Kaveri & Aero-Engine: News & Discussion

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Re: Kaveri & Aero-Engine: News & Discussion

Postby JayS » 26 Aug 2019 10:15

Do you mean to say, screech cannot be generated by the instabilities in the jet itself..?

Anyway this is off topic for Kaveri.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby ramana » 27 Aug 2019 05:11

Err, if it helps explain the issues of screech on Kaveri its quite germane right here.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby abhik » 27 Aug 2019 09:24

Kaveri is dead, there is hardly any news on what progress has been made in last 10+ years. Same vague info about about snecma core, screech issue, spreadsheet pressure ratios etc. are recycled every few years for time pass discussion here. I don't think this is really informing anybody (you have a poster who had put 2+2 together to to come to the conclusion that "screech" issue was solved by replacing the core with the French one).

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Re: Kaveri & Aero-Engine: News & Discussion

Postby agupta » 27 Aug 2019 10:04

JayS wrote:Do you mean to say, screech cannot be generated by the instabilities in the jet itself..?

Anyway this is off topic for Kaveri.



No that's not what I meant. Just saying screech is defined as a sub-set of (and happens only in) supersonic jet phenomena. Some instability (wether driven by a sharp lip or a afterburner flame/combustion dynamics) creates the disturbances that then become part of feedback loops.

See here: http://people.ece.umn.edu/users/mihailo ... reech.html or even on wiki https://en.wikipedia.org/wiki/Jet_noise
"Screech is produced by a feedback mechanism in which a disturbance convecting in the shear layer generates sound as it traverses the standing system of shock waves in the jet" ..... the disturbance triggers can be different

To Abhik's point, its really regrettable that the Kaveri program is so inscrutable; at this point after all the heartbreak, the lies and false claims, hard work by the committed ones, leaks or info of certain metrics getting close but unknown degree of success on a "total" yardstick... we don't really know. Its clear the last 20% of the path (operability/durability etc that I mentioned) is hard to do ab initio, is a closely guarded competence. As has been pointed out, these phenomena are awfully hard to predict numerically and designing for them rely a lot on empirical testing and data gathered over generations of designs and concepts... so its not just going to just happen quickly or suddenly by turning on a funding tap (or the Chinese efforts would have borne fruits 10 yrs ago).

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Re: Kaveri & Aero-Engine: News & Discussion

Postby sum » 27 Aug 2019 12:21

^^ Remembering reading about a comment on some Kaveri related article by some poster about how the tons of stuff happening under wraps will be revealed at the right time and there will be good news.

Not sure if just some random kite flying or something ongoing under a gag order inside GTRE

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Re: Kaveri & Aero-Engine: News & Discussion

Postby maitya » 27 Aug 2019 12:40

Prasad wrote:
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.


Indigenisation of Adour HPT DS blades is almost 8 year old hand - Read here

Quote from the 2011 Tech Focus article ...
DMRL also took up the extremely challenging assignment of developing technology for production of high-pressure turbine (HPT) rotor blades of Jaguar aircraft's ADOUR MK811 engine.The blades had complex aerofoil geometry with tight dimensional tolerances and stringent metallurgical specifications. Processing technology for this critical and complex directionally solidified (DS) aerofoil casting was fully developed by DMRL and the blades were delivered to HAL, Koraput.


Normally LPTs are either at a similar, or may be one level lower, in tech level than the HPTs blades/vanes - though there is no such hard and fast rule. So this SC casted LPT blades for Adour is quite interesting.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby maitya » 27 Aug 2019 12:54

^^ Betw from the same TF 2011 doc ...
The process is currently being used for making silica cores for Kaveri aerofoil castings that include HPT turbine blades and vanes and LPT blades. It is being adapted for making alumina cores that are required for producing single crystal aerofoil casting


Producing SC casted blades/vanes are much more technology intensive than simply being able to Vacuum Investment Casting of blades/vanes (one such intricacy is vanes are much more challenging to cast, SC or DS, than blades etc etc) ... someday I'll able to finish the 4th part of the series (from the prev page). :((
Last edited by maitya on 27 Aug 2019 12:56, edited 1 time in total.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby uskumar » 27 Aug 2019 12:55


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Re: Kaveri & Aero-Engine: News & Discussion

Postby Pratyush » 27 Aug 2019 13:02

Guys, I have some queries regarding screech issue with Kaveri.

