Method for improving mixing efficiency of ramjet engine through zero-mass jet flow

Abstract

The invention discloses a method for improving the mixing efficiency of a ramjet engine through zero-mass jet flow. The method comprises the steps that a zero-mass jet flow exciter is arranged on the wall face of a combustion chamber, close to one side of supersonic airflow, of the ramjet engine; the zero-mass jet flow exciter comprises a cavity, a driver and a piston. Wherein the driver drives the piston to reciprocate in the cavity; the end of the cavity communicates with the interior of the combustion chamber, and the movement direction of the piston is perpendicular to the central axis of the combustion chamber. The movement frequency and the movement amplitude of the piston in the cavity are configured through the driver; wherein the motion frequency is the same as the unsteady frequency of the turbulence structure; unsteady dynamic oblique shock waves moving at the movement frequency are generated in the mixing layer through the change of the position of the piston and oscillate back and forth in the mixing layer, then the resonance phenomenon is generated with the turbulent flow structure, and therefore the fuel and air mixing efficiency is improved.

Description

Technical Field

[0001] The invention relates to the field of aerospace, and in particular to a method for improving the mixing efficiency of a ramjet engine by utilizing a zero-mass jet. Background Art

[0002] A scramjet engine is a ramjet engine that burns fuel in supersonic airflow. It is the core key technology for achieving long-duration hypersonic flight in the atmosphere or across the atmosphere in the future. Since the air flows through the engine for only milliseconds, the key to engine performance is to complete the efficient mixing, ignition and efficient combustion of fuel and air in such a short time.

[0003] The related solutions for improving the mixing efficiency of ramjet engines in the prior art generally have the problems of complex structure, high cost, difficult maintenance and low efficiency. Summary of the invention

[0004] The purpose of the present invention is to provide a method for improving the mixing efficiency of a ramjet engine by utilizing a zero-mass jet, so as to overcome the problems of complex structure and low efficiency in the prior art.

[0005] In order to achieve the above tasks, the present invention adopts the following technical solutions:

[0006] A method for improving the mixing efficiency of a ramjet engine by using a zero-mass jet, comprising:

[0007] A zero-mass jet exciter is arranged on the combustion chamber wall surface of the ramjet engine near the supersonic airflow side; the zero-mass jet exciter comprises a cavity, a driver and a piston; wherein the driver drives the piston to reciprocate in the cavity; the end of the cavity is connected to the interior of the combustion chamber, and the movement direction of the piston is perpendicular to the central axis of the combustion chamber;

[0008] When the fuel is injected into the combustion chamber from the fuel inlet and mixed with the supersonic airflow entering from the supersonic airflow inlet, a certain area of ​​the mixing layer will be generated, and the turbulent structure inside it will vibrate at a certain frequency;

[0009] The driver is used to configure the movement frequency and movement amplitude of the piston in the cavity; wherein the movement frequency is the same as the unsteady frequency of the turbulent structure; the change in the piston position will generate an unsteady dynamic oblique shock wave in the mixing layer that moves at the movement frequency and oscillates back and forth in the mixing layer, thereby generating a "resonance" phenomenon with the turbulent structure, thereby improving the mixing efficiency of fuel and air; wherein the setting of the movement amplitude should enable the unsteady dynamic oblique shock wave generated by the zero-mass jet exciter to interact with the mixing layer.

[0010] Furthermore, the interaction is that the unsteady dynamic oblique shock wave intersects with the mixing layer and generates oscillations in the mixing layer.

[0011] Furthermore, the method for determining the frequency of the piston movement in the cavity is:

[0012] First, the ramjet engine is modeled and simulated, and the position of the mixing layer in the combustion chamber when the ramjet engine is working normally is determined based on the simulation results.

[0013] Secondly, multiple pressure sensors are arranged at intervals along the central axis of the combustion chamber in the mixing layer and simulated again; during the simulation, the pressure sensors are used to collect pressure data at different positions in the mixing layer, and the pressure data are subjected to Fourier analysis to obtain the frequencies of turbulent structures at different positions, and then the pulsating frequency with the largest proportion is selected as the unsteady frequency, that is, the movement frequency of the piston in the cavity.

