1. Engineering Department, Cambridge University, Trumpington Street, Cambridge CB2 1PZ, UK e-mail:
2. Swedish Defence Research Agency, FOI, SE-164 90 Stockholm, Sweden
3. Linné FLOW Centre, KTH Royal Institute of Technology, Stockholm SE-100 44, Sweden e-mail:
4. School of Aeronautics, Universidad Politécnica de Madrid, Plaza Cardenal Cisneros 3, Madrid E-28040, Spain e-mail: