Carbon dioxide injection device for tracing phase change flow field of conventional hypersonic wind tunnel
By designing parallel branches of the carbon dioxide injection device and an image feedback control mechanism, the flow control and mixing problems of carbon dioxide phase change tracing technology in conventional hypersonic wind tunnels were solved, achieving a wide-range and high-precision flow field display effect to meet the needs of multiple tasks.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA ACAD OF AEROSPACE AERODYNAMICS
- Filing Date
- 2025-12-29
- Publication Date
- 2026-05-08
AI Technical Summary
In conventional hypersonic wind tunnels, carbon dioxide phase change tracing technology faces challenges such as a wide range of flow rate requirements, high control precision requirements, difficulty in mixing with the mainstream, and a lack of intelligent feedback control. In particular, it is difficult to achieve stable and reliable flow field display in noisy flow fields.
A carbon dioxide injection device was designed, comprising a gas supply module, a flow control module, an injection mixing module, an image feedback module, and a control module. Through parallel branch design, injection port position optimization, and image feedback control, a wide range of high-precision carbon dioxide flow control and uniform mixing are achieved, and the flow rate is dynamically adjusted by combining a fuzzy PID algorithm.
It achieves excellent flow field display effect under different wind tunnel operating conditions, adapts to large flow rate changes and complex working conditions, has strong engineering applicability, ensures uniform mixing of carbon dioxide with the main airflow and reduces the impact on the mainstream temperature field.
Smart Images
Figure CN121994444A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of hypersonic wind tunnel testing technology, and in particular to a carbon dioxide injection device for tracing phase change flow fields in conventional hypersonic wind tunnels. Background Technology
[0002] Hypersonic ground test facilities are important platforms for studying the aerodynamic characteristics of aircraft. Conventional hypersonic wind tunnels, in particular, have undertaken a large number of engineering test tasks due to their capabilities for long-term operation, rapid implementation, and high redundancy. However, these wind tunnels typically sacrifice low-noise flow field characteristics in exchange for the aforementioned engineering advantages, resulting in relatively low flow field quality. They are generally considered unsuitable for conducting fundamental research related to fine flow structure observation.
[0003] Carbon dioxide phase change tracing is an economical, pollution-free, and high-quality non-contact flow field visualization method. Its principle is that as carbon dioxide gas expands following the fluid within the nozzle, it undergoes a phase change due to a rapid temperature drop, condensing into nanoscale ice crystals. These particles produce Rayleigh scattering of laser light, thus visualizing the flow field structure. Studies have shown that in a CO2 / N2 mixture, only a 1% CO2 concentration is required to obtain excellent flow velocity measurement and flow visualization results. This technology has been successfully applied in several research wind tunnels and university silent wind tunnels, providing crucial data support for hypersonic flow research.
[0004] However, the application of carbon dioxide phase change tracing technology in large-diameter conventional hypersonic wind tunnels in engineering units still faces many challenges: Wide range of flow rate requirements: For large-diameter wind tunnels of 500mm or 1000mm, the carbon dioxide injection flow rate needs to cover a wide range of 20-400g / s to meet the needs of different test conditions. High precision control is required: the carbon dioxide flow rate needs to be precisely controlled, as too much will cause flow interference, while too little will result in poor tracer performance; Mixing with the mainstream is difficult: Ensuring uniform mixing of carbon dioxide with the main airflow in a large-diameter wind tunnel is a major challenge. Lack of intelligent feedback control: Existing technologies lack the ability to dynamically adjust the injected flow based on the actual tracing effect.
[0005] Especially for conventional hypersonic wind tunnels, the high noise level of the flow field further complicates the application of carbon dioxide phase change tracing technology. Although computational fluid dynamics (CFD) simulations can predict the condensation behavior of supercritical carbon dioxide in convergent-expansion nozzles, achieving stable and reliable carbon dioxide injection and phase change tracing in actual large wind tunnels still requires specially designed injection devices and control strategies. Summary of the Invention
[0006] The purpose of this invention is to address the shortcomings of existing technologies by providing a carbon dioxide injection device for tracing phase change flow fields in conventional hypersonic wind tunnels. This device can achieve wide-range, high-precision carbon dioxide flow control, and through feedback regulation with an image feedback module, it can obtain excellent flow field display effects under different wind tunnel operating conditions.
