Heat Reduction and Structural Safety Protection Method Based on Flow Control Hot Spot Periodic Movement

Abstract

The present invention discloses a method for heat reduction and structural safety protection based on the periodic movement of flow control hot spots. At least one active flow control mechanism is arranged on the thermal protection requirement surface of the aircraft and in a set area upstream of the natural transition point of the boundary layer; during the flight of the aircraft, the active flow control mechanism is periodically opened and closed to promote the periodic forced transition of the laminar boundary layer in advance downstream of the active flow control mechanism, so as to achieve the periodic movement of the transition hot spot in the local area of ​​the laminar-turbulent boundary layer transition, avoid the transition hot spot to continuously heat the same position, and thus avoid the damage of aerodynamic thermal ablation to the aircraft structure. The present invention relates to the field of aircraft safety protection, and can control the transition hot spot to periodically move on the thermal protection requirement surface, avoid the transition hot spot to continuously heat the same position on the thermal protection requirement surface, and thus avoid the damage of aerodynamic thermal ablation to the aircraft structure.

Description

Technical Field

[0001] The present invention relates to the technical field of aircraft safety protection, and in particular to a heat reduction and structural safety protection method based on flow-controlled hot spot periodic movement. Background Art

[0002] At present, the shape of aircraft with high lift-to-drag ratio is gradually developing in the direction of flattening, such as waverider configuration. Faced with this trend of flat and thin shape development, thinness has become the most severe test faced by thermal structure. First, thinning of thermal structure in key parts such as aircraft tip and wing leading edge can effectively reduce the wave drag of aircraft, thereby improving the lift-to-drag ratio of aircraft; secondly, thinning of thermal structure can significantly reduce the weight of aircraft, thereby reducing the lift conditions required for hypersonic cruise. However, aircraft have to fly for a long time in the atmosphere, and the thermal environment of the aircraft is mainly characterized by long time, high enthalpy, medium / low heat flow, and the total heating amount borne by the thermal structure is greater, and the long-term high temperature resistance / anti-ablation performance requirements are more stringent.

[0003] For aircraft, the transition from laminar to turbulent boundary layer is an important source of uncertain aerodynamic heating, which has a great impact on the thermal protection system of aircraft. It is generally believed that the enhancement of heat transfer is related to the evolution of unstable waves, thereby changing the friction coefficient. In the transition process of high Mach flow, an important mechanism of transition is the instability of expansion and compression waves and longitudinal waves, such as secondary and higher order unstable modes, and the higher the Mach number, the more significant its effect. Some recent research results show that in the transition process, there are two areas of concentrated heat transfer, one in the transition zone and the other at the tail of the transition zone. At present, for the transition hot spots generated in the boundary layer transition process, the method of increasing the thickness of the anti-insulation material is usually used to deal with it, but this method will increase the weight of the aircraft and reduce the efficiency. Some studies have adopted the method of continuous injection of air film for application, but its pipeline system is complex, and the required gas volume is large, the cost is high, and it will also affect the aerodynamic performance of the aircraft. Summary of the invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides a heat reduction and structural safety protection method based on the periodic movement of flow-controlled hot spots, which can control the periodic movement of transition hot spots on the surface requiring thermal protection, avoid the transition hot spot continuously heating the same position of the surface requiring thermal protection, and thus avoid damage to the aircraft structure by aerodynamic thermal ablation.

[0005] To achieve the above-mentioned object, the present invention provides a method for heat reduction and structural safety protection based on periodic movement of flow-controlled hot spots, wherein at least one active flow control mechanism is arranged on the thermal protection required surface of the aircraft and in a set area upstream of the natural transition point of the boundary layer, wherein the active flow control mechanism is an active jet device or a surface discharge device;

[0006] During the flight of the aircraft, the active flow control mechanism is periodically opened and closed to promote the periodic forced transition of the laminar boundary layer in advance downstream of the active flow control mechanism, so as to achieve the periodic movement of the transition hotspot in the local area of ​​the laminar-turbulent boundary layer transition, avoid the transition hotspot from continuously heating the same position, and thus avoid damage to the aircraft structure due to aerodynamic thermal ablation.

[0007] In one embodiment, the number of the active flow control mechanisms is more than two, and the active flow control mechanisms are spaced apart along the flow direction;

[0008] The periodic opening and closing of the active flow control mechanism to promote the forced transition of the laminar boundary layer in advance at the set position is specifically:

[0009] The active flow control mechanisms are controlled to be opened and closed in sequence according to a set order, so that the transition hot spots appear periodically at the natural transition points and at the downstream positions of the active flow control mechanisms.

