A method for reducing heat and drag of hypersonic aircraft

Abstract

The present invention discloses a method for reducing heat and drag on hypersonic aircraft. By generating a wall-normal cold jet and / or a wall-tangential cold jet on the hypersonic aircraft wall, the cold jet interacts with the incoming flow to form a surface cold air film in the hypersonic aircraft's boundary layer. This method is applicable to aircraft design. The surface cold air film generated by the interaction between the cold jet and the incoming flow transforms the original gas-solid shear layer on the hypersonic aircraft surface into an air-gas shear layer, reducing the velocity shear gradient and temperature gradient of the fluid near the hypersonic aircraft wall. This reduces boundary layer frictional resistance and heat flux density, enabling cost-effective, long-term, and highly efficient heat and drag reduction for hypersonic aircraft.

Description

Technical Field

[0001] The present invention relates to the technical field of aircraft design, and in particular to a method for reducing heat and drag of a hypersonic aircraft. Background Art

[0002] Hypersonic vehicle technology represents a new frontier in 21st-century aerospace technology. Hypersonic vehicles must maintain hypersonic speeds for extended periods within the atmosphere. The demanding lift-to-drag ratio and harsh aerodynamic and thermal environment present significant design challenges. Optimizing lift-to-drag ratio solely through design inevitably results in a loss of other operational capabilities and places excessively stringent demands on thermal protection systems. Therefore, the search for new methods to reduce heat and drag in hypersonic vehicles has become an essential requirement for hypersonic vehicle development. The heat and drag reduction challenges faced by hypersonic vehicles are closely linked to boundary layer flow. It is well known that the transition from laminar to turbulent flow in the hypersonic boundary layer increases wall friction and heat flux by a factor of three to five. The aerodynamic drag and aerodynamic heat generated by the boundary layer dominate the generation of forces and heat in hypersonic vehicles, significantly impacting their performance. Therefore, exploring new methods to reduce heat and drag of hypersonic aircraft based on boundary layer flow control is of great significance for improving the technical level of hypersonic aircraft in my country and leading the development of hypersonic technology internationally.

[0003] Active flow control technology, with its wide adaptability, flexible control, and adaptive capabilities, is an effective solution to the aforementioned heat and drag reduction challenges faced by hypersonic vehicles. However, its high energy consumption is a critical weakness. Hypersonic vehicles typically need to maintain high-speed flight within the atmosphere for extended periods of time. The cumulative effect of aerodynamic drag results in significant energy losses in the vehicle. Therefore, heat and drag reduction technologies must also be able to produce a long-term cumulative effect. Simply reducing heat and drag in a short period of time is of little significance for improving the overall performance of the vehicle, requiring the heat and drag reduction methods employed to be able to operate for extended periods. However, active flow control technology, due to the need for continuous injection of additional energy, often suffers from high power and air consumption and limited operating time. This is particularly true for active flow control actuators that must reduce heat and drag under high-speed incoming airflow conditions and across a large area of the vehicle. Summary of the Invention

[0004] In view of the above-mentioned deficiencies in the prior art, the present invention provides a method for reducing heat and drag of a hypersonic aircraft, which can achieve heat and drag reduction of a hypersonic aircraft at low cost, over a long period of time and with high efficiency.

[0005] To achieve the above objectives, the present invention provides a method for reducing heat and drag of a hypersonic aircraft, which generates a wall-normal cold jet and / or a wall-tangential cold jet on the wall of the hypersonic aircraft to form a surface cold air film in the boundary layer of the hypersonic aircraft surface.

[0006] In one embodiment, the wall tangential cold jet is ejected tangentially through a backward step provided on the wall of the hypersonic aircraft, and interacts with the incoming flow to form the surface cold air film.

[0007] In one embodiment, the wall-normal cold jet is ejected normally through micropores and / or grooves provided on the wall of the hypersonic aircraft, and interacts with the incoming flow to form the surface cold air film.

