Date : June 16, 2017 (Friday), 16:00 ~
Location : E1 Seminar room (#3213)
Speaker : Prof. Christian J. Kähler, Bundeswehr University Munich, Germany
Characterization and interaction of coherent flow structures
in turbulent boundary layers
The analysis of coherent flow structures in turbulent boundary layers along flat plates with zero pressure gradient was intensively studied in the past decades. The discovery of highly ordered coherent fluid motions is very important as the complex turbulent exchange phenomena can be explained qualitatively taking the presence and interaction of these structures into account. Large scale PIV measurements were performed to characterize the turbulent superstructures Reverse flow events are shown to appear in relatively organized groupings in both spanwise and streamwise directions. Furthermore, instantaneous measurements of reverse flow events show that these events are always associated with the motion of low-momentum streaks in the near-wall region. It will be shown that low-momentum turbulent superstructures in the logarithmic region of the turbulent boundary layer flow play a significant role in the generation of reverse flow events. Both the large scale superstructures and the extreme reverse flow events will be examined based on experimentally data measured by means of large scale PIV and time resolved high resolution 3D PTV techniques in the large scale atmospheric wind-tunnel of the Bundeswehr University Munich. The facility has a 22 m long test section with a cross section of 2 by 2 square meters and the maximum flow velocity is 45 m/s. Therefore, measurements at sufficiently large Reynolds numbers are possible in this facility. To resolve the flow features using 2D PIV and time resolved 3D PTV techniques many improvement were required which will partly discussed in the talk.
Host: 기계공학과 / 성형진 교수 (Tel:3027),김형수 교수 (Tel:3049)