An air intake for an upper atmosphere air-breathing electric propulsion system

Abstract

The application discloses an air inlet of an upper atmosphere air-breathing electric propulsion system, which is designed based on the flow characteristics of the upper atmosphere region free molecular flow or near free molecular flow and in terms of the air inlet geometry and surface material, and is composed of an inlet section, a compression section, an ionization acceleration section and an outlet section; the inlet section is a cylindrical pipeline, the compression section is a contraction pipeline with a concave circular arc profile and a left end tangent to the inlet section; the ionization acceleration section comprises a contraction pipeline and a cylindrical pipeline, the contraction pipeline has a convex circular arc profile, and the two ends of the convex circular arc profile are tangent to the right end of the compression section and the cylindrical pipeline of the ionization acceleration section; and the outlet section is a conical expansion pipeline. After the geometry design of the air inlet is completed, the inner surface of the air inlet is smoothed to reduce the momentum / energy accommodation coefficient of the gas and the inner surface, so that the air inlet of the upper atmosphere air-breathing electric propulsion system is finally obtained.

Description

Technical Field

[0001] This invention relates to an air intake design scheme for an upper atmospheric air-breathing electric propulsion system, belonging to the field of aerodynamic design for high-altitude hypersonic aircraft. Background Technology

[0002] The upper atmosphere, between 120 and 300 km above the Earth's surface, lies between near space and outer space and is currently a largely untapped airspace. In recent years, due to the needs of scientific research, spacecraft operating in this airspace have gradually shown broad application prospects, including high-precision measurement of Earth's gravity gradient, accurate global ocean and climate observation, and accurate upper atmosphere modeling. Furthermore, conventional military reconnaissance satellites, operating at high altitudes, cannot obtain high-resolution ground images, while reconnaissance satellites operating in ultra-low orbits in the upper atmosphere can achieve a resolution of 0.1–0.3 m, significantly improving the accuracy of military target location.

[0003] However, spacecraft operating in this region are affected by the drag of the thin atmosphere and need to carry propulsion systems to compensate for this drag in order to ensure their long-term on-orbit operation. Electric propulsion technology, after decades of development, is currently the most commonly used atmospheric drag compensation propulsion technology. However, electric propulsion systems require a large amount of propellant, and as the limited propellant is depleted, the spacecraft's lifespan will end. Moreover, carrying a large amount of propellant not only increases launch costs but also significantly reduces the spacecraft's payload.

[0004] Air-breathing electric propulsion technology relies on solar energy to collect rarefied gas from the orbital environment as a working fluid. The collected gas is ionized and accelerated before being expelled at high speed as a beam to generate thrust. Air-breathing electric propulsion technology inherits the high specific impulse advantage of electric propulsion while overcoming its disadvantage of requiring a large number of thrusters. It boasts advantages such as long operational life, low launch cost, and high payload capacity, making it an ideal propulsion technology for compensating for atmospheric drag and other non-gravity factors in upper atmosphere spacecraft.

[0005] The air intake is a special pneumatic device in an air-breathing electric propulsion system. Its purpose is to collect rarefied gas from the upper atmosphere, compress it, and transport it to the ionization section of the propulsion system. Achieving high-efficiency ionization of the upper atmosphere requires the gas entering the ionization section to have sufficiently high pressure and a sufficient amount of propellant. Therefore, the gas compression and gas collection performance of the air intake directly determines the overall performance of the air-breathing electric propulsion system. Designing the air intake for air-breathing electric propulsion systems is a crucial first step in the research of these systems. Summary of the Invention

[0006] The technical problem solved by this invention is to overcome the shortcomings of poor air intake compression performance and low collection efficiency, and to propose an air intake for an upper atmospheric air-breathing electric propulsion system.

