Method for improving back pressure resistance of dual-mode ramjet engine based on ejection airflow

Abstract

The invention discloses a method for improving the back pressure resistance of a dual-mode ramjet engine based on ejection airflow, and a passive flow control flow channel is formed by replacing a smooth blind plate on the side wall surface of an isolation section and carrying a corresponding control structure. When a pre-combustion shock wave string induced by combustion back pressure touches a downstream drainage hole of the control structure, a natural pressure difference effect is formed by a high-pressure separation area of the boundary layer and a low-pressure area of the upstream of the isolation section, and separation flow is automatically sucked and discharged through a circulating flow channel, so that the separation result of the boundary layer is weakened, and the pre-combustion shock wave string is prevented from moving forwards; and the working margin of the dual-mode ramjet engine is improved, and the lower limit of the flight speed domain of the air-breathing aerospace vehicle is widened.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of air-breathing ramjet engine design. More particularly, the present application relates to a method for improving anti-back pressure performance of a dual-mode ramjet engine based on ejector flow. BACKGROUND

[0002] As an ideal power propulsion system for modern aerospace vehicles, the dual-mode ramjet engine can achieve free conversion between combustion modes to adapt to wide speed range flight requirements due to the advantages of synergistic work of flow path structure and combustion heat release. The high-speed ramjet characteristics of airflow are the key to the self-starting operation of the dual-mode ramjet engine, but it brings challenges to the lower expansion of the engine flight speed range. During the conversion of the dual-mode ramjet engine from the supersonic combustion mode to the subsonic combustion mode, the pre-combustion shock wave string structure induced by the combustion back pressure is often located upstream of the isolation section, approaching the inlet compression components, which is easy to cause the engine not to start. In order to improve the working margin of the dual-mode ramjet engine, researchers are keen to develop flow control methods to resist the interference caused by combustion back pressure. The traditional flow extraction technology has been proven to be effective in extracting separated flow at the exhaust boundary layer, but the problem of sacrificing the main flow and carrying large-sized extraction devices has always hindered the application of this technology to the actual flight process of the dual-mode ramjet engine. Therefore, in the dual-mode ramjet engine, it is necessary to seek a flow control structure that can not only resist the combustion back pressure by extracting the separated flow at the exhaust, but also avoid the loss of main flow and the burden of carrying external large-sized extraction devices. SUMMARY

[0003] It is an object of the present application to solve at least the above problems and / or deficiencies and to provide at least the advantages described hereinafter.

[0004] In order to achieve these objects and other advantages of the present application, a method for improving the anti-back pressure performance of a dual-mode ramjet engine based on ejector flow is provided. By constructing an ejector flow circulation channel in the smooth side wall of the isolation section of the dual-mode ramjet engine, a natural pressure difference environment is formed between the high-pressure separation zone induced by the combustion back pressure and the upstream low-pressure zone. The high-pressure separated flow is extracted and exhausted to the low-pressure region of the flow field through the ejector flow circulation channel, thereby improving the anti-back pressure performance of the dual-mode ramjet engine.

[0005] Preferably, the ejector flow circulation channel is obtained by a control assembly arranged downstream of the isolation section.

[0006] Preferably, the control assembly includes two control structures arranged in space.

[0007] Preferably, each control structure is obtained in the form of being embedded or slotted in the side wall.

[0008] Preferably, each control structure includes:

[0009] a main body arranged inside the smooth side wall;

[0010] The main body is provided with at least one jet hole and a drainage hole at the front 1 / 3 and the rear 1 / 3 of the isolation section, respectively;

[0011] The main body is provided with at least one circulation flow channel communicated with the jet hole and the drainage hole.

[0012] Preferably, the width of the jet hole and the drainage hole is less than 10mm, and the angle range of the two holes offsetting the isolation section is 15°-180°;

[0013] The length of the circulation flow channel is less than the length of the isolation section, and the height from the side wall surface of the isolation section is less than 30mm.

[0014] The present application at least includes the following beneficial effects:

[0015] Firstly, the smooth wall surface of the double-mode ramjet engine isolation section is replaced with a jet flow channel, and the high-pressure separation zone induced by the combustion back pressure forms a natural pressure difference environment with the upstream low-pressure zone. The high-pressure separation flow is pumped and discharged to the low-pressure area of the flow field through the circulation flow channel, which reduces the pre-combustion shock wave string forward transmission problem caused by the cumulative effect of the boundary layer separation, and improves the anti-back pressure performance of the double-mode ramjet engine.

