Design method of axisymmetric bending detonation engine

Abstract

A design method of an axisymmetric bending detonation engine relates to a hypersonic velocity detonation engine of an aircraft, and comprises the following steps: 1) selecting and correcting a von Karman curve as a generatrix, and rotating around a symmetric axis to generate an axisymmetric precursor; 2) determining the inlet position and shape of the air inlet channel; (3) the inlet shape is translated backwards by a proper distance to form an inlet section of the air inlet channel; 4) designing an S-shaped curve beneficial to fuel mixing and gas compression, and installing a fuel spraying device behind the S-shaped curve; 5) reversely designing a wall surface for generating a bending detonation wave; 6) designing an engine exhaust nozzle; 7) selecting and arranging a plurality of engine channels; and (8) designing an outer cover, a connecting plate and other related parts of the air inlet channel, and completing the overall design of the whole engine. The design method is simple and easy to implement, and the performance of the detonation engine can be remarkably improved by improving the displacement effect of the boundary layer and the mixing efficiency of the fuel. The flexible selection of the number of the channels can meet different thrust requirements, so that the method has great potential in engineering application.

Description

Technical Field

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

[0002] Compared with the traditional mixing and combustion mode, detonation combustion has the advantages of fast heat release rate and significant pressurization effect, so it is considered to be an ideal combustion method for air-breathing hypersonic vehicles.

[0003] Detonation engines mainly include pulse detonation engines, supersonic pulse detonation ramjet engines, rotating detonation engines, and oblique / curved detonation engines. Among them, the working principle of oblique / curved detonation engines is to inject fuel in advance in the forebody or inlet of the engine, so that it is fully mixed with air and then enters the combustion chamber. Through the induction of the wall, a detonation wave is formed that is stationary in the hypersonic airflow, realizing detonation combustion. Afterwards, the airflow after combustion expands through the nozzle to generate thrust.

[0004] Since the oblique / curved detonation wave can be stationary inside the combustion chamber without interruption, theoretically, continuous thrust can be generated as long as the supersonic premixed airflow is continuously provided. This feature makes the oblique / curved detonation engine based on detonation combustion a hot spot in current scientific research and engineering applications.

[0005] However, during flight, due to problems such as excessive back pressure in the combustion chamber, excessive low-energy flow, and insufficient fuel mixing, conventional oblique / curved detonation engines often face poor performance parameters or even fail to detonate successfully. Therefore, how to effectively organize the rapid detonation of oblique / curved detonation engines and achieve efficient combustion has become the focus of current detonation engine research.

[0006] Domestic and foreign scholars have carried out a lot of work on the performance of oblique / bent detonation engines, mainly focusing on exploring the effects of incoming flow parameters and combustion chamber geometric parameters on the detonation mechanism. The mechanism and laws of the effects of unsteady and non-uniform incoming flow disturbances, temperature disturbances, wedge angles, sudden changes in incoming flow angles, and the inclination angle of the wall after oblique splitting have been analyzed in detail. In addition, in order to improve the impact of the above problems on engine detonation, scholars have proposed measures such as changing the traditional oblique wedge configuration to achieve detonation control in recent years, such as using symmetrical wall-induced shock waves to intersect on opposite sides 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); setting a bulge on the oblique wedge surface (Han Xin, Zhang Wenshuo, Zhang Zijian, et al. Numerical study of oblique detonation 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 bending shock wave induced detonation, which has improved the performance of the engine to a certain extent (Xiong Haochen, Qiu Ruofan, Han Xin, et al. A new detonation method of bending shock wave induced detonation [J / OL]. Acta Aeronautica Sinica, 1-13[2024-09-10].http: / / kns.cnki.net / kcms / detail / 11.1929.V.20231201.1613.012.html.).