[0007] The technical solution of this invention is: an air intake for an upper atmospheric air-breathing electric propulsion system, characterized by comprising an inlet section, a compression section, an ionization acceleration section, and an outlet section; the inlet section is a cylindrical pipe, the compression section is a constricting pipe with an inwardly concave arc profile, and its left end is tangent to the inlet section; the ionization acceleration section includes a constricting pipe section and a cylindrical pipe section, the constricting pipe having an outwardly concave arc profile, the two ends of which are tangent to the right end of the compression section and the cylinder of the ionization acceleration section; the outlet section is a conical expanding pipe; the inner surface of the air intake is smoothed to reduce the momentum / energy adaptation coefficient of the gas interaction with the inner surface.

[0008] Preferably, the upper atmosphere ranges from 120 km to 300 km, and the mean free path of the incoming molecules ranges from 3.3 m to 2595 m.

[0009] Preferably, the length of the cylindrical inlet pipe... L i and radius r i The values ​​should be adjusted according to the size of the aircraft. The length of the inlet section should not be greater than the length of the aircraft, and the preferred value range is 0.05 to 0.15 times the length of the aircraft. The value range of the inlet section radius is 0.7 to 0.9 times the radius of the aircraft.

[0010] Preferably, for an aircraft with a characteristic length of 2 m and a characteristic radius of 0.75 m, the typical values ​​for the length and radius of the cylindrical inlet pipe are 0.2 m and 0.55 m, respectively.

[0011] Preferably, the length of the compressed section L c Less than half the length of the aircraft, preferably within the range of 0.4 to 0.5 times the length of the aircraft, the radius of the arc of the compressed section. r c It is necessary to ensure that the corresponding central angle range is 30°~60°. r c The value ranges from 0.4 to 1 times the length of the aircraft.

[0012] Preferably, for an aircraft with a characteristic length of 2 m and a characteristic radius of 0.75 m, the typical value of the radius of the constriction duct profile arc is 1.02 m.

[0013] Preferably, the cylindrical radius of the ionization acceleration section is... r t The value is determined based on the compression requirements of the air intake. The higher the compression ratio, the smaller the cylinder radius, and vice versa. The value range is 0.05 to 0.4 times the radius of the aircraft.

[0014] Preferably, for an aircraft with a characteristic length of 2 m and a characteristic radius of 0.75 m, the typical values ​​for the radius of the constriction pipe profile arc and the radius of the cylindrical pipe are 0.189775 m and 0.04 m, respectively.

[0015] Preferably, the length of the conical expansion pipe L o and export radius r o Adjust the value as needed; export length L o It is 0.04 to 0.08 times the length of the aircraft, and the exit radius is larger than the radius of the ionization acceleration section cylinder, with a value range of 1.5 to 2.5 times the radius of the ionization acceleration section cylinder.

[0016] Preferably, for an aircraft with a characteristic length of 2 m and a characteristic radius of 0.75 m, the length and outlet radius of the conical expansion pipe are 0.1 m and 0.08 m, respectively.

[0017] Preferably, the inner surface of the air intake is smoothed to ensure that the momentum / energy adaptability coefficient is not higher than 0.5, thus obtaining the air intake of the upper atmosphere-breathing electric propulsion system.

[0018] Advantages of this invention compared to existing technologies: (1) The current propulsion system air intake design mainly involves the aviation flight area (0 km~20 km) and near space (20 km~100 km), while the upper atmosphere is an almost undeveloped airspace, and there is no propulsion system air intake design technology for this airspace.

[0019] (2) This invention designs the air intake geometry and surface materials, proposing an air intake design scheme for an upper atmospheric air-breathing electric propulsion system. Geometrically, it adopts a four-section scheme consisting of an inlet section, a compression section, an ionization acceleration section, and an outlet section. Surface material processing technology is employed. This design scheme provides an air intake with a high compression ratio and high collection efficiency for the air-breathing electric propulsion system, effectively improving the overall performance of the system. It is an ideal method for designing air intakes for upper atmospheric spacecraft air-breathing electric propulsion systems. Attached Figure Description Figure 1 : Schematic diagram of the design scheme of this invention; Figure 2 Schematic diagram of a simple conical converging air intake; Figure 3 Schematic diagram of a traditional concave air intake in the aviation field; Figure 4Comparison of the compression ratios of the simple conical contraction type, the traditional concave contraction type, and the intake duct of this invention; Figure 5 Comparison of the mass flux of the intake duct of the simple conical contraction type, the traditional concave contraction type and the present invention. Detailed Implementation

