ramana wrote:Uprating decrease engine life and was beaten to death in Pingrezi thread.
Ummm ... True, but some tweaking is still possible without sacrificing too much on engine life etc.
In the context of the Kaveri, refer to Step 2, in
one of my earlier posts here ... where it talks about
achieving the 6th column from the left (the 1st light red one) in a simple excel of forecasted thrust increase etc.
You will see there, how both dry/wet thrust can be quite dramatically increased by allowing increasing the mass-flow - but of course, it will become a less efficient engine (as is evidenced in the impact to both Thermal and Propulsive efficiency parameters, in that excel) aka it's SFC etc will suffer.
(NOTE: What ofcourse that particular column doesn't account for, is a scenario of increasing the massflow but increasing the BPR as well, in such a way, that the massflow to the core remains exactly same - aka any incremental thrust is achieved purely from the fan-based bypass-thrust. The last column in the excel starts with it, but also goes for next gen core improvements, so doesn't fit this scenario - will work on a new version of it).
In the Kaveri context, from the recent twits etc it seems that GTRE folks have more or less frozen the baseline core (Kabini), and now wants to flight-certify it (along with the old 80KN class but overweight engine). Very good and sensible approach - refer to Step 1 in the link above.
Flight certification will provide them the necessary confidence (and of course real-time empirical performance data both on Thermodynamic, Aerodynamic and Thermo-mechanical aspects of the core as well as the overall engine etc).
Also to increase the thrust level there is always a conservative approach option as well - if GTRE decides to increase the inlet dia slightly (to F414 level) and thus increase the mass-flow but also decides to increase the BPR and keeps the core (kabini) untouched, there'll be increment in thrust levels without too much impact to the current efficiency figures and also to the engine life etc (normally engine life is basically a function of the core life - and more precisely on the HPT and combustor life, but of course there are myriad of other factors as well).
But even this modest arrangement has it's own set of challenges ...
As the biggest problem with Kaveri today is it's 105-129Kg additional weight ... increasing the inlet dia, would mean necessary changes to the fan design and it's corresponding size/dimension increase as well. So it'd mean adding more weight to an already overweight engine.
The easier aspect of mitigating the overweight (and also weight creep) part of Kaveri, is to replace the 3 stage Ti-based fan with a CFC based one ...
And there was
a tender (spotted by indranilroy) floated by GTRE in 2014 ... It talked about a
three stage 5:1 pressure ratio all Blisk fan for 75/110 kN thrust class engine - looked to be as the next evolutionary step of
uprating the Kaveri design.
Though it didn't talk about CFC (and talked about Ti based blisk manufacturing tech for the Fan stages) indicating a very conservative approach towards even mitigating this additional weight creep issue itself.
Ofcourse the difficult and "strategic" aspect of the solving weight part, is towards introducing new materials (for e.g. Ti-Al etc) for the last 3 stages of the HPC ... as alluded
in the Step 3a in this post of mine. As not only we don't have the required manufacturing technology for Ti-Al, but also touching core would mean a huge amount of re-calibration, re-testing and flight-certification etc.
And even more difficult and "strategic" aspects are graduating towards 27-30-OPR/1900-1950K-TeT class core which is where all the not-so-modern-anymore-but-somewhat-contemporary-turbofans (like F414 etc) are situated.
No easy choices …
