A flow field control system and method for aero-engine exhaust nozzles based on flash ejection and Coanda effect

Abstract

This invention discloses a flow field control system and method for aero-engine nozzles based on flash ejection and the Coanda effect, belonging to the field of aero-engine propulsion and active defense technology. This invention achieves a circumferentially uniform water mist flash jet by setting a central ejection pipe with a Coanda surface at the center of the nozzle and cooperating with an annular injector. It utilizes the latent heat of vaporization of water to rapidly lower the temperature of the nozzle flow field, achieving near-background ablation of the aircraft's infrared signature. Simultaneously, it can mix with micro-aluminum sheets to form a speed-dependent cold cloud interference field with "strong radar scattering and no infrared temperature difference," completely disabling the data fusion logic of radar / infrared composite guided missiles. More importantly, this invention relies on the Coanda wall-attached ejection effect to entrain the central airflow and compensate for exhaust momentum, solving the fatal flaw of traditional water-jet cooling that inevitably leads to significant thrust loss. This invention can switch between thrust enhancement mode, infrared stealth defense mode, and radar / infrared extreme composite defense mode, realizing a new active air combat defense system that is repeatable, non-consumable, maintains maneuverability, and counters composite guidance, significantly improving the survivability and tactical situational reversal capabilities of fighter jets in complex battlefield environments.

Description

Technical Field

[0001] This invention belongs to the fields of aero-engine propulsion technology and active control of aircraft infrared / radar characteristics. Specifically, it relates to an aero-engine tail nozzle flow field control system and method based on flash ejection and Coanda effect. It is particularly suitable for active infrared feature elimination, composite guidance interference, and lossless tactical defense in fighter jet air combat scenarios. It can quickly achieve aircraft signal feature concealment and situational self-protection during missile lock-on approach. Background Technology

[0002] Modern air combat and air defense systems are becoming increasingly sophisticated, with infrared-guided, radar-guided, and radar / infrared composite guided missiles becoming the primary means of attack for fighter jets. Composite guidance systems, relying on the advantages of multi-sensor data fusion, can identify traditional jamming methods through multiple algorithms such as spectral recognition, trajectory discrimination, Doppler velocity filtering, and hot / cold feature comparison, significantly suppressing the survivability of fighter jets.

[0003] The current mainstream active defense jamming methods for fighter jets have fundamental technical flaws, as follows: 1. Infrared decoy flares: These rely on the high-temperature combustion of a propellant charge to create a high-temperature infrared false target, only capable of deceiving by heat source. Modern infrared imaging seekers can distinguish decoys from real aircraft by their outline, motion characteristics, and spectral features, significantly reducing the success rate of deception; at the same time, decoy flares are disposable items, and the number carried by aircraft is limited, making it impossible to support multi-wave, sustained air combat defense.

[0004] 2. Radar chaff: This method creates a radar scattering cloud by releasing metal chaff, thus producing a false radar target. However, conventional dry chaff has a short loiter time and a large difference in velocity vector between it and the carrier aircraft. Radar seekers can quickly eliminate chaff interference through Doppler velocity gate filtering, resulting in extremely poor anti-Doppler guidance capability.

[0005] 3. Towed decoys: These devices use cables to tow active jamming equipment to deceive radar. This method limits the maximum maneuverability of fighter jets, has obvious physical coupling characteristics, is easily identified and countered by the enemy, and has limited reliability.

[0006] In summary, existing defense technologies are all external point sources, one-time consumption, and passive deception mechanisms. They can only achieve limited countermeasures by creating false targets, cannot eliminate the infrared and radar signatures of the carrier aircraft itself, and have shortcomings such as limited number of defense attempts, susceptibility to being cracked by composite guidance algorithms, and poor maneuverability.

[0007] Currently, there is no non-consumable, reusable air combat defense system in the industry that can actively eliminate the infrared signature of the tail nozzle, simultaneously construct a radar / infrared conflicting interference field, and without sacrificing maneuvering thrust. This is a long-standing technological gap in the field. Summary of the Invention

[0008] Modern air combat and air defense systems are becoming increasingly sophisticated, with infrared-guided, radar-guided, and radar / infrared composite guided missiles becoming the primary means of attack for fighter jets. Composite guidance systems, relying on the advantages of multi-sensor data fusion, can identify traditional jamming methods through multiple algorithms such as spectral recognition, trajectory discrimination, Doppler velocity filtering, and hot / cold feature comparison, significantly suppressing the survivability of fighter jets.