[0007] Although there has been great progress in the research on organizing the rapid and successful detonation and efficient combustion of oblique / curved detonation engines, it can be found that the research in this area is still mainly focused on the proposal of special configuration oblique splits, and lacks research on the overall layout of the engine and the design of other parts in the inlet duct. Current research shows that factors that hinder the successful detonation and efficient combustion of detonation engines include insufficient fuel mixing and excessive low-energy flow caused by the boundary layer. In addition, in actual engineering applications, multiple oblique / curved detonation engine combinations are often required to provide greater thrust. Therefore, it is urgent to propose new solutions for the overall layout and inlet configuration design when multiple detonation engines are combined.

[0008] The purpose of the present invention is to provide an axisymmetric bent detonation engine design method to address the above-mentioned technical problems existing in the prior art, thereby improving the fuel mixing efficiency and the engine's ability to resist back pressure through innovative engine structure design, thereby improving the engine's specific impulse and overall performance.

[0009] In order to achieve the above-mentioned invention object, the present invention adopts the following technical scheme:

[0010] The present invention provides an axisymmetric curved detonation engine design method, comprising the following steps:

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

[0012] 2) Determine the position and shape of the inlet entrance: Determine the position and shape of the inlet entrance according to the axisymmetric forebody shape generated in step 1) and the design conditions to ensure that the shock seal is achieved under the design conditions to effectively capture and compress the incoming air;

[0013] 3) Forming the inlet section of the air intake duct: According to the requirements of the air intake duct's back pressure bearing capacity, the inlet shape is shifted backward by a suitable distance to form the inlet section of the air intake duct; ensuring that the inlet section can smoothly transition and guide the incoming air into the air intake duct;

[0014] 4) Design of S-curve and fuel spraying device: According to the engine design size and gas compression requirements, design an S-curve that is conducive to fuel mixing and further gas compression, and install a fuel spraying device at an appropriate position after the S-curve to ensure uniform fuel distribution;

[0015] 5) Inverse design of the wall shape that generates curved detonation waves: Using the curved shock wave theory and the curved characteristic line method, inverse design of the wall shape that generates curved detonation waves is performed to optimize the propagation path and energy release efficiency of the detonation waves;

[0016] 6) Design of engine tail nozzle: Based on the thrust and other performance requirements, the engine tail nozzle is designed using the characteristic line method to ensure that the energy generated by the detonation is efficiently converted into thrust;

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

[0018] 8) Design the outer cover and connecting plate of the air inlet duct: According to the requirements of aerodynamic performance and geometric dimensions, design the outer cover and connecting plate of the air inlet duct to complete the design of the axisymmetric bent detonation engine.

[0019] In step 1), according to the design point conditions and requirements such as volume ratio, a suitable von Karman curve is selected as the generatrix, and it is appropriately corrected to ensure that the shock wave at the leading edge of the forebody is closely attached to the body to reduce energy loss; the corrected generatrix is ​​rotated around the symmetry axis 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 Karman curve library as the initial generatrix;

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

[0022] 1.3) According to the analysis results, make appropriate corrections to the von Karman curve, such as adjusting the curvature, length and other parameters of the curve, to ensure that the shock wave can fit the body closely and reduce energy loss;

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

[0024] In step 2), the specific steps of determining the position and shape of the air inlet entrance may be:

[0025] 2.1) Based on the shape of the axisymmetric precursor generated in step 1) and the design conditions, preliminarily determine the position of the inlet port.

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

[0027] 2.3) Based on the verification results, optimize the inlet shape to ensure that shock seal is achieved under the design conditions and that the incoming air is effectively captured and compressed.

[0028] In step 4), the specific steps of designing the S-shaped curve and the fuel spraying device may be:

[0029] 4.1) According to the engine design size and gas compression requirements, an S-shaped curve is designed to facilitate fuel mixing and further gas compression.

[0030] 4.2) Verify the effect of S-curve 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-bend to ensure that the fuel is evenly distributed.

