A design method of scramjet engine based on matching of profile and heat release

Abstract

This invention discloses a design method for scramjet engines based on flow channel profile and heat release matching. When the engine structure has significant thermal protection issues and excessive thermal congestion, an oscillation suppression strategy to reduce combustion heat release congestion is adopted, increasing the expansion angle of the expansion section. When the engine structure has insignificant thermal protection issues and excessive thermal congestion, an oscillation suppression strategy to enhance combustion heat release congestion is adopted, decreasing the expansion angle of the expansion section. When the engine structure has insignificant thermal protection issues and moderate thermal congestion, an oscillation suppression strategy to enhance or reduce combustion heat release congestion is adopted, increasing or decreasing the expansion angle of the expansion section. This invention is applied to the field of scramjet engine design technology, establishing a design criterion for matching flow channel profile and combustion heat release. By avoiding the sensitive region of flow separation and combustion heat release coupling, flow separation-induced combustion oscillations can be effectively suppressed, significantly improving the robustness of scramjet engine operation.

Description

Technical Field

[0001] This invention relates to the field of scramjet engine design technology, specifically a scramjet engine design method based on profile and heat release matching. Background Technology

[0002] There are very few reports on the formation mechanism of combustion oscillations in the combustor of scramjet engines in the existing technology, especially the lack of research on the matching of flow channel profile and combustion heat release. In 2018, Ouyang Hao's doctoral dissertation "Study on Unsteady Combustion Process in Scramjet Engine Combustor" studied the combustion oscillation mechanism in the combustor of scramjet engines, and reported the transient process, induction and formation mechanism of periodic low-frequency combustion oscillations in the combustor of scramjet engines. However, this study mainly refers to the specific flame flashback phenomenon induced by the upward movement of the pre-burning shock train, and does not focus on the more general unsteady combustion process caused by the combustion heat release effect. The paper "Research Progress on Unsteady Supersonic Combustion" (Chinese Journal of Aerodynamics, 2020, 38(3):532-551) sorts out the unsteady characteristics and influencing mechanisms of supersonic combustion, and summarizes the research results in five aspects of unsteady supersonic combustion: acoustic oscillation, flow-induced combustion instability, ignition process, flame flashback and flame instability near the extinction limit. However, it did not conduct in-depth research on the combustion oscillation phenomenon caused by improper matching between flow channel expansion and combustion heat release. In the current design process of scramjet engines, the matching between the flow channel expansion and combustion heat release is mostly improper, which easily leads to the technical problem of combustion oscillation. Summary of the Invention

[0003] To address the technical problem in the prior art where improper matching between the flow channel profile expansion and combustion heat release in scramjet engines easily leads to combustion oscillations, this invention provides a scramjet engine design method based on profile and heat release matching. It establishes design criteria for matching the flow channel profile with combustion heat release, thereby suppressing combustion oscillations in the combustion chamber.

[0004] To achieve the above objectives, the present invention provides a design method for a scramjet engine based on profile and heat release matching, wherein the profile of the scramjet engine combustion chamber includes a sequentially connected isolation section, a fuel injection section, a cavity, and an expansion section.

[0005] The design method includes the following steps:

[0006] When low-frequency combustion oscillations occur in the combustion chamber cavity and the engine structure has significant thermal protection problems and excessive thermal congestion effect, an oscillation suppression strategy to reduce the combustion heat release congestion effect is adopted, and the expansion angle of the expansion section is increased based on the existing preliminary profile.

[0007] When low-frequency combustion oscillations occur in the combustion chamber cavity and the engine structure's thermal protection is not significant and the thermal congestion effect is too low, an oscillation suppression strategy that enhances the combustion heat release congestion effect is adopted, reducing the expansion angle of the expansion section based on the existing preliminary profile.

[0008] When low-frequency combustion oscillations occur in the combustion chamber cavity, and the engine structure's thermal protection problem is not significant and the thermal congestion effect is moderate, an oscillation suppression strategy that enhances or reduces the combustion heat release congestion effect is adopted, increasing or decreasing the expansion angle of the expansion section based on the existing preliminary profile.

[0009] In one embodiment, the process of determining whether low-frequency combustion oscillations occur within the combustion chamber cavity is as follows:

[0010] Pressure monitoring points (pt) are arranged on the upper wall of the fuel injection section. 6,u Pressure monitoring points (pt) are arranged on the lower wall of the fuel injection section. 6,d And pressure monitoring point pt 6,u With pressure monitoring point pt 6,d Symmetrical along the engine axis;

[0011] Based on pressure monitoring point pt 6,u The monitoring data yielded the peak frequency f of the upper concave cavity flame. top,u And based on the pressure monitoring point pt 6,d The monitoring data yielded the peak frequency f of the concave cavity flame. top,d ;

[0012] Take the peak frequency f of the upper concave cavity flame top,u With the peak frequency f of the concave cavity flame top,d The average value is used as the peak frequency f of the flame oscillation in the combustion chamber. top That is, f top =(f top,u +f top,d ) / 2;

[0013] When the peak frequency of flame oscillation in the combustion chamber is f top If the value exceeds the threshold, it is determined that low-frequency combustion oscillation has occurred in the combustion chamber cavity.

