An experimental table and experimental method with variable reynolds number pipe flow characteristics

Abstract

The application discloses a test bench with variable Reynolds number pipe flow characteristics and a test method. aip From 0.2 to 0.7 stepless regulation, the flow conditions under different flight conditions are simulated. In addition, at the model inlet, there is a boundary layer suction device composed of four ball valves, an electric control system controls the opening degree of the ball valve, and the bypass channel is connected to the rear side of the second plug valve at the model inlet, so that the boundary layer suction degree can be controlled by controlling the opening degree of the ball valve, and the inlet conditions with different boundary layer thicknesses can be simulated.

Description

Technical Field

[0001] This invention relates to the field of experimental fluid mechanics, specifically to the technical field of a variable Reynolds number wind tunnel experimental device. Background Technology

[0002] Variable Reynolds number wind tunnel experimental setups primarily involve achieving Reynolds number simulations that closely match actual flight conditions, which is crucial for aircraft experiments. The Reynolds number is an important dimensionless number in fluid dynamics characterizing the effects of fluid viscosity; it is defined as the ratio of inertial force to viscous force. Under a given airflow velocity, the main methods for increasing the Reynolds number in wind tunnel experiments include the following:

[0003] Heavy gases are used as the experimental medium in wind tunnels. The Reynolds number of the experiment is increased by increasing the gas density and decreasing the viscosity coefficient. For example, NASA's TDT wind tunnel uses dichlorodifluoromethane as the experimental medium.

[0004] Increasing the size of the wind tunnel and its operating pressure is one of the direct ways to increase the Reynolds number. However, it has certain limitations, such as the construction and operating costs increasing significantly with the increase in size.

[0005] Lowering the airflow temperature inside a wind tunnel increases density and decreases viscosity, thus raising the experimental Reynolds number. Lowering the airflow temperature is one of the advantageous methods for increasing the Reynolds number. Cryogenic wind tunnels allow for independent adjustment of airflow velocity, total temperature, and total pressure during experiments, offering advantages unmatched by conventional wind tunnels. Examples include the KKK low-speed cryogenic wind tunnel at the German Aerospace Center, the NTF wind tunnel in the United States, and the ETW transonic wind tunnel in Europe.

[0006] In summary, large-scale low-temperature, high Reynolds number wind tunnels are technically complex and difficult to design and construct. While both domestic and international institutions have initially established the necessary technology and industrial foundation for their design and construction, further in-depth research into key technologies is still needed. Increasing the size of the wind tunnel is a simple and quick method, but it presents challenges in controlling construction and operating costs. Summary of the Invention

[0007] The purpose of this invention is to address the shortcomings of the aforementioned background technology by proposing an experimental platform with variable Reynolds number tube flow characteristics to simulate the performance of experimental models under different flight conditions.

[0008] The present invention also provides the experimental method for the experimental platform.

[0009] To achieve the above technical objectives, the present invention adopts the following technical solution:

[0010] An experimental platform with variable Reynolds number pipe flow characteristics includes an air inlet, a stable section, a first connecting pipe connecting the air inlet and the stable section, a boundary layer removal device connecting the outlet of the stable section, an observation chamber, an air inlet model connecting the boundary layer removal device and the observation chamber, a vacuum tank, a second gate valve located between the observation chamber and the vacuum tank, a second connecting pipe connecting the second gate valve and the observation chamber, a third connecting pipe connecting the second gate valve and the vacuum tank, and a bypass pipe; one end of the bypass pipe is connected to the boundary layer removal device and the other end is connected to the third connecting pipe; the first connecting pipe is provided with a perforated plate, which has several through circular holes.

[0011] Furthermore, the No. 1 gate valve, the boundary layer suction device, and the No. 2 gate valve are integrated into the same electrical control device for unified control.

[0012] Furthermore, the boundary layer removal device at the outlet of the stable section is connected to the third connecting pipe through a bypass channel, and the boundary layer thickness at the inlet is adjusted by controlling the opening of the boundary layer removal device.

[0013] Furthermore, the perforated plate is detachable.

[0014] Furthermore, the stabilizing section is provided with a honeycomb plate, which has several through honeycomb-shaped holes.

[0015] Compared with existing technologies, this invention has the following advantages: The "variable Reynolds number" in the variable Reynolds number pipe flow characteristics and flow control technology experimental rig is achieved through the flow control of the first and second gate valves and the total pressure loss applied to the incoming flow by adding a perforated plate after the first gate valve. By changing the Reynolds number, the conditions of high-altitude flight are simulated. Compared with traditional wind tunnel experimental rigs, the experimental rig of this invention allows M... aip The flow rate is infinitely adjustable from 0.2 to 0.7 to simulate incoming flow conditions under different flight conditions. Additionally, at the model inlet, there is a boundary layer removal device consisting of four ball valves. The opening of these ball valves is controlled by an electronic control system. This device is connected to the model inlet and the rear of the second gate valve via a bypass channel. This allows control of the boundary layer removal degree by adjusting the ball valve opening, thus simulating inlet conditions with different boundary layer thicknesses.

