Mach number regulation and control method without changing spray pipe, wind tunnel test system and device

Abstract

The invention discloses a Mach number regulation and control method without changing a spray pipe, and a wind tunnel test system and device, and relates to the technical field of aerodynamics testing, and the method comprises the steps: determining a target Mach number, and determining a target gas specific heat ratio needed for achieving the target Mach number according to a fixed molded surface of the spray pipe; selecting at least two target pressure gases with different specific heat ratios as gas sources; according to the specific heat ratio of the target gas, determining the mixing ratio of each target pressure gas in the gas source; mixing the target pressure gases according to the mixing ratio to form a mixed test gas; and introducing the mixed test gas into a wind tunnel system, operating the wind tunnel system, and controlling the mixed test gas to flow through a spray pipe so as to generate a supersonic flow field corresponding to the target Mach number in the test section. And the Mach number of the wind tunnel is regulated and controlled by adopting the mixed gas without changing a spray pipe and a wind tunnel main body structure.

Description

Technical Field

[0001] This invention relates to the field of aerodynamic testing technology, and in particular to a method for controlling Mach number without modifying the nozzle, a wind tunnel testing system and apparatus. Background Technology

[0002] High-speed wind tunnels (in this case, wind tunnels with a test Mach number greater than 1) generate high-speed airflow through Laval nozzles. The main parameters determining the Mach number of the test section are the gas specific heat ratio and the nozzle profile. Conventional high-speed wind tunnels use air as the test gas, and air has a specific heat ratio of 1.4. Therefore, the predetermined test Mach number is mainly achieved through the wind tunnel profile; once the nozzle profile is determined, the test Mach number is also determined. To generate different test Mach numbers, the common practice is to design and manufacture different nozzles, changing the test Mach number by replacing the nozzle. This leads to high costs, low efficiency, and inconvenient operation. Another method is to use flexible nozzles, controlling the nozzle profile through a carefully designed nozzle adjustment mechanism. However, flexible nozzles have complex mechanisms and high maintenance costs, and their use is not widespread domestically or internationally. It is necessary to develop a Mach number adjustment method that does not require modification of the nozzle.

[0003] The Reynolds number achievable in wind tunnel testing is very limited; the Reynolds number of a scaled-down model is typically about an order of magnitude lower than that of actual flight. Therefore, high Reynolds number wind tunnels are crucial. Since the Reynolds number is inversely proportional to viscosity, and lowering the temperature can reduce air viscosity, cryogenic techniques are often used to increase the Reynolds number. For example, the ETW (European Transonic Windtunnel) wind tunnel uses liquid nitrogen cooling to achieve a high Reynolds number. However, the construction and operating costs of cryogenic high Reynolds number wind tunnels are extremely high.

[0004] Once the high-speed wind tunnel is designed, the mainstream velocity of the test section is essentially fixed, meaning it is the product of the Mach number and the speed of sound. When cryogenic technology is used, the speed of sound in the test medium decreases, and the mainstream velocity of the test section decreases. Therefore, even if the Mach number and Reynolds number of the wind tunnel flow field are the same as in the real flight environment, the velocity field still differs significantly from that in the real flight environment. Summary of the Invention

[0005] In view of this, the purpose of this invention is to provide a method, wind tunnel testing system, and apparatus for controlling Mach number without modifying the nozzle, which can control the wind tunnel Mach number by only changing the test gas. The specific solution is as follows: In a first aspect, this application discloses a method for Mach number control without modifying the nozzle, including: Determine the target Mach number, and based on the fixed profile of the nozzle, determine the target gas specific heat ratio required to achieve the target Mach number; wherein the target Mach number is lower than the standard Mach number of the nozzle; Select at least two target pressure gases with different specific heat ratios as gas sources; Based on the specific heat ratio of the target gas, determine the mixing ratio of each target pressure gas in the gas source; The target pressure gases are mixed according to the specified mixing ratio to form a mixed test gas; The mixed test gas is introduced into the wind tunnel system, the wind tunnel system is operated, and the mixed test gas is controlled to flow through the nozzle to generate a supersonic flow field corresponding to the target Mach number in the test section.

[0006] Optionally, the gas source includes a first target pressure gas and a second target pressure gas; Accordingly, determining the mixing ratio of each of the target pressure gases in the gas source based on the specific heat ratio of the target gas includes: The mixing ratio of the first target pressure gas and the second target pressure gas in the gas source is determined by the first equation and based on the specific heat ratio of the target gas. Wherein, the first equation is ; This represents the mole fraction of the gas at the first target pressure. This represents the isobaric specific heat of the gas at the first target pressure. This represents the specific heat at constant volume of the gas at the first target pressure. This represents the mole fraction of the gas at the second target pressure. This represents the isobaric specific heat of the gas at the second target pressure. This represents the isochoric specific heat of the gas at the second target pressure. This indicates the specific heat ratio of the target gas.