[0014] In one embodiment, the design method further includes:

[0015] Pressure monitoring points (pt) are arranged on the upper wall at the inlet of the expansion section. 8,u Pressure monitoring points (pt) are arranged on the lower wall surface at the inlet of the expansion section. 8,d And pressure monitoring point pt 8,u With pressure monitoring point pt 8,d Symmetrical along the engine axis;

[0016] Take pressure monitoring point pt 8,uWith pressure monitoring point pt 8,d The average value of the measurements is used as the evaluation standard for thermal congestion effect p. chock ;

[0017] If the cavity does not experience flameout, and the p condition is satisfied... chock If / p0<1, it is determined that the engine structure has significant thermal protection problems and the thermal congestion effect is too high;

[0018] If the cavity does not experience flameout, and the condition 1 ≤ p is satisfied. chock If / p0<2, it is determined that the engine structure thermal protection problem is not significant and the thermal congestion effect is moderate;

[0019] If the cavity does not experience flameout, and the p condition is satisfied... chock If / p0≥2, it is determined that the engine structure thermal protection problem is not significant and the thermal congestion effect is too low;

[0020] Where p0 is the combustion chamber inlet pressure.

[0021] In one embodiment, the process for determining whether flameout has occurred in the combustion chamber cavity is as follows:

[0022] Pressure monitoring points pt are arranged on the upper wall of the cavity. 7,u Pressure monitoring points pt are arranged on the lower wall of the cavity. 7,d And pressure monitoring point pt 7,u With pressure monitoring point pt 7,d Symmetrical along the engine axis;

[0023] When the pressure monitoring point pt 7,u Measured value pt 7,u When / p0<3, it is determined that the flame in the upper concave cavity has been extinguished;

[0024] When the pressure monitoring point pt 7,d Measured value pt 7,d When / p0<3, it is determined that the flame in the concave cavity has been extinguished;

[0025] When the flame is blown out in both the upper and lower recesses of the combustion chamber, it is determined that the combustion chamber has experienced a flameout.

[0026] In one embodiment, the oscillation suppression strategy for reducing the combustion heat release blockage effect specifically includes:

[0027] Step 101: Denote the expansion angle of the expansion segment in the initial profile as β0, and set the iteration parameter k = 1;

[0028] Step 102: Based on the current expansion angle, increase the expansion angle of the expansion segment by X degrees to obtain a new expansion angle β. k ;

[0029] Step 103, at the expansion angle β k Based on this, the suppression effect of combustion oscillations was evaluated using FFT spectral analysis:

[0030] If low-frequency combustion oscillations no longer occur within the combustion chamber cavity, then the output expansion angle β k The corresponding combustion chamber profile of the scramjet engine;

[0031] If the low-frequency combustion oscillations within the combustion chamber cavity are enhanced, then in the expansion angle range [β]... k-1 ,β k The expansion angle β within the combustion chamber cavity is used to prevent low-frequency combustion oscillations. x Then the output expansion angle β x The corresponding combustion chamber profile of the scramjet engine;

[0032] If the low-frequency combustion oscillation in the combustion chamber cavity weakens, then set k = k + 1 and repeat step 102.

[0033] In one embodiment, the oscillation suppression strategy for enhancing the combustion heat release congestion effect specifically includes:

[0034] Step 201: Denote the expansion angle of the expansion segment in the initial shape as β0, and let the iteration parameter k = 1;

[0035] Step 202: Based on the current expansion angle, reduce the expansion angle of the expansion segment by X degrees to obtain a new expansion angle β. k ;

[0036] Step 203, at the expansion angle β k Based on this, the suppression effect of combustion oscillations was evaluated using FFT spectral analysis:

[0037] If low-frequency combustion oscillations no longer occur within the combustion chamber cavity, then the output expansion angle β k The corresponding combustion chamber profile of the scramjet engine;

[0038] If the low-frequency combustion oscillations within the combustion chamber cavity are enhanced, then in the expansion angle range [β]... k ,β k-1 The expansion angle β within the combustion chamber cavity is used to prevent low-frequency combustion oscillations. x Then the output expansion angle β x The corresponding combustion chamber profile of the scramjet engine;

[0039] If the low-frequency combustion oscillation in the combustion chamber cavity weakens, then set k = k + 1 and repeat step 202.

[0040] In one embodiment, during the process of reducing or increasing the expansion angle of the expansion section based on the existing preliminary profile, the shock wave train is prevented from being pushed forward to the combustion chamber inlet, thus preventing the intake duct from not starting. At the same time, the flames in the upper and lower concave cavities are prevented from being blown out, thus preventing combustion from being organized and losing power.

[0041] In one embodiment, the step of preventing the shock wave train from being pushed forward to the combustion chamber inlet and causing the intake manifold to fail to start specifically involves:

[0042] Pressure monitoring points (pt) are arranged at intervals along the flow direction on the upper wall surface at the inlet of the isolation section. 1,u With pressure monitoring point pt 2,u Pressure monitoring points (pt) are arranged at intervals along the flow direction on the lower wall surface at the inlet end of the isolation section. 1,d With pressure monitoring point pt 2,d ;

[0043] Based on the existing preliminary profile, the pressure monitoring point pt 1,u Pressure monitoring point pt 2,u Pressure monitoring point pt 1,d With pressure monitoring point pt 2,d Measured value pt 1,u-0 pt 2,u-0 pt 1,d-0 pt 2,d-0 The average value is taken as the combustion chamber inlet pressure p0, i.e., p0 = (pt 1,u-0 +pt 2,u-0 +pt 1,d-0 +pt 2,d-0 ) / 4;

[0044] While reducing or increasing the expansion angle of the expansion section based on the existing preliminary profile, maintain the pressure monitoring point pt. 1,u Pressure monitoring point pt 2,u Pressure monitoring point pt 1,d With pressure monitoring point pt 2,d Real-time measurement value pt 1,u-1 pt 2,u-1 pt 1,d-1 pt 2,d-1 Satisfy (pt) 1,u-1 +pt 2,u-1 +pt 1,d-1 +pt 2,d-1 ) / 4<1.5p0.

