1. Osney Thermo-Fluids Laboratory, Department of Engineering Science, University of Oxford, Oxford OX2 0ES, Oxfordshire, UK e-mail:
2. Osney Thermo-Fluids Laboratory, Department of Engineering Science, University of Oxford, Oxford OX2 0ES, Oxfordshire, UK
3. Structural Systems Design, Rolls-Royce plc, Derby DE24 8BJ, UK e-mail: