to the technical field of turbine cascade gas thermal performance tests. The problem that in the testing process of an existing secondary flow system, multiple paths of secondary flow cannot be provided for the cascade at the same time for testing is solved. An air compression assembly, a drying machine, a surge tank, a switching valve, a regulating valve, a flow meter and a multi-nozzle surge tank are sequentially connected from left to right and then connected with a test chamber, and multiple paths of secondary flow are provided for a plurality of cascade blades in the test chamber through the multi-nozzle surge tank at the same time; when throttling is carried out on an inlet of a test piece, the pressure of a test section is low, at the moment, compressed air is provided for the surge tank through a suction unit in the wind tunnel system, and then an air source needed by a secondary flow test is provided; when the pressure of the test section is high, compressed air is provided for the surge tank through an air compressor of the air compression assembly, and then an air source needed by the secondary flow test is provided. The multi-path secondary flow turbine cascade test device is used for multi-path secondary flow turbine cascade tests.

Description

Technical Field

[0001] The invention relates to the technical field of turbine blade cascade gas thermal 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 the aircraft is operating at high altitude (above 10,000 meters), the density of the atmosphere is greatly reduced compared to the density of the ground, and the key aerodynamic parameter affecting the flow, the Reynolds number, becomes very low, which will bring about low Reynolds number flow problems. Among them, when the turbine blade cascade is operating at a low Reynolds number, the flow in the blade slot is often in a laminar or laminar-turbulent mixed flow state, which is easy to produce flow separation on the suction surface of the blade, which can cause flow blockage in severe cases, thereby affecting the matching between the compressor and turbine blade rows, resulting in reduced efficiency and performance of engine components, and ultimately causing a reduction in engine thrust, increased fuel consumption, and poor working stability and reliability, which has a huge impact on the completion of flight missions.

[0003] In the past few decades, many scholars have conducted extensive and in-depth research on the low Reynolds number problem of low-pressure turbines. For example, the boundary layer of the suction surface of the blade maintains a laminar state in the front part of the chord length range, and is affected by the adverse pressure gradient in the diffusion zone behind the blade, and separation is very likely to occur. The separated boundary layer may develop into a "long" or "short" closed separation bubble, and even open separation may occur in some environments. First, the transition mechanism of the separation bubble was extensively and in-depth studied. The size of the separation bubble gradually increases with the decrease of the Reynolds number. Under extremely low Reynolds number conditions, the separated boundary layer no longer attaches to the blade surface, forming an open separation. Subsequent researchers have conducted a large number of experiments to study the effects of factors such as periodic wake flow and flow turbulence on the low Reynolds number problem of low-pressure turbines. The study found that the periodic sweep of the upstream wake can affect the development of the boundary layer, thereby suppressing the size of the laminar separation bubble, and its suppression effect is related to the passing frequency of the wake. 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 the above tests or numerical simulation studies are conducted under low-speed conditions (the exit Mach number is usually not greater than 0.3). Therefore, it is necessary to carry out experimental research on the aero-thermal performance of turbine blades under low Reynolds number environment, and gradually establish and improve the database of turbine blades under low Reynolds number.

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

[0006] During the test of the existing secondary flow system, in order to improve the test efficiency, multiple turbine blade arrays 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 blade array for testing at the same time.

[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 purpose of the present invention is to solve the problem that the existing secondary flow system cannot provide multiple secondary flows to the blade cascade for testing at the same time during the test process, and further provide a secondary flow system for a low Reynolds number wind tunnel.

[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 is an air compressor and a suction unit, and also includes a dryer, a pressure-stabilizing tank, a switch valve, a regulating valve, a flow meter and a multi-mouth pressure-stabilizing tank. The air compression component, the dryer, the pressure-stabilizing tank, the switch valve, the regulating valve, the flow meter and the multi-mouth pressure-stabilizing tank are connected in sequence from left to right and then connected to a test cabin, and the multi-mouth pressure-stabilizing tank provides simultaneous multi-path secondary flows to multiple blade grids in the test cabin; 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-stabilizing 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-stabilizing 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 has a plurality of nozzles, which are 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 90 degrees to the axis of the tank body.

[0016] Furthermore, an axis of each nozzle forms an acute angle with an 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 which is connected between the air compressor and the dryer, and the other end of which 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 test (the special environment refers to: when the aircraft is working at high altitude (above 10,000 meters), the density of the atmosphere is greatly reduced compared with the density of the ground, and the key aerodynamic parameter affecting the flow, the Reynolds number, becomes very low, which will bring about low Reynolds number flow problems. At the same time, the high temperature environment of the turbine operation may cause the aerodynamic and heat transfer performance of the turbine blades to decay). When the inlet is throttled, the system effectively utilizes the lower pressure of the test section and compresses the gas into the pressure regulating tank 3 through the function of the suction unit, so as to carry out 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 can use the suction unit of the wind tunnel to provide a secondary flow air source. The suction unit not only exhausts air for 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 (when the suction unit is used alone, carbon emissions can be reduced and tests under different conditions can be met); turbine blade grid tests are generally carried out on multiple turbine blade grids. The 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 also multiple interfaces can 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, provide 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 the in-depth study of the engine blades.