[0045] The present invention has the following beneficial technical effects:

[0046] 1. This invention establishes a design criterion for matching the flow channel profile with combustion heat release. By avoiding the sensitive region of flow separation and combustion heat release coupling, a flow channel design method for scramjet engines is established, which can effectively suppress combustion oscillations induced by flow separation.

[0047] 2. Based on existing scramjet engine technology, this invention significantly improves the robustness of scramjet engine operation by balancing the flow channel expansion effect and the combustion heat release effect. Attached Figure Description

[0048] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0049] Figure 1 This is a schematic diagram of the combustion chamber structure of the scramjet engine in an embodiment of the present invention;

[0050] Figure 2 This is a diagram showing the injection position and cross-sectional dimensions of the scramjet engine combustion chamber in an embodiment of the present invention.

[0051] Figure 3 This is a schematic diagram showing the distribution of pressure measuring points on the combustion chamber wall of a scramjet engine in an embodiment of the present invention.

[0052] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0054] It should be noted that all directional indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present invention are only used to explain the relative positional relationship and movement of each component in a certain specific posture (as shown in the figure). If the specific posture changes, the directional indication will also change accordingly.

[0055] Furthermore, in this invention, descriptions involving "first," "second," etc., are for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0056] In this invention, unless otherwise explicitly specified and limited, the terms "connection," "fixed," etc., should be interpreted broadly. For example, "fixed" can mean a fixed connection, a detachable connection, or an integral part; it can mean a mechanical connection, an electrical connection, a physical connection, or a wireless communication connection; it can mean a direct connection or an indirect connection through an intermediate medium; it can mean the internal communication of two elements or the interaction between two elements, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0057] Furthermore, the technical solutions of the various embodiments of the present invention can be combined with each other, but only if they are feasible for those skilled in the art. If the combination of technical solutions is contradictory or cannot be implemented, it should be considered that such combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0058] This embodiment discloses a design method for a scramjet engine based on flow channel profile and heat release matching. By adopting a strategy of matching the flow channel profile with combustion heat release to avoid the sensitive area of ​​combustion oscillation, the combustion oscillation phenomenon of the scramjet engine is suppressed. It is mainly used to solve the technical problem that existing scramjet engine design methods cannot effectively avoid combustion oscillation caused by the coupling between flow channel profile and combustion heat release.

[0059] refer to Figure 1 This is a preliminary schematic diagram of the scramjet engine combustor in this embodiment. The scramjet engine combustor has a symmetrical structure, mainly including an isolation section 1, a fuel injection section 2, a concave section 3, and an expansion section 4 connected in sequence. The isolation section 1 contains a pre-burning shock wave train to reduce the incoming flow velocity and achieve pressure balance between low-pressure intake and high-pressure combustion. The concave injection section 2 is equipped with nozzles for fuel injection, ensuring thorough fuel / air mixing. The concave section 3 mainly houses a concave flame stabilizer, primarily used for ramjet combustion organization within a certain range of flight Mach numbers (Ma4-7). The expansion section 4 connects the combustor and the exhaust nozzle, with the airflow gradually increasing in speed and decreasing in pressure.

[0060] It should be noted that the preliminary profile of the scramjet engine combustion chamber in this embodiment is the profile of the scramjet engine combustion chamber determined according to mission requirements, such as the profile suitable for the jet wake flame stabilization mode, the profile of the cavity shear layer flame stabilization mode, etc. The configuration of the scramjet engine combustion chamber can be a rectangular cross-section or an axisymmetric circular cross-section. In the rectangular cross-section engine combustion chamber, the cavities are symmetrically arranged on the upper and lower walls; in the axisymmetric circular cross-section engine combustion chamber, the cavities are annular structures.

[0061] Reference Figure 2 , is a schematic diagram of the fuel injection position and specific dimensions of the scramjet engine combustion chamber in this embodiment. In Figure 2 , l1 is the length of the isolator section, l2 is the length of the fuel injection section, l3 is the length of the cavity section, l4 is the length of the expansion section, d1 is the height of the inlet flow channel of the isolator section, d2 is the height of the outlet flow channel of the isolator section, d 31 is the height of the flow channel at the leading edge of the cavity, d 32 is the height of the flow channel at the trailing edge of the cavity, d4 is the height of the outlet flow channel of the expansion section, h is the depth of the cavity, α is the inclination angle of the rear wall of the cavity, β is the wall expansion angle of the expansion section, l jet is the length of the fuel injection hole center position from the leading edge of the cavity. Among them, the arrow represents the fuel injection hole position and injection direction. In the specific implementation process, the injection hole position is determined according to the actual cruise state, that is, the flow distance l jet of the fuel injection hole from the leading edge of the cavity is determined according to the flame stabilization state required by the actual combustion condition, and is not strictly restricted. The fuel injection holes are all preferably round holes and hot oil injection holes. For the two-dimensional rectangular cross-section combustion chamber, the number of injection holes Jet on the upper and lower walls of the fuel injection section is preferably 10; for the circular cross-section combustion chamber, the number of injection holes Jet on the fuel injection section is preferably 20, and all the injection hole arrangements are preferably evenly distributed along the radial direction. The diameter of a single injection hole is preferably d jet ≤ 5mm. The nozzle configuration of all injection holes is preferably a sonic nozzle, which is set at 90° perpendicular to the axial direction.