[0007] Optionally, the gas source includes a first target pressure gas, a second target pressure gas, and a third target pressure gas; Accordingly, determining the mixing ratio of each of the target pressure gases in the gas source based on the specific heat ratio of the target gas includes: Set the corresponding initial mole fraction for the first target pressure gas; The mixing ratio of the first target pressure gas, the second target pressure gas, and the third target pressure gas in the gas source is determined by the second equation and based on the specific heat ratio of the target gas. Wherein, the second equation is ;in, This represents the initial mole fraction of the gas at the first target pressure. This represents the isobaric specific heat of the gas at the first target pressure. This represents the specific heat at constant volume of the gas at the first target pressure. This represents the mole fraction of the gas at the second target pressure. This represents the isobaric specific heat of the gas at the second target pressure. This represents the isochoric specific heat of the gas at the second target pressure. This indicates the mole fraction of the gas at the third target pressure. This represents the isobaric specific heat of the gas at the third target pressure. This represents the specific heat at constant volume of the gas at the third target pressure. This indicates the specific heat ratio of the target gas.

[0008] Optionally, the sound velocity of the mixed test gas is different from that of the standard test gas, and the sound velocity of the mixed test gas is used to obtain a mainstream velocity different from that of the standard test gas in the test section at the target Mach number.

[0009] Optionally, the Mach number control method that does not require modification of the nozzle further includes: When at least two target pressure gases are selected, the dynamic viscosity coefficient, mass ratio, and reduction frequency of the mixed test gas are different from the corresponding parameters of the standard test gas, so as to adjust the flow field parameters of the supersonic flow field in the test section.

[0010] Optionally, the operation of the wind tunnel system further includes: Monitor the total pressure and total temperature of the mixed test gas; The Reynolds number of the supersonic flow field in the test section is adjusted by regulating the total pressure and / or the total temperature.

[0011] Secondly, this application discloses a wind tunnel testing system for implementing the aforementioned Mach number control method without modifying the nozzle, the wind tunnel testing system comprising: At least two gas supply units; A mixing tank is used to mix target pressure gases from different gas sources. The control system is used to adjust the mixing ratio of the various gas sources; The main structure of the wind tunnel includes the nozzle, test section, diffuser section, and vacuum system.

[0012] Thirdly, this application discloses a Mach number control device that does not require modification of the nozzle, comprising: A specific heat ratio determination module is used to determine the target Mach number and, based on the fixed profile of the nozzle, determine the target gas specific heat ratio required to achieve the target Mach number; wherein the target Mach number is lower than the standard Mach number of the nozzle; The gas source selection module is used to select at least two target pressure gases with different specific heat ratios as gas sources. The proportion determination module is used to determine the mixing ratio of each target pressure gas in the gas source based on the specific heat ratio of the target gas; A gas mixing module is used to mix the target pressure gases according to the mixing ratio to form a mixed test gas; The wind tunnel operation module is used to introduce the mixed test gas into the wind tunnel system, operate the wind tunnel system, and control the mixed test gas to flow through the nozzle to generate a supersonic flow field corresponding to the target Mach number in the test section.

[0013] Fourthly, this application discloses an electronic device, comprising: Memory, used to store computer programs; A processor is used to execute the computer program to implement the steps of the aforementioned disclosed method for controlling Mach number without modifying the nozzle.

[0014] Fifthly, this application discloses a computer-readable storage medium for storing a computer program; wherein, when the computer program is executed by a processor, it implements the steps of the aforementioned disclosed Mach number control method without modifying the nozzle.

[0015] As can be seen, this invention provides a method for determining a target Mach number and, based on a fixed nozzle profile, determining the target gas specific heat ratio required to achieve the target Mach number; wherein the target Mach number is lower than the standard Mach number of the nozzle; selecting at least two target pressure gases with different specific heat ratios as gas sources; determining the mixing ratio of each target pressure gas in the gas sources based on the target gas specific heat ratio; mixing the target pressure gases according to the mixing ratio to form a mixed test gas; introducing the mixed test gas into a wind tunnel system, operating the wind tunnel system, and controlling the mixed test gas to flow through the nozzle to generate a supersonic flow field corresponding to the target Mach number in the test section. Therefore, by precisely preparing a mixed test gas with a specific specific heat ratio under the premise of a fixed nozzle, a supersonic flow field with a uniform flow field and a Mach number lower than the original design value was successfully generated in the wind tunnel test section. This solution avoids the problems of high cost, low efficiency, and inconvenient operation caused by changing nozzles to change the test Mach number. It realizes a solution that can flexibly, economically, and efficiently expand the low-speed Mach number test capability of a wind tunnel by simply adjusting the gas composition without changing any hardware. It avoids the high cost and operational drawbacks of mechanically changing nozzles or using complex flexible nozzle mechanisms, enabling a single wind tunnel platform to have the test capability of multiple Mach numbers. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of the present invention or 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 embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0017] Figure 1 This is a flowchart of a Mach number control method that does not require modification of the nozzle, as disclosed in this application. Figure 2 This is one of the disclosures in this application. (Air) nozzle Mach number distribution diagram; Figure 3 This is one of the disclosures in this application. (C2F6) Nozzle Mach number distribution diagram; Figure 4 This is one of the disclosures in this application. (Argon) nozzle Mach number distribution diagram; Figure 5 This application discloses a Mach number distribution diagram at the nozzle exit interface under three specific heat ratios. Figure 6 This is a structural diagram of a wind tunnel testing system for expanding the testing capabilities of a high-speed wind tunnel system using mixed gases, as disclosed in this application. Figure 7 This is a schematic diagram of a Mach number control device that does not require modification of the nozzle, as disclosed in this application. Figure 8 This is a structural diagram of an electronic device disclosed in this application. Detailed Implementation

[0018] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0019] High-speed wind tunnels (referring in this article to wind tunnels with test Mach numbers greater than 1) generate high-speed airflow through Laval nozzles. The main parameters determining the Mach number of the test section are the gas specific heat ratio and the nozzle profile. Conventional high-speed wind tunnels use air as the test gas, and air has a specific heat ratio of 1.4. Therefore, the predetermined test Mach number is mainly achieved through the wind tunnel profile; once the nozzle profile is determined, the test Mach number is also determined. To generate different test Mach numbers, the common practice is to design and manufacture different nozzles, changing the test Mach number by replacing the nozzle. This leads to high costs, low efficiency, and inconvenient operation. Another method is to use flexible nozzles, controlling the nozzle profile through a carefully designed nozzle adjustment mechanism. However, flexible nozzles have complex mechanisms and high maintenance costs, and their use is not widespread domestically or internationally. It is necessary to develop a Mach number adjustment method that does not require modification of the nozzle.

[0020] When changing the Reynolds number in a high-speed wind tunnel, the total pressure is typically altered, or both total pressure and total temperature are changed simultaneously. Due to limitations in wind tunnel structure and operation / maintenance, the range of adjustable total pressure and temperature is limited, resulting in a narrow coverage of Reynolds numbers. Since actual aircraft have high Reynolds numbers, while wind tunnel tests have very limited Reynolds numbers (model-scaled Reynolds numbers are typically about an order of magnitude lower than actual flight numbers), high Reynolds number wind tunnels are crucial. Because the Reynolds number is inversely proportional to viscosity, and lowering temperature reduces air viscosity, cryogenic techniques are often used to increase the Reynolds number. For example, the ETW wind tunnel uses liquid nitrogen cooling to achieve high Reynolds numbers. However, the construction and operating costs of cryogenic high Reynolds number wind tunnels are extremely high.

[0021] When extending high-speed wind tunnels designed for air to other test gases, certain constraints must be met, but these constraints have not yet been given in the currently available literature.

[0022] Once the high-speed wind tunnel is designed, the mainstream velocity of the test section is essentially fixed, meaning it is the product of the Mach number and the speed of sound. When cryogenic technology is used, the speed of sound in the test medium decreases, and the mainstream velocity of the test section decreases. Therefore, even if the Mach number and Reynolds number of the wind tunnel flow field are the same as in the real flight environment, the velocity field still differs significantly from that in the real flight environment.

[0023] Therefore, the present invention provides a Mach number control scheme that does not require modification of the nozzle, which can control the wind tunnel Mach number by simply changing the test gas.

[0024] Reference Figure 1 As shown, this embodiment of the invention discloses a Mach number control method without modifying the nozzle, comprising: Step S11: Determine the target Mach number, and based on the fixed profile of the nozzle, determine the target gas specific heat ratio required to achieve the target Mach number; wherein the target Mach number is lower than the standard Mach number of the nozzle.

[0025] In this embodiment, the desired target Mach number is first determined. Then, based on the conventional nozzle fixed profile, the target gas specific heat ratio required to achieve the target Mach number is determined. Specifically, the nozzle of a high-speed wind tunnel is usually designed according to a predetermined Mach number to ensure that the flow field quality in the test section is optimal at that Mach number. The actual Mach number of the wind tunnel operation is often calculated using the following formula: ; in, This indicates the total pressure after the normal shock wave, obtained using a Pitot probe. Represents the Mach number. This indicates the total pressure at the nozzle inlet. Indicates the specific heat ratio of a gas. Indicates specific heat at constant pressure. This represents the specific heat at constant volume. From the above formula, it can be seen that the Mach number of the test section is related to... The ratio and specific heat ratio related. Determined by the nozzle profile, once the nozzle is fixed, The value is thus fixed; the Mach number is only related to the specific heat ratio. related.

[0026] Therefore, when preparing to obtain multiple target Mach numbers, first determine the nozzle profile information required for this experiment. Once the profile information is fixed, further design the target gas specific heat ratio required to achieve the target Mach number based on the relationship between Mach number and specific heat ratio.

[0027] Furthermore, the nozzle first gradually contracts and then gradually expands, and the Mach number gradually increases. The relationship between the Mach number and the nozzle cross-sectional area is as follows: ; Where A represents the nozzle cross-sectional area, when the Mach number is less than 1, the Mach number increases as the cross-sectional area decreases; this region is the nozzle's contraction section. When the Mach number is greater than 1, the Mach number increases as the cross-sectional area increases; this region is the nozzle's expansion section. The cross-sectional area is smallest at the junction of the contraction and expansion sections, i.e., the throat. From the above formula, it can also be seen that when the nozzle profile (cross-sectional area) is fixed, the Mach number distribution within the nozzle is only related to the specific heat ratio. Therefore, as long as the specific heat ratio of the test medium is the same, the same Mach number distribution can be obtained.

[0028] Therefore, when the specific heat ratio is fixed, the Mach number can be changed by adjusting the nozzle profile; when the nozzle profile is fixed, the Mach number can also be changed by adjusting the specific heat ratio. However, changing only the specific heat ratio may cause uneven Mach number at the nozzle exit. Therefore, in the wind-driven Mach number control process of this scheme, the nozzle profile information is determined first, and then the specific heat ratio of the target gas is adjusted.