[0007] This specification provides one or more embodiments of a carbon dioxide injection device for tracing phase change flow fields in conventional hypersonic wind tunnels, comprising: The gas supply module includes a carbon dioxide cylinder module for supplying carbon dioxide gas; A flow control module, connected to the outlet of the gas supply module, is used to control the output flow rate of carbon dioxide gas; The injection mixing module includes an injection port and a wind tunnel heater. The injection port is connected to the outlet of the flow control module and is located at the front end of the wind tunnel heater to ensure that carbon dioxide gas is fully mixed with the mainstream as the incoming flow. In the hypersonic wind tunnel test section, the outlet of the wind tunnel heater injects mixed gas into the hypersonic wind tunnel test section through a nozzle; The image feedback module includes an image acquisition unit and an image processing unit. The image acquisition unit is used to acquire Rayleigh scattering images within the hypersonic wind tunnel test section, and the image processing unit is used to analyze the quality indicators of the Rayleigh scattering images. The image acquisition unit is connected to the image processing unit. The control module dynamically adjusts the flow regulation module based on the deviation between the quality index and the set value. The control module is connected to the image feedback module and the flow regulation module.
[0008] Preferably, the gas supply module includes a plurality of carbon dioxide cylinder modules connected in series, and each carbon dioxide cylinder module includes a plurality of cylinders connected in parallel.
[0009] Preferably, the flow control module includes a main control section and a sub-control section connected in sequence. The inlet of the main control section is connected to the outlet of the gas supply module. The sub-control section includes a high-flow branch and a low-flow branch connected in parallel. The outlets of the main control section and the sub-control section are connected to the injection port through pipelines.
[0010] Preferably, the main control section is provided with a main control shut-off valve, a main filter, a flow regulating valve, a Coriolis mass flow meter and a pressure sensor in sequence; The high-flow branch is provided with a first electromagnetic control valve, a first check valve, a first filter and a first regulating orifice plate in sequence, and the low-flow branch is provided with a second electromagnetic control valve, a second check valve, a second filter and a second regulating orifice plate in sequence.
[0011] Preferably, the injection port is located 2-3 meters in front of the wind tunnel heater.
[0012] Preferably, the injection pressure at the injection port is 0.1-0.3 MPa greater than the pressure in the stable section of the hypersonic wind tunnel test section.
[0013] Preferably, the mainstream mass flow rate of the hypersonic wind tunnel in the test section is... The estimation formula is as follows: (1); in, The specific heat ratio is a function of the specific heat ratio, and the calculation formula is as follows: (2); This is the specific heat ratio of the gas, typically taken as 1.4. For the total incoming pressure, Where R is the nozzle throat area, and R is the gas constant, typically taken as 287 J / (kg•K). The total temperature of the incoming flow.
[0014] Preferably, the nozzle throat area is calculated using the following formula: (3); in, The nozzle exit area, This refers to the nozzle exit Mach number. This is the nozzle exit diameter.
[0015] Preferably, the quality indicators of the Rayleigh scattering image include image signal-to-noise ratio, contrast, and uniformity.
[0016] Preferably, analyzing the signal-to-noise ratio (SNR) of the Rayleigh scattering image includes: The image signal-to-noise ratio (SNR) is defined as: (4); in, The average intensity of the signal image region, expressed as image grayscale value, is acquired in real time through image acquisition. The average intensity of the noise image was obtained by running the system before the experiment.
[0017] Beneficial effects: Using the embodiments of the present invention, a wide range and high precision carbon dioxide flow control can be achieved, and through feedback regulation with the image feedback module, a high-quality flow field display effect can be obtained under different wind tunnel operating conditions; it is specifically designed for engineering-type large-diameter hypersonic wind tunnels, adaptable to complex working conditions such as multi-task requirements and large flow rate changes, and has strong engineering applicability.
