Variable Exhaust Nozzle Exit Area Control via Fluidic Flow Separation
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Solution Overview
Problem
Existing nozzle exit area control systems for jet engines face challenges such as weight penalties from mechanical systems, undesirable shock generation in fluidic systems, and limitations in cyclic area control, particularly in maintaining engine mass flow and minimizing thrust losses.
Innovation Solution
The implementation of a convergent-divergent nozzle with a divergent wall angle of at least 12° and symmetrical disturbance generators, such as injection flow slots, to induce non-shock flow separation, reducing the effective exit area without altering the nozzle throat area or generating shocks, even at supersonic speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If mechanical control surfaces and actuators are used to control exit area, then exit area control is achieved, but weight penalty increases
Solution Approach 1:
The patent replaces mechanical control surfaces and actuators with a fluidic system that uses injected flow to induce shock waves and alter the effective exit area. This substitution eliminates heavy mechanical components while achieving the same exit area control function through fluid dynamics.
Solution Approach 2:
The invention uses injected flow (gas or liquid) into the divergent section to create shock waves that modify the flow pattern and reduce the effective exit area. This pneumatic/hydraulic approach provides lightweight, responsive control without mechanical moving parts.
2Adaptability or versatility
If fluidic systems are used to control throat area, then exit area control is achieved, but shock waves are generated in the divergent section
Solution Approach 1:
The patent applies local quality by injecting flow at specific locations in the divergent section and creating shocks only in localized regions away from the throat area. The shock waves are generated in the divergent section where they can effectively reduce exit area without interfering with the throat flow and mass flow rate.
3Adaptability or versatility
If combustibles are used to control exit area, then variable area is achieved, but cyclic changes cannot be made and combustion on walls is undesirable
Solution Approach 1:
The patent replaces combustible materials with a fluidic injection system that uses controlled flow injection to create shock waves and reduce exit area. This substitution eliminates the need for combustion on nozzle walls and enables cyclic, reversible area control by simply adjusting the injection flow rate.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach effectively reduces the nozzle exit area while maintaining constant throat area and avoiding shock formation, enhancing thrust efficiency and simplifying implementation, thereby improving engine performance without weight penalties or thrust losses.
Implementation Method 1
induce flow separation where the predetermined wall angle is sufficient for the induced flow separation to extend upstream from disturbance generator substantially to the throat of the nozzle
Implementation Method 2
Large amounts of injected flow in fluidic systems are not preferable due to the performance impact on the engine to supply the large amounts of secondary flow for injection (flow that could otherwise be used to produce thrust)
Data Source
Figure 1
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Figure 3A
AI summary
A nozzle effective exit area control system is created with a convergent - divergent nozzle (10) with a divergent portion (14) of the nozzle having a wall at a predetermined angle of at least 12° from the freestream direction. Disturbance generators (24,26) are located substantially symmetrically oppositely on the wall to induce flow separation from the wall with the predetermined wall angle inducing flow separation to extend upstream from each disturbance generator (24,26) substantially to a throat of the nozzle pressurizing the wall and reducing the effective area of the jet flow at the nozzle exit.