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Turbine Aero-Thermal External Flows 2


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

Project objectives

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, and 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.
MT1 turbine stage investigated in QinetiQ (WP1)
MT1 turbine stage investigated in QinetiQ (WP1)

Description of the work

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 will be worked on in parallel in four different technical Work Packages:

Work Package 1 is divided into three subtasks. The first assesses the MT1 turbine stage efficiency in the Isentropic Light Piston Facility (ILPF) of QinetiQ. The second subtask aims 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 investigates the swirl effects on the steady and unsteady aero-thermal performance of a cooled high-pressure turbine.

Work Package 2 is conducted in the CT3 blow down facility of VKI. It consists of four subtasks. The first aims to complete the available detailed information on the turbine stage, already investigated in two previous European projects (IACA and TATEF). Its purpose is to determine more global quantities, like mass flow, shaft power and mechanical losses. The second part is 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 focuses on the understanding of the heat transfer process on the rotor platform. The last objective is 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 is divided into three experimental subtasks. The first is 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 is 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 is investigated. The first two subtasks are conducted in the University of Karlsruhe and the third takes place in EPFL. Experimental investigations are conducted to analyse film cooling effectiveness and heat transfer coefficients on a MT1 NGV profile assembled in a linear cascade. The MT1 airfoil is equipped with multi-row film cooling on pressure and suction side. Additionally, film-cooling performance on the NGV’s platforms is studied.

Work Package 4 represents the CFD part among the technical work packages. It is led by the University of Florence and is composed of four subtasks. The first addresses the CFD tools for heat transfer in turbine stage components. The second subtask is related to the strategies and methods for the simulation of unsteady stage aerodynamic and heat transfer. The third task is related to the CFD activity of the industrial partners, running simulations on selected test cases coming from the project database. This will lead to an improved validation of the CFD tools to be used for the design of the turbine components. Then the general consensus on what is relevant in the comparison, both on the research side as well as for industrial application, will be stated. The objective of the fourth task is to develop suitable post-processing methods for a critical review of the available data.

Expected results

The results of these investigations will be the following:

1. 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 will yield gains in accuracy and confidence, resulting in better calculation of high-cycle fatigue and blade life cycles.

2. 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.

3. The testing of an innovative combined aerodynamic and structural low-pressure vane, with both structural and classical airfoils, will allow assessment of the aero-thermal benefits of such configurations.

Mach number around the 2nd stator including structural struts (WP2)
Mach number around the 2nd stator including structural struts (WP2)