Development of the XWB-97 follows the 2011 decision by Rolls and Airbus to increase the A350-1000 thrust requirement from 93,000 lb. To maximize commonality with the baseline XWB and avoid changing the outer mold line with an expensive increase in fan diameter, Rolls sought to meet the higher power need by scaling up the core and boosting the flow. The fan will spin 5% faster, and the annulus at the base of the fan blades has also been redesigned with an inflection to 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 adds the focus is on putting new technology into the turbine. 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, for the first time on a Trent, will be shroudless.
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. The blades will also have an advanced tip-cooling treatment. Other improvements designed to help the XWB-97 maintain the same relative fuel-burn improvement as the basic XWBs, despite the thrust jump, include a more sophisticated adaptive bleed system that is designed to turn off cooling air bleed during cruise when not required.
The intermediate (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. The engine will also include an impingement effusion combustor design that uses a combination of metallic tiles and film cooling to reduce the cooling air required, thereby boosting efficiency.
“We will be testing one of the 84,000-lb.-thrust (XWB-84) development engines and putting a selection of '97K' new turbine technology into the engine so we can run it as close as possible to XWB conditions,” says Young. The prototype XWB-97 engine is expected to start first runs around the middle of the year, he adds.