[0016] Secondly, by setting the jet flow control mechanism, the number of drainage holes, jet holes and circulation flow channels in the jet flow control mechanism can be increased in actual application, thereby changing the space-time evolution characteristics of the combustion flow field and forming multiple suction and discharge circulation flows, so that the anti-back pressure performance of the double-mode ramjet engine is improved.

[0017] Thirdly, by adjusting the geometric parameters (angle and width) of the drainage hole component, the geometric parameters (angle and width) of the jet hole component, and the geometric parameters (position, width, length, and height from the isolation section wall) of the circulation flow channel component, the direction, process and flow of the pumped and discharged low-speed high-pressure zone separation flow, and the re-acting form of the flow field are changed, and the working ability of the control structure to resist the combustion back pressure of the double-mode ramjet engine is further strengthened.

[0018] Other advantages, objects and features of the present application will be partly embodied in the following description, and partly understood by those skilled in the art through research and practice of the present application. BRIEF DESCRIPTION OF DRAWINGS

[0019] Figure 1 The overall schematic diagram of the anti-back pressure performance improvement technology applied to the double-mode ramjet engine;

[0020] Figure 2A schematic diagram of the internal flow passage of a dual-mode ramjet engine with anti-back pressure performance enhancement technology;

[0021] Figure 3 A schematic diagram of the pressure monitoring points of the isolation section without and with anti-back pressure performance enhancement technology;

[0022] Figure 4 A schematic diagram of the schlieren monitoring of the isolation section without anti-back pressure performance enhancement technology;

[0023] Figure 5 A schematic diagram of the schlieren monitoring of the isolation section with anti-back pressure performance enhancement technology. DETAILED DESCRIPTION

[0024] The present application will be further described in detail below with reference to the accompanying drawings, so that those skilled in the art can implement the present application according to the description.

[0025] A flow recycling technology based on the effect of ejector airflow, which uses a corresponding control structure to re-inject the high-pressure separated flow that is originally sucked and discharged into the upstream low-pressure area of the dual-mode ramjet engine. The main technical idea is to replace the smooth wall of the isolation section of the dual-mode ramjet engine with an ejector flow channel, and to form a natural pressure difference environment between the high-pressure separation area induced by the combustion back pressure and the upstream low-pressure area, so as to suck and discharge the high-pressure separated flow to the low-pressure area of the flow field through the circulating flow channel, thereby reducing the problem of pre-combustion shock wave string forward transmission caused by the cumulative effect of boundary layer separation, and achieving the effect of improving the anti-back pressure performance of the dual-mode ramjet engine.

[0026] Further, the ejector flow channel is formed by modifying the smooth side wall of the isolation section of the dual-mode ramjet engine, and installing a control mechanism for the flow recycling bypass of the ejector airflow in the flow channel, to control the pre-disturbance of the pre-combustion shock wave string of the supersonic combustion chamber, enhance the resistance to combustion back pressure of the isolation section, reduce the risk of intake duct non-starting state, and further widen the working margin of the air-breathing power propulsion system. The working principle of the control mechanism is as follows: the high-pressure separated flow near the wall is sucked into the circulating flow channel component through the drainage hole component downstream of the isolation section, and then the separated flow is discharged to the low-pressure area of the flow field through the jet hole component upstream of the isolation section by the action of natural pressure difference, thereby achieving the anti-back pressure effect. This working principle not only avoids unnecessary trouble of installing external low-pressure devices, but also overcomes the problem of main flow loss.

[0027] As shown in Figure 1 The isolation section component of the dual-mode ramjet engine direct connection model is installed, and the smooth side wall blind plate of the isolation section of the dual-mode ramjet engine during the test is replaced with the flow recycling control structure designed by the present application. For Figure 1Wherein, 1 area is the upper wall of the isolation section, which is used to monitor the flow field information by optical glass or wall pressure sensor; 2 area is the fuel injector, which is opened at the upstream 10mm and downstream 25mm positions of the cavity, and is used to inject fuel; 3 area is the upper wall of the cavity section and the expansion section, which is used to monitor the flow field information by wall pressure sensor; 4 area is the side wall of the isolation section, which is used to replace the smooth side wall blind plate or install the control structure with anti-back pressure performance improvement technology; 5 area is the side wall of the cavity section and the expansion section, which is used to monitor the flow field information by optical glass, and the control structure is installed in the middle of the isolation section, the jet flow hole is located near the upstream 1 / 3 of the isolation section, and the jet flow hole is located near the downstream 1 / 3 of the isolation section.

