The uses of coherent structure (Dryden Lecture)

The concept of coherent structure in turbulent flow is a revolutionary idea which is being developed by evolutionary means. The main objective of this review is to list some solid achievements, showing what can be done by using the concept of coherent structure that cannot be done without it. The nature of structure is described in terms of some related concepts, including celerity, topology, and the phenomenon of coalescence and splitting of structure. The main emphasis is on the mixing layer, as the one flow whose structure is well enough understood so that technical applications are now being made in problems of mixing and chemistry. An attempt is made to identify some conceptual and experimental obstacles that stand in the way of progress in other technically important flows, particularly the turbulent boundary layer. A few comments are included about the role of structure in numerical simulations and in current work on manipulation and control of turbulent flow. Some recent developments are cited which suggest that the time is nearly right for corresponding advances to occur in turbulence modeling

Concept for measuring aeroacoustic noise transmission in trains derived from experience gained in aircraft testing

Measuring aeroacoustic noise and its transmission into the passenger compartment of an aircraft provides a way to evaluate the vibrational energy caused by the turbulent boundary layer and other aeroacoustic sources, the transmission path and the sound radiation into the compartment. The measurement results are used to validate numerical models and to identify parameters for a turbulent boundary layer model. This was used in a flight test campaign at the DLR to separate different sources and determine their transmission into an aircraft. The measurement concept and results from the flight test will be presented, whereupon the potential in applying this concept to high-speed train measurements will be discussed