[0020] This invention, based on the flow characteristics of free or near-free molecular flow in the upper atmosphere, proposes an inlet design scheme for an upper atmospheric air-breathing electric propulsion system by simultaneously designing the inlet geometry and surface materials. The design principle is as follows: Based on the flow characteristics of free or near-free molecular flow in the upper atmosphere, and considering the strong viscosity effect and lack of shock wave structure in such flows, a concave, contracting pipe is used to facilitate gas compression. Furthermore, considering that collisions between gases are negligible in such flows, while collisions between gas and the inlet surface are dominant, the smoothing of the inlet surface reduces the momentum / energy adaptation coefficient in the gas-solid interaction process, making it closer to specular reflection. This facilitates the entry of collected gas into the ionization section, thereby improving the gas collection efficiency of the inlet. Thus, without affecting the basic aerodynamic drag performance, the design of both the inlet geometry and surface materials achieves a high gas compression ratio and high gas collection efficiency.

[0021] Example: The air intake consists of an inlet section, a compression section, an ionization acceleration section, and an outlet section.

[0022] The inlet section is a cylindrical pipe, the length of which is ( L i ) and radius ( r i The values ​​can be adjusted according to the size of the aircraft: the inlet section length cannot exceed the length of the aircraft, and the value range is 0.05 to 0.15 times the length of the aircraft; the inlet section radius is slightly smaller than the radius of the aircraft, and the value range is 0.7 to 0.9 times the radius of the aircraft. For an aircraft with a characteristic length of 2 m and a characteristic radius of 0.75 m, the typical values ​​for the length and radius of the cylindrical inlet pipe are 0.2 m and 0.55 m, respectively.

[0023] The compression section is a contraction pipe, and its length is ( L c The radius of the arc is less than half the length of the aircraft, ranging from 0.4 to 0.5 times the length of the aircraft. The left end is tangent to the entrance section, and its outline is a concave arc with a radius of ( ). r cThe corresponding central angle needs to be within the range of 30° to 60°, and its value range is 0.4 to 1 times the length of the aircraft. For an aircraft with a characteristic length of 2 m and a characteristic radius of 0.75 m, the typical value for the length of the contraction tube is 0.83 m, and the typical value for the radius of the contour arc is 1.02 m.

[0024] The ionization acceleration section consists of a constricting conduit and a cylindrical conduit. The constricting conduit has an outwardly concave arc profile, and the cylinder has a radius of (…). r t The value is determined based on the compression requirements of the air intake. A higher compression ratio results in a smaller cylinder radius, and vice versa. The value ranges from 0.05 to 0.4 times the aircraft radius. The contraction duct needs to ensure that both ends of the arc are tangent to the cylinders of the compression and ionization acceleration sections. Its contour arc radius (…) r e The radius of the compression section and the cylindrical shape of the ionization acceleration section are uniquely determined by the radius of the compression section and the cylindrical shape of the ionization acceleration section. For an aircraft with a characteristic length of 2 m and a characteristic radius of 0.75 m, the typical values ​​for the radius of the arc of the contraction duct profile and the radius of the cylindrical duct are 0.189775 m and 0.04 m, respectively.

[0025] The outlet section is a conical expansion pipe, the length of which is ( L o ) and export radius ( r o The values ​​can be adjusted as needed: export length ( L o The length of the conical expansion duct is 0.04 to 0.08 times the length of the aircraft, and the outlet radius is larger than the radius of the ionization acceleration section cylinder, ranging from 1.5 to 2.5 times the radius of the ionization acceleration section cylinder. For an aircraft with a characteristic length of 2 m and a characteristic radius of 0.75 m, the length and outlet radius of the conical expansion duct are 0.1 m and 0.08 m, respectively.