[0018] This invention achieves precise control over a wide range of 10-400 g / s by setting two parallel branches in the sub-control section of the flow regulation module, thus solving the problem that a single branch cannot handle both large and small flow rates. By placing the injection port at the front end of the wind tunnel heater, the mixing distance between carbon dioxide and the main airflow is significantly increased. The high turbulence region in front of the wind tunnel heater promotes uniform mixing, while effectively reducing the impact of the injected gas on the mainstream temperature field. An image quality-based feedback control mechanism was introduced, enabling the control module to automatically optimize the injection parameters based on the actual tracing effect. The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described below. Attached Figure Description
[0019] To more clearly illustrate the technical solutions in one or more embodiments of this specification or in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this specification. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0020] Figure 1 This is a schematic diagram of a first structure of a carbon dioxide injection device for tracing phase change flow fields in a conventional hypersonic wind tunnel, provided for one or more embodiments of this specification.
[0021] Explanation of reference numerals in the attached figures: 1-Gas cylinder, 2-Carbon dioxide cylinder module, 3-Main control shut-off valve, 4-Main filter, 5-Flow regulating valve, 6-Coriolis mass flow meter, 7-Pressure sensor, 8-Bypass pressure relief valve, 901-First solenoid control valve, 902-Second solenoid control valve, 1001-First check valve, 1002-Second check valve, 1101-First filter, 1102-Second filter, 1201-First regulating orifice plate, 1202-Second regulating orifice plate, 13-Injection port, 14-Wind tunnel heater, 15-Nozzle, 16-Hypersonic wind tunnel test section, 17-Image acquisition unit, 18-Image processing unit, 19-Control module. Detailed Implementation
[0022] To enable those skilled in the art to better understand the technical solutions in one or more embodiments of this specification, the technical solutions in one or more embodiments of this specification will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this specification, and not all of the embodiments. Based on one or more embodiments of this specification, all other embodiments obtained by those skilled in the art without creative effort should fall within the protection scope of this document.
[0023] Device Examples According to embodiments of the present invention, a carbon dioxide injection device is provided for tracing phase change flow fields in conventional hypersonic wind tunnels. Figure 1 This is a structural schematic diagram of an embodiment of the present invention, as shown below. Figure 1 As shown, the carbon dioxide injection device according to an embodiment of the present invention specifically includes: The gas supply module includes a carbon dioxide cylinder module 2 for supplying carbon dioxide gas; The gas supply module includes several carbon dioxide cylinder modules 2 connected in series. Each carbon dioxide cylinder module 2 includes several cylinders 1 connected in parallel, and the cylinders 1 are connected to each other via stainless steel gas collecting pipes. The parallel connection of the cylinders 1 ensures a sufficient gas supply. The "parallel-then-series" connection method not only guarantees the flow rate requirement but also improves system reliability, enabling stable adjustment of flow rate and pressure over a wide range.
[0024] Carbon dioxide is mostly in a liquid state inside cylinder 1, and the pressure is maintained in the range of 4~7MPa at room temperature (10-30℃). Carbon dioxide cylinder module 2 not only provides a continuous and stable gas source, but also achieves a large flow supply capacity through the parallel design of multiple cylinders, meeting the peak flow demand of 400g / s.
[0025] The flow control module is connected to the outlet of the gas supply module and is used to control the output flow rate of carbon dioxide gas. The flow control module includes a main control section and a sub-control section connected in sequence. The inlet of the main control section is connected to the outlet of the gas supply module, and the outlets of the main control section and the sub-control section are connected to the injection port 13 through an injection pipe.
[0026] The main control section is equipped with a main control shut-off valve 3, a main filter 4, a flow regulating valve 5, a Coriolis mass flow meter 6, and a pressure sensor 7 in sequence. A bypass is provided between the main filter 4 and the flow regulating valve 5, and a bypass pressure relief valve 8 is provided on the bypass. The main control section is used to achieve preliminary filtration, pressure stabilization, and overall flow monitoring of carbon dioxide gas. The main control section uses DN25 stainless steel pipeline, and the main filter 4 is preferably 2.5μm in accuracy to filter out impurities in the gas collection pipeline process and ensure gas purity. The flow regulating valve 5 is an electric regulating valve, preferably with an adjustment accuracy of 0.5%. The Coriolis mass flow meter 6 has a measurement accuracy of ±0.2%.