I ask as I have no clue what so ever regarding a jet engine.

1) If it is related to after burner then non after burning application should still have a flyable engine? Correct?

2) the screech, is it is physical issue that will adversely effect the safety of the aircraft?

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Re: Kaveri & Aero-Engine: News & Discussion

Postby Gyan » 27 Aug 2019 16:23

GE 414 Engine is only USD 5 Million, how come Jaguar upgrade engineering be is USD 13 Million each?

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Re: Kaveri & Aero-Engine: News & Discussion

Postby JayS » 27 Aug 2019 16:35

agupta wrote:
JayS wrote:Do you mean to say, screech cannot be generated by the instabilities in the jet itself..?

Anyway this is off topic for Kaveri.



No that's not what I meant. Just saying screech is defined as a sub-set of (and happens only in) supersonic jet phenomena. Some instability (wether driven by a sharp lip or a afterburner flame/combustion dynamics) creates the disturbances that then become part of feedback loops.

See here: http://people.ece.umn.edu/users/mihailo ... reech.html or even on wiki https://en.wikipedia.org/wiki/Jet_noise
"Screech is produced by a feedback mechanism in which a disturbance convecting in the shear layer generates sound as it traverses the standing system of shock waves in the jet" ..... the disturbance triggers can be different


Screech is a phenomenon characterized by high frequency tonal acoustic waves. Again, what you are talking about is for Supersonic Jets - jet screech. And there is screech in context of After burner induced by combustion instability which is separate from the jet screech, that you have been referring to. These acoustic waves generated by the combustion instability in the A/B are trapped inside the jet pipe (they cannot travel downstream of the nozzle beyond the throat as flow becomes supersonic there and are reflected. They cannot travel upstream as well, due to presence of turbines, so they keep getting reflected back and forth in the jet pipe. ) and they can damage the HW inside. To attenuate them, acoustic liner with holes is used inside the jet pipe. If the frequency is low like 100Hz, they are called Rumble or buzz ( there is another buzz phenomenon for supersonic inlets but that's different one) and if the frequency is high like 500Hz they are call Screech.

These screech waves produced by A/B may or may not induce Jet screech, depending on whether they can induce flow instabilities in the flow at the throat of the nozzle strong enough that would travel thru the diffuser and then in the outside jet shock structure. I am not too sure about this part whether it will at all kick start screech outside in the jet. But the acoustic waves remain inside as they cannot pass thru the throat (its a physical boundary for them) and are reflected back.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby ArjunPandit » 27 Aug 2019 16:40

Gyan wrote:GE 414 Engine is only USD 5 Million, how come Jaguar upgrade engineering be is USD 13 Million each?

should be because of amortization over 1000 engines and no design/ip inputs
PS: 1500 engine was delivered in 2015
Last edited by ArjunPandit on 27 Aug 2019 16:49, edited 1 time in total.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby JayS » 27 Aug 2019 16:48

maitya wrote:
Prasad wrote: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.


Indigenisation of Adour HPT DS blades is almost 8 year old hand - Read here

Quote from the 2011 Tech Focus article ...
DMRL also took up the extremely challenging assignment of developing technology for production of high-pressure turbine (HPT) rotor blades of Jaguar aircraft's ADOUR MK811 engine.The blades had complex aerofoil geometry with tight dimensional tolerances and stringent metallurgical specifications. Processing technology for this critical and complex directionally solidified (DS) aerofoil casting was fully developed by DMRL and the blades were delivered to HAL, Koraput.


Normally LPTs are either at a similar, or may be one level lower, in tech level than the HPTs blades/vanes - though there is no such hard and fast rule. So this SC casted LPT blades for Adour is quite interesting.


Adour 871 (AJT Hawk) has SCB LPT blades.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby JayS » 27 Aug 2019 16:51

Pratyush wrote:Guys, I have some queries regarding screech issue with Kaveri.

I ask as I have no clue what so ever regarding a jet engine.

1) If it is related to after burner then non after burning application should still have a flyable engine? Correct?

2) the screech, is it is physical issue that will adversely effect the safety of the aircraft?


1. That's why Ghatak is going ahead with dray Kaveri.
2. Screech or rumble related to the A/B can damage the engine from inside. That's a safety issue. Loss of thrust is another issue, but it need not be a safety issue.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby agupta » 27 Aug 2019 18:42

Pratyush wrote:Guys, I have some queries regarding screech issue with Kaveri.

