Project Objectives

Introduction and overview of objectives and impact

As there is a persisting economic and environmental pressure on aero engine and industrial gas turbine manufacturers to decrease weight and cost, increase performance, reduce noise and speed up time-tomarket, there is a strong need for a joint European effort in order to meet these demands. The focus of the AITEB-2 project is, hence, on enhancing research collaboration on the European level as well as on establishing advanced aerodynamic and aerothermal technologies for cooling and heat transfer management in the annulus of an entire turbine module.

The development of more efficient turbine modules is one of the key steps to meet the challenges stated in the Aeronautics and Space Work Programme (2002 – 2006) and the Strategic Research Agenda (ACARE). By advancing the current state-of-the art in aerodynamic and aerothermal turbine design with new cooling concepts, measurement techniques and improved CFD processes, the AITEB-2 project will lead to shortterm benefits in terms of lighter and more efficient turbine modules whereas the mid-term and long-term benefits of the project are seen in combining the results of the present project with other projects running within the 6th Framework Programme such as AIDA and TATEF-2. Thereby 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 will be possible.

The importance of the AITEB-2 project is highlighted by the fact that the proposal gathers strong support from major turbo-machinery companies in Europe. AITEB-2 further brings together research centers-ofexcellence from all over Europe in order to reach the following ambitious scientific & technical objectives. Consistent with the ACARE goals, the impact on turbine design and aircraft systems resulting is referenced to the baseline of proven in-flight technology for a 2-stage high pressure turbine as of 2000.

Scientific and technical objectives:

Improved understanding of film cooling and heat transfer in regions of separated flow
Decrease the amount of coolant flow required by establishing advanced cooling concepts in regions of separated flow, as well as in trailing edge, rotor tip and platform regions
Develop novel techniques to measure heat transfer in rotating systems and in unsteady flow
Establish a validation database, correlations and “CFD Best Practice Guidelines” for designing the entire annulus of a turbine component
Accelerate industrial design by developing CAD-to-Mesh tools for speeding up the CFD

Impact on turbine design:

20% reduction in turbine weight due to reduced part count and component length
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>
20% decrease in uncertainty of wall temperature prediction

Impact on aircraft system:

20% reduction in time-to-market
10% reduction in aero engine cost
1% reduction in CO2 emissions

Project technical objectives

The AITEB-2 project is carefully planned to cover all aspects relevant to improving industrial processes for designing competitive and environmentally friendly aero engines and industrial gas turbines. Within the project, new and integrated approaches for advanced aerodynamic and aerothermal design concepts will be developed and tested. These are tailored for all components of a modern turbine module consisting of high and low pressure as well as an interduct between high and low pressure annulus of the turbine.

The consortium brings together major European aero engine and gas turbine manufactures as well as leading European experts in the field of Aerothermodynamics to jointly address future challenges associated with the design of high-lift turbine components which are feasible from an aerodynamic, aerothermal, economic and environmental point of view.

Building upon the state-of-the-art as described in the proposal (Section B1.3), AITEB-2 represents a significant step beyond the achievements of the previous AITEB project. The work planned includes a number of complementary experiments, computational work, development of CFD best-practice guidelines, tests of advanced aerodynamic and aerothermal concepts leading to a class of highly loaded designs for high and low pressure turbines as well as to the development of novel concepts to enhance the CFD approach within industrial design processes, and finally, tests of break-through measurement technologies like new concepts for measuring unsteady heat transfer.

The new challenges distinguishing AITEB-2 from AITEB are:

Focus on aerodynamic and aerothermal aspects of high-lift technology throughout the project,
Development of new aerodynamic and aerothermal technology for single stage high pressure turbines with supersonic exit Mach numbers,
Establishment of advanced micro-hole cooling technologies for turbine platforms,
Development of concepts for passive control of flow separation in most work packages,
Break-through technologies like new concepts for measuring unsteady heat transfer,
Tool development for enhanced and accelerated industrial CFD processes.

The choice of the following technical objectives ensures that the AITEB-2 project will reach its ambitious goals.

Improved understanding of flow physics in regions of separated flow
The vast majority of geometries tested within AITEB-2 will represent high and ultra high-lift geometries required for a substantial decrease in component weight and cost. This implies the presence of large regions of separated flows on suction and pressure sides as well as strong secondary flows near platforms and in the tip region of un-shrouded blades. Thus, the questions to be answered within the project by tests on generic and complex geometries as well as by steady and unsteady CFD calculations are:

How well do the different numerical approaches available (steady and unsteady RANS, Large Eddy Simulation (LES) or Detached Eddy Simulation (DES)) predict separated flows?
Where are the optimal positions to delay or even avoid turbulent separation on suction and pressure side by passive control?
To which accuracy can these tools predict film cooling effectiveness and heat transfer in these regions?