[0029] like Figure 2 As shown, Figure 2 Given (Air) Mach number distribution within the nozzle, such as Figure 3 As shown, Figure 3 Given Mach number distribution within the nozzle, such as Figure 4 As shown, Figure 4 Given Mach number distribution within the nozzle, such as Figure 5 As shown, Figure 5The Mach number distribution at the nozzle exit (test section inlet) interface was compared under three conditions. Since the nozzle in this embodiment was designed for air, the Mach number distribution of air was the most uniform at the nozzle exit cross-section.

[0030] This nozzle is designed for airflow, when The nozzle exit Mach number is approximately 6, and excluding the nozzle boundary layer region, the relative deviation of the Mach number is 0.42%; when The nozzle exit Mach number is approximately 3.7, with a relative deviation of 0.43%, still meeting the advanced indicator (below 0.5%) in the national standard; when At this time, the uniformity of the Mach number at the nozzle exit is disrupted, and the Mach number in the mainstream region is about 9 to 12, with the highest Mach number at the center of the nozzle and gradually decreasing on both sides.

[0031] In this way, reducing the specific heat ratio can decrease the Mach number at the nozzle exit without significantly affecting the uniformity of the Mach number. Increasing the specific heat ratio can increase the Mach number at the nozzle exit, but the uniformity of the Mach number is significantly affected. Therefore, by reducing the specific heat ratio of the gas, the Mach number in the test section can be extended to a lower speed while still maintaining the uniformity of the Mach number in accordance with national standards.

[0032] Step S12: Select at least two target pressure gases with different specific heat ratios as gas sources.

[0033] In this embodiment, without changing the nozzle, by using a target pressure gas with a specific heat ratio lower than that of air as the gas source, the Mach number in the wind tunnel test can be extended to lower speeds, while the uniformity of the Mach number at the nozzle exit remains essentially unchanged. It is difficult to adjust the specific heat ratio using only a single gas; therefore, a method of mixing gases with different specific heat ratios in different proportions can be used to improve the adjustability of the specific heat ratio.

[0034] Step S13: Determine the mixing ratio of each target pressure gas in the gas source according to the specific heat ratio of the target gas.

[0035] In this embodiment, examples of mixing two gases and mixing three gases are given, and formulas for the mixing gas ratio (first equation and second equation) are provided to determine the mixing ratio of gases at each target pressure.

[0036] In one specific embodiment, the gas source includes a first target pressure gas and a second target pressure gas; correspondingly, determining the mixing ratio of each of the target pressure gases in the gas source according to the specific heat ratio of the target gas includes: determining the mixing ratio of the first target pressure gas and the second target pressure gas in the gas source by means of a first equation and according to the specific heat ratio of the target gas. Wherein, the first equation is ; This represents the mole fraction of the gas at the first target pressure. This represents the isobaric specific heat of the gas at the first target pressure. This represents the specific heat at constant volume of the gas at the first target pressure. This represents the mole fraction of the gas at the second target pressure. This represents the isobaric specific heat of the gas at the second target pressure. This represents the isochoric specific heat of the gas at the second target pressure. This indicates the specific heat ratio of the target gas.

[0037] It is understandable that, given a specific heat ratio of the target gas... Then, set the specific heat ratio of gas 1 (the first target pressure gas). Less than The specific heat ratio of gas 2 (the second target pressure gas) Greater than By mixing the two gases in a certain proportion, the specific heat ratio of the target gas can be obtained as equal to... The mole fractions of the two gases in the mixture are determined by the first equation mentioned above.

[0038] For easy reference, Table 1 provides the parameters of some common gases at 0°C and 1 standard atmosphere, and Table 2 provides the parameters of these gases at -46°C and 0.012 atmospheres (approximately 30km altitude).

[0039] Table 1. Gas parameters at 0°C and one standard atmosphere. Table 2. Gas parameters at 0.012 atmospheres -46°C (approximately 30 km altitude). Taking a mixture of krypton and carbon tetrafluoride (CF4) as an example, the gas composition is calculated; the mixing ratios of other gases can be calculated similarly. At 0°C and 1 standard atmosphere, the specific heat ratio of krypton is 1.67, and that of CF4 is 1.17. To achieve the same specific heat ratio as air... According to the first equation, the ratio of krypton to CF4 is 0.768:0.232. Temperature changes cause variations in isobaric and isochoric specific heats, and consequently, the specific heat ratio. If temperature significantly affects the specific heat ratio of a gas, it is necessary to find the specific heat at the corresponding temperature and pressure, and then calculate the mixing ratio of the two gases using the first equation.

[0040] In another specific embodiment, the gas source includes a first target pressure gas, a second target pressure gas, and a third target pressure gas; correspondingly, determining the mixing ratio of each of the target pressure gases in the gas source according to the specific heat ratio of the target gas includes: setting a corresponding initial mole fraction for the first target pressure gas; and determining the mixing ratio of the first target pressure gas, the second target pressure gas, and the third target pressure gas in the gas source through a second equation and according to the specific heat ratio of the target gas. Wherein, the second equation is ;in, This represents the initial mole fraction of the gas at the first target pressure. This represents the isobaric specific heat of the gas at the first target pressure. This represents the specific heat at constant volume of the gas at the first target pressure. This represents the mole fraction of the gas at the second target pressure. This represents the isobaric specific heat of the gas at the second target pressure. This represents the isochoric specific heat of the gas at the second target pressure. This indicates the mole fraction of the gas at the third target pressure. This represents the isobaric specific heat of the gas at the third target pressure. This represents the specific heat at constant volume of the gas at the third target pressure. This indicates the specific heat ratio of the target gas.