[0014] Furthermore, after the movement frequency of the piston is determined, the arrangement parameters of the zero-mass jet actuator are determined according to the following method:

[0015] First, a zero-mass jet actuator is modeled and added to the ramjet model;

[0016] Secondly, the initial range of the arrangement parameters of the zero-mass jet actuator is set, where the arrangement parameters include the length L of the cavity of the zero-mass jet actuator from the supersonic airflow inlet. j , the width W of the cavity opening and the movement amplitude A of the piston;

[0017] Finally, multiple groups of length L are sampled from the initial range. j , width W and motion amplitude A; for each combination, according to the length L in the combination j The zero-mass jet actuator is arranged with a predetermined motion frequency and motion amplitude A on the piston of the zero-mass jet actuator by using a driver, and a simulation test of the normal operation of the ramjet is carried out. Based on the simulation results, an optimal set of parameters is determined as the arrangement parameters when the zero-mass jet actuator is actually applied to the ramjet.

[0018] Furthermore, the length L in the initial range j It is set to be no less than 7% of the length of the combustion chamber wall 1 , and the width W is 1 / 180 to 1 / 220 of the length of the combustion chamber wall 1 .

[0019] Furthermore, the optimal set of parameters is determined based on the simulation results, specifically:

[0020] For each combination of simulation test results, a density gradient cloud map of the flow field in the combustion chamber that changes with time is constructed. Based on the density gradient cloud map, a set of parameters that has the best mixing effect of the unsteady dynamic oblique shock wave generated by the zero-mass jet actuator in the mixing layer is determined as the optimal parameters.

[0021] A ramjet engine, wherein a zero-mass jet exciter is provided in the ramjet engine;

[0022] The massless jet exciter is arranged on the combustion chamber wall surface of the ramjet engine near the supersonic airflow side, and the massless jet exciter comprises a cavity, a driver and a piston; wherein the driver drives the piston to reciprocate in the cavity; the end of the cavity is connected to the interior of the combustion chamber, and the movement direction of the piston is perpendicular to the central axis of the combustion chamber;

[0023] When the fuel is injected into the combustion chamber from the fuel inlet and mixed with the supersonic airflow entering from the supersonic airflow inlet, a certain area of ​​the mixing layer will be generated, and the turbulent structure inside it will vibrate at a certain frequency;

[0024] The driver is used to configure the movement frequency and movement amplitude of the piston in the cavity; wherein the movement frequency is the same as the unsteady frequency of the turbulent structure; the change in the piston position will generate an unsteady dynamic oblique shock wave in the mixing layer that moves at the movement frequency and oscillates back and forth in the mixing layer, thereby generating a "resonance" phenomenon with the turbulent structure, thereby improving the mixing efficiency of fuel and air; wherein the setting of the movement amplitude should enable the unsteady dynamic oblique shock wave generated by the zero-mass jet exciter to interact with the mixing layer.

[0025] A hypersonic aircraft adopts the ramjet engine.

[0026] Compared with the prior art, the present invention has the following technical features:

[0027] The present invention has the unique advantage of not requiring an additional air source or moving parts, which makes it have many advantages such as simple and compact structure, light weight, low cost, and convenient maintenance, and successfully improves the mixing effect of air and fuel. The zero-mass jet is used to generate an unsteady shock wave to improve the mixing efficiency of fuel and air in the ramjet engine. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the arrangement of the zero-mass jet exciter on the combustion chamber in the present invention;

[0029] Figure 2 A schematic diagram of a calculation domain when performing simulation in an embodiment of the present invention;

[0030] Figure 3 The density gradient cloud diagrams of the flow field under three conditions in the embodiment of the present invention; (a) is the density gradient cloud diagram of the flow without jet, (b) is the density gradient cloud diagram of the flow under a steady zero mass jet, and (c) is the density gradient cloud diagram of the flow under a zero mass jet that changes with time.