[0016] Based on the above-mentioned experimental platform, the present invention also provides a technical solution for an experimental method, comprising the following steps:

[0017] After S1 has checked the sealing of the experimental bench door, connect the power supply and power on the control console.

[0018] S2 adjusts the opening of the No. 1 slide valve to 100%;

[0019] S3 provides suitable boundary layer thickness inlet conditions to the inlet section of the inlet model through the boundary layer removal device at the stable section outlet;

[0020] S4. Based on the required flow rate for the experiment, refer to the opening-Mach number comparison table and adjust the opening of the second gate valve.

[0021] After the pressure inside the experimental chamber drops to the target pressure, open the butterfly valve after the No. 1 slide gate valve to start the experiment. Attached Figure Description

[0022] Figure 1 This is a three-dimensional schematic diagram of the experimental rig for variable Reynolds number tube flow characteristics and flow control technology in this invention.

[0023] Figure 2 This is a two-dimensional schematic diagram of the experimental rig for variable Reynolds number tube flow characteristics and flow control technology in this invention.

[0024] Figure 3 This is a schematic diagram of the perforated plate in this invention.

[0025] Figure 4 This is a schematic diagram of the honeycomb panel in this invention. Detailed Implementation

[0026] The present invention will be further explained below with reference to the accompanying drawings and specific embodiments.

[0027] Example 1

[0028] This embodiment provides an experimental platform with variable Reynolds number pipe flow characteristics, including an air inlet 1, a first gate valve 2 after the air inlet, a butterfly valve 5 after a perforated plate, a honeycomb plate 6 inside the stabilization section after the butterfly valve, a downstream stabilization section 7 of the honeycomb plate, a first connecting pipe 4 connecting the air inlet 1 and the stabilization section 7, a boundary layer removal device 8 at the outlet of the stabilization section, an observation chamber 11, an air inlet model 10 connecting the boundary layer removal device 8 and the observation chamber 11, a second gate valve 13 after the observation chamber, a second connecting pipe 12 connecting the second gate valve 13 and the observation chamber 11, a third connecting pipe 14 connecting the second gate valve 13 and the vacuum tank connecting pipe 15, and a bypass pipe 9 providing a vacuum source for the boundary layer removal device; one end of the bypass pipe 9 is connected to the boundary layer removal device 8 and the other end is connected to the third connecting pipe 14.

[0029] The first connecting pipe 4 is provided with a perforated plate 3, which has several through round holes.

[0030] The stabilizing section 7 is provided with a honeycomb plate 6, which has several through honeycomb-shaped holes. The honeycomb plate 6 plays a role in rectifying the flow and reducing turbulence.

[0031] The boundary layer removal device 8 is connected to the third connecting pipe 14 via a bypass channel 9. The four ball valves of the boundary layer removal device 8 are controlled by an electronic control system. The inlet of the air intake model 10 is rectangular, and the four ball valves are connected to the four sides of the inlet respectively. The boundary layer thickness at the inlet is adjusted by controlling the opening degree of the ball valves. The opening degree of the four ball valves can be controlled independently, allowing for separate adjustment of the boundary layer thickness on the four sides of the rectangular inlet as needed. One end of each ball valve is connected to the boundary layer removal device, and the other end is connected to the third connecting pipe 14 via the bypass channel 9. After the experiment begins, low-pressure gas is drawn from the third connecting pipe 14 through the bypass pipe 9 to remove the boundary layer. The larger the opening degree of the ball valve, the more low-pressure gas is introduced, resulting in a thicker and thinner boundary layer.

[0032] The "variable Reynolds number" is achieved through flow control of the first and second gate valves and by applying a total pressure loss to the incoming flow using a perforated plate 3 installed after the first gate valve. This simulates high-altitude flight conditions by changing the Reynolds number. The specific principle for adjusting the Reynolds number throughout the experimental setup is based on Ergé's equation:

[0033]

[0034] Ergé's equations are used to analyze the pressure drop of a fluid passing through a porous medium. Here, ΔP is the pressure drop after the airflow passes through the porous plate 3, μ is the fluid dynamic viscosity, L is the flow path length, and ε is the porosity of the porous plate 3. Porosity is defined as the ratio of pore volume to total volume in a porous medium and is an important parameter for evaluating the structure of porous media. Porosity reflects the size of the space for fluid flow in the porous medium; the larger the porosity, the larger the fluid flow space. v is the apparent velocity, Dp is the particle diameter, and ρ is the fluid density.

[0035] After the airflow passes through the perforated plate 3, the total pressure decreases, and the airflow velocity decreases under the condition of constant static pressure. The Reynolds number is:

[0036]

[0037] The airflow velocity V decreases, thereby reducing the incoming Reynolds number and thus playing the role of "variable Reynolds number".

[0038] Example 2

[0039] This embodiment provides an experimental method using the experimental platform described in Embodiment 1, including the following steps:

[0040] Step 1: After checking the sealing of the experimental platform door, connect the power supply and power on the control console.