[0027] The sub-control section includes a high-flow-rate branch and a low-flow-rate branch connected in parallel. The high-flow-rate branch is equipped with a first solenoid control valve 901, a first check valve 1001, a first filter 1101, and a first regulating orifice plate 1201 in sequence. The low-flow-rate branch is equipped with a second solenoid control valve 902, a second check valve 1002, a second filter 1102, and a second regulating orifice plate 1202 in sequence. The structural design of the sub-control section ensures control accuracy over a wide range while improving the system's response speed.
[0028] The high-flow branch has a diameter of DN1=25mm. The first electromagnetic control valve 901 adopts a high-frequency response electromagnetic valve (response time <50ms). The orifice diameter of the first regulating orifice plate 1201 is DK1=λ1×DN1, where λ1 is 0.4, which is DK1=10mm, covering a flow range of 80-320g / s. For the small flow branch with a diameter of DN2=10mm, the second electromagnetic control valve 902 also adopts a high-frequency response electromagnetic valve, and the orifice diameter of the regulating orifice plate is DK2=λ2×DN2, where λ2 is 0.3, which is DK2=3mm, covering a flow range of 10-100g / s. After the two branch outlets merge, they are connected to injection port 13 via an injection pipe with a diameter of DN3=30mm.
[0029] The injection mixing module includes an injection port 13 and a wind tunnel heater 14. The injection port 13 is connected to the outlet of the flow control module and is located at the front end of the wind tunnel heater 14 to ensure that carbon dioxide gas is fully mixed with the mainstream as the incoming flow. Several small holes are radially arranged on the sidewall of the injection pipe at inlet 13 to ensure uniform injection of carbon dioxide gas into the mainstream. Preferably, eight holes with a diameter of 10 mm are provided. Inlet 13 is located 2-3 meters in front of the wind tunnel heater 14, significantly increasing the mixing distance between carbon dioxide and the main gas flow. This utilizes the high turbulence region before the wind tunnel heater 14 to promote uniform mixing while effectively reducing the impact of the injected gas on the mainstream temperature field. A high-precision pressure sensor 7 is installed in the injection section to monitor the total injection pressure in real time, providing feedback for flow control. An insulation layer is provided on the outer layer of the injection section to reduce heat loss.
[0030] In the hypersonic wind tunnel test section 16, the outlet of the wind tunnel heater 14 sprays mixed gas into the hypersonic wind tunnel test section 16 through the nozzle 15. Based on the principles of gas dynamics, the mainstream mass flow rate of the hypersonic wind tunnel test section 16 was determined. The estimation formula is as follows: (1); in, The specific heat ratio is a function of the specific heat ratio, and the calculation formula is as follows: (2); This is the specific heat ratio of the gas, typically taken as 1.4. For the total incoming pressure, Let R be the throat area of nozzle 15, and R be the gas constant, typically taken as 287 J / (kg•K). The total temperature of the incoming flow.
[0031] The throat area of nozzle 15 is calculated using the following formula: (3); in, This refers to the outlet area of nozzle 15. This is the nozzle exit Mach number of 15. The nozzle outlet diameter is 15.
[0032] Therefore, the four parameters determining the airflow rate of a hypersonic wind tunnel can be summarized as: total temperature, total pressure, exit Mach number, and exit diameter. For a typical operating condition with a 500mm Ma=6 nozzle, an exit diameter of 15, an incoming total pressure of 2MPa, and an incoming total temperature of 453K, the calculated mainstream flow rate is approximately 13.8 kg / s.
[0033] Table 1 shows the recommended values for carbon dioxide injection flow rate under different wind tunnel conditions, estimated based on the mainstream flow rate of 0.5-1%.
