Axisymmetric bending knock engine design method

Abstract

The design method for axisymmetric bending detonation engines, applicable to hypersonic detonation engines for aircraft, includes the following steps: 1) Selecting and modifying the von Kármán curve as the generatrix, rotating it around the axis of symmetry to generate an axisymmetric forebody; 2) Determining the inlet location and shape; 3) Shifting the inlet shape backward by a suitable distance to form the inlet section of the inlet; 4) Designing an S-shaped bend that facilitates fuel mixing and gas compression, and installing a fuel spraying device behind it; 5) Reverse designing the wall surface that generates the bending detonation wave; 6) Designing the engine exhaust nozzle; 7) Selecting and arranging multiple engine channels; 8) Designing the inlet casing and connecting plates, and other related components to complete the overall engine design. The design method is simple and easy to implement, and can significantly improve the performance of detonation engines by enhancing the boundary layer displacement effect and fuel mixing efficiency. The flexible selection of the number of channels can meet different thrust requirements, giving it great potential for engineering applications.

Description

Technical Field

[0001] This invention relates to the field of hypersonic detonation engines for aircraft, and in particular to a design method for an axisymmetric bending detonation engine. Background Technology

[0002] Compared to the traditional mixing and combustion mode, detonation combustion has the advantages of rapid heat release and significant pressurization effect, and is therefore considered the ideal combustion method for air-breathing hypersonic vehicles.

[0003] Knock engines mainly include pulse knock engines, supersonic pulse knock ramjet engines, rotary knock engines, and oblique / bending knock engines. The working principle of an oblique / bending knock engine is as follows: fuel is injected in advance into the engine's forebody or intake, allowing it to mix thoroughly with air before entering the combustion chamber. Induced by the walls, a detonation wave is formed stationary in the hypersonic airflow, achieving detonation combustion. After combustion, the airflow expands through the nozzle to generate thrust.

[0004] Because the oblique / bent detonation wave can remain stationary inside the combustion chamber without interruption, theoretically, continuous thrust can be generated as long as a supersonic premixed airflow is continuously provided. This characteristic makes oblique / bent detonation engines based on detonation combustion a hot topic in current scientific research and engineering applications.

[0005] However, during flight, conventional slant / bend detonation engines often suffer from poor performance parameters or even fail to ignite successfully due to problems such as excessively high combustion chamber back pressure, excessive low-energy flow, and insufficient fuel mixing. Therefore, how to effectively organize the rapid ignition and achieve efficient combustion of slant / bend detonation engines has become a key research direction for detonation engines.

[0006] Domestic and international scholars have conducted extensive research on the performance issues of inclined / bending detonation engines, primarily focusing on exploring the influence of incoming flow parameters and combustion chamber geometry on the detonation mechanism. Detailed analyses have been performed on the mechanisms and patterns of influences such as the effects of unsteady and non-uniform incoming flow, temperature disturbances, wedge angle, abrupt changes in incoming flow angle, and the tilt angle of the wedge-shaped rear wall. In addition, in order to improve the impact of the above problems on engine detonation, in recent years scholars have proposed measures such as changing the traditional wedge configuration to achieve detonation control. For example, using symmetrical wall-induced shock waves with opposite-side intersection to promote detonation (Zhang Y, Xiang G, Jia YU, et al. Accelerated initiation of oblique detonation induced by disturbance in detonative zone[J]. Chinese Journal of Aeronautics, 2023, 36(11): 153-164); and setting bulges on the wedge surface (Han Xin, Zhang Wenshuo, Zhang Zijian, et al. Numerical study on oblique detonation shock waves induced by bulges[J. Propulsion Technology, 2022, 43(05):190-201) and double wedge configuration (Honghui T, Zhang Y, Pengfei Y, et al. Oblique detonation wave triggered by a double wedge in hypersonic flow[J]. Chinese Journal of Aeronautics, 2022, 35(4): 176-184.) to achieve accelerated detonation; in addition, some scholars have proposed a method of detonation induced by bending shock wave, which improves the performance of the engine to a certain extent (Xiong Haochen, Qiu Ruofan, Han Xin, et al. A new detonation method of detonation induced by bending shock wave [J / OL]. Acta Aeronautica Sinica, 1-13 [2024-09-10]. http: / / kns.cnki.net / kcms / detail / 11.1929.V.20231201.1613.012.html.).