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

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

[0034] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0035] The design method is simple and easy to implement, and improves the performance of the engine in many aspects. First, by adopting the configuration of the axisymmetric forebody, a lateral pressure gradient pointing to both sides of the inlet is formed at the intersection of each inlet and the forebody, thereby promoting the displacement of the boundary layer to both sides in the inlet. In addition, a sufficiently large leakage channel is set between adjacent inlets to ensure sufficient space for displacement and avoid mutual interference between the inlets. Therefore, the design method significantly enhances the displacement effect of the boundary layer of the inlet. In addition, due to the adoption of the S-bend configuration, the mixing distance of the fuel and the airflow is increased, and the change in the flow direction promotes a more complete mixing of the airflow and the fuel, so that the two can achieve more efficient mixing in a limited space. At the same time, the S-bend design also enables the inlet to transition more smoothly to the wall surface that generates the curved detonation wave, thereby reducing the occurrence of complex flows in the inlet and the isolation section. Finally, the axisymmetric arrangement provides greater flexibility for the selection of the number of engine channels, and the appropriate number of channels can be selected according to different thrust requirements. The above advantages make the engine proposed by the present invention have the advantages of higher specific impulse and compact structure. This makes it show great potential for engineering applications. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1The schematic diagram of the design method of the axisymmetric curved detonation engine forebody rotation generatrix of the present invention is shown in FIG. The dotted line OA represents the original curve before correction, the solid line O'A represents the curve after correction to ensure shock wave attachment, and point A is the intersection of the curve before correction and the curve after correction.

[0037] Figure 2 It is a cross-sectional view of an axisymmetric bent detonation engine near the symmetry plane, mainly showing the structure inside the axisymmetric bent detonation engine channel.

[0038] Figure 3 This is a front view of the axisymmetric bent detonation engine when the connecting plate is not installed, mainly showing the leakage channels between the engine channels.

[0039] Figure 4 A front view of an axisymmetric bent detonation engine with a connecting plate installed thereon, mainly showing the configuration and installation position of the connecting plate.

[0040] Figure 5 Side view of an axisymmetric bent detonation engine.

[0041] Figure 6 Rear view of an axisymmetric bent detonation engine.

[0042] Figure 7 This is the positive triaxial side view of the axisymmetric bent detonation engine. DETAILED DESCRIPTION

[0043] In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer and more understandable, the present invention is further described in detail below with reference to the accompanying drawings. It should be noted that since the present invention is an axisymmetric structure, the following description only marks and describes part of the structure, and the same symmetrical part design method is applied.

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

[0045] 1) Determine the forebody length L according to design conditions such as volume ratio cone and bottom diameter length R B .

[0046] 2) Determine the von Karman curve according to the formula below.

[0047]

[0048] 3) In order to ensure the shock wave attachment, the von Karman curve is corrected from point A, and the dotted line AO ​​is corrected to AO', so as to obtain the final rotation generatrix of the generated precursor.

[0049] like Figure 2 As shown, the design method of the intake duct, transition section, combustion chamber and nozzle of one channel of the axisymmetric bent detonation engine mainly includes:

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

[0051] 2) The position of the inlet lip 3 is determined according to the incident shock wave position at the design point and the capture flow rate and other design requirements, so as to ensure that the shock wave seal can be achieved at the design point and improve the intake efficiency.

[0052] 3) The area of ​​the inlet cross section can be determined according to the design requirements, thereby determining the aspect ratio of the inlet. Then, according to the engine geometric constraints and engine weight restrictions, the inlet will be pulled flat a certain distance to optimize the inlet performance.

[0053] 4) According to the given intake duct pressure ratio and the requirement for the ability to resist back pressure, the S-shaped wall 4 of the transition section is designed using the characteristic line method, so that the gas is further compressed and the fuel is mixed more fully.

[0054] 5) According to geometric constraints and other conditions, a device 5 capable of injecting fuel forward and backward is installed after the transition section 4 to ensure that the fuel is evenly distributed in the combustion chamber and improve the combustion efficiency.