[0034] Table 1
[0035] The pressure estimation at the injection point needs to consider the pressure in the stable section of the wind tunnel, the drag loss at the injection location, and the dynamic pressure of the carbon dioxide injection itself. Experience shows that the injection pressure at injection port 13 is 0.1-0.3 MPa higher than the pressure in the stable section of the hypersonic wind tunnel test section 16, which can ensure stable injection.
[0036] The image feedback module includes an image acquisition unit 17 and an image processing unit 18. The image acquisition unit 17 is used to acquire Rayleigh scattering images within the hypersonic wind tunnel test section 16, and the image processing unit 18 is used to analyze the quality indicators of the Rayleigh scattering images. The image acquisition unit 17 is connected to the image processing unit 18. Preferably, the image acquisition unit 17 uses a high-speed CCD camera.
[0037] The quality metrics for Rayleigh scattering images include image signal-to-noise ratio, contrast, and uniformity.
[0038] The signal-to-noise ratio (SNR) of Rayleigh scattering images includes: The image signal-to-noise ratio (SNR) is defined as: (4); in, The average intensity of the signal image region, expressed as image grayscale value, is acquired in real time through image acquisition. The average intensity of the noise image was obtained by running the system before the experiment.
[0039] The control module 19 dynamically adjusts the flow control module based on the deviation between the quality index and the set value using a fuzzy PID algorithm. The control module 19 is connected to the image feedback module and the flow control module.
[0040] When SNR < 15dB, the image quality is deemed insufficient, and the control system increases the carbon dioxide flow rate by 20%-50%. When 15dB≤SNR≤25dB, the image quality is considered good, and the current flow rate is maintained. When SNR > 25dB, the image is considered oversaturated, and the carbon dioxide flow rate is reduced by 10%-30%.
[0041] This invention is based on the phase transition characteristics of carbon dioxide under specific temperature and pressure conditions. When carbon dioxide gas enters the expansion zone of a hypersonic wind tunnel, it undergoes rapid adiabatic expansion, resulting in a sharp drop in temperature. Under appropriate supercooling, the carbon dioxide gas undergoes homogeneous condensation, forming nanoscale solid ice crystal particles. These particles act as scattering centers, generating strong Rayleigh scattering signals when irradiated by a laser.
[0042] Studies have shown that high-quality flow velocity measurement and flow visualization can be achieved in CO2 / N2 mixed gas streams with a carbon dioxide concentration of approximately 0.5% to 1%. Planar laser CO2 Rayleigh scattering technology can visualize the cross-sections of supersonic flows and turbulent boundary layers, which is of great significance for characterizing the flow field quality and finely depicting boundary layer flows in hypersonic wind tunnels.
[0043] Method Implementation Examples A carbon dioxide injection method for tracing phase change flow fields in conventional hypersonic wind tunnels, using the aforementioned apparatus, includes the following steps: S1. The gas supply module is connected to gas cylinder 1 in parallel and then in series to provide a continuous and stable gas source, realizing a large flow supply. S2. Carbon dioxide gas enters the main control section, where it undergoes preliminary filtration, pressure stabilization, and overall flow monitoring. Afterward, the carbon dioxide gas is split into two streams, one into a high-flow branch and the other into a low-flow branch. The high-flow branch provides a larger flow rate of carbon dioxide gas, while the low-flow branch allows for small-range adjustment of the carbon dioxide gas flow rate. The two streams work together to ensure the control accuracy of the carbon dioxide gas over a wide range. S3. Carbon dioxide gas enters the injection port 13 after the two branch outlets converge. The carbon dioxide gas is fully mixed with the main airflow between the injection port 13 and the wind tunnel heater 14. The high-precision pressure sensor 7 monitors the total injection pressure in real time. S4. The outlet of the wind tunnel heater 14 injects mixed gas into the hypersonic wind tunnel test section 16 through the nozzle 15. The recommended value of carbon dioxide injection flow rate under different wind tunnel conditions is calculated, and carbon dioxide gas is injected according to the recommended value. Rayleigh scattering images were collected and analyzed within section 16 of the hypersonic wind tunnel test. Based on the deviation between the quality index and the set value, the flow control module was dynamically adjusted using a fuzzy PID algorithm. When SNR < 15dB, the image quality is deemed insufficient, and the control system increases the carbon dioxide flow rate by 20%-50%. When 15dB≤SNR≤25dB, the image quality is considered good, and the current flow rate is maintained. When SNR > 25dB, the image is considered oversaturated, and the carbon dioxide flow rate is reduced by 10%-30%.