[0008] In one embodiment, the thickness of the surface cold air film does not exceed the linear bottom layer of the turbulent boundary layer, and forms a slip phenomenon with the original boundary layer to reduce the original velocity gradient and temperature gradient of the boundary layer.

[0009] In one embodiment, the wall normal cold jet and / or the wall tangential cold jet may be formed by a self-sustaining synthetic jet based on utilizing the hypersonic flow's own energy, or may be formed by a jet actuator.

[0010] The present invention provides a method for reducing heat and drag of a hypersonic aircraft. The method generates a wall-normal cold jet and / or a wall-tangential cold jet on the wall of the hypersonic aircraft, so that a surface cold air film is formed in the boundary layer of the hypersonic aircraft surface under the interaction of the cold jet and the incoming flow. The surface cold air film converts the original gas-solid shear layer on the surface of the hypersonic aircraft into an gas-gas shear layer, reducing the velocity shear gradient and temperature gradient of the fluid near the wall of the hypersonic aircraft, thereby reducing the friction resistance and heat flux density of the boundary layer. The method can achieve heat and drag reduction of the hypersonic aircraft at low cost, over a long period of time and with high efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. 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 any creative work.

[0012] Figure 1 Schematic diagram of boundary layer control of wall tangential cold jet in an embodiment of the present invention;

[0013] Figure 2 Schematic diagram of boundary layer control of wall normal cold jet in an embodiment of the present invention;

[0014] Figure 3 Schematic diagram of a first embodiment of the cold jet gas source and jet flow control in an embodiment of the present invention;

[0015] Figure 4 Schematic diagram of a second embodiment of the cold jet gas source and jet flow control in an embodiment of the present invention;

[0016] Figure 5 Schematic diagram of drag reduction results according to an example of an embodiment of the present invention;

[0017] Figure 6 Schematic diagram of fever reduction results exemplified in an embodiment of the present invention.

[0018] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings and in conjunction with the embodiments. DETAILED DESCRIPTION

[0019] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0020] 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 various components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0021] 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 this field can implement it. When the combination of technical solutions is mutually contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0022] This embodiment discloses a method for reducing heat and drag of a hypersonic aircraft. By generating a wall-normal cold jet and / or a wall-tangential cold jet on the wall of the hypersonic aircraft, a surface cold air film is formed in the boundary layer of the hypersonic aircraft surface due to the interaction between the cold jet and the incoming flow. The surface cold air film converts the original gas-solid shear layer on the surface of the hypersonic aircraft into an air-gas shear layer, reducing the velocity shear gradient and temperature gradient of the fluid near the wall of the hypersonic aircraft, thereby reducing the friction resistance and heat flux density of the boundary layer. The method can achieve low-cost, long-term, and high-efficiency heat and drag reduction of the hypersonic aircraft.

[0023] refer to Figure 1 For the wall tangential cold jet, a backward step can be arranged on the wall of the hypersonic aircraft, and a jet hole can be set on the backward step, so that the wall tangential cold jet is ejected tangentially through the jet hole on the backward step and interacts with the high-speed incoming flow to form a surface cold air film.

[0024] refer to Figure 2 For the wall-normal cold jet, micropores and / or grooves can be arranged on the wall of the hypersonic aircraft so that the wall-normal cold jet is ejected normally through the micropores and / or grooves and interacts with the high-speed incoming flow to form a surface cold air film.

[0025] refer to Figure 3 As for the gas source and jet flow control of the cold jet, a gas storage tank can be arranged inside the hypersonic aircraft, and a gas inlet can be set at the head position of the hypersonic aircraft. The air inlet end of the gas storage tank is connected to the gas inlet through a pressurized air flow pipe, and the air outlet end of the gas storage tank is connected to the jet holes, micropores or grooves through multiple jet pipes, which are used to provide gas sources for the wall normal cold jet and the wall tangential cold jet, and a flow valve is arranged on each jet pipe to control the flow of the wall normal cold jet and the wall tangential cold jet in real time.

