Kaveri & Aero-Engine: News & Discussion

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Prasad
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Re: Kaveri & Aero-Engine: News & Discussion

Postby Prasad » 21 Aug 2019 10:59

Screech is an afterburner related issue, not core.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby ldev » 21 Aug 2019 21:08

That may be so but supposedly the screech was eliminated by replacing the Kaveri core with a modified M-88 core. So the conclusions were that un-defined parameters within the Kaveri core were causing the screech during re-heat/afterburning. Had a decision been made to go and buy the M-88 core, the resulting engine would have been a M-88-Kaveri "hybrid".

Again, one of the options for getting rid of the screech, without a total re-design is fitting in acoustic liners and resonators. So while a basic design deficiency will cause the screech, fitting acoustic liners and resonators absorbs/neutralizes the high frequency waves. The problem supposedly is that DRDO has not yet perfected the materials used in these acoustic liners i.e. capable of withstanding those temperatures (and neither Safran or anybody else will give this closely guarded technology). Other engines from other countries make use of acoustic liners and resonators to damp down high frequency waves caused by a less than optimal design.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby Indranil » 21 Aug 2019 22:01

ldev wrote:That may be so but supposedly the screech was eliminated by replacing the Kaveri core with a modified M-88 core. So the conclusions were that un-defined parameters within the Kaveri core were causing the screech during re-heat/afterburning. Had a decision been made to go and buy the M-88 core, the resulting engine would have been a M-88-Kaveri "hybrid".

How easy is it to modify the M-88 core, fit into Kaveri, run tests? If you answer that question, you would realize that the rest of your comment is based on news makers who don't understand what they are saying.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby ldev » 21 Aug 2019 22:11

Indranil wrote:
ldev wrote:That may be so but supposedly the screech was eliminated by replacing the Kaveri core with a modified M-88 core. So the conclusions were that un-defined parameters within the Kaveri core were causing the screech during re-heat/afterburning. Had a decision been made to go and buy the M-88 core, the resulting engine would have been a M-88-Kaveri "hybrid".

How easy is it to modify the M-88 core, fit into Kaveri, run tests? If you answer that question, you would realize that the rest of your comment is based on news makers who don't understand what they are saying.


That is why I stated, "supposedly". But the inability to eliminate the screech based on the Kaveri core existing design was expressed by Safran. Now, whether they really worked on it or whether they took this as an opportunity to fulfill their offset obligations by selling some M-88 cores......?????

Bottom line is nobody is going to hold your hands and explain to you as to how they did it......or how to help you solve your problem if it means parting with closely guarded technology.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby Prasad » 21 Aug 2019 22:53

ldev wrote: So the conclusions were that un-defined parameters within the Kaveri core were causing the screech during re-heat/afterburning. Had a decision been made to go and buy the M-88 core, the resulting engine would have been a M-88-Kaveri "hybrid".

Again, one of the options for getting rid of the screech, without a total re-design is fitting in acoustic liners and resonators. So while a basic design deficiency will cause the screech, fitting acoustic liners and resonators absorbs/neutralizes the high frequency waves. The problem supposedly is that DRDO has not yet perfected the materials used in these acoustic liners i.e. capable of withstanding those temperatures (and neither Safran or anybody else will give this closely guarded technology). Other engines from other countries make use of acoustic liners and resonators to damp down high frequency waves caused by a less than optimal design.

Helmholtz resonators. We were and are tech-denied. So we do what we have to do in this regard.
Cannot keep running to snecma to give us a core instead of finding out how to do things right as you said. So we plod on.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby Vivek K » 21 Aug 2019 23:29

Screech was supposedly fixed was it not? This report seems off the mark.

Saurav Jha on April 17 2018

"Ok, the GTRE folks I spoke to say that the six main design issues with the Kaveri engine have mostly been solved now, either in-house or with foreign inputs. Apparently, screech is not an issue anymore.