[0062] The scramjet engine combustion chamber in this embodiment is not limited to the parallel single cavity combustion chamber configuration, and can also be applied to the double cavity or multi-cavity combustion chamber configuration. The range of the cavity length-depth ratio is 6 < l3 / h < 8, preferably 7, and the inclination angle of the rear wall of the cavity is α = 45°. In the scramjet engine combustion chamber in this embodiment, when cruising at a flight Mach number of 4 - 7, the ratio of the height of the flow channel at the trailing edge of the cavity to the height of the inlet of the intake duct should satisfy 1.0 ≤ d 32 / d1 ≤ 1.5, preferably 1.3. The range of the wall expansion angle of the expansion section is between 0.5° ≤ β ≤ 3.5°, and preferably 2° is taken.

[0063] In this embodiment, a total of 16 pressure detection points are arranged in the scramjet engine combustion chamber, with 8 arranged on each of the upper and lower walls, that is Figure 3As shown. Reference Figure 3 Pressure monitoring points (pt) are arranged at intervals along the flow direction on the upper wall surface at the inlet end of the isolation section. 1,u With pressure monitoring point pt 2,u Pressure monitoring points (pt) are arranged at intervals along the flow direction on the lower wall surface at the inlet end of the isolation section. 1,d With pressure monitoring point pt 2,d Pressure monitoring points (pt) are arranged at intervals along the flow direction on the upper wall surface at the outlet end of the isolation section. 3,u Pressure monitoring point pt 4,u With pressure monitoring point pt 5,u Pressure monitoring points (pt) are arranged at intervals along the flow direction on the lower wall surface at the outlet end of the isolation section. 3,d Pressure monitoring point pt 4,d With pressure monitoring point pt 5,d Pressure monitoring points (pt) are arranged on the upper wall of the fuel injection section. 6,u Pressure monitoring points (pt) are arranged on the lower wall of the fuel injection section. 6,d Pressure monitoring points pt are arranged on the upper wall of the cavity. 7,u Pressure monitoring points pt are arranged on the lower wall of the cavity. 7,d Pressure monitoring points (pt) are arranged on the upper wall at the inlet of the expansion section. 8,u Pressure monitoring points (pt) are arranged on the lower wall surface at the inlet of the expansion section. 8,d The preferred hardware system for the pressure monitoring point is Pressure System Inc. (PSI) 9116, with a sampling frequency of 50-200Hz, the higher the better, and 100Hz is preferred.

[0064] Specifically, the pressure monitoring point pt at the front of the isolation section 1,u pt 2,u Used to monitor the pressure at the inlet of the upper wall, pt 1,d pt 2,d Used to monitor the pressure at the inlet of the lower wall. To reduce interference from the background wave system, the average value of the four pressure monitoring points at the front of the isolation section in the cold flow field is taken as the inlet pressure, i.e., the pressure monitoring point pt on the existing preliminary profile foundation. 1,u Pressure monitoring point pt 2,u Pressure monitoring point pt 1,d With pressure monitoring point pt 2,d Measured value pt 1,u-0 pt 2,u-0 pt 1,d-0 pt 2,d-0 The average value is taken as the combustion chamber inlet pressure p0, i.e., p0 = (pt 1,u-0 +pt 2,u-0 +pt 1,d-0 +pt 2,d-0) / 4, and at the same time, under this combustion chamber configuration, p0 is used as the reference pressure.

[0065] For a two-dimensional rectangular cross-section combustion chamber, the pressure monitoring point pt at the rear of the isolation section... 3,u pt 4,u pt 5,u Used to assess the forward thrust of the pre-burning shock train on the upper wall, pt 3,d pt 4,d pt 5,d Used to assess the forward thrust of the pre-burning shock train on the lower wall; for circular cross-section combustion chambers, the pressure monitoring point pt at the rear of the isolator section. 3,u pt 4,u pt 5,u With pt 3,d pt 4,d pt 5,d The pressure monitoring points are symmetrically distributed on the same central cross section. i,u pt i,d The measured values ​​for (i = 3, 4, 5) are pt respectively. i,u pt i,d Then it can be determined by the pressure ratio pt i,u / p0 and pt i,d / p0 is used to determine the forward position of the pre-ignition shock train. Specifically:

[0066] For the required operating equivalence ratio of the engine, when pt i,u / p0≥1.5 or pt i,d When / p0≥1.5, it is determined that the pre-burning shock wave train has been pushed forward to the pressure monitoring point pt at the rear of the isolation section. i,u or pt i,d The location.

[0067] To identify the presence of flow field structural asymmetry caused by the Coanda effect, pressure monitoring points on the upper and lower walls need to be estimated separately. When the ratio of the difference between the measured values ​​at the symmetrical pressure monitoring points to the inlet pressure exceeds a threshold, i.e., |pt i,u -pt i,d When | / p0≥0.2, it is determined that an asymmetric phenomenon has occurred in the flow field structure. If the pre-burning shock wave train shifts towards the upper wall, then pt i,u >pt i,d If the pre-ignition shock wave train deviates towards the lower wall, then pt i,u <pt i,d Therefore, the forward position of the pre-ignition shock train is determined by pt. i,u and pt i,d The larger of the two values ​​shall prevail.