[0023] 3. The present invention can directly utilize 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 blade grids. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a temperature-controllable 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. switch valve, 5. regulating valve, 6. flow meter, 7. multi-nozzle pressure regulating tank, 7-1. tank body, 7-2. air intake pipe, 7-3. two sets of nozzles, 8. pipeline, C. air intake 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 The present embodiment is described. The present embodiment includes an air compression assembly, which is an air compressor 1 and a suction unit, and 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 compression assembly, the dryer 2, the pressure-stabilizing tank 3, the switch valve 4, the regulating valve 5, the flow meter 6 and the 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 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-stabilizing tank 3 through the suction unit of the air compression assembly, 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-stabilizing tank 3 through the air compressor 1 of the air compression assembly, thereby providing the air source required for the secondary flow test.

[0029] The present invention is aimed at the test environment of low Reynolds number in the conventional secondary flow system, especially when the inlet throttling is performed, the pressure of the test section is relatively low. At this time, the function of the suction machine can be directly used to compress the gas into the pressure-stabilizing tank, and then the experimental research related to the secondary flow can be carried out; at the same time, in the test related to the thermal performance of the turbine blade gas, a plurality of blades are usually used for the test, so it is necessary for multiple secondary flows to flow to each blade, and a multi-mouth pressure-stabilizing tank is designed to solve the situation where multiple secondary flows are needed 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 tank body 7-1 along the upper and lower axes.

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

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

[0034] In this way, in actual use, the number of each group of nozzles 7-3 is designed according to the test requirements. However, in order to ensure the controllability of the secondary flow, the nozzles 7-3 are designed with equal spacing, which is convenient for accurately calculating the parameters of each secondary flow and ensuring the accuracy of the test. The other components and connection relationships are the same as those of the specific implementation method one or two.

[0035] Specific implementation method four: Combination Figures 2 to 3 To explain this embodiment, the number of each group of nozzles 7-3 in this embodiment is 8-16. In this way, if the number of blades to be tested at the same time is large, a large number of nozzles 7-3 are selected, and each nozzle 7-3 can realize independent control of start and stop and jet volume, and other components and connection relationships are the same as any one of the specific embodiments one to three.

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

[0037] In this way, in actual use, preferably 12 nozzles 7-3 are used. This number of nozzles 7-3 is suitable for most test situations. In addition, the number of nozzles 7-3 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 any one of the specific embodiments 1 to 4.

[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 arrangement is suitable for the case where the secondary flow directly ejected from the nozzle 7-3 acts directly on the blade, which is more in line with the actual working conditions of the engine turbine blade and is also the most commonly used test condition. The other components and connection relationships are the same as any one of the specific implementation modes 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] Such a setting is suitable for the research and development design between blades and secondary flows, mainly for expanding the research on the impact of blade secondary flows on blades at different angles and parameters, providing a broader research space for new blade structural parameters and blade tests of different materials, and there is no need to redesign the secondary flow system, saving research and development costs and providing more research directions. The other components and connection relationships are the same as any one of the specific implementation methods one to six.

[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 arrangement 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 implementation modes 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-channel secondary flow tests performed after conventional blades are rotated by 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 explain this embodiment, this embodiment further includes a pipeline 8, one end of the pipeline 8 is connected between the air compressor 1 and the dryer 2, and the other end of the pipeline 8 is connected to the exhaust system B.

[0047] Such a configuration 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] Combination 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 diagram. Its working principle is: under the suction action of the exhaust unit (the exhaust unit adopts variable frequency control, which can reduce the 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 temperature, 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 by a heater (which is installed at the front end of the wind tunnel body and is used to heat the air) (oil or electric heating is possible). The main and auxiliary pressure regulating valves in the air intake system C are adjusted, and the air enters the stable section from the diffusion section, and then enters 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 blade gas.

[0051] It should be noted that the test chamber A in the present invention includes a contraction section A-1, a nozzle section A-2 and a test section A-3, which are connected in sequence from left to right, and the test section A-3 is connected to the multi-nozzle pressure-surge tank 7 through a pipeline. Multiple nozzles 7-3 in the multi-nozzle pressure-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 inlet of the test piece, the pressure in the test section is relatively low. At this time, the function of the suction unit 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 makes better and more reasonable use of the device 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-stabilizing tank structure is adopted, in which air flow interfaces are evenly opened on both sides of the pressure-stabilizing tank (or the bottom corresponding to the inlet), which are directly connected to the pipeline when needed and are 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 the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. 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 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). An air compression component, a dryer (2), a pressure regulating tank (3), a switch valve (4), a regulating valve (5), a flow meter (6) and a multi-mouth pressure regulating tank (7) are connected in sequence from left to right and then connected to a test chamber (A), and the multi-mouth pressure regulating tank (7) provides multiple secondary flows to multiple blade grids in the test chamber (A) at the same time; 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 provides compressed air to the pressure regulating 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 provides compressed air to the pressure regulating tank (3), thereby providing the air source required for the secondary flow test.

2. A secondary flow system for a low Reynolds number wind tunnel according to claim 1, characterized in that: 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), and two groups of nozzles (7-3) are symmetrically installed on the tank body (7-1) with respect to the upper and lower axes.

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

4. A 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 8-16.

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

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

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

8. A 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 25°-50°.

9. A secondary flow system for a low Reynolds number wind tunnel according to claim 8, 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°.

10. A secondary flow system for a low Reynolds number wind tunnel according to claim 9, 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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