[0026] The inner surface of the air intake is smoothed to reduce the momentum / energy adaptation coefficient of the gas interaction with the inner surface, ensuring that the momentum / energy adaptation coefficient is not higher than 0.5. This process ultimately yields the air intake for the upper atmosphere-breathing electric propulsion system.

[0027] Specific design examples are as follows: Taking a cylindrical spacecraft with a length of 2 m and a radius of 0.75 m as an example, a specific design example of an air intake design scheme for an air-breathing electric propulsion system in the upper atmosphere is given: (1) Length of cylindrical pipe at the inlet section L i = 0.2 m, radius r i = 0.55 m; (2) Radius of the concave arc of the compression section shrinkage pipe profiler c =1.02 m; (3) Radius of the concave arc of the ionization acceleration section constriction pipe profile r e =0.189775 m, cylinder radius r t =0.04 m; (4) Outlet section conical expansion pipe L o = 0.1 m and exit radius r o = 0.08 m; (5) After the inner surface of the intake duct is smoothed, the momentum / energy adaptation coefficient of the gas interacting with the surface is 0.08 m; σ = 0.5.

[0028] For upper atmosphere-breathing electric propulsion systems, the performance of the air intake is mainly measured by its gas compression performance and gas collection performance. Gas compression performance is measured by the gas compression ratio. η press Characterized by, defined as, the gas pressure in the ionization section. p chamber With the inlet gas pressure p ∞ The ratio, i.e.

[0029] Gas collection performance is measured by the gas mass flow rate in the ionization section. It is used to characterize and is defined as the mass of gas entering the ionization section per unit time.

[0030] To evaluate this intake design, two other conventional intake configurations are considered: one is a simple conical converging duct configuration (see...). Figure 2 Another type is the traditional concave contraction tube in the aviation field (see...). Figure 3 By comparing the gas compression ratio and gas collection efficiency of the two conventional air intakes mentioned above and the air intake using the present invention, the performance of the air intake of this design is quantitatively evaluated. The incoming flow conditions were taken from standard atmosphere at an altitude of 180 km, with a nitrogen molecule volume fraction of 0.4829, an oxygen atom volume fraction of 0.4820, and an oxygen molecule volume fraction of 0.0351. Specific parameters are shown in Table 1.

[0031] Table 1. Inflow conditions for the inlet evaluation example of an air-breathing electric propulsion system.

[0032] Figure 4The ratio of inlet pressure to incoming flow pressure in the ionization acceleration section is distributed along the radial direction. The results are compared between a simple conical contraction configuration, a traditional concave contraction configuration, and the intake of this invention. The horizontal axis in the figure represents the radius of the ionization acceleration section. r t Dimensionlessness has been achieved. Clearly, the compression ratios of simple conical contraction and traditional concave contraction intake configurations are around 100, while the compression ratio of the intake designed using this invention can reach approximately 1000, indicating that this invention improves the compression performance of the intake by about 10 times.

[0033] Figure 5 The figure shows the distribution of gas mass flux (i.e., the gas mass passing through a unit area per unit time) at the inlet of the ionization acceleration section along the radial direction. A comparison was made between the results of a simple conical contraction configuration, a traditional concave contraction configuration, and the inlet of this invention. The vertical axis in the figure is dimensionless, using the incoming flow mass flux. It can be seen that, overall, the gas mass flux of the inlet of this invention is more than twice that of the incoming flow mass flux, while the gas mass flux of the simple conical contraction configuration and the traditional concave contraction configuration inlets is lower than the incoming flow mass flux. This indicates that the present invention can improve the gas collection performance of the inlet.

[0034] Table 2 provides a quantitative comparison of the compression and collection performance of the simple conical contraction configuration, the traditional concave contraction configuration, and the inlet duct of the present invention. Clearly, compared to the conical contraction configuration and the traditional concave contraction configuration inlet duct, the inlet duct of the present invention increases the compression ratio by approximately 9 times and the gas collection performance by approximately 3 times.