[0041] It is understandable that when a given target gas specific heat ratio is obtained by using the ratio of three gases... When mixing gases, different mixing ratios can be obtained. Therefore, based on practical application requirements, a free parameter (initial molar parameter) can be set first, and then the mixing ratio of the other two gases can be solved further. The mole fraction of gas 1 is set. for Then the mole fractions of gas 2 and gas 3 (the third target pressure gas) can be obtained from the second equation above.

[0042] Step S14: Mix the target pressure gases according to the mixing ratio to form a mixed test gas.

[0043] In this embodiment, the mole fractions of each target pressure gas calculated according to the above equation are used as the mixing ratio, and they are mixed to obtain a mixed test gas.

[0044] Step S15: Introduce the mixed test gas into the wind tunnel system, operate the wind tunnel system, and control the mixed test gas to flow through the nozzle to generate a supersonic flow field corresponding to the target Mach number in the test section.

[0045] In this embodiment, the mixed test gas is introduced into the wind tunnel system, the wind tunnel system is operated, and the mixed test gas is controlled to flow through the nozzle to generate a supersonic flow field corresponding to the target Mach number in the test section.

[0046] In this embodiment, when at least two target pressure gases are selected, the dynamic viscosity coefficient, mass ratio, and reduction frequency of the mixed test gas are different from the corresponding parameters of the standard test gas, so as to adjust the flow field parameters of the supersonic flow field in the test section. It should be noted that, to further expand the mainstream velocity / sound velocity / reduction frequency / mass ratio, etc., by selecting a suitable mixed gas, in addition to adjusting the test Mach number, the mainstream velocity of the test section can also be adjusted. Specifically, the sound velocity of the mixed test gas is different from that of the standard test gas, and the sound velocity of the mixed test gas is used to obtain a different mainstream velocity in the test section than that of the standard test gas at the target Mach number. The mainstream velocity adjustment formula is as follows: ; Where U represents the mainstream speed of the test section, and These are the Mach number and the speed of sound for the test section, respectively. Once the Mach number is fixed, the mainstream speed of the test section can be adjusted by changing the speed of sound.

[0047] Among unimolecular gases, helium and neon have a higher speed of sound than air; among multimolecular gases, methane and others also have a higher speed of sound than air. By mixing these gases, it is possible not only to create a mixture with the same specific heat ratio as air, but also a mixture with a higher speed of sound than air. Similarly, among unimolecular gases, krypton and xenon have a lower speed of sound than air, while most multimolecular heavy gases (such as CF4) have a lower speed of sound than air. By mixing these gases, it is possible to create a mixture with the same specific heat ratio as air but a lower speed of sound than air, thereby reducing the mainstream velocity in the test section.

[0048] The formula for calculating the speed of sound in a gas mixture is as follows: ; in, Represents the universal gas constant. Represents absolute temperature. Indicates the average molar mass of the gas mixture ( (This represents the molar mass of the corresponding gas).

[0049] The extended test section's mainstream speed has a special purpose: simulating the reduced frequency is necessary when conducting flutter tests. , .

[0050] Among them, the molecule on the right side of the above equation These are the parameters of the experimental model, which are obtained by changing the mainstream velocity of the wind tunnel flow field. This can increase the abbreviated frequency. The simulation range.

[0051] When conducting flutter tests on scaled-down models, the mass ratio It is also a very important dimensionless parameter.

[0052] ; in, It is the mass per unit length of the experimental model. It is the density of the gas. This is half the model's span. Taking a mixture of CF4 and krypton as an example, its density is about three times that of air, meaning that the scaled-down model size can be reduced to 0.577 of the original, or a denser material can be used to make the model, thus greatly improving its strength.

[0053] As shown in Tables 1 and 2, the dynamic viscosity (or simply viscosity coefficient) of helium, neon, etc., is greater than that of air, while the viscosity coefficient of R14 (i.e., CF4), R134A, etc., is smaller than that of air. Different gas combinations can be selected as needed to obtain the required viscosity coefficient. The formula for calculating the dynamic viscosity coefficient of a gas mixture is as follows: ; ; in, Indicates the viscosity coefficient of the mixture. Indicates the corresponding first The viscosity coefficient of a pure component, Indicates the corresponding first The viscosity coefficient of a pure component, Indicates the corresponding first The molar mass of each pure component Indicates the corresponding first The molar mass of each pure component This represents the interaction coefficient between components.

[0054] Since the kinematic viscosity coefficient is easier to use than the dynamic viscosity coefficient, the formula for calculating the kinematic viscosity coefficient of a gas mixture is as follows: ; ; in, Represents the kinematic viscosity coefficient. ρ represents the density of the mixture, p represents the pressure, R represents the universal gas constant, and T represents the thermodynamic temperature of the gas.