I ask as I have no clue what so ever regarding a jet engine.

1) If it is related to after burner then non after burning application should still have a flyable engine? Correct?

2) the screech, is it is physical issue that will adversely effect the safety of the aircraft?



Yes to both. Assuming there are no other operability/durability issues. What it does in terms of mission capability depends on the aircraft - that switch may go off or stay on

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Re: Kaveri & Aero-Engine: News & Discussion

Postby agupta » 27 Aug 2019 19:27

JayS wrote:These screech waves produced by A/B may or may not induce Jet screech, depending on whether they can induce flow instabilities in the flow at the throat of the nozzle strong enough that would travel thru the diffuser and then in the outside jet shock structure. I am not too sure about this part whether it will at all kick start screech outside in the jet. But the acoustic waves remain inside as they cannot pass thru the throat (its a physical boundary for them) and are reflected back.

You are mixing up cause and effect, my friend. And as far as I know I have never heard of any screech but jet screech and the phrase screech is again AFAIK, always seen as a branch of supersonic noise. There can be many types of combustion instabilities/dynamics related acoustics and tones, but never heard to them referred to as "screech".

Anyways my last on this topic. If you have any interest in going deeper to understand this better, an old classic: https://apps.dtic.mil/dtic/tr/fulltext/u2/a241141.pdf

I suppose its a good thing I didn't go into teaching ;)

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Re: Kaveri & Aero-Engine: News & Discussion

Postby JayS » 27 Aug 2019 23:21

Overview of Gas Turbine Augmentor Design, operation
And Combustion Oscillation
https://engineering.purdue.edu/AAECours ... r%20Review

The phenomenon referred to as “screech” (see Section 6.2) is a type of combustion instability
characterized by high frequency, high amplitude pressure oscillations. The high pressures and
temperatures accompanying low-altitude, high-speed flight is conducive to screech. The onset
of screech during the combustion process contributes to an increased rate of flame propagation
and improved augmentor combustion efficiency. However, screech also results in higher
operating temperatures in the augmentor. Moderate to severe screeching conditions can cause
rapid deterioration and failure of the augmentor liner, flameholder, and the fuel injection
system. Numerous documented hardware failures have been encountered affecting the
augmentor liner, flameholders and fuel system components after only a few minutes of
operation during screeching conditions (Refs. 14, 17-26, 34). To counteract this, practical
augmentors are designed with a screech liner that consists of a hot (core) side and cold (fan
duct) side. This allows for film cooling and some amount of screech suppression. The screech
liner is generally designed to address high frequency combustion oscillations (> 1000 Hz).
Due to hardware damage of the augmentor during screech operating conditions, it is essential
that an understanding of the screech phenomenon is gained and methods for eliminating
screech are devised. Several investigators have studied augmentor screech phenomena (Refs.
20, 26, 34). From these studies, several theories have emerged that attempt to describe the
screech phenomenon. Thus far, the capability of these analyses to predict screech and the low
pressure acoustic coupling referred to as “rumble” has been limited. Rumble is a phenomenon
similar to screech caused by low frequency oscillations in the augmentor. Rumble is a concern
because it causes extreme structural vibrations in the engine, which can cause the engine to
break apart, resulting in mission failure and, in extreme cases, loss of the entire aircraft.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby Indranil » 28 Aug 2019 01:39

agupta wrote:Anyways my last on this topic.

I woul request you both to continue discussing, because (at least) I get to get a crash course in this. I don't understand screech at all.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby agupta » 28 Aug 2019 02:04

JayS wrote:Overview of Gas Turbine Augmentor Design, operation
And Combustion Oscillation
https://engineering.purdue.edu/AAECours ... r%20Review

The phenomenon referred to as “screech” (see Section 6.2) is a type of combustion instability
characterized by high frequency, high amplitude pressure oscillations. The high pressures and
temperatures accompanying low-altitude, high-speed flight is conducive to screech......

JayS:

With all humility, this exercise demonstrates some of the risks of insufficiently deep google-search-and-read "learning". I can't explain why Google's first references returned are not very good for a first understanding - but that's my opinion.

But even in this one, E.g., You are quoting a passage on Page 8. On Page 3 specifically after the 3rd time the word screech shows up, and multiple times before in the first few pages, its clear that the reference is for military supersonic jet flows; see the link to "converging-diverging" nozzles - as u well know, those are for supersonic flows.

