caa a22 4500 606199004 CHVBK 20210128100936.0 cr unu---uuuuu 210128e20150201xx s 000 0 eng 10.1007/s00348-015-1914-x doi (NATIONALLICENCE)springer-10.1007/s00348-015-1914-x Investigation of coherent structures generated by acoustic tube in turbulent flow separation control [Elektronische Daten] [Xingyu Ma, Reinhard Geisler, Janos Agocs, Andreas Schröder] An acoustic tube was designed in order to control the turbulent flow separation downstream of a backward-facing step. The Reynolds number based on the free-stream velocity and the step height was Re h=2.0×104. As an active flow control device, the acoustic tube generated periodic pressure perturbations at a frequency of f a=100Hz, which was close to the most amplified frequency of the shedding instability of the turbulent shear layer. Spanwise vortices rolled up due to the perturbations. 2D-2C particle image velocimetry was used to measure separated shear layer and the reattachment area downstream of the BFS. The flow control results show that the acoustic tube can suppress recirculation regions behind the step and reduce the reattachment length by 43.7%. The roll-up and pairing processes of the vortices lead to an increase in the total Reynolds shear stress. The coherent structures are extracted by proper orthogonal decomposition and represented by two pairs of modes, of which the coherence is analyzed by the corresponding coefficients. Both the primary and secondary series of vortices are reconstructed as traveling waves with the fundamental frequency f a and the overtone frequency 2f a, respectively. Springer-Verlag Berlin Heidelberg, 2015 Ma Xingyu Institute of Aerodynamics and Flow Technology, German Aerospace Center (DLR), Bunsenstrasse 10, 37073, Göttingen, Germany aut Geisler Reinhard Institute of Aerodynamics and Flow Technology, German Aerospace Center (DLR), Bunsenstrasse 10, 37073, Göttingen, Germany aut Agocs Janos Institute of Aerodynamics and Flow Technology, German Aerospace Center (DLR), Bunsenstrasse 10, 37073, Göttingen, Germany aut Schröder Andreas Institute of Aerodynamics and Flow Technology, German Aerospace Center (DLR), Bunsenstrasse 10, 37073, Göttingen, Germany aut Experiments in Fluids Springer Berlin Heidelberg 56/2(2015-02-01), 1-13 0723-4864 56:2<1 2015 56 348 https://doi.org/10.1007/s00348-015-1914-x text/html Onlinezugriff via DOI BK010053 XK010053 XK010000 Metadata rights reserved Springer special CC-BY-NC licence nationallicence 1 research-article jats NATIONALLICENCE NATIONALLICENCE NL-springer NATIONALLICENCE 856 40 https://doi.org/10.1007/s00348-015-1914-x text/html Onlinezugriff via DOI NATIONALLICENCE 700 1- Ma Xingyu Institute of Aerodynamics and Flow Technology, German Aerospace Center (DLR), Bunsenstrasse 10, 37073, Göttingen, Germany aut NATIONALLICENCE 700 1- Geisler Reinhard Institute of Aerodynamics and Flow Technology, German Aerospace Center (DLR), Bunsenstrasse 10, 37073, Göttingen, Germany aut NATIONALLICENCE 700 1- Agocs Janos Institute of Aerodynamics and Flow Technology, German Aerospace Center (DLR), Bunsenstrasse 10, 37073, Göttingen, Germany aut NATIONALLICENCE 700 1- Schröder Andreas Institute of Aerodynamics and Flow Technology, German Aerospace Center (DLR), Bunsenstrasse 10, 37073, Göttingen, Germany aut NATIONALLICENCE 773 0- Experiments in Fluids Springer Berlin Heidelberg 56/2(2015-02-01), 1-13 0723-4864 56:2<1 2015 56 348