[0068] Pressure monitoring point pt on fuel injection section 6,uUsed to monitor the pressure on the upper wall of the fuel injection section, pressure monitoring point pt 6,d Used to monitor the pressure on the lower wall of the fuel injection section, the combined data from both can determine the frequency of flame oscillation within the combustion chamber. Specifically, during a period of operation in the combustion chamber, the pressure monitoring point pt... 6,u With pressure monitoring point pt 6,d The time interval between two consecutive arrivals of the flame front at this position was recorded, and the pressure oscillation spectrum curve was analyzed using FFT (Fast Fourier Transform). The peak frequency f of the flame in the upper concave cavity was observed. top,u and the peak frequency f of the concave cavity flame top,d Therefore, the average of the two values ​​is taken as the peak frequency f of flame oscillation during the combustion chamber operation period. top =(f top,u +f top,d ) / 2, when f top If the value exceeds a certain threshold, preferably 20ms, it can be determined that low-frequency combustion oscillation (below 50Hz) has occurred in the combustion chamber.

[0069] Pressure monitoring point pt on the cavity 7,u Used to monitor the pressure at the bottom wall of the concave cavity, pressure monitoring point pt 7,d This is used to monitor the pressure at the bottom wall of the combustion chamber. Combining the data from both sources allows for the determination of whether flameout has occurred in the combustion chamber's cavity. Specifically, when the combustion chamber is in operation, a flameout is considered to have occurred in the cavity when the pressure at the bottom wall is below three times the inlet pressure. That is, the pressure monitoring point pt... 7,u Measured value pt 7,u Satisfy pt 7,u When / p0<3, it is determined that the flame in the upper concave cavity has been extinguished; pressure monitoring point pt 7,d Measured value pt 7,d Satisfy pt 7,d If / p0 < 3, it is determined that the flame in the lower cavity has been extinguished. If both the upper and lower cavities show signs of flameout, it is considered that the engine is unable to organize combustion and has lost power.

[0070] Pressure monitoring point pt at the inlet of the expansion section 8,u Used to monitor the pressure on the upper wall surface at the inlet of the expansion section; pressure monitoring point pt 8,d Used to monitor the pressure on the lower wall surface at the inlet of the expansion section; combining the data from both sources can assess the strength of the thermal congestion effect. The pressure monitoring point is pt. 8,u Measured value pt 8,u With pressure monitoring point pt 8,d Measured value pt 8,d The average value is used as the evaluation standard for thermal congestion effect p. chock That is, p chock =(pt) 8,u +pt 8,d) / 2. If it is determined through the pressure monitoring points on the bottom wall of the cavity that the cavity has not experienced flameout, and the p condition is met... chock If / p0<1, it is determined that the thermal congestion effect is too high and the engine structure has significant thermal protection problems; if the pressure monitoring points at the bottom wall of the cavity confirm that no engine shutdown has occurred in the cavity, and 1≤p chock If p0 < 2, then the engine structure's thermal protection problem is determined to be insignificant, and the thermal congestion effect is moderate; if the pressure monitoring points at the bottom wall of the aforementioned cavity confirm that no engine shutdown has occurred in the cavity, and p is satisfied... chock If / p0≥2, then the engine structure's thermal protection problem is deemed insignificant, and the thermal congestion effect is too low. If the pressure monitoring points at the bottom wall of the aforementioned cavity determine that the cavity is experiencing engine shutdown, then discussing the thermal congestion effect is meaningless.

[0071] When low-frequency combustion oscillations occur within the combustion chamber cavity, it is because the increased pressure in the combustion zone typically triggers boundary layer separation on the upstream wall, forming a shock wave train within the combustion chamber. When the back pressure is near a critical value, under the combined effects of the flow channel profile expansion and the thermal congestion effect generated by combustion heat release, both flow separation and the shock wave train exhibit inherent instability, accompanied by significant airflow parameter oscillations. This leads to combustion oscillations dominated by flow instability. Throughout this process, the shock wave train position abruptly changes from a relatively stable position to a large axial oscillation, exhibiting a clear shift in operating conditions. Therefore, this embodiment proposes a flow channel profile and combustion heat release matching criterion, and based on this, proposes an oscillation suppression strategy to enhance / reduce the combustion heat release congestion effect, avoiding sensitive areas where the profile expansion and combustion heat release are mismatched, thereby achieving the goal of suppressing combustion oscillations.

[0072] The design method in this embodiment can determine which strategy to adopt based on the cruise flight Mach number conditions and other constraints. Specifically:

[0073] When low-frequency combustion oscillations occur in the combustion chamber cavity and the engine structure has significant thermal protection problems and excessive thermal congestion effect (i.e., p) chock When / p0<1), an oscillation suppression strategy to reduce the combustion heat release blockage effect is adopted. The expansion angle of the expansion section is increased based on the existing preliminary profile. At this time, care should be taken to avoid the flame being blown out.

[0074] When low-frequency combustion oscillations occur in the combustion chamber cavity and the engine's structural thermal protection is insignificant and the thermal congestion effect is too low (i.e., p... chock When / p0≥2), an oscillation suppression strategy that enhances the combustion heat release congestion effect is adopted. Based on the existing preliminary profile, the expansion angle of the expansion section is reduced. At this time, care should be taken to avoid excessive forward push of the shock wave train, which may cause the intake to fail to start.

[0075] When low-frequency combustion oscillations occur in the combustion chamber cavity and the engine's thermal protection is not significant and the thermal congestion effect is moderate (i.e., 1≤p), chockWhen / p0<2), an oscillation suppression strategy is adopted to enhance or reduce the combustion heat release blockage effect. Based on the existing preliminary profile, the expansion angle of the expansion section is increased or decreased. At this time, care should be taken to avoid flame extinguishing or excessive forward push of the shock wave train, which may cause the intake to fail to start.