When the paper describes the nozzle throat as acoustically closed (See write up on Page 12), its a reference to the throat being sonic which means downstream of that (unless its perfectly expanded) you will see shock cells - and that's why screech is considered a subset of supersonic jet noise phenomena

I get what you are saying - that the Kaveri issue seems to be driven by afterburner combustion instabilities; all I am pointing out is that its NOT an EITHER/OR situation... its an "IN" situation, screech due to combustion instabilities IN a supersonic (afterburner operational) jet flow

Indranil - thx for the encouragement ;). Hope this helps to close out topic !

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Re: Kaveri & Aero-Engine: News & Discussion

Postby Ravi Karumanchiri » 28 Aug 2019 02:18

In depth and full-flavoured detail on SCREECH (from Newfoundland).

Also was wondering... Just as golf balls are dimpled which makes them fly further than they would otherwise, AND just as certain metal finishes that produce a sputtered or shot-blasted surface texture that is rough and uneven... MIGHT the solution to screech be hidden in the chaos of a similar "surface imperfection"?

Has this parameter been tested for, during Kaveri R&D?

Furthermore, insofar as the screech problem adds unwanted temperatures and vibrations/stresses to an engine; to what extent can these problems be mitigated with the adoption of silicon carbide ceramics in lieu of metals for rotating hot parts? These non-metallic materials are not only lighter and will spin faster; but they're stiffer and remain so up to much higher peak temperatures, than do their metal analogues.

Any insight into the use of ceramic matrix composites in the Kaveri would be of great interest to me. TIA

ALTERNATIVELY, the LCA Tejas should be fitted with India-made M88s that will power the Rafales also. Imagine the cost-savings if both platforms could support quick-swapping-out of SNECMA M88 engines; with Rafales loading two and Tejas loading one M88 powerplant.

The cost savings would be considerable; and operating this way could improve uptime/serviceability which would otherwise be constrained by the numbers of platforms. By holding an excess number of spare engines and making quick work of swapping them out all the time; platform availability would certainly improve.

Just sayin'.....

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Re: Kaveri & Aero-Engine: News & Discussion

Postby Indranil » 28 Aug 2019 02:48

agupta wrote:Indranil - thx for the encouragement ;). Hope this helps to close out topic !

I am never in favour of closing a perfectly fine discussion where two parties are respectfully disagreeing on technical details. These are too few these days. Keep them coming. I know I speak for JayS too.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby JayS » 28 Aug 2019 11:25

Ravi Karumanchiri wrote:In depth and full-flavoured detail on SCREECH (from Newfoundland).

Also was wondering... Just as golf balls are dimpled which makes them fly further than they would otherwise, AND just as certain metal finishes that produce a sputtered or shot-blasted surface texture that is rough and uneven... MIGHT the solution to screech be hidden in the chaos of a similar "surface imperfection"?

Has this parameter been tested for, during Kaveri R&D?

Furthermore, insofar as the screech problem adds unwanted temperatures and vibrations/stresses to an engine; to what extent can these problems be mitigated with the adoption of silicon carbide ceramics in lieu of metals for rotating hot parts? These non-metallic materials are not only lighter and will spin faster; but they're stiffer and remain so up to much higher peak temperatures, than do their metal analogues.

Any insight into the use of ceramic matrix composites in the Kaveri would be of great interest to me. TIA

ALTERNATIVELY, the LCA Tejas should be fitted with India-made M88s that will power the Rafales also. Imagine the cost-savings if both platforms could support quick-swapping-out of SNECMA M88 engines; with Rafales loading two and Tejas loading one M88 powerplant.

The cost savings would be considerable; and operating this way could improve uptime/serviceability which would otherwise be constrained by the numbers of platforms. By holding an excess number of spare engines and making quick work of swapping them out all the time; platform availability would certainly improve.

Just sayin'.....


Food for Thought - if dimples make golf ball fly longer, why the Airplane surfaces are not dimpled to increase their range..?
Sorry couldn't resist. :D

Completely difference physics. They use screech liners which is plate with holes to attenuate acoustic waves. Its difficult to eliminate generation of acoustic waves as any small change in any of the myriads of factors could bring it back in some regime or the other. Its better to provide sufficient dampening capability inside the jet pipe. Screech liners do that job. Similar acoustic liners are seen on the Fan side of turbofan as well, in in some other places in the engine.

