Deployable Flow Restrictor for Hypersonic Inlet Buzz Mitigation
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Solution Overview
Problem
Hypersonic vehicles equipped with scramjet engines face challenges of inlet buzz and unstart due to high inlet contraction ratios, which lead to shockwave formation, airflow separation, and structural stress, particularly during acceleration and deceleration, where existing solutions like rotating cowl flaps and bypass doors are complex and not feasible for 3D inlets.
Innovation Solution
A deployable flow restrictor is positioned in front of a fixed cowling of the converging inlet, allowing air to be smoothly deflected around the inlet at subsonic and supersonic speeds, maintaining a consistent gap to prevent boundary layer separation and unstart conditions, while enabling high inlet internal contraction ratios for efficient operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a high inlet contraction ratio is used to improve engine performance at high speeds, then engine efficiency is improved, but inlet buzz and unstart occur during acceleration and deceleration
Solution Approach 1:
The inlet system employs variable geometry through movable cowl flaps and bypass doors that can dynamically adjust the inlet area ratio. During acceleration and deceleration, the cowl flaps rotate and bypass doors open to reduce contraction ratio, preventing unstart. At cruise conditions, the components return to their original positions to restore high contraction ratio for optimal engine performance.
2Reliability
If rotating cowl flaps or bypass doors are used to prevent inlet unstart, then inlet flow stability is improved, but device complexity and weight increase
Solution Approach 1:
The inlet system is divided into separate functional components: fixed cowling, movable cowl flaps, and bypass doors. Each segment performs a specific function - the cowl flaps control the main inlet area while bypass doors provide additional flow management. This segmentation allows independent optimization of each component and simplifies the control system compared to a fully variable geometry inlet.
3Reliability
If rotating cowl flaps are used to control inlet area, then inlet area ratio can be reduced to prevent unstart, but the solution is not feasible for 3D curved inlets
Solution Approach 1:
The flow control mechanism is applied locally at specific positions on the inlet - the cowl flaps are positioned at the inlet lips and bypass doors are located at strategic points on the inlet surface. This localized approach allows the solution to be adapted to both 2D rectangular and 3D curved inlet geometries, as the local flow control principle remains the same regardless of the overall inlet shape.
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
The flow restrictor effectively mitigates inlet buzz and unstart by reducing airflow ingestion, preserving structural integrity and maintaining high contraction ratios, allowing continuous operation during acceleration and deceleration without mechanical complexity, and can be actuated to allow full airflow during engine start.
Implementation Method 1
allowing air to be smoothly deflected around the inlet at subsonic and supersonic speeds
Implementation Method 2
maintaining a consistent gap to prevent boundary layer separation and unstart conditions
Implementation Method 3
a strong shockwave system will form in front of the inlet, reducing the flow speed and spilling a fraction of the oncoming air flow around the inlet
Data Source
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AI summary
A hypersonic vehicle (10) has a body (20), a control surface (30), and a hypersonic air-breathing engine (40). The engine includes a converging inlet (100) having a fixed cowling (110) having a first cross-sectional area and a throat (120) having a second cross-sectional area. A flow restrictor (200) is movable between a stowed position and a fully deployed position. The flow restrictor (200) has a third cross-sectional area that is smaller than the first cross-sectional area, such that a consistent gap (210) is formed between a periphery (220) of the flow restrictor (200) and an inner surface (114) of the cowling (110) with the flow restrictor (200) in the fully deployed position and the difference between the first cross-sectional area and the third cross-sectional area is approximately equal to the second cross-sectional area.