[0009] The current mainstream active defense jamming methods for fighter jets have fundamental technical flaws, as follows: 1. Infrared decoy flares: These rely on the high-temperature combustion of a propellant charge to create a high-temperature infrared false target, only capable of deceiving by heat source. Modern infrared imaging seekers can distinguish decoys from real aircraft by their outline, motion characteristics, and spectral features, significantly reducing the success rate of deception; at the same time, decoy flares are disposable items, and the number carried by aircraft is limited, making it impossible to support multi-wave, sustained air combat defense.

[0010] 2. Radar chaff: This method creates a radar scattering cloud by releasing metal chaff, thus producing a false radar target. However, conventional dry chaff has a short loiter time and a large difference in velocity vector between it and the carrier aircraft. Radar seekers can quickly eliminate chaff interference through Doppler velocity gate filtering, resulting in extremely poor anti-Doppler guidance capability.

[0011] 3. Towed decoys: These devices use cables to tow active jamming equipment to deceive radar. This method limits the maximum maneuverability of fighter jets, has obvious physical coupling characteristics, is easily identified and countered by the enemy, and has limited reliability.

[0012] In summary, existing defense technologies are all external point sources, one-time consumption, and passive deception mechanisms. They can only achieve limited countermeasures by creating false targets, cannot eliminate the infrared and radar signatures of the carrier aircraft itself, and have shortcomings such as limited number of defense attempts, susceptibility to being cracked by composite guidance algorithms, and poor maneuverability.

[0013] Currently, there is no non-consumable, reusable air combat defense system in the industry that can actively eliminate the infrared signature of the tail nozzle, simultaneously construct a radar / infrared conflicting interference field, and without sacrificing maneuvering thrust. This is a long-standing technological gap in the field. Detailed Implementation

[0014] Example 1: Thrust Enhancement Mode (Attack Condition) In offensive combat scenarios where fighter jets need to accelerate, climb, and perform super-maneuverability, the system connects to the waste heat preheating pipeline through a mode switching valve.

[0015] The water is preheated to 90–95°C using waste heat from the engine turbine casing and the outer wall of the exhaust nozzle. This preheated water is then uniformly sprayed circumferentially into the exhaust nozzle via an annular injector, where it rapidly flashes to form a high-speed annular steam jet. The steam jet flows stably along the Coanda surface, continuously drawing in cold air from the central duct and the main exhaust gas from the engine. This results in a more uniform velocity field distribution in the exhaust nozzle, reduces flow separation losses, effectively improves engine propulsion efficiency, and achieves active thrust enhancement without increasing fuel consumption.

[0016] This mode does not change the stealth characteristics of the fighter jet and is specifically designed for air combat attacks, positioning, and escape acceleration scenarios.

[0017] Example 2: Pure Infrared Defense Mode (Single Infrared Threat Scenario) When the airborne missile approach warning system detects an approaching infrared-guided missile, the system automatically switches to normal temperature, high-flow water supply mode and enters infrared-specific defense mode.

[0018] A large amount of room-temperature water is sprayed into the high-temperature flow field of the tail nozzle through the annular injector. It instantly flashes and vaporizes, absorbing a large amount of latent heat. This rapidly lowers the overall temperature of the tail flame and tail nozzle flow field, causing the core infrared radiation characteristics of the carrier aircraft to quickly approach the environmental background. The infrared seeker is unable to capture targets with temperature differences, and the incoming infrared missile is directly unlocked and becomes ineffective.

[0019] Once the threat is eliminated, the system shuts down quickly, the engine immediately resumes full thrust operation, and the fighter jet quickly regains its maneuverability.

[0020] Example 3: Extreme Composite Defense Mode (Radar / Infrared Composite Threat Scenario) When the fighter jet is locked onto by a beyond-visual-range composite guided missile or an air defense composite guided weapon, the system simultaneously activates the aluminum sheet delivery module in addition to the infrared defense mode.

[0021] The miniature aluminum scattering unit mixes thoroughly with low-temperature water mist and flash vapor to form a low-temperature suspended interference cloud that moves at speed behind the aircraft's tail. The cold cloud exhibits a high scattering RCS characteristic to radar and shows no difference in infrared thermal radiation, causing conflicting detection results from the dual sensors of the composite guided missile, disrupting the logic of the data fusion algorithm, and preventing it from locking onto the actual aircraft target.

[0022] During tracking, missiles are highly susceptible to accidentally locking onto jamming clouds or losing the target altogether. Once the missile's guidance logic fails, the carrier aircraft can quickly maneuver away from the kill zone, thus completing an efficient, safe, and lossless air combat defense.

[0023] This embodiment can be adapted to high-risk tactical scenarios such as beyond-visual-range air combat, penetrating strikes, and breakthroughs in ground-based air defense zones.

