Chinese Engine Development


Hendrik_2000

Brigadier
Well I found this explanation

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In almost every large turbofan I see, the LP turbine stages outnumber the HP turbine stages by a factor of at least 2. Here's a photo of the RR Trent 900:
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The Trent 900 (like most Rolls-Royce turbofans) is a 3-spool turbofan, rather than a 2-spool. But even here, my observation holds. There are far more LP turbine stages than the middle or high pressure stages.
Why is this?

Because the LP turbine extracts power for the fan, which requires the most power. The HP and IP turbine only extract power for their connected compressors - the LP turbine extracts power for the fan and the LP compressor. The fan does work on all airflow through the engine, the compressors only on a fraction (10:1 for a high bypass like the Trent 1000). The fan produces up to 75% of the thrust of the engine.

From
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: the cross section of the Trent 1000. It shows that the LP, IP and HP rotors have different rotational speeds, but does not list them. Another (older) presentation lists them as 3600. 6800 and 10200 RPM. Rotational speed goes down as the volume of the mass stream goes up.

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An old textbook of mine gives the power P extracted from a turbine stage as:



P=m˙⋅u⋅vax⋅[tan(α2)+tan(α3)]P=m˙⋅u⋅vax⋅[tan(α2)+tan(α3)]


with

  • m˙m˙ = mass flow [kg/s]
  • u = tangential blade velocity [m/s]
  • vaxax = axial gas velocity [m/s]
  • α2α2 and α3α3 angles according to the figure below.
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So the tangential speed of the turbine blade is in the equation for power extraction, which is composed of rotational velocity and blade radius. The faster the turbine turns, the more power can be extracted per stage, and the fewer stages required. Why then does rotational velocity go down with pressure? (HP = 10,200; IP = 6,800).

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The reason is the constructional limits of the turbine. As the gas stream expands, the turbine blades become larger and are mounted at a greater axial distance, which results in greater centrifugal forces which are proportional to blade mass, rotational speed and distance from the axis. In order to limit centrifugal forces, the rotational velocity of the rotor is reduced: each subsequent stage turns at a lower RPM. Notice that a lower RPM can be compensated by mounting the blade further away from the rotational axis.

The LP rotor of an un-geared engine runs at the same rotational velocity as the fan. Its optimal RPM for the turbine may be higher, and that can be accommodated by the geared fan. As the bypass ratio gets higher, the LP turbine will be extracting a higher fraction of total power from the airstream - turboprops and turboshafts have a gearbox in between the LP shaft and the propeller/rotor, and the high bypass fan approaches the relative dimensions of a propeller...
 

Hendrik_2000

Brigadier
It was first observed tested in IL76 back in June 2014. So 8 years has gone by with many set back and disappointment along the way
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1617980370950.png

Recently, a photo of a large bypass ratio turbofan engine was exposed on a Chinese aerial test bed. This photo shows a new engine completely different from the Russian-made D-30 engine, which was installed on an aerial test bed. According to the test, the nacelle and structure of the engine are similar to the American CFM56-7 engine and GE90 engine.

According to foreign media reports, China has imported a batch of Il-76 transport aircraft from Russia, which were converted into a batch of unknown number of engine test platforms dedicated to testing new domestic engines. China's heavy-duty strategic transport aircraft Yun 20 has no suitable domestic engines for use, so the test flight of the Yun 20 is the same as the current Il-76, equipped with D-30 engines. The aircraft exposed this time is the Il-76 test platform. The engine mounted on the inside of the left wing of this aircraft has a short and thick shape, which is obviously different from the other three relatively slender D30. It is likely to be the WS-20 (turbofan 20). Dowby turbofan engine, and WS-20 is the "genuine" engine of Yun-20.

Russia does not export more advanced engines to China

The D-30 engine is not advanced. Compared with the new-generation engine, its duct is relatively small and the fuel consumption rate is high. Russia’s newly improved Il 476 transport aircraft has replaced the D-30 with a more advanced PS-90 engine. Russian media claimed that Russia has refused to export PS-90 engines to China. The D-30 is currently China's only usable turbofan engine with no afterburner bypass ratio. The US media called the localized model WS-18. Currently, China's three main combat models: Il-76, H6K "God of War", and Yun-20 are all equipped with D-30 series engines.
 

Deino

Lieutenant General
Staff member
Super Moderator
Registered Member
By the way ... any idea what type of engine under the Il-76LL could be? It looks slimmer than the D30-KP-2 and as such could be an engine for a fighter-sized type? ... maybe the WS-13E, WS-19??? I have no idea.


1617982194255.png
 

latenlazy

Colonel
By the way ... any idea what type of engine under the Il-76LL could be? It looks slimmer than the D30-KP-2 and as such could be an engine for a fighter-sized type? ... maybe the WS-13E, WS-19??? I have no idea.


View attachment 70757
A middle weight weight military turbofan should have an engine diameter of about half the D-30KP, and a heavy weight military turbofan should have a diameter about 2/3 the D-30KP. The only two heavy weight engines still in development that might be at flying test bed stage I can think of are the WS-15 and whatever WS-10 variant the H-20 might end up flying with.
 

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