Pratyush wrote:Maitya,
1) In one of your posts above you have mentioned the difference between the RPM of both the 404 and the Kaveri.
2) one of the you tube defence channels has reported that GTRE has approached the MOD for approval for work on a 55 kn dry thrust kaveri. On the basis of the work done on the current kaveri by it.
Can the gap between the two levels of dry thrust be met by having higher RPM on Kaveri?
If yes.
Do the existing materials used in the current iteration permit and increase in the RPM without any issues?
Or the whole development excercise has to be repeated by the GTRE for the higher levels of dry thrust?
Pratyush-ji, there I'd compared the published rpm difference between the LPT stages of F404 and Kaveri.
Now there're not enough open-source literature available wrt exact perf parameters of these, so very difficult to provide an accurate answer.
However, generically speaking, going from 50-51KN to 55KN is approx 10% growth, which should be doable via LPT-FAN improvement route.
Do note a
lower LPC/FAN rpm would indicate suboptimal perf of the LPT (which drives the LPC/FAN shaft) - but, the published isentropic efficiency figures, were decent (not great) though - IIRC 87-88% with good surge margin to boot.
So basically if the LPT efficiency can be increased by 3-4% and graduate to low 90s, that should do it, IMVHO - as
any increase in FAN rpm would increase the mass-flow-rate, increasing dry thrust (more on this bit, at the end*).
What is very difficult to even speculate is how would this LPT efficiency gain going to come about.
It doesn't look like it'll be via LPT weight reduction route - as, per published data, Kaveri LPT uses CMX-4 SC
solid blades (I always thought it was DS casted solid blades), without any air-cooling etc.
Which is fine, as CMX-4 (3rd gen SC material) has raw temp handling properties of ~1050-1100 deg C, which is enough for most LPT applications - even, I'd wager, Equiaxed casted blades of the same/equiv material (say around 900-950 deg C) would also be enough for Kaveri LPT.
So, these blades wouldn't be too "heavy", so that they can be made lighter - making blades lighter, would mean lesser centrifugal force load for the LPT disk to contend with, which in turn allows introduction of blings (results upto 70% weight reduction) etc.
If not the blades, then the LPT disc could have been looked into - but there also it's currently PM (Powder Metallurgy) based mfg, so quite contemporary, not much scope there as well.
However, there maybe still some possibility of introducing blisks, which are known to provide ~25-30% weight reduction (enough for the modest efficiency gains, being talked about) – there were recent reports about blisks being designed and used in HTFE/HTSE (?), so quite doable.
Other option is to look at the HPT blade-design itself to make them more efficient etc - which alone, I don't think, would be a viable route for such an efficiency improvement route.
However, the LP shaft can definitely be made lighter, which would result some additional torque being transported to the LPC/FAN.
Do note however, using
intermetallic (like Y-TiAl) or CMC based LPT etc, is big-huge-giant technological leap (we are nowhere close to such technological levels) - we are then
looking at 20+ % thrust gain, and is thus best left for 65KN/98KN (K11) program etc.
But if LPT improvements is not going to cut-it, the only option left is
to re-look at the FAN design wrt Fan blade geometry etc. GTRE have had multiple FAN designs implemented in recent years, so it's definitely within their reach - however, if that alone would be enough to provide this 10% etc thrust gain etc, wouldn't know.
Do note here, the recently unveiled high-distortion-tolerant FAN for the dry Kaveri variant wouldn't really work out here - as that had kept the mass-flow-rate exactly same as that of K9.
Of course, there the focus was wrt countering higher distortion inflow imposed by serpentine intakes, so additional IGV etc may have got introduced - for std intakes, these are not required, so another FAN design may just about work out.
(
there's another post of mine wrt this aspect, in last couple of pages of this thread - you may want to refer to that)
Normally, both LPT efficiency improvement along with LPC/FAN improvements together, are generally tried for such dry thrust improvement initiatives.
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*Increasing LPC/FAN rpm would increase the mass-flow-rate, increasing dry thrust level - but since the core remains same (so mass-flow thru core also remains same), the BPR needs to be increased proportionally. So that additional mass flow is bypassed. Kaveri has 0.16:1 BPR, while F414 has 0.25:1 (so higher proportion of the overall dry thrust produced by F414 is via this LPT-FAN route).