Three Fan architectures
An alternative for future
The technologies developed by the VITAL programme will be incorporated in three basic configurations involving the low-pressure section including the fan. The improvements expected from each of these layouts will be evaluated in against the requirements of the type of flight (short or long-haul). Three basic architectures are being investigated:
- Direct Drive Turbofan (DDTF), a re-optimized tradeoff between fan and turbine requirements considering the low weight technologies introduced by the VITAL programme.
- Geared Turbofan (GTF), combining a fan with a reduction gear train, to allow different rotating speeds for the fan on one hand, and the booster and turbine on the other.
- Contra Rotating Turbofan (CRTF), with two fans turning in opposite directions, allowing even lower rotation speeds, since the two fans split the loads involved.
The three VITAL engine concepts
COUNTER-ROTATING FAN
The counter-rotating turbofan (CRTF) concept developed by Snecma is particularly innovative. This layout simply means that there are two independent shafts, rotating in opposite directions. At the other end of the low-pressure section, they are joined to a low-pressure turbine with several stages of counter-rotating blades. For a given aerodynamic load, this configuration will reduce the fan rotating speed by 30 percent or more.
This fan concept is a great leap by offering the same performance as a conventional fan – it manages the same airflow -, but with slower tip speeds, reducing fan noise. Therefore, engines development would be able to follow a new trend enabling a higher bypass ratio with lower fuel burn.
Acoustic tests will be carried out at different speeds, with different blade configurations.
Each rotor will have significantly fewer blades than a conventional fan.
Tests will be performed on a 1/4-scale model at the Russian research center CIAM (Central Institute of Aviation Motors), already a partner to Snecma on several initiatives.
DIRECT DRIVE TURBOFAN
The Direct Drive Turbofan (DDTF), concept developed by Rolls-Royce, remains on a similar configuration as engines of today, but would contain the increase of weight of the engine through novel lightweight materials and structures. The targeted high bypass ratio is 10 to 12. As a result of the higher bypass ratio the fan speed and pressure ratio will be reduced. Acoustic and aerodynamic tests of a fan rig will be performed at Anecom in Germany. Designs for low weight and noise LP turbines will be aerodynamically and acoustically tested in Germany, Italy and Spain.
Mechanical tests of the novel fan blade, casings and structures will also be carried out.
GEARED TURBOFAN
The Geared Turbofan (GTF), concept developed by MTU, is also based on a standard technology but targeting higher bypass ratios (12-15). The GTF which revivals through the use of a “gear” placed on the engine axe, needs that VITAL teams to develop new technologies for compressors and the low-pressure turbine. The GTF evaluations will use the same fan technology as the DDTF, both aerodynamic and mechanical.