A non-uniformly opened expansion section structure of a permeable nozzle

Abstract

The present invention discloses a non-uniformly distributed expansion section structure for a permeable nozzle. The expansion section structure can be divided into four sections based on the density of the openings on the wall. The section closest to the nozzle throat is a conventional expansion section with no openings. The remaining three sections, starting from the nozzle throat, are arranged in descending order of opening density: a sparsely distributed hole wall surface, a moderately distributed hole wall surface, and a densely distributed hole wall surface. The porosity decreases closer to the nozzle throat and increases closer to the nozzle outlet. After the present invention uses a non-uniformly distributed expansion section structure, the gas leakage rate of the permeable nozzle is effectively reduced under high-altitude flight conditions, thereby improving high-altitude performance; at the same time, it does not affect the permeable nozzle's good thrust compensation capability under low-altitude flight conditions.

Description

Technical Field

[0001] The invention belongs to the field of aerospace technology, and in particular relates to a non-uniform opening expansion section structure of a permeable nozzle. Background Art

[0002] For large, high-orbit vehicles, the use of fixed, high-expansion-ratio nozzles can lead to severe non-fitness losses due to the dramatic changes in nozzle pressure ratio. Currently, this problem is primarily addressed by designing nozzles with altitude compensation capabilities, such as double-bell nozzles, plug nozzles, expansion-deflection nozzles, and extended nozzles. While these nozzles provide altitude compensation capabilities to a certain extent, they suffer from disadvantages such as profile discontinuity, low reliability, complex structure, and the need for mechanical devices. The permeable altitude-compensating nozzle (permeable nozzle) has a profile consistent with that of a conventional nozzle and offers advantages such as profile continuity, high reliability, simple structure, no need for mechanical devices, and continuous compensation. The base section of the permeable nozzle shares the same structure as a conventional nozzle, while the permeable section utilizes a porous plate material or structure. An inherent drawback of the permeable nozzle is its poor high-altitude performance, due to the inevitable gas leakage at high altitudes, resulting in a reduction in thrust. For permeable nozzles using a porous plate structure, one way to solve their poor high-altitude performance is to increase the resistance coefficient of the permeable section (i.e., reduce the porosity of the openings and the diameter of the pores). However, the increase in the resistance coefficient will reduce the low-altitude compensation effect of the permeable nozzle. It is known that the pressure of the gas will become lower and lower after the accelerated expansion through the nozzle, so the pressure in the nozzle will become lower and lower along the axial direction, from the throat to the outlet. In order to improve the high-altitude performance of the permeable nozzle without affecting its low-altitude compensation capability, the present invention provides a non-uniformly distributed expansion section structure for the permeable nozzle. The permeable nozzle using this expansion section structure is called a non-uniformly distributed permeable nozzle. The non-uniform openings of the nozzle can make the resistance coefficient of the permeable section smaller and smaller from the throat to the outlet, and the degree of airflow penetration from difficult to easy. Summary of the Invention

[0003] The object of the present invention is to provide a non-uniform opening expansion section structure of a permeable nozzle, which solves the problem of thrust loss of the permeable nozzle when working at high altitude.

[0004] The purpose of the present invention is achieved through the following technical solutions:

[0005] The non-uniform pore expansion section of the permeable nozzle is divided into four sections based on the density of pores on the expansion section. The section closest to the nozzle throat is a traditional expansion section with no pores. The remaining three sections, starting from the nozzle throat, are arranged in descending order of pore density: sparsely distributed pore wall, moderately distributed pore wall, and densely distributed pore wall. As the flight altitude increases, the operating state of the non-uniform permeable nozzle changes between the following three states:

[0006] State 1: When the nozzle flies below the designed flight altitude, the back pressure is very high. The external airflow enters the nozzle through the non-uniformly distributed expansion section structure, avoiding gas backflow and suppressing the shock wave intensity, thereby improving the low-altitude performance of the nozzle.

[0007] State 2: When the nozzle is at the designed flight altitude, the nozzle outlet pressure is close to the ambient pressure, and the nozzle inner wall pressure is slightly higher than the ambient pressure. The non-uniformly distributed expansion section structure can reduce the leakage of the nozzle airflow. At this time, the performance of the permeable nozzle is close to that of the traditional nozzle.

[0008] State 3: When the nozzle flies above the designed flight altitude, the external atmospheric pressure is low. Since the pressure on the inner wall of the nozzle expansion section gradually decreases from the throat to the outlet, the pressure difference between the inside and outside of the expansion section also gradually decreases from the throat to the outlet. Some gas leaks from the permeable nozzle, and the performance is slightly lower than that of the traditional nozzle. However, compared with the uniformly distributed permeable nozzle, the performance loss is reduced.