[0076] In practical implementation, the oscillation suppression strategy for reducing the combustion heat release blockage effect includes the following steps:

[0077] Step 101: Denote the expansion angle of the expansion segment in the initial profile as β0, and set the iteration parameter k = 1;

[0078] Step 102: Based on the current expansion angle, increase the expansion angle of the expansion segment by X degrees to obtain a new expansion angle β. k ;

[0079] Step 103, at the expansion angle β k Based on this, the suppression effect of combustion oscillation is evaluated using FFT spectrum analysis. In the FFT spectrum analysis results, if the pressure oscillation spectrum curve shows low-frequency combustion oscillation (below 50Hz) flame oscillation peak frequency f top If the peak value of the spectrum curve shifts backward or decreases, it indicates that the combustion oscillation has been suppressed; conversely, if the peak frequency of the flame oscillation f increases... top If the peak value of the spectrum curve shifts forward or increases, it indicates that there is no suppression effect on combustion oscillation; if the spectrum curve does not change significantly, it indicates that the change in the combustion heat release congestion effect is small and the suppression effect on combustion oscillation is not significant enough. Specifically, the subsequent operations are selected based on the FFT spectrum analysis results, and the process is as follows:

[0080] If low-frequency combustion oscillations no longer occur within the combustion chamber cavity, i.e., the peak frequency f of the flame oscillations as analyzed by FFT spectrum... top If the low-frequency combustion oscillation is ≥50Hz and no further low-frequency combustion oscillation is detected for 30 consecutive seconds, then the low-frequency oscillation is considered to have been effectively suppressed, and the expansion angle β is output. k The corresponding combustion chamber profile of the scramjet engine;

[0081] If the low-frequency combustion oscillations within the combustion chamber cavity are enhanced, i.e., the peak frequency f of the flame oscillations is analyzed using FFT spectrum... top If the expansion angle shifts forward or the peak value of the spectral curve increases, it indicates that step 102 has a counterproductive effect on suppressing combustion oscillations, and also indicates that the optimal expansion angle is in the interval [β]. k-1 ,β k Within ], therefore it can be within the expansion angle [β] k-1 ,β k The internal search eliminates low-frequency combustion oscillations within the combustion chamber cavity (i.e., the peak frequency f of the flame oscillations analyzed by FFT spectral analysis). topExpansion angle β (≥50Hz and no low-frequency combustion oscillations detected for 30 consecutive seconds) x Then output the expansion angle β x The corresponding combustion chamber profile of the scramjet engine;

[0082] If the low-frequency combustion oscillations within the combustion chamber cavity weaken, i.e., the peak frequency f of the flame oscillations in the FFT spectrum analysis... top If the peak value of the spectrum curve is shifted or reduced, but the combustion oscillation is not completely suppressed, then let k = k + 1 and proceed to step 102 again.

[0083] In practical implementation, the oscillation suppression strategy to enhance the combustion heat release congestion effect includes the following steps:

[0084] Step 201: Denote the expansion angle of the expansion segment in the initial shape as β0, and let the iteration parameter k = 1;

[0085] Step 202: Based on the current expansion angle, reduce the expansion angle of the expansion segment by X degrees to obtain a new expansion angle β. k ;

[0086] Step 203, at the expansion angle β k Based on this, the suppression effect of combustion oscillation is evaluated using FFT spectrum analysis. In the FFT spectrum analysis results, if the pressure oscillation spectrum curve shows low-frequency combustion oscillation (below 50Hz) flame oscillation peak frequency f top If the peak value of the spectrum curve shifts backward or decreases, it indicates that the combustion oscillation has been suppressed; conversely, if the peak frequency of the flame oscillation f increases... top If the peak value of the spectrum curve shifts forward or increases, it indicates that there is no suppression effect on combustion oscillation; if the spectrum curve does not change significantly, it indicates that the change in the combustion heat release congestion effect is small and the suppression effect on combustion oscillation is not significant enough. Specifically, the subsequent operations are selected based on the FFT spectrum analysis results, and the process is as follows:

[0087] If low-frequency combustion oscillations no longer occur within the combustion chamber cavity, i.e., the peak frequency f of the flame oscillations as analyzed by FFT spectrum... top If the low-frequency combustion oscillation is ≥50Hz and no further low-frequency combustion oscillation is detected for 30 consecutive seconds, then the low-frequency oscillation is considered to have been effectively suppressed, and the expansion angle β is output. k The corresponding combustion chamber profile of the scramjet engine;

[0088] If the low-frequency combustion oscillations within the combustion chamber cavity are enhanced, i.e., the peak frequency f of the flame oscillations is analyzed using FFT spectrum... top If the expansion angle shifts forward or the peak value of the spectral curve increases, it indicates that step 202 has a counterproductive effect on suppressing combustion oscillations, and also indicates that the optimal expansion angle is in the interval [β]. k ,β k-1Within ], therefore it can be within the expansion angle [β] k ,β k-1 The internal search eliminates low-frequency combustion oscillations within the combustion chamber cavity (i.e., the peak frequency f of the flame oscillations analyzed by FFT spectral analysis). top Expansion angle β (≥50Hz and no low-frequency combustion oscillations detected for 30 consecutive seconds) x Then output the expansion angle β x The corresponding combustion chamber profile of the scramjet engine;

[0089] If the low-frequency combustion oscillations within the combustion chamber cavity weaken, i.e., the peak frequency f of the flame oscillations in the FFT spectrum analysis... top If the peak value of the spectrum curve is shifted or reduced, but the combustion oscillation is not completely suppressed, then let k = k + 1 and proceed to step 202 again.