[0035] Table 2 Performance evaluation of the air intake scheme of the present invention

[0036] Based on the comparison of the above gas compression and collection performance, the following conclusions can be drawn: This invention can not only improve the gas compression performance of the air intake, but also improve the gas collection performance of the air intake, effectively improving the overall performance of the air intake, thereby improving the propulsion performance of the upper atmosphere spacecraft's air-breathing electric propulsion system, and further promoting the development and utilization of the upper atmosphere airspace.

[0037] The undisclosed technologies in this invention are common knowledge to those skilled in the art.

Claims

1. An air intake for an upper atmosphere-breathing electric propulsion system, characterized in that... It consists of an inlet section, a compression section, an ionization acceleration section, and an outlet section. The inlet section is a cylindrical pipe, and the compression section is a constricting pipe with an inwardly concave arc profile, the left end of which is tangent to the inlet section. The ionization acceleration section includes a constricting pipe section and a cylindrical pipe section. The constricting pipe has an outwardly concave arc profile, the two ends of which are tangent to the right end of the compression section and the cylinder of the ionization acceleration section. The outlet section is a conical expansion pipe. The inner surface of the inlet is smoothed to reduce the momentum / energy adaptation coefficient of the gas interaction with the inner surface. The upper atmosphere ranges from 120 km to 300 km, and the mean free path of the incoming molecules ranges from 3.3 m to 2595 m; the length of the cylindrical inlet pipe... L i and radius r i The values ​​are adjusted according to the size of the aircraft; the length of the inlet section cannot exceed the length of the aircraft; the radius of the inlet section is 0.7 to 0.9 times the radius of the aircraft; the length of the compression section... L c Less than half the length of the aircraft, the radius of the arc of the compressed section r c It is necessary to ensure that the corresponding central angle range is 30°~60°. r c The value ranges from 0.4 to 1 times the length of the spacecraft; the cylinder radius of the ionization acceleration section. r t The value is determined based on the compression requirements of the air intake; a higher compression ratio results in a smaller cylinder radius, and vice versa. The value range is 0.05 to 0.4 times the aircraft radius. The length of the conical expansion duct... L o and export radius r o Adjust the value as needed; export length L o The length of the air intake is 0.04 to 0.08 times that of the aircraft, and the exit radius is larger than the cylindrical radius of the ionization acceleration section. The inner surface of the air intake is smoothed to ensure that the momentum / energy adaptability coefficient is not higher than 0.

5.

2. The air intake of an upper atmosphere-breathing electric propulsion system according to claim 1, characterized in that: The length of the inlet section ranges from 0.05 to 0.15 times the length of the aircraft.

3. The air intake of an upper atmosphere-breathing electric propulsion system according to claim 1, characterized in that: For an aircraft with a characteristic length of 2 m and a characteristic radius of 0.75 m, the length and radius of the cylindrical inlet pipe are 0.2 m and 0.55 m, respectively.

4. The air intake of an upper atmosphere-breathing electric propulsion system according to claim 1, characterized in that: The length of the compressed section L c The value ranges from 0.4 to 0.5 times the length of the aircraft.

5. The air intake of an upper atmosphere-breathing electric propulsion system according to claim 1, characterized in that: For an aircraft with a characteristic length of 2 m and a characteristic radius of 0.75 m, the radius of the arc of the converging duct profile is 1.02 m.

6. The air intake of an upper atmosphere-breathing electric propulsion system according to claim 1, characterized in that: For an aircraft with a characteristic length of 2 m and a characteristic radius of 0.75 m, the values ​​of the radius of the constriction pipe profile arc and the radius of the cylindrical pipe are 0.189775 m and 0.04 m, respectively.

7. The air intake of an upper atmosphere-breathing electric propulsion system according to claim 1, characterized in that: The range of the exit radius is 1.5 to 2.5 times the radius of the cylinder in the ionization acceleration section.

8. The air intake of an upper atmosphere-breathing electric propulsion system according to claim 1, characterized in that: For an aircraft with a characteristic length of 2 m and a characteristic radius of 0.75 m, the length and outlet radius of the conical expansion pipe are 0.1 m and 0.08 m, respectively.

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