[0055] In this embodiment, the operation of the wind tunnel system further includes: monitoring the total pressure and total temperature of the mixed test gas; and adjusting the Reynolds number of the supersonic flow field in the test section by adjusting the total pressure and / or the total temperature. It is understood that the Reynolds number is a very important parameter in fluid mechanics, and the range of Reynolds numbers that a wind tunnel test can simulate is one of the key indicators of a wind tunnel. Due to model scaling, gas density, and other factors, the test Reynolds number in wind tunnel tests is usually lower than the actual flight Reynolds number. Increasing the Reynolds number in wind tunnel tests is one of the key challenges. Cryogenic wind tunnels are commonly used to increase the test Reynolds number, but the construction and maintenance costs of cryogenic wind tunnels are high. In conventional wind tunnels, heavy gases with low viscosity can be used to increase the test Reynolds number. Taking a reference length L=1m as an example, the unit Reynolds number (also called Reynolds number per meter) of the test section is: ; Since velocity is the product of the speed of sound and the Mach number, the Reynolds number for the speed of sound is defined as: ; Therefore, the unit Reynolds number of the test section is: ; As can be seen from Tables 1 and 2, if a suitable gas is used, the sound speed Reynolds number can be increased by more than three times, that is, the unit Reynolds number can be increased by more than three times, which greatly expands the Reynolds number simulation capability of the wind tunnel.

[0056] Taking a mixture of krypton and CF4 as an example, when the mole fractions of the components satisfy krypton:CF4 = 0.768:0.232, the specific heat ratio of the mixture is the same as that of air. Under the temperature and pressure conditions at an altitude of 30 km, the Reynolds number of the sound velocity in the test section is... The speed of sound in air and the Reynolds number At the same Mach number, the Reynolds number per unit speed of sound for a mixture of krypton and CF4 is 1.4 times that of pure air.

[0057] As can be seen, this invention provides a method for determining a target Mach number and, based on a fixed nozzle profile, determining the target gas specific heat ratio required to achieve the target Mach number; wherein the target Mach number is lower than the standard Mach number of the nozzle; selecting at least two target pressure gases with different specific heat ratios as gas sources; determining the mixing ratio of each target pressure gas in the gas sources based on the target gas specific heat ratio; mixing the target pressure gases according to the mixing ratio to form a mixed test gas; introducing the mixed test gas into a wind tunnel system, operating the wind tunnel system, and controlling the mixed test gas to flow through the nozzle to generate a supersonic flow field corresponding to the target Mach number in the test section. Therefore, by precisely preparing a mixed test gas with a specific specific heat ratio under the premise of a fixed nozzle, a supersonic flow field with a uniform flow field and a Mach number lower than the original design value was successfully generated in the wind tunnel test section. This solution avoids the problems of high cost, low efficiency, and inconvenient operation caused by changing nozzles to change the test Mach number. It realizes a solution that can flexibly, economically, and efficiently expand the low-speed Mach number test capability of a wind tunnel by simply adjusting the gas composition without changing any hardware. It avoids the high cost and operational drawbacks of mechanically changing nozzles or using complex flexible nozzle mechanisms, enabling a single wind tunnel platform to have the test capability of multiple Mach numbers.

[0058] Reference Figure 6 As shown, the present invention also discloses a wind tunnel testing system for implementing the aforementioned Mach number control method without modifying the nozzle. The wind tunnel testing system includes: At least two gas supply units; A mixing tank is used to mix target pressure gases from different gas sources. The control system is used to adjust the mixing ratio of the various gas sources; The main structure of the wind tunnel includes the nozzle, test section, diffuser section, and vacuum system.

[0059] Specifically, when the gas source includes a first target pressure gas and a second target pressure gas, numbers 01 and 04 are combined into two gas supply devices. Number 01 represents Gas 1 storage cylinder, which, according to the experimental conditions, fills the experimental platform with the target pressure gas; this can be air or other types of gas as needed. Number 04 represents Gas 2 storage cylinder, which, according to the experimental conditions, fills the experimental platform with the target pressure gas. Number 05 represents a mixing tank, used to uniformly mix the gases and provide the gas source for high-speed wind tunnel operation. Number 06 represents a... The heater heats the air source in the wind tunnel, preventing condensation of the airflow in the test flow field; section 07 represents the stabilization section, which contains multiple layers of perforated metal plates, woven metal mesh, and sintered wire mesh, primarily serving a rectifying function; sections 08, 09, 010, and 011 form the main structure of the wind tunnel, where section 08 represents the nozzle, mainly used to generate high-speed airflow; section 09 represents the test section, used to install test models and provide optical observation windows; section 010 represents the diffusion section; and section 011 represents the vacuum chamber, providing a vacuum environment for the entire wind tunnel, typically maintained at 100°C during experiments. Below Pa; the control system is used to adjust the flow ratio of each gas source, specifically including gas supply valves that directly execute commands to open, close, and adjust the opening degree, as well as sensors and a data acquisition system that provide real-time judgment of the current flow field state as a basis for flow adjustment. Therefore, the control system specifically includes numbers 02, 03, 012, 013, and 014, where number 02 represents the gas 1 supply valve, used to control the start and stop of gas 1 charging; number 03 represents the gas 2 supply valve, used to control the start and stop of gas 2 charging; number 012 represents the pressure sensor, used to measure the total operating pressure of the wind tunnel; number 013 represents the temperature sensor, used to measure the total operating temperature of the wind tunnel; number 014 represents the data acquisition system, used to collect and monitor the total operating temperature and total pressure data of the wind tunnel in real time; the thick solid lines from number 01 to number 07 represent the gas supply pipelines. It should be noted that in the control system, the data acquisition system 014 receives pressure and temperature data from sensors 012 and 013. Based on the preset mixing ratio and target total pressure, and running the control algorithm, the required opening degree of each valve is calculated, and the opening command is issued to valves numbered 02 and 03 to control their action, so that they open gas storage cylinders 01 and 05 to release the target pressure gas to mixing tank 05. At the same time, heater 06 heats the wind tunnel air source to prevent the airflow in the test flow field from condensing.

