1. Ph.D. Student, School of Mechanical Engineering, National Technical Univ. of Athens, Fluids Section, Heroon Polytechniou 9, 15773 Zografos, Athens, Greece.
2. Mechanical Engineer, School of Mechanical Engineering, Graduate of National Technical Univ. of Athens, 15780 Zografou, Greece.
3. Professor, School of Mechanical Engineering, National Technical Univ. of Athens, Fluids Section, Heroon Polytechniou 9, 15773 Zografos, Athens, Greece (corresponding author).