[0031] Explanation of the numbers in the figure: 1 combustion chamber wall, 2 zero-mass jet exciter, 3 cavity, 4 driver, 5 piston, 6 mixing layer, 7 supersonic airflow inlet, 8 fuel inlet, 9 unsteady dynamic oblique shock wave, 10 combustion chamber. DETAILED DESCRIPTION

[0032] The use of zero-mass jet involved in the present invention refers to the use of the reciprocating motion of the piston to blow / inhale gas to generate a jet; during the blowing process, the cavity fluid forms a vortex ring / pair outside the orifice under the compression of the piston, and moves away from the orifice under their own induced action, while in the suction process, the vortex ring / pair is far away from the orifice and will not be sucked into the orifice; therefore, the zero-mass jet has the significant feature of only outputting momentum to the outside and the output mass is zero, and has the unique advantages of not requiring an additional gas source and not requiring moving parts, so that it has many advantages such as simple and compact structure, light weight, low cost, and easy maintenance.

[0033] From the knowledge of aerodynamics, we know that as the zero-mass jet moves away from the nozzle, the momentum of the jet gradually decreases, and the compression effect of the transverse jet on the supersonic flow gradually weakens. Therefore, when the supersonic airflow intersects with the transverse jet, an oblique shock wave will be generated at the intersection; if the transverse jet in the supersonic airflow moves with a certain frequency and amplitude, a moving oblique shock wave with the same frequency will inevitably be generated in the flow field.

[0034] The present invention provides a method for improving the mixing efficiency of a ramjet engine by using a zero-mass jet, and utilizing a moving oblique shock wave to increase the pulsation of the flow, thereby significantly enhancing the mixing effect of fuel and air; the method comprises:

[0035] A zero-mass jet exciter 2 is arranged on a combustion chamber wall 1 on a side of the ramjet engine close to the supersonic airflow; the zero-mass jet exciter 2 comprises a cavity 3, a driver 4 and a piston 5; wherein the driver 4 drives the piston 5 to reciprocate in the cavity 3; the end of the cavity 3 is connected to the interior of the combustion chamber 10, and the movement direction of the piston 5 is perpendicular to the central axis of the combustion chamber 10;

[0036] When the fuel is injected into the combustion chamber 10 from the fuel inlet 8 and mixed with the supersonic airflow entering from the supersonic airflow inlet 7 and burned, a mixing layer 6 of a certain area will be generated, and the turbulent structure inside it will vibrate at a certain frequency;

[0037] The movement frequency and movement amplitude of the piston 5 in the cavity 3 are configured by the driver 4; the movement frequency is the same as the unsteady frequency of the turbulent structure; due to the change in the position of the piston 5, an unsteady dynamic oblique shock wave 9 moving at the movement frequency will be generated in the mixing layer 6 and oscillate back and forth in the mixing layer 6, thereby generating a "resonance" phenomenon with the turbulent structure, thereby improving the mixing efficiency of fuel and air; wherein the setting of the movement amplitude should make the unsteady dynamic oblique shock wave generated by the zero-mass jet exciter 2 interact with the mixing layer 6; the interaction is that the unsteady dynamic oblique shock wave 9 intersects with the mixing layer 6 and oscillates in the mixing layer 6.

[0038] In this solution, the method for determining the movement frequency of the piston 5 in the cavity 3 is:

[0039] First, the ramjet engine is modeled and then simulated, and the position of the mixing layer 6 in the combustion chamber 10 when the ramjet engine works normally is determined according to the simulation results.

[0040] Secondly, multiple pressure sensors are arranged at intervals along the central axis of the combustion chamber 10 in the mixing layer 6 and simulated again; during the simulation, the pressure sensors are used to collect pressure data at different positions in the mixing layer 6, and the pressure data are subjected to Fourier analysis to obtain the frequencies of turbulent structures at different positions, and then the pulsating frequency with the largest proportion is selected as the unsteady frequency, that is, the movement frequency of the piston 5 in the cavity 3.