[0028] Figure 2 Further, the double-mode ramjet engine with anti-back pressure performance improvement technology is separated from the external test mechanical structure, and the internal flow channel schematic diagram is shown. Figure 2 Wherein, F1 area is the jet flow hole position of the control structure; F2 area is the circulation flow channel position of the control structure; F3 area is the jet flow hole position of the control structure. F1-F3 areas jointly constitute a control assembly for improving the anti-back pressure performance of the double-mode ramjet engine under the effect of the jet air flow effect designed by the application, which can be a separate structure and then embedded in the side wall of the isolation section, or can be directly slotted on the side wall of the isolation section.

[0029] Figures 3-5 The monitoring information of the combustion flow field of the double-mode ramjet engine in the state of whether the anti-back pressure performance improvement technology is installed is given respectively. Under the two groups of working conditions, Figure 3 To feedback the complex flow structure front disturbance condition induced by fuel injection, combustion chamber combustion and combustion back pressure; Figures 4-5 To feedback the schlieren image condition that the combustion back pressure induced complex flow structure moves to the front end of the isolation section in the optical monitoring area of the isolation section flow field during the whole test process.

[0030] For Figure 3 "H2" represents Figure 1 The pressure of the monitoring point at the fuel injector in area 2; "r1" represents Figure 1 The pressure at the first pressure monitoring point in area 3, which is located at x=476mm position. "g10" represents Figure 1 The pressure at the 10th pressure monitoring point in area 1, which is located at x=255mm position. "U" and "C" symbols respectively represent the working conditions without anti-back pressure performance improvement technology and with anti-back pressure performance improvement technology.

[0031] For Figure 4The entire schlieren image is taken by the optical monitoring window and the high-speed camera. Due to the optical area limitation, the optical glass width is 100 mm, which is less than the width (150 mm) of the dual-mode ramjet engine, resulting in the loss of flow field information of the model near the two side walls, but does not affect the judgment of the front disturbance position of the shock train in the stream direction. In Figure 5 , Figure 2 The F1 region mentioned is located at x=150 mm, the F3 region is located at x=320 mm, and the entire F2 region has a length of 170 mm. Among them, Figure 4 and Figure 5 The "A", "B", and "C" regions in the above two figures respectively represent "pre-combustion shock train induced by the combustion back pressure in the isolation section in the state without the anti-back pressure performance improvement technology", "jet-induced shock generated when the cycle gas flow is discharged through the jet hole", and "pre-combustion shock train induced by the combustion back pressure in the isolation section in the state with the anti-back pressure performance improvement technology".

[0032] Figure 3 and Figure 4 The entire test process described in the above two figures is carried out in a ground direct-connected dual-mode ramjet engine test model, the incoming flow environment of which is an isolation section inlet Mach number Ma=2.0, total temperature Pt=950 K, and total pressure Pt=0.82 MPa, used to simulate a low-speed domain flight state of a Mach number 4.0. The entire test uses hydrogen as fuel, the equivalent ratio of which is 0.453, and burns in the auxiliary forced ignition of a spark plug.

[0033] For the "U" type working condition mentioned in the figure, the side wall of the isolation section of the dual-mode ramjet engine is a smooth blind plate structure, which belongs to the baseline configuration. For the "C" type working condition, the side wall of the isolation section of the dual-mode ramjet engine is replaced with the anti-back pressure performance improvement technology designed in the present application, and the specific implementation object is a flow control structure based on the effect of ejector gas flow.

[0034] From Figure 3It can be seen from the figures that, within the acceptable experimental error range, the fuel injection pressure and the combustion chamber monitoring point pressure of the "U" and "C" working conditions have the same pressure change process, indicating that the dual-mode ramjet engine with or without the anti-back pressure performance improvement technology produces the same combustion back pressure when the fuel equivalence ratio is 0.453. It should be noted that the existence of the auxiliary spark plug for forced ignition has random electrical signals, resulting in the difference in starting ignition between the "U" and "C" working conditions. In addition, considering the safety of hydrogen experiments, the injected hydrogen fuel is only supplied by an external small-capacity cylinder, resulting in an approximately linear decrease in driving pressure, and thus the fuel injection amount decreases linearly at a constant gradient. The monitoring pressure of the fuel injection site decreases from 2.0 MPa to 1.5 MPa during the entire test process. Correspondingly, the combustion pressure monitoring value fed back by r1 also decreases from 0.33 MPa to 0.30 MPa, but this weak combustion intensity phenomenon is not enough to affect the normal development of the test.

