malushahi wrote:^^^ please consider writing a blurb for tech-and-time-challenged people like me who don't have a clue about how the above 2395 words relate to kaveri.
It is quite tempting to create a write-up to what brar_w is alluding to, of course in lay-man words, but the level of bandwidth required for that is not permitting me to even attempt it.
However, key sentence, in his quotes, is
... At the heart of adaptive engines are variable-geometry devices that dynamically alter the fan pressure ratio and overall bypass ratio, the two key factors influencing specific fuel consumption and thrust ....
And quite a bit info is scattered here and there in the Kaveri Sticky Thread
If those and the "Turbofan back-of-the-envelope Performance Estimator" (found in that thread) are played around with, a lot of it will make sense as to where the current turbofan giants are aiming for.
So I will stop ... but do consider the following high-level deductions if you attempt to do the deductive analysis yourself:
1) The sledge-hammer way of increasing the thrust-level (dry) is by increasing the mass-flow
2) The mass-flow can be increased by tinkering (read increasing in mm level) the inlet diameter - so overall airframe compatibility, inlet design etc needs to be taken into account.
3) Increasing the mass-of-air thru the core - will reduce BPR - aka you are slipping back to turbojet territory
4) But plain-vanilla increasing mass-flow thru core will impact engine efficiency (read thermodynamic efficiency) - piss poor "dry SFC", leading to complaints like "fuel guzzler" etc.
As more work being extracted at HPT - will lead to reduction in work available for extraction in LPT (which drives the fan) - even more impact in stagnation pressure recovery before combustion etc.
5) The elegant way out of it is increase the OPR (actually the SPRs of both the Fan and the Compressor stages) - so that you skirt this reduction-of-stagnation-pressure-recovery issue.
6) But OPR increase will require more extraction of work at BOTH HPT (for the HPC stages) and LPT (for the FAN stages), so that the rotational energy available for these compressor stages are more than what is it now.
7) Increase in work extraction at the turbine (bot HPT and LPT) stages, means higher TeT - so better material (from thermo-mechanical efficiency stand-point), next-gen manufacturing processes (SC blades and vanes) and next-gen cooling techniques (TBC, serpentine paths for convective cooling etc)
BACK TO SQUARE ONE ... Turbofan 101 issues.
8 ) So some wise folks went and did a statistical study of which part (and what %) of a typical military flight profile is high-thrust demanding ones - and arrived at a classical contradiction of average performance vs peak-performance trade-offs. This is a pretty clever attempt to minimizing that performance gap.
Wrt Kaveri - well, these are all fancy-book stuff, as the dal-chawal basic turbofan configuration is itself not flight-qualified.