[0041] In this solution, after the movement frequency of the piston 5 is determined, the arrangement parameters of the zero-mass jet actuator 2 are determined according to the following method:

[0042] First, the zero-mass jet actuator 2 is modeled and added to the ramjet model;

[0043] Secondly, the initial range of the arrangement parameters of the zero-mass jet actuator 2 is set, wherein the arrangement parameters include the length L of the cavity 3 of the zero-mass jet actuator 2 from the supersonic airflow inlet 7. j , the width W of the opening of the cavity 3 and the movement amplitude A of the piston 5; in one embodiment of the present invention, the length L in the initial range j It is set to be no less than 7% of the length of the combustion chamber wall 1, and the width W is 1 / 180 to 1 / 220 of the length of the combustion chamber wall 1; these initial parameters are data determined by the inventor's team after long-term experimental research, combined with a large amount of experience and relevant literature; the initial range of the motion amplitude A should be determined depending on the size of the zero-mass jet exciter 2.

[0044] Finally, multiple groups of length L are sampled from the initial range. j , width W and motion amplitude A; for each combination, according to the length L in the combination jThe zero-mass jet exciter 2 is arranged with a width W, and the driver 4 is used to apply the determined motion frequency and motion amplitude A to the piston 5 of the zero-mass jet exciter 2, and a simulation test of the normal operation of the ramjet is carried out. Based on the simulation results, an optimal set of parameters is determined as the arrangement parameters when the zero-mass jet exciter 2 is actually applied to the ramjet.

[0045] The optimal set of parameters determined based on the simulation results is specifically:

[0046] For each combination of simulation test results, a density gradient cloud map of the flow field in the combustion chamber 10 that changes with time is constructed, and based on the density gradient cloud map, a set of parameters with the best mixing effect of the unsteady dynamic oblique shock wave 9 generated by the zero-mass jet exciter 2 in the mixing layer 6 is determined as the optimal parameters.

[0047] In summary, the present invention arranges a zero-mass jet exciter 2 on the wall 1 of the supersonic combustion chamber, and through the driver 4, the piston 5 is made to reciprocate in the cavity 3 at a certain movement frequency (the frequency is equal to the unsteady frequency of the turbulent structure in the mixing layer) to blow / suck gas, thereby generating an unsteady dynamic oblique shock wave 9 moving at the same frequency in the mixing layer 6; through this unsteady dynamic oblique shock wave 9 oscillating back and forth in the mixing layer 6, the "resonance" phenomenon between the unsteady dynamic oblique shock wave 9 and the turbulent structure is stimulated, thereby improving the mixing efficiency of fuel and air.

[0048] Example:

[0049] In this embodiment, the driver 4 of the zero-mass jet exciter 2 is set to drive the piston 5 to reciprocate in the form of a sine function to generate a total pressure in the form of a sine function, thereby generating an unsteady dynamic oblique shock wave 9; the setting of the sine function includes two parts: the motion amplitude and the motion frequency. The principle of the motion amplitude setting is to ensure that the dynamic oblique shock wave 9 generated by the changing total pressure can always interact with the mixing layer 6 and generate oscillations during the movement; and the frequency value is the same as the pulsation frequency with the largest proportion of turbulent structure in the mixing layer. Figure 2 As shown, after simulation in this embodiment, the optimal parameters obtained are:

[0050] The width L of the combustion chamber wall 1 y is the length L of the combustion chamber wall 1 x In the case of one fifth of the mass of the jet actuator 2, the length L between the cavity 3 of the zero-mass jet actuator 2 and the supersonic airflow inlet 7 is j It is 8% of the wall length, and the width W of the opening of the cavity 3 is one two hundredth of the wall length.

