Insane Jet Maneuvers, where do they get the mass flow?

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Discussion Overview

The discussion revolves around the performance of fighter jet engines, specifically focusing on how these aircraft manage to execute rapid maneuvers while maintaining sufficient mass flow to prevent compressor stall. The inquiry touches on aspects of inlet distortion, boundary layer management, and the engineering solutions employed in jet engine design.

Discussion Character

  • Technical explanation
  • Exploratory
  • Debate/contested

Main Points Raised

  • One participant questions how fighter jets can perform quick turns without stalling the compressors, noting the importance of uniform flow into the compressor.
  • Another participant mentions that compressor designs are tested under non-ideal inlet conditions, acknowledging that performance may decrease but these conditions are typically short-lived.
  • A different participant adds that distortion screens can be used to manage expected inlet distortion, suggesting a method (KD2) used by the Air Force for quantifying distortion effects.
  • A participant shares a thesis link that may provide additional background information on the topic.

Areas of Agreement / Disagreement

Participants express varying perspectives on the management of inlet distortion and its effects on engine performance, indicating that multiple competing views remain on the topic.

Contextual Notes

The discussion does not resolve the complexities of how mass flow is maintained during rapid maneuvers, nor does it clarify the specific limitations of the methods mentioned.

wesmac
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So I am doing a presentation on effects of inlet distortion on fan performance, I am trying to gauge it more towards the inlet aspect, diverting boundary layers, etc. So I am wondering, how do fighter jets pull such quick turns, and still maintain enough mass flow not to stall the compressors? I mean, i know they have variable inlets and bleed, and the like, even IGV`s, but something just doesn't make sense, you have to have uniform flow into the compressor or lots of bad things happen...right?!



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We spend a lot of time designing compressors to survive with non ideal inlet conditions. The performance definitely takes a hit in those instances but luckily they are short lived events.

When we do compressor testing in the cells, we purposely distort the inlet flow to examine stall margin with non-ideal inlets. Before the airframe sees an engine, that engine has seen most of its flight envelop on the ground.
 
I see. Thanks for the info! Hadnt looked at it in that aspect
 
To add to what Fred said, we can use things like distortion screens which can be tuned to the amount of expected distortion.

Also, for quantifying the amount, I'm not sure what method you're using, but we have typically used the KD2 method in the past. It's a method that I know at least the Air Force uses as well.

A quick google gave me this thesis which looks like it has a lot of good background information if you want to dive deeper.
http://dspace.mit.edu/bitstream/handle/1721.1/42186/22926364.pdf?sequence=1
 
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