5:39 AM - 17 Apr 2018 "

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Re: Kaveri & Aero-Engine: News & Discussion

Postby Cybaru » 22 Aug 2019 00:09

Prasad wrote:
ldev wrote: So the conclusions were that un-defined parameters within the Kaveri core were causing the screech during re-heat/afterburning. Had a decision been made to go and buy the M-88 core, the resulting engine would have been a M-88-Kaveri "hybrid".

Again, one of the options for getting rid of the screech, without a total re-design is fitting in acoustic liners and resonators. So while a basic design deficiency will cause the screech, fitting acoustic liners and resonators absorbs/neutralizes the high frequency waves. The problem supposedly is that DRDO has not yet perfected the materials used in these acoustic liners i.e. capable of withstanding those temperatures (and neither Safran or anybody else will give this closely guarded technology). Other engines from other countries make use of acoustic liners and resonators to damp down high frequency waves caused by a less than optimal design.

Helmholtz resonators. We were and are tech-denied. So we do what we have to do in this regard.
Cannot keep running to snecma to give us a core instead of finding out how to do things right as you said. So we plod on.



Can't we take a two pronged approach?

Use M88 Core - get engine flying and the associated learning curve of getting an engine in plane and certifying it? Reduce risk of sanctions and growth? Create engine for MWF and AMCA to keep them independent of other vendors? Having an 85% engine that is ours is far better than having an 0% engine with our tech. There is lots to learn and create around certifying an engine.

Then continue to develop core and continue using the test bed to get over the last mile hurdle?

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Re: Kaveri & Aero-Engine: News & Discussion

Postby ramana » 22 Aug 2019 01:08

ldev and prasad, I thought screech or jet engine noise is due to the mixing of turbulent flow from the the combustion and is like air flow in an organ pipe or flute.
In supersonic flow there is expansion and contraction similar to an accordion which adds to the phenomenon. So it needs nozzle exhaust tinkering.

Helmholtz resonator is if the casing vibrates. That's not screech but case vibration due to resonance. They can add stiffening ribs on case and make the frequency go higher and avoid acoustic range.

i think there is confusion in the reporting.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby ramana » 22 Aug 2019 01:11

Cybaru,
The M-88 core is smaller in diameter than the Kaveri turbofan, casing and after burner.

So it wont swap out but needs to be scaled up. So it wont fit.
So they can redesign the core now that they know what the issues are.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby ramana » 22 Aug 2019 01:14

Vivek K wrote:Screech was supposedly fixed was it not? This report seems off the mark.

Saurav Jha on April 17 2018

"Ok, the GTRE folks I spoke to say that the six main design issues with the Kaveri engine have mostly been solved now, either in-house or with foreign inputs. Apparently, screech is not an issue anymore.

5:39 AM - 17 Apr 2018 "


The problem of using Twitter to convey such info is its not the right medium due to space.
Either write a full article or ask your friends to write it or convey the info in a series of tweets.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby ramana » 22 Aug 2019 01:17

ldev,
Is blade frequency being called screech?
For only that would be eliminated by the modified M88 core.
Real screech is due to organ pipe resonance from jet exhaust.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby ldev » 22 Aug 2019 02:49

ramana wrote:ldev and prasad, I thought screech or jet engine noise is due to the mixing of turbulent flow from the the combustion and is like air flow in an organ pipe or flute.
In supersonic flow there is expansion and contraction similar to an accordion which adds to the phenomenon. So it needs nozzle exhaust tinkering.

Helmholtz resonator is if the casing vibrates. That's not screech but case vibration due to resonance. They can add stiffening ribs on case and make the frequency go higher and avoid acoustic range.

i think there is confusion in the reporting.


Ramana,

The reporting states that it is the turbulent mixing of the hot exhaust with the cooler by-pass air that is creating a shock wave with a high frequency which cannot exit because the nozzles are smaller. This high frequency shock wave is being called a screech. Again, according to the reporting the hot exhaust is not uniform in pressure across all injectors which may be the cause which in turn could be because of the placement/spacing of the injectors, or the spacing between individual injectors and the flameholder.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby ramana » 22 Aug 2019 07:18

Ok so the phenomena is the well known acoustic noise due to organ pipe effect. So how would a modified core change the screech effect?