[0051] Figure 3The density gradient cloud diagrams of the flow field in the combustion chamber under the action of no jet, steady jet and time-varying jet are respectively shown; it can be seen that in the flow field without jet action, the mixing layer is smaller, the development of turbulent structure is more uniform and slow, and the mixing between flows is relatively weak; in the flow under the action of steady jet, the mixing layer is expanded, the turbulent structure is more complex, and the development is more intense and rapid, and the mixing between flows is enhanced; and in the flow under the action of time-varying jet using the scheme of the present invention, the mixing layer is larger, even including the upstream part where the shock wave and the mixing layer interact, the turbulent structure is very complex, and the development is very intense and rapid, achieving a very good mixing effect.

[0052] In summary, in the flow without jet action, the movement of turbulent structure will produce a series of weaker shock waves and expansion waves. These shock wave expansion wave systems exist for a very short time and contribute little to mixing. Compared with the shock waves generated by turbulent structures, the oblique shock waves generated by jets are much stronger and have a significant impact on the mixing layer. The interaction between shock waves and mixing layers will produce a series of complex shock waves and expansion wave systems. Compared with steady shock waves, the moving oblique shock waves will change the position of the intersection point and the shape of the shock waves in the lower low-speed zone, thereby enhancing the pulsation of the turbulent structure and improving the mixing effect. At the same time, the steady shock wave under the steady jet has almost no effect on the flow in the wave front, but can significantly increase the pulsation of the flow downstream of the intersection of the shock wave and the mixing layer. Compared with the mixing layer without shock wave and the interaction between the steady shock wave and the mixing layer, after applying the time-varying jet, the flow pulsation can be seen to be significantly enhanced downstream of the intersection of the moving oblique shock wave and the mixing layer; the interaction between the moving oblique shock wave and the mixing layer will cause the mixing layer to oscillate in space, resulting in pulsation in a larger flow area, thereby improving the mixing effect.

[0053] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. A method for improving the mixing efficiency of a ramjet engine by using a zero-mass jet, characterized in that: include: A zero-mass jet actuator (2) is arranged on a combustion chamber wall (1) on a side of a ramjet engine close to a supersonic airflow; the zero-mass jet actuator (2) comprises a cavity (3), a driver (4) and a piston (5); wherein the driver (4) drives the piston (5) to reciprocate in the cavity (3); the end of the cavity (3) is connected to the interior of the combustion chamber (10), and the movement direction of the piston (5) is perpendicular to the central axis of the combustion chamber (10); When the fuel is injected into the combustion chamber (10) from the fuel inlet (8) and mixed with the supersonic airflow entering from the supersonic airflow inlet (7) and burns, a mixing layer (6) of a certain area is generated, and the turbulent structure inside the mixing layer vibrates at a certain frequency; The motion frequency and motion amplitude of the piston (5) in the cavity (3) are configured by the driver (4); wherein the motion frequency is the same as the unsteady frequency of the turbulent structure; the change in the position of the piston (5) will generate an unsteady dynamic oblique shock wave (9) in the mixing layer (6) that moves at the motion frequency and oscillates back and forth in the mixing layer (6), thereby generating a "resonance" phenomenon with the turbulent structure, thereby improving the mixing efficiency of fuel and air; wherein the setting of the motion amplitude should enable the unsteady dynamic oblique shock wave generated by the zero-mass jet exciter (2) to interact with the mixing layer (6).

2. The method for improving the mixing efficiency of a ramjet engine by using a zero-mass jet according to claim 1, characterized in that: The interaction is that the unsteady dynamic oblique shock wave (9) intersects with the mixing layer (6) and oscillates in the mixing layer (6).

3. The method for improving the mixing efficiency of a ramjet engine by using a zero-mass jet according to claim 1, characterized in that: The method for determining the frequency of movement of the piston (5) in the cavity (3) is: First, a ramjet engine is modeled and then simulated, and the position of a mixing layer (6) in a combustion chamber (10) when the ramjet engine is operating normally is determined according to the simulation results; Secondly, a plurality of pressure sensors are arranged at intervals along the central axis of the combustion chamber (10) in the mixing layer (6) and simulated again; During the simulation process, pressure data at different positions in the mixing layer (6) are collected using a pressure sensor, and Fourier analysis is performed on the pressure data to obtain the frequencies of turbulent structures at different positions. The pulsating frequency with the largest proportion is then selected as the unsteady frequency, that is, the movement frequency of the piston (5) in the cavity (3).