[0035] From Figure 3 It can also be seen from the figures that, in the state without the anti-back pressure performance improvement technology, the g10 monitoring point of the isolation section has a significant pressure disturbance from t = 3.605 s to 3.73 s, with a peak pressure of 0.245 MPa. On the contrary, in the state with the anti-back pressure performance improvement technology, there is no significant pressure disturbance during the entire test process, and the pressure curve basically remains at about 0.1 MPa, which is the static pressure of the incoming flow.

[0036] From Figure 4 It can be seen from the figures that, in the state without the anti-back pressure performance improvement technology, the pre-combustion shock wave string induced by the combustion back pressure disturbs to x = 255 mm, and the shock wave nodes formed by multiple continuous reflected shock waves are clearly captured by the optical schlieren. In the state with the anti-back pressure performance improvement technology, the pre-combustion shock wave string induced by the combustion back pressure is firmly locked at the position near x = 315 mm, and the shock wave node structure formed by the reflected shock waves is correspondingly distributed downstream of this position. At the same time, the jet shock wave structure induced by the exhaust separation flow in the F1 region is formed and reflected upstream of the isolation section.

[0037] Combining Figures 3-5 analysis, when the anti-back pressure performance improvement technology mentioned in Figure 1 and Figure 2 is loaded, the pre-combustion shock wave string structure originally induced by the combustion back pressure of the combustion chamber is effectively controlled in the F3 region and downstream thereof, verifying the effect of the invented technology on resisting the combustion back pressure and improving the anti-back pressure capability of the isolation section of the dual-mode ramjet engine. This can be attributed to the fact that the near-wall boundary layer separation flow generated by the combustion back pressure is disturbed by the suction effect of the invented technology, and is exhausted to the upstream of the isolation section through the circulation flow passage, and further induces a jet shock wave structure upstream, thereby strengthening the resistance effect of the pre-combustion shock wave string.

[0038] Without departing from the key idea of the present application, the anti-back pressure performance of the dual-mode ramjet engine can be further improved by adjusting the geometric shape, parameters and the number of component parts of the design structure to form variant control configurations. Specifically, in specific implementation, the flow guide holes, the jet flow holes and the circulation flow channels in the control structure can change the space-time evolution characteristics of the combustion flow field by increasing the number of components, and form suction and discharge circulation flow at multiple positions, so that the anti-back pressure performance of the dual-mode ramjet engine is improved. At the same time, the geometric parameters of the flow guide hole component (angle: 15°-180° and width generally less than 10mm), the geometric parameters of the jet flow hole component (angle: 15°-180° and width generally less than 10mm), and the geometric parameters of the circulation flow channel component (position in the middle of the isolation section, wherein the flow guide hole is located at 1 / 3 of the upstream of the isolation section, the jet flow hole is located at 1 / 3 of the downstream of the isolation section, the width is generally less than 10mm, the length is less than the length of the isolation section, and the distance from the isolation section wall is generally less than 30mm) can be adjusted to change the guiding direction, process and flow of the suction and discharge of the low-speed high-pressure separated flow, and the form of the re-action on the flow field, and further strengthen the working ability of the control structure to resist the combustion back pressure of the dual-mode ramjet engine.

[0039] The present application can realize the resistance to combustion back pressure and improve the starting margin of the inlet duct without changing the engine incoming flow and fuel injection conditions by forming a circulation flow channel with the characteristics of an ejector air flow through the slotting of the isolation section wall, thereby widening the low-speed domain flight corridor of the aircraft. The enhanced anti-back pressure performance effect to be reproduced by the present application is shown in Figure 3 and 4 The test process described in the figure is used to simulate the state of flight Mach number 4.0, which is carried out on a ground direct-connected dual-mode ramjet engine model, and the combustion flow field is generated by forced hydrogen ignition combustion by an external spark plug.

