k prasad wrote:maitya wrote:On a related note, pls refer to
this HTSE poster (posted by Rakeshji in the AI'23 thread) ...
It says
SC HPT Blades + EVPVD Coating but a
1493K TeT for the HPT ... which should be a food-for-thought for us in BRF.
So about 400-800 K below state-of-the-art. Snecma M-88 TeT is 1850 K (probably higher on the newer variants), the F-22's F-119 engine's TeT is 1922 K, while the F-35's F-135 engine is at 2260 K.
It's good progress, but we need to keep pushing and catch up!
prasadji, that's not what I'd meant actually ...
Also these figures are from a Turboshaft, so quite different design philosophies wrt a true-blue turbofan (albeit with low BPR).
If TeT comparisons are to be made, then those from F404/414/M88 etc should be contrasted with that of Kabini/Kaveri (1455 deg C TeT).
That would lead to ~200deg difference (~1650C vs 1455C etc) - which in itself is a huge/major gulf wrt technologies involved, betw.
The point that I's trying to make is wrt
too much importance we normally attach to SC casting tech etc for HPT blades/vanes - and also when India have had SC casting tech for atleast 1.5 decades now, if not more.
The point is (and pls refer to my earlier posts in this very thread, too lazy to dig them up and re-post them here):
1250deg C is max that's possible for a single-layer TBC to withstand - so achieving higher TeT etc is not so much of an casting etc issue.
(
actually it is, which of course is contradictory, but pls bear with me for a sec, and allow me to reach there first)
Normally, g
raduating from a 3rd gen DS Casting to, say, a 2nd Gen SC etc would provide a ~50-70 odd deg TeT advantage - the real advantage there, of course, is wrt prevention-of-creep-propagation, fatigue (both HCF and LCF) strength etc etc.
But, beyond a point,
unidimensional improving purely casting tech would not achieve corresponding linear improvement in TeT etc. As such improvements, would push you merely, further and further closer to the 1250deg C limit of a TBC coating.
Do note however, this limit can be further increased, though not by very much, by say around another 50-60 deg etc, by employing latest gen of thin-film coating via Plasma Spraying tech (like electron beam — physical vapor deposition (EB-PVD)) etc – via formation of the underlying nano-sized columnar solid cluster layer etc. Pls refer to one om earlier posts on TBC for this aspect.
But I digress, as usual.
What really matters,
if wanting to increase TeT etc, is the “technological art” of air cooling of the blades – both internal (convectional and impingement) cooling and external (film/transpiration) cooling.
And this where Laser drilling etc comes into picture (for external cooling) - but there again, there's a limit upto which continuing to drill cooling holes on the blade surface will take you to. And GE reportedly had hit that hurdle for one of it's F414 variant devpt etc.
Also ambient temp is unevenly distributed across a typical blade-surface profiles - tips gets to experience the highest temp which then tapers off depending upon blade geometry etc.
However internal cooling is also very very complicated, and in fact is a true measure of Casting technology maturity attained (wrt mass manufacturing pov – already done may many years back in India, albeit at a lab level).
There’s a post of mine, in this very thread,
wrt the interplay of casting tech vis-à-vis fabricating internal cooling channels/structures in an hollow blade – pls go thru that, for further understanding on this aspect.
(
hint: 3D manufacturing tech is extensively used for mould manufacturing etc, and then there are issues wrt shrinkage warping stress etc etc etc).
So, point is, the above mentioned HTSE HPT blades may not need too much of air-cooling etc (but there may as well be some) as the max TeT is quite close to what TBC coating are able to endure.
However for even higher TeT applications (like in Kaveri/Kabini and of course other contemporary turbofans like M88/F404/F414 etc), there’s
no way out except for further advancement in the blade cooling tech.
If you look very carefully, at the video I posted just before this one, there’s a fleeting glimpse of laser drilled holes on the Kaveri/Kabini blades (and there are many photos available on internet as well).
Obviously, that was enough to take you to 1455deg C levels (and maybe even slightly higher, one never knows, what gets published vs what is truly achieved actually) – but further 150-200 deg C enhancement will
require scaling atleast a few technology gen hurdles wrt blade cooling tech.
Until ofcourse, we somehow, master
bilayer TBC, of say, Lanthanum Zirconate (LZ) over Yttrium Stabilized Zirconia (YSZ) etc where-in these 1250deg C limits are not there.
(
hint: already mastered and applied for static applications in Kaveri)
F119 etc uber turbofans surely would be using them, to achieve those stupendous TeT values, right (one would never know, as of course, these aspects are, and should be, classified). But those are for some other day …
PS: Betw what about the stators (read vanes) – they are the ones, and not the rotor blades of a turbine, who actually “first experiences” the true-blue TeT of the gas. Can’t they be made from Cobalt based Ni-superalloys (the tensile etc stress management there-in are quite different from those of rotor blades).
(
Hint: Pls refer to the Kaveri gyan thread for for further analysis and exploration)
PPS: Edited to include a URL from one of my earlier posts.