[0007] While significant progress has been made in the research of rapid and successful initiation and efficient combustion of inclined / bent detonation engines, it can be observed that this research mainly focuses on proposing special inclined wedge configurations, lacking research on the overall engine layout and design schemes of other parts within the air intake. Current research indicates that factors hindering successful initiation and efficient combustion of detonation engines include insufficient fuel mixing and excessive low-energy flow caused by the boundary layer. Furthermore, practical engineering applications often require the combination of multiple inclined / bent detonation engines to provide greater thrust. Therefore, there is an urgent need to propose new schemes for the overall layout and air intake configuration design of multiple detonation engine combinations.

[0008] The purpose of this invention is to address the aforementioned technical problems in the prior art by providing an axisymmetric bending knock engine design method. Through innovative engine structural design, the method improves fuel mixing efficiency and engine resistance to back pressure, thereby enhancing the engine's specific impulse and overall performance.

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

[0010] This invention provides a design method for an axisymmetric bending knock engine, comprising the following steps:

[0011] 1) Select and modify the von Kármán curve as the generatrix: Based on the design point conditions and volume ratio requirements, select a suitable von Kármán curve as the generatrix and modify it appropriately to ensure that the shock wave of the leading edge of the forebody fits tightly against the body to reduce energy loss; rotate the modified generatrix around the axis of symmetry to generate an axisymmetric forebody.

[0012] 2) Determine the location and shape of the intake duct: Based on the axisymmetric forebody shape generated in step 1) and the design conditions, determine the location and shape of the intake duct to ensure shock wave sealing under design conditions, so as to effectively capture and compress the incoming airflow.

[0013] 3) Forming the inlet section of the air intake: Based on the requirements such as the back pressure resistance of the air intake, the shape of the inlet is shifted back a suitable distance to form the inlet section of the air intake; ensure that the inlet section can smoothly transition and guide the incoming airflow into the air intake;

[0014] 4) Design S-shaped bend and fuel spraying device: Based on the engine design dimensions and gas compression requirements, design an S-shaped bend that facilitates fuel mixing and further gas compression, and install a fuel spraying device at an appropriate position after the S-shaped bend to ensure uniform fuel distribution.

[0015] 5) Reverse design to generate the wall shape of the bending detonation wave: Using the bending shock wave theory and the bending characteristic line method, the wall shape of the bending detonation wave is reverse designed to optimize the propagation path and energy release efficiency of the detonation wave.

[0016] 6) Engine nozzle design: Based on performance requirements such as thrust, the engine nozzle is designed using the characteristic line method to ensure efficient conversion of the energy generated by knock into thrust;

[0017] 7) Select and arrange multiple engine channels: Calculate the thrust and other performance of a single channel in the above design through theoretical estimation or numerical simulation, select an appropriate number of channels, and arrange these channels evenly on the axisymmetric forebody;

[0018] 8) Design the air intake manifold cover and connecting plate: Based on the requirements of aerodynamic performance and geometric dimensions, design the air intake manifold cover and connecting plate to complete the design of the axisymmetric bending knock engine.

[0019] In step 1), a suitable von Kármán curve is selected as the generatrix based on the design point conditions and volume ratio requirements, and it is appropriately modified to ensure that the shock wave of the leading edge of the forebody fits tightly against the body to reduce energy loss; the modified generatrix is ​​rotated around the axis of symmetry to generate an axisymmetric forebody.

[0020] 1.1) Collect design point conditions, including flight speed, altitude, thrust requirements, and design requirements such as volume ratio, and select a suitable curve from the standard von Kármán curve library as the initial generatrix;

[0021] 1.2) Analyze the adhesion between the shock wave and the organism at the leading edge of the precursor, and verify the tightness of the shock wave adhesion to the organism through numerical simulation or experimental data;

[0022] 1.3) Based on the analysis results, the von Kármán curve is appropriately modified, such as by adjusting the curvature and length of the curve, to ensure that the shock wave can closely fit the body and reduce energy loss.

[0023] 1.4) Rotate the modified generatrix around the axis of symmetry for one revolution to generate a three-dimensional model of the axisymmetric precursor.

[0024] In step 2), the specific steps for determining the location and shape of the air intake can be as follows:

[0025] 2.1) Based on the shape of the axisymmetric precursor generated in step 1) and the design conditions, the position of the intake inlet is initially determined.

[0026] 2.2) Verify the influence of different inlet shapes on the shock wave sealing effect through numerical simulation or experimental data.

[0027] 2.3) Based on the verification results, optimize the inlet shape to ensure shock wave sealing under design conditions, effectively capturing and compressing incoming airflow.

