Final design freeze for the 97,000-lb.-thrust version of the engine for the A350-1000 was accomplished this month when Rolls completed “the Stage 1 exit” for the design. The key design decisions underpinned the company's commitment made last year to boost thrust without a costly increase in the fan diameter. Instead, this will now be achieved by scaling up the core and increasing the flow by spinning the fan 5% faster. The base of the blades will also be redesigned with an inflected annulus to help boost the flow capacity around the spinner.
“We will get more power out of the core by making it bigger and improve the turbine's capabilities to run the engine hotter,” says Young, who describes the growth strategy as a combination of technology insertion and increasing overall size. “A lot of the focus is around the hot end of engine and the blade material. We have changed the design style and improved the cooling effectiveness to get a good time on wing,” he adds.
Changes for the XWB-97 include the use of next-generation CMS-X4 single crystal materials and anti-oxidation coatings in the high-pressure turbine which will also be shroudless for the first time on a Trent engine. The turbine disc will also be forged from a dual microstructure disc that will provide greater stress capability toward the center of the hub while at the same time exhibiting better creep resistance toward the tips.
Other improvements will include a more sophisticated adaptive bleed system, which is designed to turn off cooling air bleed during cruise when not required. “It is the next step in evolution from the system on the 84K engine,” Young notes. The intermediate pressure (IP) compressor features a “rising line” or inner annulus line that increases in radius, thereby increasing the tip speed of the aft stages. The high-pressure compressor is derived from the European New Aero Engine Core Concept program, and is connected to the IP by a swan-neck duct. This performed “significantly” better than expected in earlier tests, adding confidence that it will meet the thrust target of the XWB-97 with no impact on SFC.
Based on article "Final certification tests loom as first Trent XWB rolls out of pre-production site" published in Aviation Week