[0009] The present invention may also include:

[0010] 1. The porosity of the non-uniform opening expansion section structure decreases as it approaches the nozzle throat, and increases as it approaches the nozzle outlet.

[0011] 2. When the permeable nozzle is working at low altitude, the nozzle is in an over-expanded state, and the external airflow penetrates into the nozzle through the small holes in the nozzle expansion section, preventing the generation of backflow and suppressing the shock wave intensity, thereby improving the low-altitude performance of the nozzle.

[0012] 3. When the permeable nozzle is working at high altitude, the nozzle is in an underexpanded state, the pressure inside the nozzle is higher than the external atmospheric pressure, and a small amount of gas inside the permeable nozzle flows out of the nozzle from the expansion section.

[0013] The beneficial effects of the present invention are:

[0014] Compared with the permeable nozzle with uniform openings in the traditional expansion section, the permeable nozzle has a reduced degree of thrust loss at high altitude. For a nozzle with a large expansion ratio, when the nozzle is in low-altitude flight conditions, the internal and external pressure difference of the expansion section wall is much greater than the internal and external pressure difference when the nozzle is in high-altitude flight conditions. Therefore, under low-altitude flight conditions, the effect of the drag coefficient on the permeability of the airflow in the nozzle expansion section is smaller than the effect of the drag coefficient on the permeability of the airflow in the nozzle expansion section under high-altitude flight conditions. The non-uniformly distributed expansion section structure described in the present invention can make the expansion section of the permeable nozzle have small holes that are unevenly distributed from sparse to dense. The closer to the nozzle throat, the smaller the opening density and the lower the porosity, and the closer to the nozzle outlet, the larger the opening density and the higher the porosity. When the uniformly distributed permeable nozzle is working at high altitude, the leakage is most serious at the starting point of the permeable section, and the leakage is least serious near the nozzle outlet. After using the non-uniformly distributed expansion section structure, under high-altitude flight conditions, the sparsely distributed hole wall has a large internal and external pressure difference and a small porosity structure, which can reduce the leakage of gas, thereby improving the high-altitude performance of the nozzle; under low-altitude flight conditions, the internal and external pressure difference of the permeable nozzle expansion section is large, so the nozzle has better thrust compensation capability at low-altitude flight altitudes. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is a schematic diagram of the structure of the non-uniformly distributed expansion section;

[0016] Figure 2 This is the arrangement diagram of small holes in the non-uniformly distributed expansion section structure;

[0017] Figure 3 Comparison of the flow structures of the non-uniformly distributed permeable nozzle (top) and the conventional nozzle (bottom) under low-altitude conditions;

[0018] Figure 4 Comparison of the flow structures of a non-uniformly distributed permeable nozzle (top) and a traditional nozzle (bottom) under high-altitude conditions. DETAILED DESCRIPTION

[0019] The present invention will be further described below with reference to the accompanying drawings.

[0020] Figure 1 The nozzle expansion section can be divided into four sections according to the density of openings on the wall. The section closest to the throat is the traditional expansion section with no openings on the wall. The openings are arranged from sparse to dense as follows: sparsely distributed hole wall surface 1, medium distributed hole wall surface 2 and densely distributed hole wall surface 3. The porosity decreases as it is closer to the nozzle throat, and the porosity increases as it is closer to the nozzle outlet.

[0021] Figure 2 The specific distribution of the small holes in the non-uniformly distributed expansion section structure.

[0022] Figure 3Comparison diagram of the flow structure of a non-uniformly distributed permeable nozzle (top) and a conventional nozzle (bottom) at low altitude. The upper part shows the internal flow structure of the non-uniformly distributed permeable nozzle operating at low altitude. At this time, the nozzle is in an overexpanded state. The external airflow enters the nozzle through the small holes in the nozzle expansion section, effectively preventing backflow and suppressing shock wave intensity, thereby improving the nozzle's low-altitude performance. The lower part shows the internal flow structure of the conventional nozzle operating at low altitude. Because the external atmospheric pressure is much greater than the nozzle outlet pressure, backflow occurs at the nozzle outlet section and the flow separation point. At the flow separation point, an oblique shock wave compresses the internal nozzle flow, causing the nozzle flow to be severely overexpanded, resulting in a significant loss of nozzle thrust performance. For the non-uniformly distributed permeable nozzle, the profile structure includes the nozzle inner wall surface 10 and the non-uniformly distributed expansion section structure 11. The flow structure includes the nozzle internal shock wave 4, the separation shock wave 5, the supersonic jet 6, and the external airflow entering the nozzle 7. For a conventional nozzle, the profile structure is only the nozzle inner wall surface 10 , and the conventional nozzle flow structure includes a Mach disk 8 , a shock wave 4 in the nozzle, a supersonic jet 6 , a separation shock wave 5 , and a backflow 9 , and the profile structure is only the nozzle inner wall surface 10 .