[0028] In step 4), the specific steps for designing the S-shaped curve and fuel spraying device can be as follows:

[0029] 4.1) Based on the engine design dimensions and gas compression requirements, design an S-shaped curve that facilitates fuel mixing and further gas compression.

[0030] 4.2) Verify the effect of S-shaped bends on gas flow and fuel mixing through numerical simulation or experimental data.

[0031] 4.3) Install a fuel spraying device at an appropriate position after the S-curve to ensure that the fuel is evenly distributed.

[0032] 4.4) Adjust and optimize the spraying device to ensure that the fuel spraying volume matches the gas flow rate.

[0033] In step 7), multiple engine channels are selected and arranged. The number of channels is selected according to parameters such as the total thrust required by the design. The number of channels of the axisymmetric bending detonation engine is appropriately increased or decreased according to the thrust performance requirements to meet the actual needs of the project. These multiple engines are evenly arranged on the axisymmetric forebody, and the gaps reserved between each channel can effectively displace the boundary layer.

[0034] Compared with the prior art, the beneficial effects achieved by the technical solution of this invention are:

[0035] This design method is simple and easy to implement, and improves engine performance in several aspects. First, by adopting an axisymmetric forebody configuration, a lateral pressure gradient pointing to both sides of the intake is formed at the intersection of each intake and the forebody, thereby promoting the lateral displacement of the boundary layer within the intake. Furthermore, sufficiently large venting channels are provided between adjacent intakes to ensure ample space for displacement and avoid mutual interference between intakes. Therefore, this design method significantly enhances the boundary layer displacement effect within the intake. In addition, the S-bend configuration increases the mixing distance between fuel and airflow, and the change in flow direction promotes more thorough mixing of airflow and fuel, achieving more efficient mixing within a limited space. Simultaneously, the S-bend design allows for a smoother transition of the intake to the wall surface that generates the bending detonation wave, thereby reducing the occurrence of complex flows within the intake and isolation sections. Finally, the axisymmetric arrangement provides greater flexibility in selecting the number of engine channels, allowing for the selection of an appropriate number of channels based on different thrust requirements. These advantages result in an engine with higher specific impulse and a compact structure. This gives it great potential for engineering applications. Attached Figure Description

[0036] Figure 1This is a schematic diagram of the axisymmetric bending detonation engine forebody rotation generatrix design method described in this invention. The dashed line OA represents the original curve before correction, and the solid line O'A represents the curve after correction to ensure shock wave attachment. Point A is the intersection of the original and corrected curves.

[0037] Figure 2 This is a cross-sectional view of an axisymmetric bending detonation engine near the plane of symmetry, mainly showing the structure inside the engine's channels.

[0038] Figure 3 This is a front view of an axisymmetric bending detonation engine without the connecting plate installed, mainly showing the drainage channels between the various engine passages.

[0039] Figure 4 The front view of the axisymmetric bending detonation engine with the connecting plate installed mainly shows the configuration and installation position of the connecting plate.

[0040] Figure 5 This is a side view of an axisymmetric bending detonation engine.

[0041] Figure 6 This is a rear view of an axisymmetric bending detonation engine.

[0042] Figure 7 This is a triaxial side view of an axisymmetric bending detonation engine. Detailed Implementation

[0043] To make the technical problem to be solved, the technical solution, and the beneficial effects of this invention clearer and more understandable, the invention will be further described in detail below with reference to the accompanying drawings. It should be noted that, since this invention has an axisymmetric structure, the following description only refers to and explains a portion of the structure; the design method for the same symmetrical parts is similar.

[0044] like Figure 1 As shown, the method for designing the shape of the front body wall 1 mainly includes the following steps:

[0045] 1) Determine the length L of the precursor based on design conditions such as the floor area ratio. cone and bottom diameter length R B .

[0046] 2) Determine the von Kármán curve using the formula below.

[0047]

[0048] 3) In order to ensure the shock wave attaches to the body, the von Kármán curve is modified from point A, and the dashed line AO ​​is modified to AO', thus obtaining the final generatrix of the generating precursor.

[0049] like Figure 2 As shown, the design methods for the intake, transition section, combustion chamber, and nozzle of one channel of an axisymmetric bending knock engine mainly include:

[0050] 1) Determine the position of the intake shoulder point 2 based on the already determined front body dimensions.

[0051] 2) Determine the position of the intake lip 3 based on the incident shock wave position and capture flow rate under the design point condition, so as to ensure that the shock wave can be sealed at the design point and improve the intake efficiency.