Claims

1. A flow field control system for aero-engine exhaust nozzles based on flash ejection and the Coanda effect, characterized in that, include: The central ejector pipe, the annular injector, the water supply subsystem, the aluminum sheet delivery module, and the back air evacuation subsystem; The front end of the central ejector duct is connected to the back air bleed subsystem, and the rear end extends into the core area of ​​the tail nozzle of the aero-engine. The outlet end of the central ejector duct is provided with an outwardly expanding smooth Coanda surface. The annular injector is coaxially sleeved on the outside of the central ejector pipe outlet. The annular injector has several injection holes evenly arranged circumferentially, with the injection holes facing the Coanda curved surface and the direction of the main exhaust gas flow. The water supply subsystem includes a normal temperature pipeline, a waste heat preheating pipeline, and a mode switching valve, which is used to selectively output normal temperature water or preheated water, and the water supply flow rate is adjustable. The aluminum sheet delivery module is used to quantitatively deliver micro aluminum sheet scattering units into the water mist jet; The system generates a high-speed annular steam jet through annular water mist flash evaporation. The steam jet flows along the wall of the Coanda surface and generates an entrainment effect, reconstructing the tail jet flow field. The system can selectively implement: It features pure infrared signature elimination, radar-infrared composite deception, and active defense and propulsion adjustment functions that preserve thrust while cooling.

2. The system according to claim 1, characterized in that, The Coanda surface is a continuous, smooth, outwardly expanding convex surface, which enables the annular steam jet to flow stably along the wall throughout its entire flow. By relying on the wall-attached entrainment and suction of the central pipe to draw in air and engine exhaust, a momentum-compensating flow field is formed to offset the thrust loss caused by water mist cooling.

3. The system according to claim 1, characterized in that, The water supply subsystem is configured with two working medium pathways: The preheating pipeline uses waste heat from the outer wall of the engine turbine or tail nozzle to preheat the water for the attack thrust enhancement mode. The system outputs ambient temperature water through a normal temperature pipeline, which is used for infrared stealth defense modes that require high heat absorption and strong cooling.

4. The system according to claim 1, characterized in that, In infrared defense mode, a large flow of room temperature water undergoes rapid flash evaporation and phase change within the tail nozzle, absorbing a large amount of latent heat of vaporization, causing the tail nozzle flow field temperature to rapidly approach the ambient temperature, thereby achieving the concealment and elimination of the aircraft's tail source infrared characteristics.

5. The system according to claim 1, characterized in that, In extreme composite defense mode, water mist envelops micro-aluminum sheets, forming a speed-dependent suspended cold cloud behind the aircraft; Cold clouds possess high RCS scattering characteristics for radar and infrared background characteristics with no temperature difference, creating a dual-sensor detection contradiction for composite guided missiles, causing the multi-sensor data fusion algorithm to fail and the target to be lost.

6. The system according to claim 5, characterized in that, The aluminum sheet is suspended in the steam mist layer, and the air resistance is reduced due to the airflow buffer, which significantly prolongs the loiter time. Moreover, the overall velocity vector of the cold cloud is consistent with the altitude of the carrier aircraft, and it cannot be eliminated by radar Doppler filtering.

7. The system according to claim 1, characterized in that, The air intake subsystem on the back of the engine introduces cold air from the outside into the central ejector duct, which can serve as an ejector medium to improve the uniformity of the flow field and thrust efficiency, and can also create a local negative pressure boosting effect on the back of the engine.

8. A method for controlling the flow field of an aero-engine exhaust nozzle based on flash ejection and the Coanda effect, characterized in that, Applied to the system according to any one of claims 1-7, comprising three switchable operating modes: Thrust enhancement mode: Switch the preheating pipeline water supply, and high-temperature water flash evaporation forms a high-speed steam jet attached to the wall. The uniform tail jet velocity field is achieved by the Coanda ejector and the flow loss is reduced, thus achieving thrust gain. Infrared defense mode: Switch to normal temperature high flow water supply, and quickly smooth out the high temperature infrared characteristics of the tail spray by absorbing heat through flash evaporation latent heat, so as to achieve infrared stealth unlocking defense; Extreme composite defense mode: Based on infrared cooling, micro aluminum sheets are simultaneously deployed to construct a radar-visible and infrared-stealthy follow-up contradictory interference cold cloud, thereby breaking the radar infrared composite guidance.

9. The method according to claim 8, characterized in that, During all defensive modes, the exhaust momentum is continuously compensated by the Coanda attached-to-wall ejector, ensuring that the engine thrust does not significantly decrease under defensive conditions and that the aircraft maintains its full maneuverability.

10. The method according to claim 8, characterized in that, The system consumes only water and a small amount of aluminum sheets, and can be started and stopped repeatedly to achieve continuous active air combat defense without any limit on the number of times it can be used.