The High Pressure Turbine (HPT) is a particularly sensitive element of the engine. Nowadays, HPTs are usually heavily loaded and film-cooled, but, very often, they determine the life duration of the engine. The current trends are to continue increasing the turbine inlet temperature (and thus the efficiency of the gas turbine cycle) and the turbine stage load. This tends to reduce the engine weight but may also have a negative impact on the component's life duration.Due to their speed and reduced costs, numerical methods are intensively used by engineers to design and analyse the different parts of the turbine stage, but gains must be made in flexibility, accuracy and fidelity of the modelling, especially in the field of heat transfer. In particular, the possibility of resolving fluctuations at frequencies related to blade passing events is becoming increasingly important.
Designers need to predict the heat transfer and aerodynamic losses in unsteady turbine external flows with higher accuracy. Test data acquired under representative conditions are therefore urgently needed, both at the stage scale and at the blade and coolant hole scale. Efficient and accurate prediction methods need to be developed and tested. In order to meet these needs, this project will aim to:
- enlarge the database of aerodynamic and heat transfer measurements obtained under both macroscale (turbine stage) and microscale (dedicated test rigs to investigate coolant ejection);
- validate numerical methods and assess their accuracy through comparisons with experimental data and propose new models;
- gain understanding in the complex time-averaged and time-resolved behaviour of the flow field, both for aerodynamics and the heat transfer;
- propose new designs that present potential reduction in weight and improvements in performances.
TATEF2 plans to use the critical mass in terms of test rigs, expertise, human resources and funding to go one step further and come up with breakthrough aerodynamic and aero-thermal technologies. Four main domains have been selected and were worked on in parallel in four different technical Work Packages:
Work Package 1 was divided into three subtasks. The first assessed the MT1 turbine stage efficiency in the Isentropic Light Piston Facility (ILPF) of QinetiQ. The second subtask aimed to study the temperature distortion (hot spots) at the entrance of the t urbine stage. The effects of flow migration are especially studied. The third subtask investigated the swirl effects on the steady and unsteady aero-thermal performance of a cooled high-pressure turbine.
Work Package 2 was conducted in the CT3 blow down facility of VKI. It consisted of four subtasks. The first aimed to complete the available detailed information on the turbine stage, already investigated in two previous European projects (IACA and TATEF). Its purpose was to determine more global quantities, like mass flow, shaft power and mechanical losses. The second part was related to the knowledge of the forcing function and the unsteady heat transfer field in order to predict high cycle fatigue better, both from the mechanical and thermal point of views. The third subtask focused on the understanding of the heat transfer process on the rotor platform. The last objective was to determine the steady and unsteady performance of an innovative low-pressure (LP) vane located downstream of the existing HP turbine stage, in which large chord structural vanes alternate with more classical short chord airfoils that have a better aerodynamic performance.
Work Package 3 was divided into three experimental subtasks. The first was related to the film cooling in transonic turbine stages. Data on investigations of shock-wave-coolant interaction is very limited in any great detail. This task addresses this lack, analysing the effects of quasi-steady and periodic unsteady shock waves on film cooling performance. The second subtask was dedicated to a detailed experimental study of the flow field inside the film cooling hole for various cross flow conditions at the hole inlet. Additionally, the flow field in the hole inlet and exit region was investigated. The first two subtasks were conducted in the University of Karlsruhe and the third took place in EPFL. Experimental investigations were conducted to analyse film cooling effec
The expected results of these investigations were:
- The current lack of accuracy is usually accounted for by safety margins that result in less efficient (excessive cooling) and heavier engines, and even with safety margins, the fatigue is sometimes underestimated and causes early failure. The validation and improvements of modelling in the prediction methods would yield gains in accuracy and confidence, resulting in better calculation of high-cycle fatigue and blade life cycles.
- The understanding of the detailed physical phenomena, supported by both experiments and predictions, is a key point in improving future designs. The influence of hot spots and platform cooling on the heat load of the blades is particularly important, and microscale investigations should allow optimisation of film cooling configurations to maximise film coverage and effectiveness with smaller coolant mass flows.
- The testing of an innovative combined aerodynamic and structural low-pressure vane, with both structural and classical airfoils, would allow assessment of the aero-thermal benefits of such configurations.
Considering the WP objectives, they have been reached beyond expectation. The performed work since the start of the programme has resulted in 26 milestones and 44 deliverables. On the dissemination side, TATEF2 has been prolific since 36 articles were submitted, joining a long list of more than 40 publications about TATEF1 subjects since the closure of this project.
All the collected data from calculations and experiments have been compared and some guidelines and suggestions on the best practise for improved accuracy of the CFD tools was prepared together with a report on the improvements achieved on the numerical and physical modelling of the Computational tools. Validation of numerical methods and assessment has been achieved with improvements in modelling capacity. Deep Investigation of the complex time-averaged and time resolved flow field has resulted in a better understanding of the aerodynamics and the heat transfer in basic film cooling configuration, as well as in stage behaviour.
From the point of view of the Universities the improved knowledge of the problems and tools involved in the design of aero-engines will result in a better teaching capability closer and closer to the need of an advance society based on the 'knowledge', and to the European feeling of the crucial needs for the future of our new generations: Environment, Competitiveness and skills increase as engines for the harmonic development of European and World Economy.