[0090] In practical implementation, when the expansion angle needs to be in the interval [β] k-1 ,β k ] or [β k ,β k-1 Search expansion angle β x In this case, a conventional binary search or point-by-point search method can be used. It is also worth noting that if the expansion angle is in the interval [β...] k-1 ,β k ] or [β k ,β k-1 Search expansion angle β x If the attempt to decrease or increase the expansion angle β fails, it indicates that the previous decrease or increase was too large, causing the interval positioning to fail. In this case, the value of X can be reduced, and the oscillation suppression strategy steps can be repeated. The value of X can be selected empirically, such as 1°, 0.5°, 0.3°, 0.2°, 0.1°, etc., but generally, the minimum value of X should not be less than 0°. Simultaneously, during the process of decreasing or increasing the expansion angle β, it is also necessary to ensure that the expansion angle β does not exceed the constraint of the engine exhaust nozzle on the size of the combustion chamber outlet.

[0091] Furthermore, in steps 102 and 202 above, during the process of reducing or increasing the expansion angle of the expansion section based on the existing preliminary profile, it is also necessary to prevent the shock wave train from being pushed forward to the combustion chamber inlet and causing the intake duct to fail to start, and at the same time to prevent the flames in the upper and lower concave cavities from being blown out, resulting in the inability to organize combustion and loss of power. Specifically:

[0092] According to the pressure monitoring point pt at the rear of the isolation section 3,u pt 4,u pt 5,u pt 3,d pt 4,d pt 5,dThe forward thrust of the pre-burning shock wave train on the upper and lower walls is assessed, and the presence of asymmetry in the flow field structure is determined to identify the forward thrust position of the pre-burning shock wave train. When the shock wave train is determined to have advanced to pt... 3,u pt 3,d Previously, care was taken to avoid the shock wave train being pushed forward to the combustion chamber inlet, causing the intake manifold to fail to start. This was achieved by reducing or increasing the expansion angle of the expansion section based on the existing preliminary profile, while maintaining the pressure monitoring point pt. 1,u Pressure monitoring point pt 2,u Pressure monitoring point pt 1,d With pressure monitoring point pt 2,d Real-time measurement value pt 1,u-1 pt 2,u-1 pt 1,d-1 pt 2,d-1 Satisfy (pt) 1,u-1 +pt 2,u-1 +pt 1,d-1 +pt 2,d-1 ) / 4<1.5p0. When the shock train advance position is determined to be at pt. 5,u pt 5,d Afterwards, be careful to avoid blowing out the flames in the upper and lower concave cavities, which could cause the combustion to stop and lose power.

[0093] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A design method for a scramjet engine based on profile and heat release matching, characterized in that, The combustion chamber of the scramjet engine comprises a sequentially connected isolation section, a fuel injection section, a cavity, and an expansion section. The design method includes the following steps: When low-frequency combustion oscillations occur in the combustion chamber cavity and the engine structure has significant thermal protection problems and excessive thermal congestion effect, an oscillation suppression strategy to reduce the combustion heat release congestion effect is adopted, and the expansion angle of the expansion section is increased based on the existing preliminary profile. When low-frequency combustion oscillations occur in the combustion chamber cavity and the engine structure's thermal protection is not significant and the thermal congestion effect is too low, an oscillation suppression strategy that enhances the combustion heat release congestion effect is adopted, reducing the expansion angle of the expansion section based on the existing preliminary profile. When low-frequency combustion oscillations occur in the combustion chamber cavity and the engine structure's thermal protection is not significant and the thermal congestion effect is moderate: adopt an oscillation suppression strategy to reduce the combustion heat release congestion effect by increasing the expansion angle of the expansion section based on the existing preliminary profile; or adopt an oscillation suppression strategy to enhance the combustion heat release congestion effect by reducing the expansion angle of the expansion section based on the existing preliminary profile. Pressure monitoring points are installed on the upper wall at the inlet of the expansion section. pt 8,u Pressure monitoring points are arranged on the lower wall surface at the inlet of the expansion section. pt 8,d And pressure monitoring points pt 8,u With pressure monitoring point pt 8,d Symmetrical along the engine axis; Take pressure monitoring points pt 8,u With pressure monitoring point pt 8,d The average value of the measurements is used as the evaluation standard for thermal congestion effect. p chock ; If the cavity does not experience flameout, and the following conditions are met... p chock / p If 0 < 1, it is determined that the engine structure has significant thermal protection problems and the thermal congestion effect is too high; If the cavity does not experience flameout, and the condition 1≤ p chock / p If 0 < 2, it is determined that the engine structure thermal protection problem is not significant and the thermal congestion effect is moderate; If the cavity does not experience flameout, and the following conditions are met... p chock / p If 0 ≥ 2, then the engine structure thermal protection problem is not significant and the thermal congestion effect is too low. in, p 0 represents the combustion chamber inlet pressure.

2. The design method for a scramjet engine based on profile and heat release matching as described in claim 1, characterized in that, The process for determining whether low-frequency combustion oscillations occur within the combustion chamber cavity is as follows: Pressure monitoring points are arranged on the upper wall of the fuel injection section. pt 6,u Pressure monitoring points are arranged on the lower wall of the fuel injection section. pt 6,d And pressure monitoring points pt 6,u With pressure monitoring point pt 6,d Symmetrical along the engine axis; Based on pressure monitoring points pt 6,u The monitoring data yielded the peak frequency of the flame in the concave cavity. f top,u And based on pressure monitoring points pt 6,d The monitoring data yielded the peak frequency of the concave cavity flame. f top,d ; Take the peak frequency of the upper concave cavity flame f top,u Peak frequency of concave cavity flame f top,d The average value is used as the peak frequency of flame oscillation in the combustion chamber. f top ,Right now f top = ( f top,u +f top,d ) / 2; When the peak frequency of flame oscillation in the combustion chamber f top If the value exceeds the threshold, it is determined that low-frequency combustion oscillation has occurred in the combustion chamber cavity.