[0010] In one embodiment, the jet velocity or discharge power excited by the active flow control mechanism is controlled to change periodically, so that the position of the transition hot spot changes periodically in the local range downstream of each active flow control mechanism.

[0011] In one embodiment, the jet velocity or discharge power excited by the active flow control mechanism is controlled to change periodically as follows:

[0012] The jet velocity or discharge power generated by the active flow control mechanism is controlled to change in an inverted "U" shape in the form of a quadratic function or a cubic function, that is, the jet velocity or discharge power increases from 0 to a maximum value and then decreases from the maximum value to 0.

[0013] In one embodiment, the periodic movement range of the transition hotspot is satisfy:

[0014] ;

[0015] in, is the heat flux absorption rate of the thermal insulation material on the aircraft surface, is the heat flux density of aerodynamic heating, is the width of the boundary layer transition hotspot, is the thickness of the thermal insulation material on the aircraft surface, is the thermal conductivity of the thermal insulation material on the aircraft surface; is the internal temperature of the aircraft, is the critical ablation temperature of the thermal insulation material on the aircraft surface;

[0016] The periodic movement range of the transition hotspot is defined as the length extending upstream from the natural turning point.

[0017] In one embodiment, the frequency of the periodic movement of the transition hotspot is Greater than or equal to the characteristic frequency of the incoming flow , and the frequency of the periodic movement of the transition hotspot The corresponding dimensionless frequency Strouhal number is not in the range of 0.03-0.3 to avoid inducing resonance and fatigue of the aircraft structure;

[0018] in, , Airflow velocity over the surface required for thermal protection.

[0019] In one embodiment, the active flow control mechanism is arranged on the same side of the boundary layer to induce the bypass transition by directly applying a blocking effect to the boundary layer; and / or

[0020] The active flow control mechanism is arranged on the opposite side of the boundary layer to induce an oblique shock wave incident on the boundary layer to generate a strong adverse pressure gradient to induce separation transition.

[0021] In one embodiment, when the active flow control mechanism is arranged on the same side of the boundary layer, the active jet or the jet velocity induced by the surface discharge generated by the active flow control mechanism is greater than 0.01 times , in order to force a transition in advance, where Airflow velocity over the surface required for thermal protection;

[0022] When the active flow control mechanism is arranged on the opposite side of the boundary layer, the pressure ratio of the active jet or the jet induced by surface discharge generated by the active flow control mechanism is greater than The angle of the oblique shock wave generated is greater than 45°, thereby ensuring the flow separation of the boundary layer and the occurrence of boundary layer transition.

[0023] In one embodiment, during the process of the active flow control mechanism being turned on to promote the periodic forced transition of the laminar boundary layer in advance downstream of the active flow control mechanism, the active flow control mechanism is turned on continuously or intermittently, specifically:

[0024] When the heat flux density of the transition hotspot is When the following conditions are met, the active flow control mechanism is continuously opened or intermittently opened;

[0025] When the heat flux density of the transition hotspot is greater than In the following situations, the active flow control mechanism is continuously opened.

[0026] In one embodiment, when the active flow control mechanism is an active jet device, the active jet of the active flow control mechanism is a synthetic jet, a synthetic dual jet, a plasma synthetic jet, an engine bleed jet or a high-pressure gas source jet;

[0027] When the active flow control mechanism is a surface discharge device, the surface discharge mode of the active flow control mechanism is arc discharge, glow discharge, dielectric barrier discharge or corona discharge.

[0028] Compared with the prior art, the present invention has the following beneficial technical effects:

[0029] 1. The structural safety protection method of the present invention arranges an active flow control mechanism on the thermal protection required surface of the aircraft, and uses the active flow control mechanism to periodically start and shut down, so that the transition hotspot periodically appears at the natural transition point and the downstream position of the active flow control mechanism, thereby avoiding the transition hotspot from continuously heating the same position of the thermal protection required surface, thereby avoiding the damage of the aircraft structure to the aerodynamic thermal ablation;

[0030] 2. The structural safety protection method of the present invention is not only simple in structure, flexible in control, and has low energy consumption, but can also effectively reduce the impact on the aerodynamic performance of the aircraft while achieving thermal protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0032] Figure 1 Schematic diagram of the effect of the heat reduction and structural safety protection method in an embodiment of the present invention.