[0023] Figure 4 This figure compares the flow structures of a non-uniformly distributed permeable nozzle (top) and a conventional nozzle (bottom) at high altitude. The nozzle is in an underexpanded state, with the pressure inside the nozzle higher than the external atmospheric pressure. The gas in the non-uniformly distributed permeable nozzle flows out of the nozzle from the permeable section, with a weak compression wave at the starting point of the permeable section. For a non-uniformly distributed permeable nozzle, the profile structure includes the nozzle inner wall 10 and the non-uniformly distributed expansion section structure 11. The flow structure includes a shock wave 4 within the nozzle, a shock wave 12 at the starting point of the permeable section, and the internal gas flowing out of the nozzle 13. For a conventional nozzle, the profile structure only includes the nozzle inner wall 10. The flow state in the nozzle in the underexpanded state is simple, with only the internal shock wave 4.

[0024] As the flight altitude increases, the operating state of the non-uniformly distributed permeable nozzle changes between the following three states:

[0025] (1) When the nozzle flies below its designed flight altitude, the back pressure is very high. The external airflow enters the nozzle through the non-uniformly distributed expansion section structure, which prevents gas backflow and suppresses the shock wave intensity, thereby improving the low-altitude performance of the nozzle.

[0026] (2) When the nozzle is at the designed flight altitude, the nozzle outlet pressure is close to the ambient pressure, and the nozzle inner wall pressure is slightly higher than the ambient pressure. The non-uniformly distributed expansion section structure can reduce the leakage of the nozzle airflow. At this time, the performance of the permeable nozzle is close to that of the traditional nozzle.

[0027] (3) When the nozzle flies above the designed flight altitude, the external atmospheric pressure is low. Since the pressure on the inner wall of the nozzle expansion section gradually decreases from the throat to the outlet, the pressure difference between the inside and outside of the expansion section also gradually decreases from the throat to the outlet. Some gas leaks from the permeable nozzle, and its performance is slightly lower than that of the traditional nozzle. However, compared with the uniformly distributed permeable nozzle, the performance loss is reduced.

[0028] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A non-uniformly permeable expansion section structure of a nozzle, characterized by: The wall surface of the non-uniformly distributed expansion section structure (14) is divided into four sections according to the density of openings. The section closest to the nozzle throat is a conventional expansion section wall surface without openings. The other three sections are arranged from the nozzle throat in descending order of opening density: a sparsely distributed hole wall surface (1), a moderately distributed hole wall surface (2), and a densely distributed hole wall surface (3). As the flight altitude increases, the working state of the non-uniformly distributed permeable nozzle changes between the following three states: State 1: When the nozzle flies below the designed flight altitude, the back pressure is very high. The external airflow enters the nozzle through the non-uniformly distributed expansion section structure, avoiding gas backflow and suppressing the shock wave intensity, thereby improving the low-altitude performance of the nozzle. State 2: When the nozzle is at the designed flight altitude, the nozzle outlet pressure is close to the ambient pressure, and the nozzle inner wall pressure is slightly higher than the ambient pressure. The non-uniformly distributed expansion section structure can reduce the leakage of the nozzle airflow. At this time, the performance of the permeable nozzle is close to that of the traditional nozzle. State 3: When the nozzle flies above the designed flight altitude, the external atmospheric pressure is low. Since the pressure on the inner wall of the nozzle expansion section gradually decreases from the throat to the outlet, the pressure difference between the inside and outside of the expansion section also gradually decreases from the throat to the outlet. Some gas leaks from the permeable nozzle, and the performance is slightly lower than that of the traditional nozzle. However, compared with the uniformly distributed permeable nozzle, the performance loss is reduced.

2. The non-uniformly permeable expansion section structure of a permeable nozzle according to claim 1, characterized in that: The porosity of the expansion section structure decreases as it approaches the nozzle throat, and increases as it approaches the nozzle outlet.

3. The non-uniformly permeable expansion section structure of a permeable nozzle according to claim 1, characterized in that: When the permeable nozzle is working at low altitude, the nozzle is in an over-expanded state, and the external airflow penetrates into the nozzle through the small holes in the nozzle expansion section, preventing backflow and suppressing the shock wave intensity, thereby improving the low-altitude performance of the nozzle.

4. The non-uniformly permeable expansion section structure of a permeable nozzle according to claim 1, characterized in that: When the permeable nozzle is working at high altitude, the nozzle is in an underexpanded state, the pressure inside the nozzle is higher than the external atmospheric pressure, and a small amount of combustion gas in the permeable nozzle flows out of the nozzle from the expansion section.

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