[0052] 3) The area of ​​the intake cross-section can be determined according to the design requirements, thereby determining the width-to-height ratio of the intake. Then, according to the engine geometric constraints and engine weight limits, the intake is stretched by a certain distance to optimize the intake performance.

[0053] 4) Based on the given intake pressure ratio and the requirements for back pressure resistance, the S-shaped wall 4 of the transition section is designed using the method of characteristics to further compress the gas and make the fuel mixture more complete.

[0054] 5) Based on geometric constraints and other conditions, install a device 5 after the transition section 4 that can inject fuel forward and backward to ensure that the fuel is evenly distributed in the combustion chamber and improve combustion efficiency.

[0055] 6) Based on the bending shock wave theory, the profile of the bending detonation wave is generated by reverse design. The governing equation of the bending shock wave theory is as follows, where p is the pressure, δ is the flow angle, μ is the Mach angle, ρ is the density, V is the velocity, γ is the specific heat ratio, j is the judgment factor, s is the streamline, l is the characteristic line, P is the derivative of the pressure along the streamline, and D is the derivative of the airflow angle along the streamline.

[0056]

[0057] 7) Design the profile 7 according to the method of characteristics so that it can meet the performance requirements of the nozzle at the design point.

[0058] 8) Design the outer casing 8 for a single channel of the bending knock engine designed above, based on aerodynamic performance and size requirements.

[0059] At this point, the design of a single engine channel for the bending detonation engine is complete. The next step is to design the overall configuration of the bending detonation engine, following these steps:

[0060] 1) Based on theoretical or simulation calculations of the performance of a single channel, performance indicators such as thrust of the single channel can be obtained, and then the total number of channels required can be selected according to the design specifications. Rotate the individual channels around the axis of symmetry 9 so that they are evenly distributed around the front body.

[0061] 2) Based on the relative positions of the various channel covers, a partition 10 is designed to smoothly connect the various engine channel covers, ensuring a smooth transition between them. This arrangement yields the following results: Figure 3 The configuration shown allows for the effective removal of low-kinetic-energy flows such as boundary layers and eddies through the discharge channel 11.

[0062] 3) Based on aerodynamic performance requirements, design a connecting plate 12 that meets aerodynamic performance requirements, so that the baffle 10 can be connected to the front body 1, such as... Figure 4 As shown. This design aims to achieve better aerodynamic performance.

[0063] The final configuration of the axisymmetric bending detonation engine is obtained. A side view of this configuration is shown below. Figure 5 As shown, the model is vertically symmetrical with respect to the axis of symmetry 9, and the connecting plate 12 connects the front body 1 to the baffle 10. (From the rear view of the model) Figure 6 As can be observed, the six engines are evenly arranged around the axis of symmetry 9 to provide the thrust required by the aircraft. Figure 7 The model is shown in a triaxial side view, which fully demonstrates the structure of the axisymmetric bending detonation engine. When the aircraft is in flight, the airflow first passes through the compression section of the forebody 1, then enters the intake along the channel between adjacent baffles, and finally exits along the nozzle profile 7 and the profile 6 that generates the bending detonation wave.

[0064] This design method is simple and easy to implement, and improves engine performance in several aspects. First, the design uses an axisymmetric forebody, creating a lateral pressure gradient pointing to both sides of the intake at the intersection of each intake and the forebody, thus prompting the boundary layer within the intake to move laterally. Furthermore, sufficiently large venting channels are provided between adjacent intakes to ensure adequate space for boundary layer movement, and that the movement between intakes does not interfere with each other. In summary, this design method significantly improves the boundary layer movement effect within the intake.

[0065] Furthermore, the S-bend configuration increases the mixing distance between fuel and airflow, and the change in flow direction allows for more thorough mixing of the two within a limited space, thus improving fuel mixing efficiency. Simultaneously, the S-bend design allows for a smoother transition of the intake duct to the wall surface that generates the bending detonation wave, thereby reducing complex flow patterns within the intake / isolation section. Finally, the axisymmetric arrangement provides greater flexibility in selecting the number of engine channels, allowing for selection based on different thrust requirements. These advantages give this design immense potential for engineering applications.