[0033] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0035] 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 position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0036] In addition, the technical solutions between the various embodiments of the present invention can be combined with each other, but it must be based on the fact that ordinary technicians in the field can implement it. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0037] This embodiment discloses a method for heat reduction and structural safety protection based on periodic movement of flow control hot spots. The method sets at least one active flow control mechanism on the thermal protection demand surface of the aircraft and in a set area upstream of the natural transition point of the boundary layer. During the flight of the aircraft, the active flow control mechanism is periodically opened and closed, so that the active flow control mechanism periodically excites the active jet to promote the periodic forced transition of the laminar boundary layer in the adjacent position downstream of the active flow control mechanism, so as to achieve periodic movement of the transition hot spot in the local area of ​​the laminar-turbulent boundary layer transition, avoid continuous heating of the transition hot spot at the same position, and thus avoid damage to the aircraft structure by aerodynamic thermal ablation. Among them, the active flow control mechanism is an active jet device or a surface discharge device.

[0038] In a specific implementation process, the number of active flow control mechanisms may be set to only one, that is, the turning point is periodically changed between the natural turning point position and the downstream adjacent position of the active flow control mechanism.

[0039] When the number of active flow control mechanisms is more than two, each active flow control mechanism is distributed at equal or unequal intervals along the incoming flow direction on the surface requiring thermal protection. At this time, the active flow control mechanism is periodically opened and closed to promote the laminar boundary layer to force a transition in advance at the set position. Specifically, each active flow control mechanism is controlled to be opened and closed in turn according to the set order, so that the transition hotspots appear periodically at the natural transition point and the downstream position of each active flow control mechanism.

[0040] For example Figure 1 As shown in the figure, two synthetic dual jet actuators are arranged on the surface requiring thermal protection as active flow control mechanisms, and the process of heat reduction and structural safety protection is as follows:

[0041] Step 1: Both synthetic dual jet actuators are not started, that is, Figure 1 As shown in (a), the transition hotspot is located upstream of the natural transition.

[0042] Step 2, start the second synthetic dual jet actuator to promote the laminar boundary layer to force transition in advance downstream of the second synthetic dual jet actuator, that is, Figure 1 As shown in (b), the transition hotspot is located downstream of the second synthetic dual jet actuator;

[0043] Step 3, close the second synthetic dual jet actuator and start the first synthetic dual jet actuator to promote the laminar boundary layer to force the transition in advance downstream of the first synthetic dual jet actuator, that is, Figure 1 As shown in (c), the transition hotspot is located downstream of the first synthetic dual jet actuator;

[0044] Step 4, close the first synthetic dual jet actuator, and start the second synthetic dual jet actuator, so as to promote the laminar boundary layer to force the transition in advance downstream of the second synthetic dual jet actuator, that is, Figure 1 As shown in (b), the transition hotspot is located downstream of the second synthetic dual jet actuator;

[0045] Step 5: Repeat steps 1 to 4 until the aircraft no longer requires heat reduction and structural safety protection.

[0046] It is worth noting that in Figure 1 In the example given, the periodic start and stop of the two synthetic dual jet actuators may not adopt the above steps 2 to 4. For example, step 4 may not be set separately in the above steps, that is, steps 1 to 3 may be cyclically performed.

[0047] As a preferred embodiment, for the same active flow control mechanism, the jet velocity or discharge power excited by it also changes periodically, so that the position of the transition hotspot will also change periodically in the local range downstream of each active flow control mechanism. In the specific implementation process, the control intensity of each active flow control mechanism can be changed in the form of pulses. For example, when the active flow control mechanism is an active jet device, the jet velocity generated by the active flow control mechanism is controlled to change in an inverted "U" shape in the form of a quadratic function or a cubic function, that is, the jet velocity slowly increases from 0 to the maximum value, and then slowly decreases from the maximum value to 0, and the total pulse width is controlled at about 300-500 microseconds, so that the transition hotspot at the downstream of each active flow control mechanism produces a small reciprocating motion, that is, the position of the transition hotspot downstream of each active flow control mechanism also changes periodically. For another example, when the active flow control mechanism is a surface discharge device, the discharge power of the active flow control mechanism is controlled to change in an inverted "U" shape in the form of a quadratic function or a cubic function, that is, the discharge power slowly increases from 0 to a maximum value, and then slowly decreases from the maximum value to 0. The total pulse width is controlled at about 50-500 microseconds. Similarly, the position of the transition hotspot downstream of each active flow control mechanism can also change periodically.