[0060] Reference Figure 7 As shown, the present invention provides a Mach number control device that does not require modification of the nozzle, comprising: The specific heat ratio determination module 11 is used to determine the target Mach number and, based on the fixed profile of the nozzle, determine the target gas specific heat ratio required to achieve the target Mach number; wherein, the target Mach number is lower than the standard Mach number of the nozzle; Gas source selection module 12 is used to select at least two target pressure gases with different specific heat ratios as gas sources; The proportion determination module 13 is used to determine the mixing ratio of each of the target pressure gases in the gas source according to the specific heat ratio of the target gas; Gas mixing module 14 is used to mix the target pressure gases according to the mixing ratio to form a mixed test gas; The wind tunnel operation module 15 is used to introduce the mixed test gas into the wind tunnel system, operate the wind tunnel system, and control the mixed test gas to flow through the nozzle to generate a supersonic flow field corresponding to the target Mach number in the test section.

[0061] It is evident that by encapsulating the specific heat ratio determination module and the proportion determination module, the required gas parameters for reverse propagation based on the fixed nozzle profile are encapsulated, ensuring that this scheme can be executed accurately and repeatedly. This enables a single wind tunnel to switch quickly and flexibly between different Mach numbers, expanding the application range and mission flexibility of the equipment, while avoiding high hardware modification costs. Thus, it reliably expands the Mach number without replacing the nozzle.

[0062] Furthermore, embodiments of this application also disclose an electronic device, Figure 8 This is a structural diagram of an electronic device 20 according to an exemplary embodiment. The content of the diagram should not be construed as limiting the scope of this application.

[0063] Figure 8 This is a schematic diagram of the structure of an electronic device 20 provided in an embodiment of this application. Specifically, the electronic device 20 may include: at least one processor 21, at least one memory 22, a power supply 23, a communication interface 24, an input / output interface 25, and a communication bus 26. The memory 22 stores a computer program, which is loaded and executed by the processor 21 to implement the relevant steps in the Mach number control method without modifying the nozzle disclosed in any of the foregoing embodiments. Alternatively, the electronic device 20 in this embodiment may specifically be an electronic computer.

[0064] In this embodiment, the power supply 23 is used to provide operating voltage for each hardware device on the electronic device 20; the communication interface 24 can create a data transmission channel between the electronic device 20 and external devices, and the communication protocol it follows can be any communication protocol applicable to the technical solution of this application, and is not specifically limited here; the input / output interface 25 is used to acquire external input data or output data to the outside world, and its specific interface type can be selected according to specific application needs, and is not specifically limited here.

[0065] The processor 21 may include one or more processing cores, such as a quad-core processor or an octa-core processor. The processor 21 may be implemented using at least one hardware form selected from DSP (Digital Signal Processing), FPGA (Field-Programmable Gate Array), and PLA (Programmable Logic Array). The processor 21 may also include a main processor and a coprocessor. The main processor, also known as a CPU (Central Processing Unit), is used to process data in the wake-up state; the coprocessor is a low-power processor used to process data in the standby state. In some embodiments, the processor 21 may integrate a GPU (Graphics Processing Unit), which is responsible for rendering and drawing the content to be displayed on the screen. In some embodiments, the processor 21 may also include an AI (Artificial Intelligence) processor, which is used to handle computational operations related to machine learning.

[0066] In addition, the memory 22, as a carrier for resource storage, can be a read-only memory, random access memory, disk or optical disk, etc. The resources stored thereon can include operating system 221, computer program 222, etc., and the storage method can be temporary storage or permanent storage.

[0067] The operating system 221 manages and controls the various hardware devices and computer programs 222 on the electronic device 20 to enable the processor 21 to perform calculations and processing on the massive amounts of data 223 in the memory 22. It can be Windows Server, Netware, Unix, Linux, etc. The computer program 222 includes, in addition to a computer program capable of performing the Mach number control method without modifying the nozzle as disclosed in any of the foregoing embodiments, it may further include computer programs capable of performing other specific tasks. The data 223 may include data received by the electronic device from external devices, as well as data collected by its own input / output interface 25.

[0068] Furthermore, this application also discloses a computer-readable storage medium for storing a computer program; wherein, when the computer program is executed by a processor, it implements the aforementioned Mach number control method without modifying the nozzle. Specific steps of this method can be found in the corresponding content disclosed in the foregoing embodiments, and will not be repeated here.

[0069] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since it corresponds to the method disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the method section.

[0070] Those skilled in the art will further recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, computer software, or a combination of both. To clearly illustrate the interchangeability of hardware and software, the components and steps of the various examples have been generally described in terms of functionality in the foregoing description. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application. The steps of the methods or algorithms described in conjunction with the embodiments disclosed herein can be implemented directly in hardware, software modules executed by a processor, or a combination of both. The software module may be located in random access memory (RAM), memory, read-only memory (ROM), electrically programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), registers, hard disks, removable disks, CD-ROMs (Compact Disc-Read Only Memory), or any other form of storage medium known in the art.

