Farnborough Air Show

Rolls-Royce Advances Toward UltraFan

 - July 14, 2014, 7:50 AM
Titanium-aluminide low-pressure turbine blades and proposed cooling arrangements on Rolls-Royce’s proposed future UltraFan engine may owe much to the RB3025 powerplant unsuccessfully offered to power the Boeing 777X. For example, the RB3025 featured a “vortex amplifier” to simplify turbine-blade cooling with HPC air.

New engines planned by Rolls-Royce (R-R) reflect recent powerplant trends, including steadily increasing propulsive efficiency obtained with larger-diameter fans, higher bypass ratios and smaller engine cores. The engines could power updated contemporary widebody platforms, with R-R civil large engines president Eric Schulz confirming “very live” discussions with Airbus. “If it decides to re-engine the A330 or A380, we will be here to provide support,” he said during a pre-show briefing.

R-R (Stand 4/H3 and Chalet D3) plans to focus on a two-step development of the RB211/Trent three-shaft architecture. Because the technology can be scaled, evolution could launch new medium-thrust engines for the narrowbody market–which Schulz aspires to re-enter and where Boeing needs engines for any medium-size, longer-range 757 replacement–or yield engines for large business jets.

According to R-R future programs and technology chief engineer Alan Newby, the new engines represent “the next two major steps in the evolution of the [Trent] family.” The first, he said, dubbed “Advance,” covers a collection of new technologies intended to improve thermodynamic efficiency, while the later UltraFan development will introduce a gearbox to reduce fan speed and raise propulsion efficiency.

The Advance engine will build on the Trent’s “unique” direct-drive turbine architecture and the results of several years of new-technology research, said Newby. He added that the design, which is expected to sport a bypass ratio of more than 11:1 and an overall pressure ratio of more than 60, could enter service soon after 2020.

Expected to follow about five years later, the UltraFan is aimed at offering at least a 15:1 bypass ratio and an overall pressure ratio of more than 70:1. The company suggests that, relative to the Trent 700 powering the Airbus A330, the engines will provide “significant efficiency improvements” of more than 20 percent and 25 percent, respectively. R-R plans to run its first powered gearbox next year and a demonstrator of the engine could fly before 2020.

A big change with the Advance is the core, which “redistributes the workload” between the intermediate- and high-pressure compressors and turbines (IPCs/HPCs and IPTs/HPTs). Newby said that this “good aerodynamic solution” would provide the foundation for future engine generations.

The UltraFan, which could be a stepping stone to an open-rotor design, has a similar “work split,” said Newby, but with an enhanced IP turbine driving the slower fan through a reduction gearbox, which permits deletion of the low-pressure turbine (LPT).

With deliberate product evolution, R-R has taken the Trent XWB engine’s integrated propulsion system and lightweight LTP and married them to a carbon-titanium (CTi) fan and the new core to create the Advance. In turn, the UltraFan retains the Advance core while introducing the geared multi-stage IPT to drive the fan and compressor.

Fan Reverser

Newby said that ever-bigger engines will require greater integration with nacelles and airframes. The variable-pitch CTi fan (derived from a variable-pitch-geared turbofan variant of the 1970s R-R/Snecma M45H that powered the VFW-Fokker 614) and an integrated “slim-line” nacelle allows the fan also to replace the thrust reverser.

Both engines represent an orchestration of innovation. The Advance features lightweight, high-efficiency compressors, turbines and CTi fan; advanced high-overall pressure ratio cycle, turbine cooling and materials; “smart” adaptive systems and adaptive cooling; hybrid ceramic bearings; low nitrous-oxide (NOx) combustor; and high torque-density shafts. Newby said the combustor could provide “a significant reduction in NOx” with a margin that anticipates future legislation. Dynamic blade sealing is employed to push “as much air as possible through the centre of the engine, especially for cooling at takeoff.”

Building on these characteristics, the main change on the UltraFan is the power-reduction gearbox to drive the low-speed fan. The engine’s attributes include an advanced CTi fan, hybrid ceramic bearings, cooling air (whose temperature is reduced further to permit “reasonable” cooling when the engine runs at high temperatures); integrated “slim-line” nacelle; bladed disc (“blisk”) and ring (“bling”) compressors; broader application of ceramic-matrix composites (CMCs), including titanium-aluminide (Ti-Al)/CMC IP turbine high-aspect-ratio aerofoils; and a multi-stage IPT.

The UltraFan’s Ti-Al LPT blades and proposed cooling may owe much to the RB3025. For example, the RB3025 sported a “vortex amplifier” to simplify turbine-blade cooling with HPC air. That engine, with an overall pressure ratio of 62:1 and a 12:1 bypass ratio, was offered to power the Boeing 777X. For that application, Boeing extended 777-200LR and -300ER monopoly-supply arrangements with General Electric to include new long-range variants. (The RB3025 was superseded by the RB3039, revealed last year as the genesis for a “radically different” new-generation R-R engine that “probably” would not carry the Trent name.)

In a search for “mature reliability from day one,” R-R will apply a “hierarchy of verification,” beginning with component and capability technologies used in core-integration vehicles to demonstrate “elemental” advances. Technologies will be consolidated, with the manufacturer expecting to run a “significant number” of demonstrator engines for potential use on as-yet-undefined platforms, according to Newby.

R-R is using a Trent 1000 donor powerplant for environmentally friendly engine (EFE) work exploring a high-efficiency core on a dedicated test facility at Bristol in the UK. The unit comprises the T1000 “minus fan, plus booster compressor” to test low NOx and high-temperature-combustor HPT technology, according to Newby.

Four series of testing over two years were completed recently, and the program continues through 2015 to test high-temperature capability and core technologies. The EFE program “targets” three areas of environmental concern: “reducing CO2, NOx and noise.”

Advanced Low-pressure System

A T1000 is also the basis for R-R’s advanced low-pressure system program, which will soon begin a third testing session at NASA Stennis in the U.S., following two rounds at the UK Derby factory. This will coincide with U.S. testing of a newly built flight engine. The demonstrator engine will be used to verify LP-system, “externals” and composite-fan technologies.

A third T1000 donor engine provides the vehicle for R-R’s advanced low-emission combustion system work for engines offering 30,000 to more than 100,000 pounds thrust. Detailed design had been finalized in early June, and components were being manufactured. Next year R-R plans to ground-test the first engine and flight-test a second on a Boeing 747 testbed. Newby said “lean-burn combustor subsystem verification” has been completed on the EFE and the efficiency, economy and environment core demonstrators, which “validated emissions predictions.”

The Trent XWB program, which exclusively powers the Airbus A350XWB, will yield a further donor engine to develop high-efficiency core architecture for the Advance project. R-R will use it to demonstrate a new core configuration, especially regarding the work split between IPCs/HPCs and IPTs/HPTs.

Newby reported in June that the conceptual Advance design was finalized and that the company was starting to detail externals. An initial gate review has been completed and components with a long lead times have been manufactured; R-R was also obtaining disc forgings.

Functional testing is planned next year, with endurance testing of a second engine slated for 2016. Once the architecture has been validated, R-R will look for additional technologies to insert into the basic design, according to Newby.

Finally, an Advance engine will be donated to UltraFan enabling-technologies work that will be supported by an extensive rig program for key systems alongside technologies development. Construction of a power-gearbox test facility and associated technology development has begun in Germany. Gearbox testing will take place later next year, with full ground- and flight-test demonstrations scheduled in the latter part of this decade, concluded Newby.