[0048] In this embodiment, the length extending from the natural turning point to the upstream of the incoming flow on the surface requiring thermal protection is defined as the periodic movement range. In the specific implementation process, the periodic movement range of the transition hotspot on the surface requiring thermal protection is satisfy:

[0049] ;

[0050] in, is the heat flux absorption rate of the thermal insulation material on the aircraft surface, is the heat flux density of aerodynamic heating, is the width of the boundary layer transition hotspot, is the thickness of the thermal insulation material on the aircraft surface, is the thermal conductivity of the aircraft surface insulation material, is the internal temperature of the aircraft, It is the critical ablation temperature of the thermal insulation material on the aircraft surface.

[0051] Frequency of periodic movement of transition hotspots Greater than or equal to the characteristic frequency of the incoming flow , and the frequency of the periodic movement of the transition hotspot The corresponding dimensionless frequency Strouhal number is not in the range of 0.03-0.3 to avoid causing resonance and fatigue of the aircraft structure. , The airflow velocity on the surface required for thermal protection. It is worth noting that for high-speed aircraft, the frequency of the periodic movement of the transition hot spot is The corresponding dimensionless frequency Strouhal number should not be in the range of 0.03-0.04.

[0052] In the specific implementation process, the position of the active flow control mechanism on the thermal protection required surface can be located on the same side of the boundary layer or on the opposite side of the boundary layer. When the active flow control mechanism is arranged on the same side of the boundary layer, the bypass transition is induced by directly applying a blocking effect to the boundary layer. When the active flow control mechanism is arranged on the opposite side of the boundary layer, the separation transition is induced by inducing an oblique shock wave incident on the boundary layer to generate a strong adverse pressure gradient.

[0053] Specifically, when the jet velocity is less than 1% of the incoming flow velocity, the disturbance to the boundary layer is very weak. Therefore, in this embodiment, when the active flow control mechanism is arranged on the same side of the boundary layer, the active jet generated by the active flow control mechanism or the jet induced by the surface discharge is greater than 0.01 times the velocity of the incoming flow. , in order to force a transition in advance, where When the active flow control mechanism is arranged on the opposite side of the boundary layer, the pressure ratio of the active jet generated by the active flow control mechanism or the jet induced by the surface discharge is greater than The angle of the oblique shock wave generated is greater than 45°, thereby ensuring the flow separation of the boundary layer and the occurrence of boundary layer transition.

[0054] In the specific implementation process, when the active flow control mechanism is turned on to promote the periodic forced transition of the laminar boundary layer downstream of the active flow control mechanism, the active flow control mechanism can be turned on continuously or intermittently. Specifically, when the heat flux density of the transition hotspot is low, the surface temperature of the aircraft is not easy to rise quickly and is not easy to exceed the allowed temperature, so intermittent opening can be considered. When the heat flux density of the transition hotspot is high, the risk of excessive temperature is greater, so it must be turned on continuously. Therefore, this embodiment will Set as the critical value of the heat flux density of the transition hotspot. When the heat flux density of the transition hotspot is When the heat flux density of the transition hotspot is greater than When the active flow control mechanism is continuously opened.

[0055] In the specific implementation process, when the active flow control mechanism is an active jet device, the active jet of the active flow control mechanism is a synthetic jet, a synthetic dual jet, a plasma synthetic jet, an engine bleed jet or a high-pressure gas source jet. When the active flow control mechanism is a surface discharge device, the surface discharge mode of the active flow control mechanism is arc discharge, glow discharge, dielectric barrier discharge or corona discharge.

[0056] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for heat reduction and structural safety protection based on flow-controlled hot spot periodic movement, characterized in that: At least one active flow control mechanism is arranged on the thermal protection required surface of the aircraft and in a set area upstream of the natural transition point of the boundary layer, wherein the active flow control mechanism is an active jet device or a surface discharge device; During the flight of the aircraft, the active flow control mechanism is periodically turned on and off to promote the periodic forced transition of the laminar boundary layer downstream of the active flow control mechanism in advance, so as to achieve the periodic movement of the transition hotspot in the local area of ​​the laminar-turbulent boundary layer transition, thereby avoiding the transition hotspot from continuously heating the same position, thereby avoiding the damage of the aircraft structure to aerodynamic thermal ablation; The periodic movement range of the transition hotspot satisfy: in, is the heat flux absorption rate of the thermal insulation material on the aircraft surface, is the heat flux density of aerodynamic heating, is the width of the boundary layer transition hotspot, is the thickness of the thermal insulation material on the aircraft surface, is the thermal conductivity of the thermal insulation material on the aircraft surface; is the internal temperature of the aircraft, is the critical ablation temperature of the thermal insulation material on the aircraft surface; The periodic movement range of the transition hotspot is defined as the length extending upstream from the natural turning point.