Screech can seriously damage the rear side of the engine and the damage could be catastrophic. Any change in rotatives is not going to mitigate this issue.

I have seen couple of GTRE paper talking about CMCs, but then everyone has been talking about it for decades. It was predicted TET would reach 2500K with CMCs constituting all HPT by year 2000. We are still far from it, anywhere in the world. I have not come across any serious work in CMC from Indian orgs so far, which doesn't mean there isn't any. Just that I don't know, and I don't know much frankly. I just discovered there exists a lab called ARCI. Never heard of it before even though they have been working in some Jet engine related technologies for quite some time.


M88 actually produces less power than even F404.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby JayS » 28 Aug 2019 11:41

agupta wrote:
JayS wrote:Overview of Gas Turbine Augmentor Design, operation
And Combustion Oscillation
https://engineering.purdue.edu/AAECours ... r%20Review


JayS:

With all humility, this exercise demonstrates some of the risks of insufficiently deep google-search-and-read "learning". I can't explain why Google's first references returned are not very good for a first understanding - but that's my opinion.

But even in this one, E.g., You are quoting a passage on Page 8. On Page 3 specifically after the 3rd time the word screech shows up, and multiple times before in the first few pages, its clear that the reference is for military supersonic jet flows; see the link to "converging-diverging" nozzles - as u well know, those are for supersonic flows.

When the paper describes the nozzle throat as acoustically closed (See write up on Page 12), its a reference to the throat being sonic which means downstream of that (unless its perfectly expanded) you will see shock cells - and that's why screech is considered a subset of supersonic jet noise phenomena

I get what you are saying - that the Kaveri issue seems to be driven by afterburner combustion instabilities; all I am pointing out is that its NOT an EITHER/OR situation... its an "IN" situation, screech due to combustion instabilities IN a supersonic (afterburner operational) jet flow

Indranil - thx for the encouragement ;). Hope this helps to close out topic !


I think you are talking about the final effect and I am talking about the origin of the acoustic waves. I have not denied that A/B generated acoustic waves would not result in jet screech, I just said I am not sure, they will always be able to produce strong enough instabilities. What I have been trying to say is, I think there are two distinct and unrelated sources that could produce screech - One is the A/B combustion instability and another is the instability in the jets either induced by the factors like nozzle geometry or the inherent flow instabilities in the jet itself.

Please tell me, is following situation possible..?

1. There is enough dampening built in the jet pipe and the A/B is well design, enough not to produce strong acoustic waves of high frequency, and whatever is produced is well attenuated by the screech liner. But we still have screech in the supersonic under expanded jet outside the nozzle exit (on second thought I realized at least some acoustic waves should be able to travel downstream, but no acoustic waves from outside can come in as the flow becomes supersonic beyond the throat), where due to instabilities in the shock structure produces acoustic waves which develop feedback loop with the thin shear layer near the nozzle exit generating further instabilities and forming a close loop and eventually giving rise to screech.

2. A/B design is bad or dampening in the jet pipe is not enough to attenuate produced acoustic waves from combustion instabilities. The waves start reflecting bak and forth in the jet pipe producing organ effect. They would form a feedback loop with the A/B HW and start resonating at certain high frequency. The pressure fluctuations produced by these waves eventually will damage the screech liner, the A/B and the jet pipe due to high cycle fatigue. No some of these waves are escaping thru the nozzle throat and producing instability in the exhaust jet which is under expanded and that leads to the feedback loop and jet screech like described above.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby Rakesh » 29 Aug 2019 02:04

DRDO 110 kN Engine Plan, Puzzles adding-up


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Re: Kaveri & Aero-Engine: News & Discussion

Postby agupta » 29 Aug 2019 07:20

JayS wrote:
I think you are talking about the final effect and I am talking about the origin of the acoustic waves. I have not denied that A/B generated acoustic waves would not result in jet screech, I just said I am not sure, they will always be able to produce strong enough instabilities. What I have been trying to say is, I think there are two distinct and unrelated sources that could produce screech - One is the A/B combustion instability and another is the instability in the jets either induced by the factors like nozzle geometry or the inherent flow instabilities in the jet itself.
.


This is getting closer ... and we can agree, especially on the last 2 lines - and i am suspecting here it maybe its a definition issue. In general, its ONLY called screech when there are both:
a) sources of instability e.g, combustion, or geometry/purely fluid dynamic (as you pointed out) and
b) resonance in a flow structure that has supersonic flow and shock cells.