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Re: Kaveri & Aero-Engine: News & Discussion

Postby agupta » 22 Aug 2019 08:51

ramana wrote:Ok so the phenomena is the well known acoustic noise due to organ pipe effect. So how would a modified core change the screech effect?



It won't, Ramanaji. A clean explanation that you might enjoy @ http://daniel.edgington-mitchell.com/re ... onic-jets/

In simpler terms, the organ pipe effect you talk about... can be linked to the father of the problem - noise due to shock cells; local conditions and instabilities (driven by inflow, geometry, manufacturing defects etc) at the lip can be seen as the mother.

In general this is a good example of why aircraft engines are tough. Its easy to get lost on 1 or 2 top level metrics ... thrust and SFC get attention on BRF. Lots of people pontificating about "we're just X% short so we should be able to do Y and Z". What makes a real engine work is that in addition to that, you need to manage
a) Operability.... robustness to phenomena from aeromechanics, aerodynamics (distortion, stall etc), combustion instabilities, screech etc. In simpler terms, real world "non-ideal" non lab related shit that will cause things to break apart.
b) Durability... ("life"... linked to above plus the thermal management
c) Weight... (OK this does get attention on BRF)

There are other ( 2nd order for want of a better phrase) metrics on the other -abilities, -costs but the above are the big deal. They distinguish real flying in service engines from technology demonstrators. You screw this up - engines fail and you don't have any aircraft system you can count on - unless you want a UCAV or UAV that will only fly in a straight line in pristine conditions and will survive only in some % of the scenarios every time it goes up. A lot of Kaveri's issues come under #a AFAIK... pity GTRE and the Indian system is so inscrutable and opaque.

I also see a lot of discussion here from people thinking that a FTB is the missing silver bullet and once you have it, everything will just work. Its more than that and its more than just $$ (ask the Chinese). Please note that while some Operability issues were found on the FTB, some show-stoppers were found on other ground tests or on-rig tests (this is par for the course... go look up IGTI/ASME publications) and seemingly they have yet to be solved.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby ldev » 22 Aug 2019 09:22

ramana wrote:Ok so the phenomena is the well known acoustic noise due to organ pipe effect. So how would a modified core change the screech effect?


Hi Ramana,

Again, according to the reporting, the screech in Kaveri could come from any of the following factors:

Fuel spray injector locations
Non-uniformity in the fuel-air fraction
Atomization process
Evaporation rates
Ignition process
Quality of the upstream flow
Blockages if any
Flameholder geometry

Quality of the upstream flow would include a modified core. Apparently Safran did CFD modeling on the engine to reach these conclusions. But where was it done and were folks from GTRE present is unknown.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby ramana » 22 Aug 2019 11:38

Dev, Can you point me to the reports?

agupta thanks

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Re: Kaveri & Aero-Engine: News & Discussion

Postby Prasad » 22 Aug 2019 11:44

ramana wrote:ldev and prasad, I thought screech or jet engine noise is due to the mixing of turbulent flow from the the combustion and is like air flow in an organ pipe or flute.
In supersonic flow there is expansion and contraction similar to an accordion which adds to the phenomenon. So it needs nozzle exhaust tinkering.

Helmholtz resonator is if the casing vibrates. That's not screech but case vibration due to resonance. They can add stiffening ribs on case and make the frequency go higher and avoid acoustic range.

i think there is confusion in the reporting.


There are many who have studied this in yinjineering, so please correct if i'm wrong. Screech is high frequency transverse and buzz is low frequency longitudinal combustion instability. Exhaust after LP turbine passes over afterburner assembly where more fuel is injected and ignited to generate more thrust. Jet pipe is obviously gonna get hot and hence you have a cheese grater type liner so that cooler bypass air enters the pipe to cool down the surface by not letting the afterburner exhaust touch the metal/composite surface and melt it.