2. The heat reduction and structural safety protection method based on flow control hot spot periodic movement according to claim 1 is characterized in that: The number of the active flow control mechanisms is more than two, and the active flow control mechanisms are spaced apart along the flow direction; The periodic opening and closing of the active flow control mechanism to promote the forced transition of the laminar boundary layer in advance at the set position is specifically: The active flow control mechanisms are controlled to be opened and closed in sequence according to a set order, so that the transition hot spots appear periodically at the natural transition points and at the downstream positions of the active flow control mechanisms.

3. The heat reduction and structural safety protection method based on flow control hot spot periodic movement according to claim 2 is characterized in that: The jet velocity or discharge power excited by the active flow control mechanism is controlled to change periodically, so that the position of the transition hot spot changes periodically in the local range downstream of each active flow control mechanism.

4. The heat reduction and structural safety protection method based on flow control hot spot periodic movement according to claim 3 is characterized in that: The jet velocity or discharge power excited by the active flow control mechanism is controlled to change periodically as follows: The jet velocity or discharge power generated by the active flow control mechanism is controlled to change in an inverted "U" shape in the form of a quadratic function or a cubic function, that is, the jet velocity or discharge power increases from 0 to a maximum value and then decreases from the maximum value to 0.

5. The heat reduction and structural safety protection method based on flow-controlled hot spot periodic movement according to any one of claims 1 to 4, characterized in that: The frequency of the periodic movement of the transition hotspot Greater than or equal to the characteristic frequency of the incoming flow , and the frequency of the periodic movement of the transition hotspot The corresponding dimensionless frequency Strouhal number is not in the range of 0.03-0.3 to avoid inducing resonance and fatigue of the aircraft structure; in, , Airflow velocity over the surface required for thermal protection.

6. The heat reduction and structural safety protection method based on flow-controlled hot spot periodic movement according to any one of claims 1 to 4, characterized in that: The active flow control mechanism is arranged on the same side of the boundary layer to induce bypass transition by directly applying a blocking effect to the boundary layer; and / or The active flow control mechanism is arranged on the opposite side of the boundary layer to induce an oblique shock wave incident on the boundary layer to generate a strong adverse pressure gradient to induce separation transition.

7. The heat reduction and structural safety protection method based on flow-controlled hot spot periodic movement according to claim 6 is characterized in that: When the active flow control mechanism is arranged on the same side of the boundary layer, the active jet generated by the active flow control mechanism or the jet induced by the surface discharge has a velocity greater than 0.01 times , in order to force a transition in advance, where Airflow velocity over the surface required for thermal protection; When the active flow control mechanism is arranged on the opposite side of the boundary layer, the pressure ratio of the active jet or the jet induced by the surface discharge generated by the active flow control mechanism is greater than Ma 2 The angle of the oblique shock wave generated is greater than 45°, thereby ensuring the flow separation of the boundary layer and the occurrence of boundary layer transition.

8. The heat reduction and structural safety protection method based on flow-controlled hot spot periodic movement according to any one of claims 1 to 4, characterized in that: In the process where the active flow control mechanism is opened to promote the periodic forced transition of the laminar boundary layer in advance downstream of the active flow control mechanism, the active flow control mechanism is opened continuously or intermittently, specifically: When the heat flux density of the transition hotspot is 0.1 MW / m 2 When the following conditions are met, the active flow control mechanism is continuously opened or intermittently opened; When the heat flux density of the transition hotspot is greater than 0.1 MW / m 2 In the following situations, the active flow control mechanism is continuously opened.

9. The heat reduction and structural safety protection method based on flow-controlled hot spot periodic movement according to any one of claims 1 to 4, characterized in that: When the active flow control mechanism is an active jet device, the active jet of the active flow control mechanism is a synthetic jet or a high-pressure gas source jet; When the active flow control mechanism is a surface discharge device, the surface discharge mode of the active flow control mechanism is arc discharge, glow discharge, dielectric barrier discharge or corona discharge.

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