3. The design method for a scramjet engine based on profile and heat release matching as described in claim 1, characterized in that, The process for determining whether flameout has occurred in the combustion chamber cavity is as follows: Pressure monitoring points are arranged on the upper wall of the cavity. pt 7,u Pressure monitoring points are arranged on the lower wall of the cavity. pt 7,d And pressure monitoring points pt 7,u With pressure monitoring point pt 7,d Symmetrical along the engine axis; When pressure monitoring point pt 7,u Measured values pt 7,u / p When 0 < 3, it is determined that the flame in the upper concave cavity was extinguished; When pressure monitoring point pt 7,d Measured values pt 7,d / p When 0 < 3, it is determined that the flame in the concave cavity was extinguished. When the flame is blown out in both the upper and lower recesses of the combustion chamber, it is determined that the combustion chamber has experienced a flameout.

4. The design method for a scramjet engine based on profile and heat release matching according to any one of claims 1 to 3, characterized in that, The specific oscillation suppression strategy for reducing the combustion heat release congestion effect is as follows: Step 101, record the expansion angle of the expansion segment in the preliminary profile as... β 0, and set the iteration parameter k=1; Step 102: Based on the current expansion angle, increase the expansion angle of the expansion segment by X degrees to obtain a new expansion angle. β k ; Step 103, at the expansion angle β k Based on this, the suppression effect of combustion oscillations was evaluated using FFT spectral analysis: If low-frequency combustion oscillations no longer occur within the combustion chamber cavity, then the output expansion angle... β k The corresponding combustion chamber profile of the scramjet engine; If the low-frequency combustion oscillations within the combustion chamber cavity are enhanced, then in the expansion angle range [ β k-1 , β k The expansion angle within the combustion chamber cavity prevents low-frequency combustion oscillations from occurring. β x Then the output expansion angle β x The corresponding combustion chamber profile of the scramjet engine; If the low-frequency combustion oscillation in the combustion chamber cavity weakens, then set k=k+1 and repeat step 102.

5. The design method for a scramjet engine based on profile and heat release matching according to any one of claims 1 to 3, characterized in that, The oscillation suppression strategy for enhancing the combustion heat release congestion effect is specifically as follows: Step 201, record the expansion angle of the expansion segment in the preliminary profile as... β 0, and set the iteration parameter k=1; Step 202: Based on the current expansion angle, reduce the expansion angle of the expansion segment by X degrees to obtain a new expansion angle. β k ; Step 203, at the expansion angle β k Based on this, the suppression effect of combustion oscillations was evaluated using FFT spectral analysis: If low-frequency combustion oscillations no longer occur within the combustion chamber cavity, then the output expansion angle... β k The corresponding combustion chamber profile of the scramjet engine; If the low-frequency combustion oscillations within the combustion chamber cavity are enhanced, then in the expansion angle range [ β k , β k-1 The expansion angle within the combustion chamber cavity prevents low-frequency combustion oscillations from occurring. β x Then the output expansion angle β x The corresponding combustion chamber profile of the scramjet engine; If the low-frequency combustion oscillation in the combustion chamber cavity weakens, then set k=k+1 and repeat step 202.

6. The design method for a scramjet engine based on profile and heat release matching according to any one of claims 1 to 3, characterized in that, In the process of reducing or increasing the expansion angle of the expansion section based on the existing preliminary profile, it is necessary to avoid the shock wave train being pushed forward to the combustion chamber inlet, which would cause the intake to fail to start, and at the same time, to avoid the flames in the upper and lower concave cavities being blown out, which would cause combustion to fail and power to be lost.

7. The design method for a scramjet engine based on profile and heat release matching according to claim 6, characterized in that, The specific steps to prevent the intake manifold from failing to start due to the shock wave train being pushed forward to the combustion chamber inlet are as follows: Pressure monitoring points are arranged at intervals along the flow direction on the upper wall at the entrance of the isolation section. pt 1,u With pressure monitoring point pt 2,u Pressure monitoring points are arranged at intervals along the flow direction on the lower wall surface at the inlet end of the isolation section. pt 1,d With pressure monitoring point pt 2,d ; Pressure monitoring points based on the existing preliminary profile pt 1,u Pressure monitoring points pt 2,u Pressure monitoring points pt 1,d With pressure monitoring point pt 2,d Measured values pt 1,u-0 , pt 2,u-0 , pt 1,d-0 , pt 2,d-0 The average value is used as the combustion chamber inlet pressure. p 0, that is p 0=( pt 1,u-0 + pt 2,u-0 +pt 1,d-0 + pt 2,d-0 ) / 4; While reducing or increasing the expansion angle of the expansion section based on the existing preliminary profile, maintain the pressure monitoring points. pt 1,u Pressure monitoring points pt 2,u Pressure monitoring points pt 1,d With pressure monitoring point pt 2,d Real-time measurement value pt 1,u-1 , pt 2,u-1 , pt 1,d-1 , pt 2,d-1 satisfy( pt 1,u-1 + pt 2,u-1 +pt 1,d-1 + pt 2,d-1 ) / 4<1.5 p 0.

Images