We've heard that it has been fixed fwiw. There are a lot of papers on this with work ongoing. So who knows.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby ldev » 22 Aug 2019 19:18

ramana wrote:Dev, Can you point me to the reports?

agupta thanks


This is Part 1 of the issues Kaveri is facing aired on August 2, 2019 - all in Hindi
https://www.youtube.com/watch?v=6kpPugsUzew


This is Part 2 of the issues Kaveri is facing aired on August 7, 2019 - all in Hindi
https://www.youtube.com/watch?v=vuwkyz2ImNw

This is where he comments on the termination of the Safran relationship and possible rumors
of a tie up with Rolls-Royce, could be pure speculation aired on August 17, 2019 - all in Hindi
https://www.youtube.com/watch?v=9bhbNdPtfvs

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Re: Kaveri & Aero-Engine: News & Discussion

Postby ramana » 22 Aug 2019 23:19

Ldev, Will watch. Glad folks are following it in Hindi so more people can follow and not only English speaking folks.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby ramana » 22 Aug 2019 23:31

agutpa, I have seen those characteristic shock vortices/Mach waves in rocket exhaust also.
Thanks for the paper.
The sound intensity as a function of Mach Number aka eighth power law is first formulated by Dr. Lighthill. You might be surprised but IIT Madras had quite a few books in the library on jet engine noise long back.

See the last picture on that page the need to have a rounded edge for the exhaust nozzle to reduce separation. The radius as a ratio of the exhaust velocity is the key parameter to ensure reduce flow separation that generates the mixing flow.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby JayS » 23 Aug 2019 17:16

ramana wrote:agutpa, I have seen those characteristic shock vortices/Mach waves in rocket exhaust also.
Thanks for the paper.
The sound intensity as a function of Mach Number aka eighth power law is first formulated by Dr. Lighthill. You might be surprised but IIT Madras had quite a few books in the library on jet engine noise long back.

See the last picture on that page the need to have a rounded edge for the exhaust nozzle to reduce separation. The radius as a ratio of the exhaust velocity is the key parameter to ensure reduce flow separation that generates the mixing flow.

You are talking about the shock diamonds, I suppose. They are formed due to over expanded nozzle. Basically the nozzle is designed for altitude condition where ambient pressure is low, so at ground level, the nozzle ends up over expanding the flow.

Just one point, the screech in context of Kaveri is related to the combustion instability in the Afterburner (where flow is actually low subsonic, so no shocks involved). Screech is due to the acoustic waves generated by the thermo-fluidic instabilities which results in lower than expected thrust. The F135 engine which powers F-35 also had same issue, PW fixed it later.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby JayS » 23 Aug 2019 17:18

ramana wrote:Ldev, Will watch. Glad folks are following it in Hindi so more people can follow and not only English speaking folks.


once saw video of the same guy on LCA MK2. He is basically copy pasting stuff from all over the internet. Which is not bad in itself. But I don't think he understands all that he is talking about well enough. Half knowledge could be worse than no knowledge. just sayin.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby ldev » 23 Aug 2019 20:04

JayS wrote:
ramana wrote:Ldev, Will watch. Glad folks are following it in Hindi so more people can follow and not only English speaking folks.


once saw video of the same guy on LCA MK2. He is basically copy pasting stuff from all over the internet. Which is not bad in itself. But I don't think he understands all that he is talking about well enough. Half knowledge could be worse than no knowledge. just sayin.


He is copying visuals from other sites to help explain his narration. Listen to the narration which is accurate. In fact YT has warned him about copyright issues and he has now issued a disclaimer that he only uses visuals from other sites to help explain/educate his viewers on his explanations. In the absence of the visuals in his videos would anybody other than an jet engine designer be able to understand what the issues are?