[0066] The above embodiments are merely preferred embodiments of the present invention and should not be considered as limiting the scope of the present invention. All equivalent variations and improvements made within the scope of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A design method for an axisymmetric bending knock engine, characterized in that... Includes the following steps: 1) Select and modify the von Kármán curve as the generatrix: Based on the design point conditions and volume ratio requirements, select a suitable von Kármán curve as the generatrix and modify it appropriately to ensure that the shock wave of the leading edge of the forebody fits tightly against the body to reduce energy loss; rotate the modified generatrix around the axis of symmetry to generate an axisymmetric forebody. 2) Determine the location and shape of the intake duct: Based on the axisymmetric forebody shape generated in step 1) and the design conditions, determine the location and shape of the intake duct to ensure shock wave sealing under design conditions, so as to effectively capture and compress the incoming airflow. 3) Forming the inlet section of the air intake: Based on the back pressure withstand capacity requirements of the air intake, shift the shape of the inlet back a suitable distance to form the inlet section of the air intake; ensure that the inlet section can smoothly transition and guide the incoming airflow into the air intake; 4) Design S-shaped bend and fuel spraying device: Based on the engine design dimensions and gas compression requirements, design an S-shaped bend that facilitates fuel mixing and further gas compression, and install a fuel spraying device at an appropriate position after the S-shaped bend to ensure uniform fuel distribution. 5) Reverse design to generate the wall shape of the bending detonation wave: Using the bending shock wave theory and the bending characteristic line method, the wall shape of the bending detonation wave is reverse designed to optimize the propagation path and energy release efficiency of the detonation wave. 6) Engine nozzle design: Based on thrust performance requirements, the engine nozzle is designed using the characteristic line method to ensure efficient conversion of the energy generated by knock into thrust; 7) Select and arrange multiple engine channels: Calculate the thrust performance of a single channel in the above design through theoretical estimation or numerical simulation, select an appropriate number of channels, and arrange these channels evenly on the axisymmetric forebody; 8) Design the air intake manifold cover and connecting plate: Based on aerodynamic performance and geometric requirements, design the air intake manifold cover and connecting plate to complete the design of the axisymmetric bending knock engine.

2. The axisymmetric bending detonation engine design method as described in claim 1, characterized in that... In step 1), a suitable von Kármán curve is selected as the generatrix based on the design point conditions and volume ratio requirements, and it is appropriately modified to ensure that the shock wave of the leading edge of the forebody fits tightly against the body to reduce energy loss; the modified generatrix is ​​rotated around the axis of symmetry to generate an axisymmetric forebody. 1.1) Collect design point conditions, including flight speed, altitude, thrust requirements, and volume ratio design requirements, and select a suitable curve from the standard von Kármán curve library as the initial generatrix; 1.2) Analyze the adhesion between the shock wave at the leading edge of the precursor and the organism to verify the tightness of the shock wave's fit with the organism; 1.3) Based on the analysis results, the von Kármán curve was appropriately modified, and the curvature and length parameters of the curve were adjusted to ensure that the shock wave could closely fit the body and reduce energy loss. 1.4) Rotate the modified generatrix around the axis of symmetry for one revolution to generate a three-dimensional model of the axisymmetric precursor.

3. The axisymmetric bending detonation engine design method as described in claim 1, characterized in that... In step 2), the specific steps for determining the location and shape of the air intake are as follows: 2.1) Based on the shape of the axisymmetric precursor generated in step 1) and the design conditions, the position of the intake inlet is initially determined; 2.2) Verify the effect of different inlet shapes on shock wave sealing effect; 2.3) Based on the verification results, optimize the inlet shape to ensure shock wave sealing under design conditions, effectively capturing and compressing incoming airflow.

4. The axisymmetric bending detonation engine design method as described in claim 1, characterized in that... In step 4), the specific steps for designing the S-shaped curve and fuel spraying device are as follows: 4.1) Based on the engine design dimensions and gas compression requirements, design an S-shaped curve that facilitates fuel mixing and further gas compression; 4.2) Verify the effect of the S-shaped bend on gas flow and fuel mixing; 4.3) Install a fuel spraying device at an appropriate position after the S-curve to ensure that the fuel is evenly distributed; 4.4) Adjust and optimize the spraying device to ensure that the fuel spraying volume matches the gas flow rate.

5. The axisymmetric bending detonation engine design method as described in claim 1, characterized in that... In step 7), multiple engine channels are selected and arranged. The number of channels is selected according to the total thrust parameters required by the design. The number of channels of the axisymmetric bending detonation engine is appropriately increased or decreased according to the thrust performance requirements to meet the actual needs of the project. These multiple engines are evenly arranged on the axisymmetric forebody, and the gaps reserved between each channel can effectively displace the boundary layer.

Images