[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.
Claims
1. A carbon dioxide injection device for tracing phase change flow fields in conventional hypersonic wind tunnels, characterized in that, include: The gas supply module includes a carbon dioxide cylinder module for supplying carbon dioxide gas; A flow control module, connected to the outlet of the gas supply module, is used to control the output flow rate of carbon dioxide gas; The injection mixing module includes an injection port and a wind tunnel heater. The injection port is connected to the outlet of the flow control module and is located at the front end of the wind tunnel heater to ensure that carbon dioxide gas is fully mixed with the mainstream as the incoming flow. In the hypersonic wind tunnel test section, the outlet of the wind tunnel heater injects mixed gas into the hypersonic wind tunnel test section through a nozzle; The image feedback module includes an image acquisition unit and an image processing unit. The image acquisition unit is used to acquire Rayleigh scattering images within the hypersonic wind tunnel test section, and the image processing unit is used to analyze the quality indicators of the Rayleigh scattering images. The image acquisition unit is connected to the image processing unit. The control module dynamically adjusts the flow regulation module based on the deviation between the quality index and the set value. The control module is connected to the image feedback module and the flow regulation module.
2. The carbon dioxide injection device according to claim 1, characterized in that, The gas supply module includes several carbon dioxide cylinder modules connected in series, and each carbon dioxide cylinder module includes several cylinders connected in parallel.
3. The carbon dioxide injection device according to claim 1, characterized in that, The flow control module includes a main control section and a sub-control section connected in sequence. The inlet of the main control section is connected to the outlet of the gas supply module. The sub-control section includes a high-flow branch and a low-flow branch connected in parallel. The outlets of the main control section and the sub-control section are connected to the injection port through pipelines.
4. The carbon dioxide injection device according to claim 3, characterized in that, The main control section is equipped with a main control shut-off valve, a main filter, a flow regulating valve, a Coriolis mass flow meter, and a pressure sensor in sequence. The high-flow branch is provided with a first electromagnetic control valve, a first check valve, a first filter and a first regulating orifice plate in sequence, and the low-flow branch is provided with a second electromagnetic control valve, a second check valve, a second filter and a second regulating orifice plate in sequence.
5. The carbon dioxide injection device according to claim 1, characterized in that, The injection port is located 2-3 meters in front of the wind tunnel heater.
6. The carbon dioxide injection device according to claim 1, characterized in that, The injection pressure at the injection port is 0.1-0.3 MPa greater than the pressure in the stable section of the hypersonic wind tunnel test section.
7. The carbon dioxide injection device according to claim 1, characterized in that, The mainstream mass flow rate of the hypersonic wind tunnel test section The estimation formula is as follows: （1）； in, The specific heat ratio is a function of the specific heat ratio, and the calculation formula is as follows: （2）； This is the specific heat ratio of the gas, typically taken as 1.
4. For the total incoming pressure, Where R is the nozzle throat area, and R is the gas constant, typically taken as 287 J / (kg•K). The total temperature of the incoming flow.
8. The carbon dioxide injection device according to claim 7, characterized in that, The nozzle throat area is calculated using the following formula: （3）； in, The nozzle exit area, This refers to the nozzle exit Mach number. This is the nozzle exit diameter.
9. The carbon dioxide injection device according to claim 1, characterized in that, The quality metrics of the Rayleigh scattering image include image signal-to-noise ratio, contrast, and uniformity.
10. The carbon dioxide injection device according to claim 9, characterized in that, The analysis of the image signal-to-noise ratio (SNR) of the Rayleigh scattering image includes: The image signal-to-noise ratio (SNR) is defined as: （4）； in, The average intensity of the signal image region, expressed as image grayscale value, is acquired in real time through image acquisition. The average intensity of the noise image was obtained by running the system before the experiment.