In fact it was only on this site that I learnt that the final offer from Safran was supply of modified M-88 cores to meet their offset obligations under the 36 Rafale contract without any TOT. All other MSM sites and in fact even so called defence correspondents by omission made it sound as if there was a dispute over the amount i.e. Euro 250 + Euro 500 for supply of TOT which is not the case at all. And GTRE/DRDO is right to walk away from such an offer which is in fact a non-offer.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby agupta » 23 Aug 2019 21:32

JayS wrote:
Just one point, the screech in context of Kaveri is related to the combustion instability in the Afterburner (where flow is actually low subsonic, so no shocks involved). Screech is due to the acoustic waves generated by the thermo-fluidic instabilities which results in lower than expected thrust. The F135 engine which powers F-35 also had same issue, PW fixed it later.



Err...not quite, JayS. Yes - Absolutely correct its in the afterburner fuel injectors - and the region where the combustion instability sets up ("the driver") may be subsonic, but does not change the fact that "screech" is associated with supersonic jet flows. Remember usually the AB injectors are upstream of (variable geometry) throats of (usually for military) supersonic nozzles.

See here: reference to "when" (full afterburner)
https://www.military.com/dodbuzz/2011/0 ... -fix-found

When you get screech, you cannot throttle / power/ augment the engine as aggressively as you want to, hence reduced thrust. The instability , or the acoustic waves by themselves, do not result in lower thrust...but maybe here I am just being too literal with your words vs. your intent ! In which case sorry in advance.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby agupta » 23 Aug 2019 21:39

ramana wrote:agutpa, I have seen those characteristic shock vortices/Mach waves in rocket exhaust also.
Thanks for the paper.
The sound intensity as a function of Mach Number aka eighth power law is first formulated by Dr. Lighthill. You might be surprised but IIT Madras had quite a few books in the library on jet engine noise long back.

See the last picture on that page the need to have a rounded edge for the exhaust nozzle to reduce separation. The radius as a ratio of the exhaust velocity is the key parameter to ensure reduce flow separation that generates the mixing flow.


Oh, the IITs have birthed many worthies in this space ! In general, you will find many Indians/Indian Americans as stalwarts in Aeroacoustics... a Google search on say Aeroacoustics Fellows in AIAA. But that's true for Jets in general too... go to an IGTI conference and you'll be surprised how many Indians line the engineering/technical leadership of both the OEM & R&D communities; and a few of them have associations with GTRE too.

Why they left or do not engage further is a matter for private discussion; lets just say - since we are discussing work cultures of ISRO vs. others (Like DRDO) that there is a "dharmic & results-first" country first work culture in ISRO and then there are many other sub-entities where the work culture is "anything to look good first"

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Re: Kaveri & Aero-Engine: News & Discussion

Postby JayS » 24 Aug 2019 17:47

agupta wrote:
JayS wrote:
Just one point, the screech in context of Kaveri is related to the combustion instability in the Afterburner (where flow is actually low subsonic, so no shocks involved). Screech is due to the acoustic waves generated by the thermo-fluidic instabilities which results in lower than expected thrust. The F135 engine which powers F-35 also had same issue, PW fixed it later.



Err...not quite, JayS. Yes - Absolutely correct its in the afterburner fuel injectors - and the region where the combustion instability sets up ("the driver") may be subsonic, but does not change the fact that "screech" is associated with supersonic jet flows. Remember usually the AB injectors are upstream of (variable geometry) throats of (usually for military) supersonic nozzles.

See here: reference to "when" (full afterburner)
https://www.military.com/dodbuzz/2011/0 ... -fix-found

When you get screech, you cannot throttle / power/ augment the engine as aggressively as you want to, hence reduced thrust. The instability , or the acoustic waves by themselves, do not result in lower thrust...but maybe here I am just being too literal with your words vs. your intent ! In which case sorry in advance.


What I meant is, the Jet screech references you guys were discussing were of cases where screech originated due to the jet itself, without any upstream influence from the flow. So one can have screech even when entire engine is working OK, but if there is some issue with the nozzle exit geometry itself perhaps which gives rise to feedback of acoustic waves to the nozzle exit setting a cyclic response with high frequency. But in case of Kaveri the problem is one of "Screech in Afterburner", as far as my understanding goes. And due to improper combustion there, the thrust augmentation does not happen to the full extent, hence the loss of thrust.