You need both to happen to create the damage that makes it worth worrying about and its only this combo phenomenon that's called (supersonic) jet screech.


HTH

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Re: Kaveri & Aero-Engine: News & Discussion

Postby agupta » 29 Aug 2019 07:26

JayS wrote:Please tell me, is following situation possible..?

1. There is enough dampening built in the jet pipe and the A/B is well design, enough not to produce strong acoustic waves of high frequency, and whatever is produced is well attenuated by the screech liner. But we still have screech in the supersonic under expanded jet outside the nozzle exit (on second thought I realized at least some acoustic waves should be able to travel downstream, but no acoustic waves from outside can come in as the flow becomes supersonic beyond the throat), where due to instabilities in the shock structure produces acoustic waves which develop feedback loop with the thin shear layer near the nozzle exit generating further instabilities and forming a close loop and eventually giving rise to screech.

2. A/B design is bad or dampening in the jet pipe is not enough to attenuate produced acoustic waves from combustion instabilities. The waves start reflecting bak and forth in the jet pipe producing organ effect. They would form a feedback loop with the A/B HW and start resonating at certain high frequency. The pressure fluctuations produced by these waves eventually will damage the screech liner, the A/B and the jet pipe due to high cycle fatigue. No some of these waves are escaping thru the nozzle throat and producing instability in the exhaust jet which is under expanded and that leads to the feedback loop and jet screech like described above.




Specific answers

#1 Yes... we can still have screech even if A/B combustion dynamics are damped if there are alternate sources/triggers e.g., the sharp lip can create one.

#2. I didn't understand this one.

I think you're thinking there are different (competing) sources... one in the shock-cell region and one (or more) elsewhere. Not so... its one coupled phenomena.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby Vips » 29 Aug 2019 07:49

India, France to hold talks on defence buys today.

Of much greater significance and far more ambitious is a new India-France project to co-develop and co-build a next generation jet engine for use by India. The lead French defence company in the reckoning here is Safran. There is little clarity on how this will be developed in India, including agencies and companies to be involved. What is clear is that the project has been nicknamed INFRA. Modi may have been hinting at this when he said after his meeting with Macron here that India and France were building INFRA in several sectors.

If it happens, this would be momentous — there aren’t that many companies in the world that can build jet engines. If India does achieve the feat, it would go a long way in giving the country autonomy in defence purchases.

It is rumoured that the outgoing French ambassador to India, Alexander Ziegler may be joining Safran, making negotiations much less problematic. This kind of movement is fairly common among envoys who have served in India where they get get snapped up by the private sector to help navigate the opaque Indian system.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby ldev » 29 Aug 2019 22:53

An interesting post from a poster on the f-16.net forum discussing the screech phenomenon encountered during development of the PW-f135 engine for the F-35.

Screech occurs when the pressure fluctuations due to combustion process couple, mechanically, with the natural acoustics of a structure. it is not limited to afterburners. It is seen in main burners of aircraft engines and aeroderivative engines, boilers in steel plants/power plants, etc., etc..

Screech is particulary dangerous in aferburners due to the high level of heat release which occurs over a realtively short length and the, generally, axis-symetric round tailpipe (like an organ pipe).

The air is NEVER flowing at Mach 3 inside the engine. In fact, the flow is completely subsonic until after the throat plane in the exhaust nozzle. For the JSF, the gases will never exit the nozzle anywhere near Mach 3. The maximum Mach Number for the JSF on the envelope is significantly lower than 2.0. Thus, the gases will EXIT the aircraft at Mach numbers lower than 2. Yes, temperatures can be very high at Max AB (3500R potentially, locally), but the stream will be even much lower than Mach 1 upstream of the nozzle throat.

Though true that, SOMETIMES, fueling adjustments can/MAY eliminate/minimize various screech modes under specific circumstances, screech often is caused by an aero-design that has NUMEROUS inadequacies that RESULT in screech from the outset.

Though PW may CLAIM they have a "fix", I find that disengenuous, at best based onb my own experiences with this issue. Most likely, like they often do, they will bob and weave and minimize the issue to get thru development. In the end, SOLVING the problem will involve, most likely, a significant design change, which often is at odds with low observable requirements.

I have been in the engine business a long time. I have NEVER heard of a "simple" screech fix, once the problem is present in a significant magnitude.

