Overview
Today's market for civil aircraft continuously demands lighter, cheaper, more efficient, cleaner and quieter engines. For the turbine component of a competitive future aero-engine, these requirements result in higher thermal loads in the high-pressure stage due to flatter temperature traverses at the turbine inlet as a result of new combustion concepts, and hence, the need for advanced cooling concepts. Moreover, the weight and cost requirements lead to high or ultra-high lift blade concepts for the decreasing number of parts, and to unshrouded blade concepts to decrease weight while maintaining a high efficiency level. Finally, the demand for higher by-pass ratios leads to more advanced designs of interducts (so-called aggressive) in order to shorten the axial component length.
Consistent with the ACARE goals, the resulting impact on turbine design and aircraft systems was referenced to the baseline of proven in-flight technology for a two-stage high-pressure turbine as of 2000. The following objectives are stated for the turbine design: 20% reduction in turbine weight, 10% reduction in coolant consumption, 1.5% increase in turbine efficiency, 50% reduction in time for detailed design with state-of-the-art CFD tools and 20% decrease in uncertainty of wall temperature prediction, thereby leading to a 20% reduction in time-to-market, a 10% reduction in cost and a 1% reduction in CO2 emissions for an entire aero-engine.
The AITEB-2 project led to short-term benefits in terms of lighter and more efficient turbine modules, whereas the mid-term and long-term benefits of the project were seen when combining the results of the project with other projects which ran within the Sixth Framework Programme, such as AIDA and TATEF-2. By covering both aerodynamic and aerothermal aspects of ambitious future turbine designs, the development of highly efficient, low-noise and ultra-high, by-pass ratio, commercial aero engines was possible.
The project structure comprised seven Work Packages, including one devoted to project management (Work Package 7). The work in Work Package 1 focused on aerodynamic and aerothermal investigations of high-lift technology for high and low-pressure turbines. Particular emphasis was placed on the development and testing of concepts for passive control of flow separation. Work Package 2 was targeted at the establishment of efficient cooling technologies for trailing edge cooling. Most importantly, the outcome of this work was essential for the development of highly efficient cooling concepts for high-pressure, single stage turbines for new generation small and medium-size aero-engines.
The experimental and numerical work in Work Package 3 established novel platform cooling approaches based on micro-hole technologies. Moreover, the aspects of passive control of secondary flows near the platform to be investigated for high-lift rotor blades was another essential building block for the high-lift technology also investigated in Work Packages 1 and 4. The final aspects of high-lift technology investigated in AITEB-2 are cooling concepts for highly loaded, high-pressure turbine blades. This was accomplished experimentally and numerically for shrouded and unshrouded blades in Work Package 4. The work in Work Package 5 was focused on aerothermal aspects of advanced turbine interducts.
The extensive tests included investigations of passive flow control aspects, and the development of breakthrough technology for unsteady heat transfer measurements had a major impact on research methodologies in the aero-engine and gas turbine industry. The tool development resulting from the work in Work Package 6 allowed for tremendously decreased turn-around times in the detailed design phase with high-end CFD methods. Providing a highly improved CFD process, Work Package 6 forms the basis for future investigations in all research areas of industrial interest.
Funding
Results
Main Project Conclusions:
- Within the AITEB-2 project, a wide variety of CFD applications was applied … RANS, URANS, LES, particle separation, approaches using Conjugate Heat Transfer methods (CHT).
- Meshing of complex geometries and handle meshes with ~10 Mio cells has become standard, an efficient CFD process from CAD – Solve was shown.
- CFD predicts flow separation well, but has significant difficulties with predicting re-attachment locations in complex flows.
- The inclusion of transition models – as available in commercial CFD codes and as developed at Univ. Florence – improved agreement with exp. data.
- Focus on unsteady CFD for unsteady problems vs. iterating various turbulence models.
- Even unsteady CFD with transition (URANS) do not fully accurately capture experimental data for film-cooling effectiveness and heat transfer coefficient.
- CFD captures trends but is still off quantitatively for complex flows.
- We still need experiments and will continue to do so!
- Increasing CFD capabilities require more detailed boundary conditions (not just flow, but more turbulence quantities).
- Comments to CFD vendors and academic CFD partners:
- Mesh quality control essential for controlling standards of flow results in particular during CFD based optimisation
- Need for readily available higher level CFD methods for assessment of detailed flow features (e.g. trailing edge cooling)
- Need for readily applicable conjugate CFD methods for very complex geometries with related requirements for meshing tools
- Need for dedicated turbulence model development for Turbo-machinery capable of coping with very strong streamline curvature