Here is a PhD thesis from IISC. The work might have been associated with Kaveri itself.

http://cgpl.iisc.ernet.in/site/Portals/ ... Thesis.pdf

Two types of instabilities are encountered in afterburners. They are buzz and
screech. Reheat buzz is a low frequency, self-excited oscillation that can occur
above a certain fuel-air ratio. Screech is accompanied by high frequency pressure
oscillations that may be of such magnitude as to cause rapid deterioration of the
burner. Screech might be, or closely related to, some form of resonant oscillation
or also known as flame-driven resonant oscillations or combustion instability.
The afterburner-inlet conditions at which screech occur differs widely for various
afterburner designs. Combustion-driven flow oscillations that arise in combustors
and the afterburners are difficult to predict

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Re: Kaveri & Aero-Engine: News & Discussion

Postby Gyan » 24 Aug 2019 19:56

Can our Resident Experts comment on HTFE & HTSE also?

What's the comparison between say, HTSE & Airdiden-3 Turbomeca engine?

Similarly, Al-55 & HTFE?

Are the specifications realistic, achievable? Are the engines future ready?

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Re: Kaveri & Aero-Engine: News & Discussion

Postby JayS » 25 Aug 2019 20:16

HAL has a tender to outsource Single Crystal Blade casting for LPT and HPT blades. My best guess, this is for Adour 871 engine. Because this doesn't look like its for either Al31FP or HTSE/HTFE. Looks like this is one of the Desikaran initiative and word reverse engineering is used in it...!!

https://hal-india.co.in/Tender_Details. ... ivkey=OQ==

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Re: Kaveri & Aero-Engine: News & Discussion

Postby Indranil » 25 Aug 2019 20:51

The tenders says that the HPT blade is for a turboshaft engine while the LPT blade is for a turbofan engine.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby fanne » 25 Aug 2019 20:57

in English please

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Re: Kaveri & Aero-Engine: News & Discussion

Postby JayS » 25 Aug 2019 21:13

Indranil wrote:The tenders says that the HPT blade is for a turboshaft engine while the LPT blade is for a turbofan engine.

Thanks for pointing that out. I did not catch that one.

So HPT SCB could be either Shakti or HTSE-1200, later being the obviously likely one.

LPT blades are for Adour 871, its LPT has 94 blades and the material is a RR developed alloy.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby Gyan » 25 Aug 2019 21:35

Should not HAL be doing this Single Crystal blade casting. After all who else in India would have such technology lying around? And it's odd that we have still not indigenised Adour Engine after 40 years

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Re: Kaveri & Aero-Engine: News & Discussion

Postby fanne » 25 Aug 2019 23:12

Adour 871 (for Hawk, not Jags) - is the current LPT - SC or DS (from RR that is?)? Are we upping it to SC blade? (Maybe to get experience). Same Q as Gyan, why the tender. It is not that Abdul has this technology in his Garage, most likely 1-2 shops (Karaput? or some DRDO lab - MDNL?) has that technology, why this charade? to be above board and not anyone accused of hanky panky?

Answering my own question it does
https://watermark.silverchair.com/v002t ... o8bmpHXESc

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Re: Kaveri & Aero-Engine: News & Discussion

Postby JayS » 25 Aug 2019 23:32

^^ Link doesn't work.

Adour 871 uses SCB for LPT.

unless we know who will end up making the SCB, lot of questions will remain unanswered. But given this is an indigenization efforts, it must be some desi entity. Would it be a MNC owned pvt subsidiary or shuddh desi company..? Who knows.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby chetak » 25 Aug 2019 23:35

fanne wrote:Adour 871 (for Hawk, not Jags) - is the current LPT - SC or DS (from RR that is?)? Are we upping it to SC blade? (Maybe to get experience). Same Q as Gyan, why the tender. It is not that Abdul has this technology in his Garage, most likely 1-2 shops (Karaput? or some DRDO lab - MDNL?) has that technology, why this charade? to be above board and not anyone accused of hanky panky?