[0041] Step 2: Adjust the opening of slide gate valve 2 to 100%.

[0042] Step 3: Based on the actual experimental conditions, adjust the opening of the four ball valves on the four sides of the corresponding model inlet section through the boundary layer suction device 8 at the outlet of the stable section to provide suitable boundary layer thickness inlet conditions for the model inlet section.

[0043] Step 4: According to the required flow rate for the experiment, refer to the opening-Mach number comparison table and adjust the opening of the second gate valve 13.

[0044] Step 5: After the pressure inside the experimental chamber drops to the target pressure, open the butterfly valve 5 after the first slide gate valve 2 to start the experiment.

[0045] The following is a set of experimental data before and after the installation of the perforated plate.

[0046] The local atmospheric pressure was 101770 Pa, the local temperature was 21℃, and the opening degree of the No. 2 slide valve 7 was 28%. The total pressure and static pressure without the perforated plate were measured to be 101270 Pa and 76781 Pa, respectively. With all other conditions unchanged, the total pressure and static pressure with the perforated plate were 93221 Pa and 70030 Pa, respectively.

[0047] For compressible flow, the relationship between total pressure and static pressure is as follows:

[0048]

[0049] k = Cp / Cv, where Cp is the specific heat ratio of the gas. For air, k = 1.4. The Mach number of the airflow can be obtained from the total static pressure relationship. The relationship between flow velocity V and Ma is:

[0050]

[0051] The relationship between fluid density ρ and static pressure P derived from the ideal gas equation is as follows:

[0052]

[0053] Substituting the above relationship into the Reynolds number formula, we get:

[0054]

[0055] The dynamic viscosity μ of a fluid is only related to the fluid temperature T. Therefore, under the conditions of constant temperature and constant model geometry, the Reynolds number of a compressible flow is proportional to the product of static pressure and Mach number, P*Ma. Based on the total static pressure relationship before and after adding the perforated plate, it can be concluded that the Reynolds number decreased by 7.2% after adding the perforated plate. The total pressure loss exerted by the perforated plate on the incoming flow can reduce the Reynolds number, verifying that the experimental setup has the characteristic of "variable Reynolds number".

[0056] Furthermore, there are many specific methods and approaches to implement this invention, and the above description is only a preferred embodiment of this invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the principle of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention.

Claims

1. An experimental platform with variable Reynolds number pipe flow characteristics, characterized in that, Includes an air inlet (1), a first gate valve (2) after the air inlet, a butterfly valve (5) after the perforated plate (3), a honeycomb plate (6) inside the stabilization section after the butterfly valve, a stabilization section (7) downstream of the honeycomb plate, a first connecting pipe (4) connecting the air inlet (1) and the stabilization section (7), a boundary layer removal device (8) at the outlet of the stabilization section, an observation chamber (11), an air inlet model (10) connecting the boundary layer removal device (8) and the observation chamber (11), a second gate valve (13) after the observation chamber, a second connecting pipe (12) connecting the second gate valve (13) and the observation chamber (11), a third connecting pipe (14) connecting the second gate valve (13) and the vacuum tank connecting pipe (15), and a bypass pipe (9) providing a vacuum source for the boundary layer removal device; one end of the bypass pipe (9) is connected to the boundary layer removal device (8) and the other end is connected to the third connecting pipe (14); The first connecting pipe (4) is provided with a perforated plate (3), which has several through round holes.

2. The experimental rig with variable Reynolds number tube flow characteristics according to claim 1, characterized in that, The No. 1 gate valve (2), the boundary layer suction device (8), and the No. 2 gate valve (13) are integrated on the same electrical control device for unified control.

3. The experimental rig with variable Reynolds number tube flow characteristics according to claim 1, characterized in that, The perforated plate (3) is detachable.

4. The experimental rig with variable Reynolds number pipe flow characteristics according to claim 1, characterized in that, The stable section (7) is provided with a honeycomb plate (6), which has several through honeycomb-shaped holes.

5. The experimental rig with variable Reynolds number tube flow characteristics according to claim 1, characterized in that: The boundary layer removal device (8) at the outlet of the stable section is connected to the third connecting pipe (14) through the bypass pipe (9). The boundary layer thickness at the inlet is adjusted by controlling the opening of the boundary layer removal device (8).

6. An experimental method for an experimental setup with variable Reynolds number pipe flow characteristics according to any one of claims 1 to 5, characterized in that, Includes the following steps: After S1 has checked the sealing of the experimental bench door, connect the power supply and power on the control console. S2 adjusts the opening of the first slide gate valve (2) to 100%; S3 provides suitable boundary layer thickness inlet conditions to the inlet section of the inlet model (10) through the boundary layer removal device (8) at the outlet of the stable section; S4 adjusts the opening of the second gate valve (13) according to the required flow rate for the experiment and with reference to the opening-Mach number comparison table; After the pressure inside the experimental chamber drops to the target pressure, open the butterfly valve (5) after the first slide gate valve (2) to start the experiment.

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