Passive Shroud Cooling in High Pressure Turbines

RESEARCH ASSOCIATE IN TURBINE SHROUD COOLING

RESEARCH STUDENTSHIP TURBINE SHROUD COOLING

INTRODUCTION

The challenge of adequately cooling turbine blade shrouds has become increasingly important in recent years. Active shroud cooling is achieved by means of internal cooling passages in the shroud. This is effective, but requires thick, heavy shrouds. This project aims to investigate the use of passive shroud cooling. This seeks to reduce the gas temperatures adjacent to the shroud by ejecting coolant from stationary parts. Given the complex nature of the flow in the casing/shroud region, the trajectories of the coolant and their effectiveness will undoubtedly be influenced by, and perhaps enhanced by, local three-dimensional flow structures.

This research forms part of a 5^th Framework RTD-Project funded by the European Commission under the "Efficient and Environmentally Friendly Aero Engine" programme.

Figure 1 Schematic of Passive Cooling Concept

Figure 2 Typical HP turbine blade showing shroud arrangement

THE RESEARCH

Objectives

The objectives of this research project are to develop a thorough understanding of the physical phenomena associated with the passive shroud cooling concept, to develop a design methodology to optimise the use of passive shroud cooling and to develop alternative concepts. The specific objectives are as follows:

To measure the cooling effectiveness of "rail cooling" of the shroud of a model HP turbine
To gain an understanding of the development and interaction of the primary and cooling flow fields
To develop an improved method of passive shroud cooling
To provide a data base for the validation of state-of-the-art CFD codes.
To use CFD calculations to enhance the understanding and to generate design rules for the future.

Figure 3 Large Scale Research Turbine ("Peregrine Rig")

DESCRIPTION OF THE WORK

Aerodynamic and Thermal Design

The aerodynamic design of the stator and rotor blades will be based on blading already existing. However, changes will be made in order to match the turbine to modern design rules and to incorporate the passive cooling system. The design will be performed by Rolls-Royce Deutschland in conduction with the Whittle Laboratory and by agreement with the other partners. This design will provide a baseline for improvements.

Build 1, instrumentation and test of 1^st concept (baseline)

The experimental work is to be conducted the large scale research turbine known as the "Peregrine" rig. Both the aerodynamics penalties and the cooling benefits of passive shroud cooling are to be investigated. At present, only the stator and rotor blade surfaces are film-cooled. It is proposed to retain the existing stator geometry. However, to implement the rail cooling and other similar geometries, new profiles will be manufactured. Master profiles will be created using stereolithography. These will be used to create moulds from which the actual blades will be cast in an epoxy-based resin.

Experimental visualisations of the flow will be obtained using oil-and-dye surface coatings. The ammonia-Diazo technique will be used to provide quantitative cooling effectiveness data. Traverse data will be obtained using pressure probes, thermal anemometers, and a laser-Doppler anemometer. Hot-wire anemometers will be used in particular to map the flow field within the shroud clearance region. The Whittle Laboratory has extensive experience of measuring this type of flow. Gas-tracing techniques will be used to track the development of the cooling air within the flow field. Traverse mechanisms provide movement in the circumferential, radial and yaw directions downstream of each blade row in the stationary frame. In addition, by means of an advanced traverse system the determination of the 3-D unsteady flow field within the rotor passages will be provided.

Analysis and new concept definition

Models of the flow provide an essential framework for any research programme. In particular, unsteady experimental data is difficult to interpret without models and simple models are increasingly inadequate. More sophisticated CFD analyses are now required. Accordingly, existing in-house codes (3-D steady and unsteady, structured and unstructured, Navier-Stokes) and commercial codes of will be used to assess the experimental data, to direct the research and to expand the experimental data base. A new concept for passive shroud cooling will be defined by the other industrial partners on the basis of this 1^st tests.

Build 2, instrumentation and test of advanced concept

The test program for this second build will be similar to the 1^st build. The obtained experimental data will be evaluated comparatively.

Comparative Analysis (incl. CFD) and reporting

This final task will include a comparative analysis of all CFD-work performed within this project in order to understand the physical phenomena of passive shroud cooling and to define a "best practice" for passive shroud cooling concepts for high pressure turbines in production engines.

THE WHITTLE LABORATORY

The research will be carried out at the Whittle Laboratory, Cambridge University Engineering Department. The Whittle Laboratory was established in 1971 and has played a leading role in the field of Turbomachinery. The Laboratory specialises in research into the fluid dynamics and thermodynamics of all types of turbomachinery. The laboratory has excellent contacts with industry and other research organisations. Much of the research is supported by contracts from industries and governments from around the world. The work in the Laboratory is equally divided between the numerical prediction of the flow through turbomachines and the experimental research using a wide variety of facilities. The Laboratory has first class computational and experimental facilities and offers many unique opportunities for high quality research.

The University aims to achieve the highest quality in teaching and research.

THE RESEARCH ASSOCIATE

The successful applicant will be responsible for the research described above under the direction of Dr. Howard Hodson and Prof. Bill Dawes. PhD students are also recruited for the same project. The Research Associate will be responsible for the team working in this important area of research. The Research Associate will be expected to work closely these students and members of the technical staff at the Whittle Laboratory who are engaged in this research. He/she will have direct responsibility for the experimental research and will also be expected to conduct computational studies in support of the experiments. It is expected that applicants will have, or expect to have a PhD degree or equivalent experience in the general area of turbomachinery with an experimental background.

The appointment is for three years in the first instance with a starting salary up to a maximum of £18,915 per annum which is subject to annual review (from April 2000) and increments. Applications in the form of a CV, including the names and addresses of two referees should be sent to Dr. H.P. Hodson (hph@eng.cam.ac.uk) or Prof. W.N. Dawes (wnd@eng.cam.ac.uk), Whittle Laboratory, Madingley Road, Cambridge CB3 ODY from whom further details may be obtained. Applicants should have, or expect to have a PhD degree or equivalent experience in the general area of turbomachinery with an experimental background. The starting date is 1August 2000 or as soon as possible thereafter. The closing date for applications is 31^st March 2000. Further information can be found at http://www.eng.cam.ac.uk/~hph/

The University follows and equal opportunities policy and aims to achieve the highest quality in teaching and research.

Further information can be found at http://www.eng.cam.ac.uk/~hph/

PhD RESEARCH STUDENTSHIP

The successful applicant will be responsible for the research described above under the supervision of Dr. Howard Hodson and Prof. Bill Dawes. The research student will be part of a team working in this important area of research. The successful applicant will be mainly responsible for the computational studies but he/she will also be expected to conduct experiments in support of this work.

The studentship will be for three years, with a starting date of 1^st August 2000 or as soon as possible thereafter. A minimum annual maintenance grant (currently £6,455 p.a.) is offered. Depending upon the applicant's circumstances, a further award up to the value of a CASE award (currently £3000 p.a.) may be available. The fees for registration as a PhD student and for membership of a Cambridge college are also covered. The candidate will be expected to register for a Ph.D. It is envisaged that the successful candidate will have a First Class Honours or Masters degree in Mechanical or Aeronautical Engineering.

Further details and application forms may be obtained from Dr. H.P. Hodson (hph@eng.cam.ac.uk) or Prof. W.N. Dawes (wnd@eng.cam.ac.uk), Whittle Laboratory, Madingley Road, Cambridge CB3 ODY. Completed application forms and a current curriculum vitae, including the names and addresses of two referees should be sent to the above not later than 20^th April 2000.