[0055] 6) According to the bending shock wave theory, the profile 6 for generating the bending detonation wave is inversely designed. The governing equation of the bending shock wave theory is shown below, 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 profile 7 according to the characteristic line method so that it can meet the performance requirements of the nozzle at the design point.

[0058] 8) Design the outer cover 8 for the single channel of the bent detonation engine designed above according to the requirements of aerodynamic performance and size.

[0059] At this point, the design of a single engine channel of the bent detonation engine has been completed. Next, the overall configuration of the bent detonation engine is designed. The steps are as follows:

[0060] 1) The thrust and other performance indicators of a single channel can be obtained by theoretical or simulation calculation of the performance of a single channel, and then the total number of channels required can be selected according to the design indicators. The single channels are rotated around the symmetry axis 9 so that they are evenly arranged around the front body.

[0061] 2) According to the relative positions between the channel covers, a partition 10 is designed to smoothly connect the engine channel covers to each other, so that the transition between the channel covers is smooth. Figure 3 In the configuration shown, the leakage channel 11 can effectively remove the boundary layer and low kinetic energy flows such as eddies.

[0062] 3) According to the requirements of aerodynamic performance, a connecting plate 12 that meets the requirements of aerodynamic performance is designed so that the baffle 10 can be connected to the front body 1, such as Figure 4 This design is intended to achieve better aerodynamic performance.

[0063] Finally, the configuration of the axisymmetric bent detonation engine is obtained. The side view of this configuration is shown in Figure 5 As shown, the model is symmetrical about the symmetry axis 9, and the connecting plate 12 connects the front body 1 and the baffle 10. Figure 6 It can be observed that the six engines are evenly arranged around the symmetry axis 9 to provide the thrust required by the aircraft. Figure 7 The model is shown in a three-axis side view, fully showing the structure of the axisymmetric bent detonation engine. When the aircraft is flying, the airflow first passes through the compression part of the front body 1, then enters the air inlet along the channel between the adjacent baffles, and finally ejects along the nozzle profile 7 and the profile 6 that generates the bent detonation wave.

[0064] This design method is simple and easy to implement, and improves the performance of the engine in many aspects. First, the design configuration adopts an axisymmetric forebody, so that a certain lateral pressure gradient pointing to both sides of the inlet is generated at the intersection of each inlet and the forebody, thereby causing the boundary layer in the inlet to shift to both sides. In addition, a sufficiently large leakage channel is set between adjacent inlets to ensure that the inlet has enough space for displacement and the displacement between the inlets will not interfere with each other. In summary, this design method significantly improves the displacement effect of the boundary layer of the inlet.

[0065] In addition, due to the adoption of the S-bend configuration, the mixing distance between the fuel and the airflow is increased, and the change in the flow direction allows the airflow and the fuel to be fully mixed, so that the two can be more fully mixed in a limited space, thereby improving the fuel mixing efficiency. At the same time, the S-bend design can make the inlet duct transition more smoothly to the wall surface that produces the curved detonation wave, thereby reducing the occurrence of complex flows in the inlet duct / isolation section. Finally, the axisymmetric arrangement makes the selection of the number of engine channels more flexible, and the number of engine channels can be selected according to different thrust requirements. The above advantages make this design have great potential in engineering applications.

[0066] The above embodiments are only preferred embodiments of the present invention and cannot be considered to limit the scope of the present invention. All equivalent changes and improvements made within the scope of the present invention should still fall within the scope of the present invention.

