Isolator Obstruction for Supersonic Engine Flow Control
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Solution Overview
Problem
Supersonic and hypersonic airbreathing engines face challenges with inlet unstart and combustion instability due to shock-boundary layer interactions in isolators, leading to flow distortion and reduced combustion efficiency.
Innovation Solution
Incorporating an obstruction with a wedge shape that protrudes into the flowpath within the isolator, diverting flow perpendicular to the longitudinal direction, which increases pressure rise and improves flow mixing, reducing shock interactions and flow separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If shock systems are setup along the isolator length to create pressure rises, then the pressure demand of the combustor is met, but pressure communications can travel through the isolator boundary layer and upstream past the inlet throat resulting in inlet unstart
Solution Approach 1:
A porous material is introduced as an intermediary between the shock system and the boundary layer to block pressure communications while allowing the shock system to maintain pressure rise. The porous material acts as a filter that prevents pressure waves from traveling upstream through the boundary layer while still permitting the necessary pressure buildup for combustor operation.
Solution Approach 2:
A porous material is placed within the isolator to selectively block pressure communications upstream past the inlet throat. The porous structure allows the material to attenuate pressure waves and prevent unstart conditions while maintaining the overall pressure rise required by the combustor, thus resolving the contradiction between meeting pressure demands and preventing inlet unstart.
2Stress or pressure
If strong shock-boundary layer interactions occur within the isolator, then pressure rise is achieved, but high distortion of the flow profile at the isolator exit occurs which reduces combustion efficiency or causes engine stall
Solution Approach 1:
A porous material is introduced as an intermediary to decouple the strong shock-boundary layer interactions from the exit flow path. This material allows pressure rise to be maintained while preventing the highly distorted flow patterns generated by strong shock interactions from reaching the combustor, thus preserving combustion efficiency.
Solution Approach 2:
The porous material serves to filter and smooth the flow profile downstream of the shock system. By placing porous material in the isolator, the harsh shock-boundary layer interactions are dampened and the flow distortion is reduced before the flow reaches the combustor, maintaining both pressure rise and combustion efficiency.
3Stress or pressure
If the isolator provides additional pressure rise upstream of the combustor, then the combustor pressure demand is met, but the shock train may extend upstream of the inlet throat causing unstart
Solution Approach 1:
A porous material is positioned within the isolator to act as a barrier that allows pressure rise to be generated upstream of the combustor while preventing the shock train from extending further upstream past the inlet throat. The porous material blocks the propagation of shock waves while permitting the pressure buildup necessary for combustor operation.
Solution Approach 2:
The porous material is strategically placed to contain the shock train within the isolator region. It allows the shock system to generate the required pressure rise upstream of the combustor while preventing the shock train from propagating upstream of the inlet throat, thus resolving the contradiction between pressure rise and unstart prevention.
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 solution enhances combustion efficiency by ensuring a more uniform flow profile at the isolator exit, reduces the risk of inlet unstart, and improves the operability margin of the propulsion system across various flight conditions.
Implementation Method 1
the obstruction causing diversion of flow in a direction perpendicular to a longitudinal direction through the isolator, around the obstruction
Implementation Method 2
which increases pressure rise and improves flow mixing
Implementation Method 3
improves flow mixing, reducing shock interactions and flow separation
Implementation Method 4
reducing shock interactions and flow separation
Implementation Method 5
reducing shock interactions and flow separation
Data Source
Figure 1~3
Figure 4~6
Figure 7~9
AI summary
A flight vehicle has a propulsion system that includes an air inlet, an isolator (or diffuser) downstream of the air inlet, and a combustor downstream of the isolator. The isolator includes an obstruction that protrudes inwardly from an inner wall of the isolator, into the flow channel in which air flows through the isolator. The obstruction diverts the flow to either side of it. Downstream of the obstruction the flow on either side of the obstruction comes together again, leading to mixing of the flow, for example including mixing of low energy and boundary layer flow with high energy flow. This mixing of flow may make for a more uniform flow at the exit of the isolator. In addition the obstruction may help fix the location of shocks within the isolator, providing longer flow mixing length in the isolator.