Answering my own question it does
https://watermark.silverchair.com/v002t ... o8bmpHXESc


tech available only in govt/public sector in India unless some Indian player is able to outsource it abroad.

Gyan
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Re: Kaveri & Aero-Engine: News & Discussion

Postby Gyan » 25 Aug 2019 23:41

If HAL/DRDO are looking at Reaper and Avenger Class UCAVs then we will need both Turboprop engine and turbofan engine
Turbofan Engine requirement will met by HTFE and Kaveri.
I wonder if HTSE can have a turboprop variant of 1500hp class for a Reaper Class UCAV

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Re: Kaveri & Aero-Engine: News & Discussion

Postby Cain Marko » 26 Aug 2019 01:41

Is Hal trying to upgrade the Jag engine in-house? That would be something...

Indranil
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Re: Kaveri & Aero-Engine: News & Discussion

Postby Indranil » 26 Aug 2019 04:21

What is most interesting to me is that HAL does not consider its crown jewels to protect. Or, it really wants to become the systems' integrator. Both of which are great signs.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby Prasad » 26 Aug 2019 09:33

Cain Marko wrote:Is Hal trying to upgrade the Jag engine in-house? That would be something...

Adour engine project has been ongoing for a while now. compressor side appears to be done and turbine side is being done now. Blades were machined by a private company in bangalore earlier. Not sure if they're being done now also.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby agupta » 26 Aug 2019 09:53

JayS wrote:
agupta wrote:

Err...not quite, JayS. Yes - Absolutely correct its in the afterburner fuel injectors - and the region where the combustion instability sets up ("the driver") may be subsonic, but does not change the fact that "screech" is associated with supersonic jet flows. Remember usually the AB injectors are upstream of (variable geometry) throats of (usually for military) supersonic nozzles.

See here: reference to "when" (full afterburner)
https://www.military.com/dodbuzz/2011/0 ... -fix-found

When you get screech, you cannot throttle / power/ augment the engine as aggressively as you want to, hence reduced thrust. The instability , or the acoustic waves by themselves, do not result in lower thrust...but maybe here I am just being too literal with your words vs. your intent ! In which case sorry in advance.


What I meant is, the Jet screech references you guys were discussing were of cases where screech originated due to the jet itself, without any upstream influence from the flow. So one can have screech even when entire engine is working OK, but if there is some issue with the nozzle exit geometry itself perhaps which gives rise to feedback of acoustic waves to the nozzle exit setting a cyclic response with high frequency. But in case of Kaveri the problem is one of "Screech in Afterburner", as far as my understanding goes. And due to improper combustion there, the thrust augmentation does not happen to the full extent, hence the loss of thrust.

Here is a PhD thesis from IISC. The work might have been associated with Kaveri itself.

http://cgpl.iisc.ernet.in/site/Portals/ ... Thesis.pdf

Two types of instabilities are encountered in afterburners. They are buzz and
screech. Reheat buzz is a low frequency, self-excited oscillation that can occur
above a certain fuel-air ratio. Screech is accompanied by high frequency pressure
oscillations that may be of such magnitude as to cause rapid deterioration of the
burner. Screech might be, or closely related to, some form of resonant oscillation
or also known as flame-driven resonant oscillations or combustion instability.
The afterburner-inlet conditions at which screech occur differs widely for various
afterburner designs. Combustion-driven flow oscillations that arise in combustors
and the afterburners are difficult to predict



JayS: Screech never originates due to the "jet itself"...it always needs a driving source - that source can be purely "fluidic", like geometry induced @ nozzle lip (see Ramana's comment about lip radii) or can driven by combustion (dynamic) phenomena. Suggest a deeper reading of the material.

PM me for references if you prefer


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