Claims

1. Axisymmetric bending detonation engine design method, characterized in that The following steps are involved: 1) Select and modify the von Karman curve as the generatrix: According to the design point conditions and volume ratio requirements, select the appropriate von Karman curve as the generatrix, and modify it appropriately to ensure that the shock wave at the leading edge of the forebody fits the body tightly to reduce energy loss; rotate the modified generatrix around the symmetry axis to generate an axisymmetric forebody; 2) Determine the position and shape of the inlet entrance: Determine the position and shape of the inlet entrance according to the axisymmetric forebody shape generated in step 1) and the design conditions to ensure that the shock seal is achieved under the design conditions to effectively capture and compress the incoming air; 3) Forming the inlet section of the air intake duct: According to the requirements of the air intake duct's back pressure bearing capacity, the inlet shape is shifted backward by a suitable distance to form the inlet section of the air intake duct; ensuring that the inlet section can smoothly transition and guide the incoming air into the air intake duct; 4) Design of S-curve and fuel spraying device: According to the engine design size and gas compression requirements, design an S-curve that is conducive to fuel mixing and further gas compression, and install a fuel spraying device at an appropriate position after the S-curve to ensure uniform fuel distribution; 5) Inverse design of the wall shape that generates curved detonation waves: Using the curved shock wave theory and the curved characteristic line method, inverse design of the wall shape that generates curved detonation waves is performed to optimize the propagation path and energy release efficiency of the detonation waves; 6) Design of engine tail nozzle: Based on the thrust and other performance requirements, the engine tail nozzle is designed using the characteristic line method to ensure that the energy generated by the detonation is efficiently converted into thrust; 7) Select and arrange multiple engine channels: Calculate the thrust and other performance of the above-designed single channel through theoretical estimation or numerical simulation, select the appropriate number of channels, and evenly arrange these channels on the axisymmetric forebody; 8) Design the outer cover and connecting plate of the air inlet duct: According to the requirements of aerodynamic performance and geometric dimensions, design the outer cover and connecting plate of the air inlet duct to complete the design of the axisymmetric bent detonation engine.

2. The design method of an axisymmetric bent detonation engine according to claim 1, characterized in that In step 1), according to the design point conditions and requirements such as volume ratio, a suitable von Karman curve is selected as the generatrix, and it is appropriately corrected to ensure that the shock wave at the leading edge of the forebody is closely attached to the body to reduce energy loss; the corrected generatrix is ​​rotated around the symmetry axis to generate an axisymmetric forebody; 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 Karman curve library as the initial generatrix; 1.2) Analyze the fit between the shock wave at the leading edge of the forebody and the fuselage to verify the tightness of the shock wave to the fuselage; 1.3) According to the analysis results, make appropriate corrections to the von Karman curve, such as adjusting the curvature, length and other parameters of the curve, to ensure that the shock wave can fit the body closely and reduce energy loss; 1.4) Rotate the corrected generatrix around the axis of symmetry to generate a three-dimensional model of the axisymmetric precursor.

3. The design method of an axisymmetric bent detonation engine according to claim 1, characterized in that In step 2), the specific steps of determining the position and shape of the air inlet are: 2.1) Based on the shape of the axisymmetric forebody generated in step 1) and the design conditions, preliminarily determine the position of the inlet port; 2.2) Verify the effect of different inlet shapes on the shock seal effect; 2.3) Based on the verification results, optimize the inlet shape to ensure that shock seal is achieved under the design conditions and that the incoming air is effectively captured and compressed.

4. The design method of an axisymmetric bent detonation engine according to claim 1, characterized in that In step 4), the specific steps of designing the S-shaped curve and the fuel spraying device are: 4.1) Design an S-shaped curve that is conducive to fuel mixing and further gas compression according to the engine design size and gas compression requirements; 4.2) Verify the effect of S-curve on gas flow and fuel mixing; 4.3) Install a fuel spraying device at an appropriate position after the S-bend to ensure that the fuel can be evenly distributed; 4.4) Debug and optimize the spraying device to ensure that the fuel spraying amount matches the gas flow rate.

5. The design method of an axisymmetric bent detonation engine according to 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 and other parameters required by the design. The number of channels of the axisymmetric bent detonation engine is appropriately increased or decreased according to the thrust performance and other requirements to meet the actual needs of the project. These multiple engines are evenly arranged on the axisymmetric forebody, and the gaps reserved between the channels can effectively displace the boundary layer.

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