[0040] Comparative example

[0041] In order to adapt to the wide-speed domain flight demand of air-breathing aerospace vehicles, the power propulsion system tends to carry dual-mode ramjet engines with the advantage of mode free conversion. However, in the low flight speed domain corridor environment, the working mode of the dual-mode ramjet engine relying on the pre-combustion shock wave train of the isolation section and the combustion heat release of the combustion chamber often has limitations. This is because the pre-combustion shock wave train structure induced by the combustion back pressure is prone to approach the inlet of the inlet duct when it is disturbed upstream of the isolation section, which brings the risk of engine non-starting. Figure 3 and Figure 4The "U" type operating condition information shows that, without the application of anti-back pressure performance enhancement technology, when the hydrogen equivalence ratio does not reach 0.453, the leading edge of the pre-combustion shock wave induced by combustion back pressure is disturbed to x=255mm. If the isolation section is set too short at this time, the pre-combustion shock wave will have already pushed back out of the isolation section, causing the intake to fail to start.

[0042] Example

[0043] In this embodiment, a typical control structure is as follows: Figure 2 As shown, the enhanced back pressure performance technology is mainly achieved through a circulating flow channel based on the ejector airflow effect. The control structure is installed on both sides of the engine, 150mm from the isolation section, with a total length of 170mm; the width of both ejector and injection holes is 8mm, and the angle of offset from the isolation section is 45°; the circulating flow channel is 170mm long and 25mm from the side wall of the isolation section. During the experiment, a spark plug-forced hydrogen ignition method was used to generate the combustion flow field, thereby forming combustion back pressure downstream of the isolation section, with a hydrogen equivalence ratio of 0.453. To ensure that the combustion state in the combustion chamber is consistent with the comparative example, one of the wall pressure monitoring points in the fuel injector and combustion chamber was selected (…). Figure 3 Feedback is obtained using H2 and r1 to achieve the same combustion back pressure under the same hydrogen injection rate. The location of the pre-combustion shock train induced by the back pressure is captured by a wall pressure monitoring point (g10) selected in the isolation section and an optical monitoring area. Combined with... Figure 3 and Figure 5 As can be seen from the flow field information, after applying the control structure designed in this invention, the forward disturbance position of the pre-burning shock train is significantly shortened, and the anti-back pressure performance of the isolation section of the dual-mode ramjet engine is significantly enhanced.

[0044] The above solution is merely an illustration of a preferred example and is not limited thereto. When implementing this invention, appropriate substitutions and / or modifications can be made according to the user's needs.

[0045] The number of devices and processing scale described herein are for the purpose of simplifying the description of the invention. Applications, modifications, and variations of the invention will be readily apparent to those skilled in the art.

[0046] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be applied to various fields suitable for the present invention. Other modifications can be readily made by those skilled in the art. Therefore, without departing from the general concept defined by the claims and their equivalents, the present invention is not limited to the specific details and examples shown and described herein.

Claims

1. A method for improving anti-back pressure performance of a dual-mode ramjet engine based on ejector air flow, characterized in that, By constructing an ejector flow circulation channel at the two sides of the isolation section of the cavity type dual-mode ramjet engine, a natural pressure difference environment is formed by the high pressure separation area induced by the combustion back pressure and the upstream low pressure area, the high pressure separation flow is pumped and discharged to the low pressure area of the flow field through the ejector flow circulation channel, and the anti-back pressure performance of the dual-mode ramjet engine is improved.

2. The anti-back pressure performance enhancement method of the dual-mode ramjet engine based on the ejector airflow according to claim 1, characterized in that, The ejector flow circulation channel is obtained by a control assembly arranged downstream of the isolation section; The control assembly comprises two control structures arranged oppositely in space.

3. The anti-back pressure performance enhancement method of the dual-mode ramjet engine based on the ejector airflow according to claim 2, characterized in that, Each control structure is obtained in the form of being embedded or being slotted in the side wall surface.

4. The anti-back pressure performance enhancement method of the dual-mode ramjet engine based on the ejector airflow according to claim 2, characterized in that, Each control structure comprises: a main body arranged inside the smooth side wall; The main body is provided with at least one jet hole and a drainage hole at the front 1 / 3 and the rear 1 / 3 of the isolation section, respectively; The main body is provided with at least one circulation channel communicated with the jet hole and the drainage hole.

5. The anti-back pressure performance enhancement method of the dual mode ramjet engine based on the ejector airflow according to claim 3, characterized in that, The width of the jet hole and the drainage hole is less than 10mm, and the angle range of the two holes offsetting the isolation section is 15°-180°; The length of the circulation channel is less than the length of the isolation section, and the distance from the side wall surface of the isolation section is less than 30mm.

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