Establishment of advanced cooling concepts for decreasing coolant mass flows
Based on the improved understanding of the flow physics in regions of separated flow and the results of the previous AITEB project, advanced concepts for cooling for all aerothermally highly loaded regions of turbine vanes and blades will be developed and tested. In particular, the focus is on advanced cooling concepts forregions of separated flow on pressure and suction side, as well as the regions near the trailing edge, the rotor-tip of shrouded and un-shrouded blades and on hub and casing endwalls.

Near the trailing edge, where effective cooling techniques are essential to assure aerodynamic efficiency and the projected life-time of the blade or vane, fundamental investigations on generic flat plate geometries and various internal geometry configurations will be followed by cascade testing for supersonic exit Mach numbers. The latter tests, in particular, are of tremendous interest for the development of high-work high pressure turbines consisting of just a single stage, thus significantly decreasing part count and axial length of the entire turbine component. Furthermore, for the high and ultra-high-lift concepts to be investigated, the rotor tip region will be subject to high aerodynamic and aerothermal loads. Here, an integrated approach of advanced aerodynamic designs for rotor tip geometries and a cooling design aimed at efficient cooling as well as decreasing aerodynamic losses will be pursued.

Finally, a variety of novel approaches to platform cooling will be tested. Here, the clear focus is on developing advanced techniques to cool efficiently localised areas of high thermal loads. These include passive flow control aspects as well as micro-hole cooling concepts. The outcome of all investigations on advanced cooling concepts will directly translate into an estimated 10% savings of coolant flow required.

Novel measurement techniques
A number of the emerging methodologies for measuring heat transfer rates (especially heat transfer coefficient) will be employed in various aspects of this project. Two of these are of particular interest: Infrared techniques and anisotropic heat flux sensors. Although relatively new, that these techniques work is beyond dispute, so the main challenge will be to apply them in the curved geometries and operational environments of the blades, endwalls and ducts, especially with rotation. There appears no reason to doubt that this is possible, and in fact, the work proposed within AITEB-2 is the logical next step in their development. Regardless, care will be taken to ensure these new tools are properly applied, and this will be accomplished by using more conventional surface resistance heating methodologies in parallel.

In parallel with these conventional and relatively new methodologies, the Chalmers group will develop a new methodology based on pulsed thin films. It is well known that heat flux can not be inferred from thin films except in short duration measurements. In fact, the length of the measurement duration is limited by the size of the film, since the thermal penetration depth must be small compared to the film dimension to ensure that the one-dimensional conduction equation can be applied in the substrate. This virtually eliminates the use of unheated thin films in steady-state environments. The same considerations complicate (or render useless) heated films, since most of the heat flows into the substrate, by-passes the film itself and goes into the flow directly from adjacent surfaces (or the reverse, depending on whether the wall is hot or cold). Thus, the true heating area (and hence heat flux) is never known and certainly strongly frequency dependent, thus rendering static calibration useless.

Chalmers proposes to reverse the traditional approach, creating the transient, or short duration measurement techniques by pulsing the electric heating current electronically, then using the traditional thin film one-dimensional approach (by analog or digital implementation) to obtain the heat loss to the substrate. The difference between this and the rate at which heat is added is the heat transfer rate to the flow. Since the surface temperature is also known (from the resistance or dynamical film response equation), the heat transfer coefficient is directly obtainable. Preliminary experiments at Chalmers have indicated great promise; moreover a similar methodology has already been commercialised (by another group at Chalmers) to measure thermal conductivity (by blocking off the convection, the very part of interest herein). Open questions like the dependence of pulse duration needed for a given substrate thickness to avoid lateral conduction and its dependence on the thermal product will be addressed in the course of the project. If successful, because of the small size (<10 microns is possible) and high frequency response (> 1kHz, perhaps much higher) it will be possible to apply the same methodology to a wide variety of problems, like endwalls and blades (included in the proposed AITEB-2 work), and perhaps even on full-stage turbines.

CFD Process enhancement tools
With the emerging software platforms tailored for the multidisciplinary optimisation of entire engine components, the definition of common interfaces for the design of various engine components is essential.