[0026] As another embodiment of the gas source and jet flow control of the cold jet, refer to Figure 4 A plenum chamber can be arranged inside the hypersonic aircraft, and an air inlet can be set at the head of the hypersonic aircraft. At the same time, jet actuators can be set at the positions corresponding to the jet holes, microholes and grooves inside the hypersonic aircraft. The air inlet end of the plenum chamber is connected to the air inlet through a first airflow duct, and the air outlet end of the gas storage tank is connected to each jet actuator through multiple second airflow ducts. The jet outlet of each jet actuator is connected to the corresponding jet hole, microhole or groove, which is used to provide a gas source for the wall normal cold jet and the wall tangential cold jet. At the same time, the flow rate of the wall normal cold jet and the wall tangential cold jet can be controlled in real time by the jet actuator. Preferably, the jet actuator adopts a three-electrode plasma synthetic jet actuator. Compared with the existing two-electrode actuator, the three-electrode plasma synthetic jet actuator adds a trigger electrode. The actuator working process increases from the three stages of the two-electrode actuator to four stages, which are distributed as the ignition trigger stage, the energy deposition stage, the jet ejection stage and the air intake recovery stage. The three-electrode plasma synthetic jet actuator significantly reduces the actuator's discharge breakdown voltage by creating an electron flow channel between the trigger electrode and the cathode. Under the same breakdown voltage conditions, the three-electrode actuator can have a larger anode / cathode spacing, actuator cavity volume, and gas working fluid mass, which is conducive to improving the jet momentum.

[0027] In a preferred embodiment, the thickness of the surface cooling air film does not exceed the linear bottom layer of the turbulent boundary layer, and forms a slip phenomenon with the original boundary layer to reduce the original velocity gradient and temperature gradient of the boundary layer. The thickness of the surface cooling air film can be controlled by controlling the blowing flow rate, for example, using a flow meter.

[0028] The method for reducing heat and drag of a hypersonic aircraft in the present invention is further described below with reference to specific examples.

[0029] The wind tunnel experiment of heat reduction and drag reduction of hypersonic boundary layer before and after wall normal jet control was carried out at Mach number 6. The wind tunnel test was verified and the results were obtained. Figure 5-6 The drag reduction effect diagram and heat reduction effect diagram are shown in FIG. Figure 5-6 It can be seen that compared with the original uncontrolled state, the heat reduction and drag reduction method of the hypersonic aircraft in the present invention can reduce the local friction coefficient of the wall by more than 30% and the wall temperature by more than 20K, which has a good heat reduction and drag reduction effect.

[0030] 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 transformations made by using the contents of the present invention description and drawings under the inventive concept of the present invention, or direct / indirect application in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A method for reducing heat and drag of a hypersonic vehicle, characterized in that: Generate wall-normal cold jets and wall-tangential cold jets on the wall of the hypersonic aircraft to form a surface cold air film on the boundary layer of the hypersonic aircraft surface, isolate the direct interaction between the hypersonic mainstream and the wall, transform the original gas-solid shear layer into an gas-gas shear layer, reduce the original velocity gradient and temperature gradient of the boundary layer, and thus achieve the reduction of hypersonic boundary layer friction resistance and heat flux density, achieving the effect of reducing heat and drag of the hypersonic aircraft; The wall tangential cold jet is ejected tangentially through a rearward step provided on the wall of the hypersonic aircraft, and interacts with the incoming flow to form the surface cold air film. The thickness of the surface cold air film does not exceed the linear bottom layer of the turbulent boundary layer, and forms a slip phenomenon with the original boundary layer to reduce the original velocity gradient and temperature gradient of the boundary layer. The wall normal cold jet and the wall tangential cold jet are formed by a self-sustaining synthetic jet based on utilizing the energy of the hypersonic flow.

2. The method for reducing heat and drag of a hypersonic vehicle according to claim 1, characterized in that: The wall-normal cold jet is ejected normally through micropores and / or grooves provided on the wall of the hypersonic aircraft, and interacts with the incoming flow to form the surface cold air film.

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