[0071] Finally, it should be noted that in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0072] The solution provided by the present invention has been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only for helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A method for controlling Mach number without modifying the nozzle, characterized in that, include: Determine the target Mach number, and based on the fixed profile of the nozzle, determine the target gas specific heat ratio required to achieve the target Mach number; wherein the target Mach number is lower than the standard Mach number of the nozzle; Select at least two target pressure gases with different specific heat ratios as gas sources; Based on the specific heat ratio of the target gas, determine the mixing ratio of each target pressure gas in the gas source; The target pressure gases are mixed according to the specified mixing ratio to form a mixed test gas; The mixed test gas is introduced into the wind tunnel system, the wind tunnel system is operated, and the mixed test gas is controlled to flow through the nozzle to generate a supersonic flow field corresponding to the target Mach number in the test section.

2. The Mach number control method without modifying the nozzle according to claim 1, characterized in that, The gas source includes a first target pressure gas and a second target pressure gas; Accordingly, determining the mixing ratio of each of the target pressure gases in the gas source based on the specific heat ratio of the target gas includes: The mixing ratio of the first target pressure gas and the second target pressure gas in the gas source is determined by the first equation and based on the specific heat ratio of the target gas. Wherein, the first equation is ; This represents the mole fraction of the gas at the first target pressure. This represents the isobaric specific heat of the gas at the first target pressure. This represents the specific heat at constant volume of the gas at the first target pressure. This represents the mole fraction of the gas at the second target pressure. This represents the isobaric specific heat of the gas at the second target pressure. This represents the isochoric specific heat of the gas at the second target pressure. This indicates the specific heat ratio of the target gas.

3. The Mach number control method without modifying the nozzle according to claim 1, characterized in that, The gas source includes a first target pressure gas, a second target pressure gas, and a third target pressure gas; Accordingly, determining the mixing ratio of each of the target pressure gases in the gas source based on the specific heat ratio of the target gas includes: Set the corresponding initial mole fraction for the first target pressure gas; The mixing ratio of the first target pressure gas, the second target pressure gas, and the third target pressure gas in the gas source is determined by the second equation and based on the specific heat ratio of the target gas. Wherein, the second equation is ;in, This represents the initial mole fraction of the gas at the first target pressure. This represents the isobaric specific heat of the gas at the first target pressure. This represents the specific heat at constant volume of the gas at the first target pressure. This represents the mole fraction of the gas at the second target pressure. This represents the isobaric specific heat of the gas at the second target pressure. This represents the isochoric specific heat of the gas at the second target pressure. This represents the mole fraction of the gas at the third target pressure. This represents the isobaric specific heat of the gas at the third target pressure. This represents the specific heat at constant volume of the gas at the third target pressure. This indicates the specific heat ratio of the target gas.

4. The Mach number control method without modifying the nozzle according to claim 1, characterized in that, The sound velocity of the mixed test gas is different from that of the standard test gas, and the sound velocity of the mixed test gas is used to obtain a mainstream velocity different from that of the standard test gas in the test section at the target Mach number.

5. The Mach number control method without modifying the nozzle according to claim 1, characterized in that, Also includes: When at least two target pressure gases are selected, the dynamic viscosity coefficient, mass ratio, and reduction frequency of the mixed test gas are different from the corresponding parameters of the standard test gas, so as to adjust the flow field parameters of the supersonic flow field in the test section.

6. The Mach number control method without modifying the nozzle according to any one of claims 1 to 5, characterized in that, The operation of the wind tunnel system also includes: Monitor the total pressure and total temperature of the mixed test gas; The Reynolds number of the supersonic flow field in the test section is adjusted by regulating the total pressure and / or the total temperature.

7. A wind tunnel testing system, characterized in that, For implementing the Mach number control method without nozzle modification as described in any one of claims 1 to 6, the wind tunnel testing system comprises: At least two gas supply units; A mixing tank is used to mix target pressure gases from different gas sources. The control system is used to adjust the mixing ratio of the various gas sources; The main structure of the wind tunnel includes the nozzle, test section, diffuser section, and vacuum system.

8. A Mach number control device that does not require modification of the nozzle, characterized in that, include: A specific heat ratio determination module is used to determine the target Mach number and, based on the fixed profile of the nozzle, determine the target gas specific heat ratio required to achieve the target Mach number; wherein the target Mach number is lower than the standard Mach number of the nozzle; The gas source selection module is used to select at least two target pressure gases with different specific heat ratios as gas sources. The proportion determination module is used to determine the mixing ratio of each target pressure gas in the gas source based on the specific heat ratio of the target gas; A gas mixing module is used to mix the target pressure gases according to the mixing ratio to form a mixed test gas; The wind tunnel operation module is used to introduce the mixed test gas into the wind tunnel system, operate the wind tunnel system, and control the mixed test gas to flow through the nozzle to generate a supersonic flow field corresponding to the target Mach number in the test section.

9. An electronic device, characterized in that, include: Memory, used to store computer programs; A processor for executing the computer program to implement the steps of the Mach number control method without modifying the nozzle as described in any one of claims 1 to 6.

10. A computer-readable storage medium, characterized in that, Used to store computer programs; wherein, when executed by a processor, the computer programs implement the steps of the Mach number control method without modifying the nozzle as described in any one of claims 1 to 6.

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