In fact, I am unaware of an afterburner anywhere in the past that has NOT had SOME sort of acoustics issues---minor, or, god-forbid, major. If someone makes that claim, they are uninformed, or outright lying. The problem may be fixed, or desinged out in the end, but not before LOADS of development testing is paid for
--- assuming the problem was there to begin with.

Afterburning Turbojets are more suceptible to the problem than turbofans, for reasons I choose not to get into here.

To those in the business and knowledgable of this issue, they would have to agree that there are no screech experts, only victims.

IF anyone honestly believes PW has a *simple* fix, I have some swamp land I can sell you in Louisiana. I'm not saying they CAN'T fix it... in the end they must... it will just cost us taxpayers boat loads of more money than planned.

just my $0.05.


If this analysis is accurate, it will account for the offer made by Safran to just replace the Kaveri core as opposed to re-designing Kaveri.
Last edited by ldev on 29 Aug 2019 22:59, edited 1 time in total.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby ldev » 29 Aug 2019 22:58

Vips wrote:India, France to hold talks on defence buys today.

Of much greater significance and far more ambitious is a new India-France project to co-develop and co-build a next generation jet engine for use by India. The lead French defence company in the reckoning here is Safran. There is little clarity on how this will be developed in India, including agencies and companies to be involved. What is clear is that the project has been nicknamed INFRA. Modi may have been hinting at this when he said after his meeting with Macron here that India and France were building INFRA in several sectors.

If it happens, this would be momentous — there aren’t that many companies in the world that can build jet engines. If India does achieve the feat, it would go a long way in giving the country autonomy in defence purchases.

It is rumoured that the outgoing French ambassador to India, Alexander Ziegler may be joining Safran, making negotiations much less problematic. This kind of movement is fairly common among envoys who have served in India where they get get snapped up by the private sector to help navigate the opaque Indian system.


For Safran to actually jointly design a clean sheet engine with DRDO/GTRE they will not settle for Euro 250 MM or Euro 750 MM, more like Euro 25-30 Billion. That will mean India placing an order for as many or more Rafales than the Armee del Air has. At last count they have placed orders for 180 Rafales.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby LakshmanPST » 30 Aug 2019 00:28

Rumours are true after all...
https://twitter.com/ANI/status/1167144345620770816?s=19

Alexandre Ziegler, outgoing ambassador of France to India, has been named Safran's Senior Executive Vice President, International&Public Affairs, effective Sept 2.
Safran is an international high-technology group, operating in aircraft propulsion&equipment, space&defense markets

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Re: Kaveri & Aero-Engine: News & Discussion

Postby Rakesh » 30 Aug 2019 00:36

OH.MY.GOODNESS

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Re: Kaveri & Aero-Engine: News & Discussion

Postby Vips » 30 Aug 2019 03:37

So long as the ambassador is a Safran employee, it means that some deal is cooking or under negotiation with Delhi babudom. The day he quits or is fired we will know that a deal is not happening.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby SaiK » 30 Aug 2019 07:21

Rakesh wrote:OH.MY.GOODNESS

caveat?
This kind of movement is fairly common among envoys who have served in India where they get get snapped up by the private sector to help navigate the opaque Indian system.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby Vips » 31 Aug 2019 21:52

Ukrainian Aero-Engine mfg company up for sale.


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Re: Kaveri & Aero-Engine: News & Discussion

Postby JayS » 31 Aug 2019 23:01

Rakesh wrote:DRDO 110 kN Engine Plan, Puzzles adding-up



I tweeted following stuff few days back.

Tender from HAL for outsourcing of Single Crystal Blade castings for HPT and LPT. Interesting. My best guess is this is for Adour 871 engines which power IAF's Hawk AJT fleet.

Not the first tender from HAL related to Single Crystal Blades. There was one similar tender for SCB, which I suppose meant for HPT of HTSE-1200 few years back and then a follow up tender for TBC coatings for the same.


And interestingly, GTRE has floated tender for machining and TBC quoting for SC blades and vanes meant for HP Turbine early 2019. Which engine it is meant for exactly, is anyone's guess. Kaveri engine as of now is known to be using DS blades only.

Even more interestingly, GTRE is looking for 3D printed HPT Nozzle Guide Vanes out of In718 using DMLS technology.