4. The method for improving the mixing efficiency of a ramjet engine by using a zero-mass jet according to claim 1, characterized in that: After the movement frequency of the piston (5) is determined, the arrangement parameters of the zero-mass jet actuator (2) are determined according to the following method: First, a zero-mass jet actuator (2) is modeled and added to the ramjet model; Secondly, the initial range of the arrangement parameters of the zero-mass jet actuator (2) is set, wherein the arrangement parameters include the length L of the cavity (3) of the zero-mass jet actuator (2) from the supersonic airflow inlet (7) j , the width W of the opening of the cavity (3) and the movement amplitude A of the piston (5); Finally, multiple groups of length L are sampled from the initial range. j , width W and motion amplitude A; for each combination, according to the length L in the combination j The zero-mass jet actuator (2) is arranged with a width W, and a driver (4) is used to apply the determined motion frequency and motion amplitude A to the piston (5) of the zero-mass jet actuator (2), and a simulation test of the normal operation of the ramjet engine is carried out. Based on the simulation results, an optimal set of parameters is determined as the arrangement parameters when the zero-mass jet actuator (2) is actually applied to the ramjet engine.

5. The method for improving the mixing efficiency of a ramjet engine by using a zero-mass jet according to claim 4, characterized in that: Initial range length L j The width W is set to be no less than 7% of the length of the combustion chamber wall (1), and the width W is 1 / 180 to 1 / 220 of the length of the combustion chamber wall (1).

6. The method for improving the mixing efficiency of a ramjet engine by using a zero-mass jet according to claim 4, characterized in that: The optimal set of parameters is determined based on the simulation results, specifically: For each combination of simulation test results, a density gradient cloud map of the flow field in the combustion chamber (10) that changes with time is constructed, and based on the density gradient cloud map, a set of parameters that best achieves the mixing effect of the unsteady dynamic oblique shock wave (9) generated by the zero-mass jet exciter (2) in the mixing layer (6) is determined as the optimal parameters.

7. A ramjet engine, characterized in that: The ramjet engine is provided with a zero-mass jet exciter (2); A zero-mass jet actuator (2) is arranged on a combustion chamber wall (1) on a side of a ramjet engine close to a supersonic airflow, and the zero-mass jet actuator (2) comprises a cavity (3), a driver (4) and a piston (5); wherein the driver (4) drives the piston (5) to reciprocate in the cavity (3); an end of the cavity (3) is connected to the interior of a combustion chamber (10), and a movement direction of the piston (5) is perpendicular to a central axis of the combustion chamber (10); When the fuel is injected into the combustion chamber (10) from the fuel inlet (8) and mixed with the supersonic airflow entering from the supersonic airflow inlet (7) and burns, a mixing layer (6) of a certain area is generated, and the turbulent structure inside the mixing layer vibrates at a certain frequency; The motion frequency and motion amplitude of the piston (5) in the cavity (3) are configured by the driver (4); wherein the motion frequency is the same as the unsteady frequency of the turbulent structure; the change in the position of the piston (5) will generate an unsteady dynamic oblique shock wave (9) in the mixing layer (6) that moves at the motion frequency and oscillates back and forth in the mixing layer (6), thereby generating a "resonance" phenomenon with the turbulent structure, thereby improving the mixing efficiency of fuel and air; wherein the setting of the motion amplitude should enable the unsteady dynamic oblique shock wave generated by the zero-mass jet exciter (2) to interact with the mixing layer (6).

8. A hypersonic aircraft, characterized in that: The aircraft adopts the ramjet engine according to claim 7.

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