In Single Crystal Blade technology, the investment casting of SC is one piece of puzzle. From stock casting to final blade needs two more critical technologies

1. Laser drilling for cooling holes 2. Thermal Barrier Coating (TBC). While DMRL has been making SCB castings for a decade now, we lacked these key technologies. But it looks like some steady progress is happening on TBC at least. DMRL indicated preliminary success in

Electron Beam Physical Vapour Deposition (EBPVD) based Yttrium Stabilized Zirconium 7YSZ coating in 2017 (this is the cutting edge tech). Now, in 2019 they are looking to estb a pilot facility for EBPVD based TBC application. ARCI also working in EBPVD and seems to have made good

progress. It is likely that ARCI was the one which did TBC for HAL's HTSE-1200 HPT blades and vanes. Whether DMRL is following separate path or its in collabaration with ARCI is not clear. But definitely steady progress on TBC technology. It seems multiple instances of tech dev

is happening in key technology areas like SCB, TBC, Composites and so on. Much is going on in the background, but real test is to productionise and operationalise the technologies. We can definitely develop all those "super-secret" technologies given proper push from the top.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby JayS » 31 Aug 2019 23:10

agupta wrote:
JayS wrote:Please tell me, is following situation possible..?

1. There is enough dampening built in the jet pipe and the A/B is well design, enough not to produce strong acoustic waves of high frequency, and whatever is produced is well attenuated by the screech liner. But we still have screech in the supersonic under expanded jet outside the nozzle exit (on second thought I realized at least some acoustic waves should be able to travel downstream, but no acoustic waves from outside can come in as the flow becomes supersonic beyond the throat), where due to instabilities in the shock structure produces acoustic waves which develop feedback loop with the thin shear layer near the nozzle exit generating further instabilities and forming a close loop and eventually giving rise to screech.

2. A/B design is bad or dampening in the jet pipe is not enough to attenuate produced acoustic waves from combustion instabilities. The waves start reflecting bak and forth in the jet pipe producing organ effect. They would form a feedback loop with the A/B HW and start resonating at certain high frequency. The pressure fluctuations produced by these waves eventually will damage the screech liner, the A/B and the jet pipe due to high cycle fatigue. No some of these waves are escaping thru the nozzle throat and producing instability in the exhaust jet which is under expanded and that leads to the feedback loop and jet screech like described above.




Specific answers

#1 Yes... we can still have screech even if A/B combustion dynamics are damped if there are alternate sources/triggers e.g., the sharp lip can create one.

#2. I didn't understand this one.

I think you're thinking there are different (competing) sources... one in the shock-cell region and one (or more) elsewhere. Not so... its one coupled phenomena.


What I meant in #2 is there is, screech phenomenon going on in the exhaust jet (what we understand by "Jet screech"), and at the same time, the organ pipe effect going inside the jet pipe with acoustic waves bouncing back and forth in the jet pipe (both originated from the Combustion in AB of coarse) which damage the internal HW such as A/B or Screech liner eventually.

The text posted by Idev is interesting.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby ashbhee » 01 Sep 2019 02:57

USA is trying to prevent sale of Ukrainian Engine make Motor Sich to Chain. Should India throw its hat in the ring?
https://www.rt.com/news/467345-ukraine-factory-china-bolton/

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Re: Kaveri & Aero-Engine: News & Discussion

Postby Rakesh » 01 Sep 2019 06:54

^^^ Engine Tech lies in the hands of a select few. Why would the select few allow a future competitor to come in?

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Re: Kaveri & Aero-Engine: News & Discussion

Postby ramana » 01 Sep 2019 09:06

Vips wrote:Ukrainian Aero-Engine mfg company up for sale.

India should buy it.

Test US partnership.

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Re: Kaveri & Aero-Engine: News & Discussion

Postby ldev » 01 Sep 2019 09:43

ramana wrote:
Vips wrote:Ukrainian Aero-Engine mfg company up for sale.

India should buy it.

Test US partnership.

Russia wants to build a modernized AN-124 heavy lift military freighter with all Russian parts including Russian engines. The traditional AN-124 used D-18T turbofans made by Motor-Sich, the Ukrainian engine maker which is in financial trouble. India should buy it and then buy the modernized AN-124 from Russia and equip it with a modernized version/newer development of the D-18T engine. This will mitigate the lack of heavy lift capacity because of the C-17 shutdown and expose India to this turbofan technology.

Ilyushin to design modernised An-124 with Russian components


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