The manipulated transitional backward-facing step flow: an experimental and direct numerical simulation investigation |
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| Institution: | 1. Institut für Strömungsmechanik u. Aerodynamik, LRT/WE 7, Universität der Bundeswehr München, 85577 Neubiberg, Germany;2. Hermann-Föttinger-Institut für Strömungsmechanik, Technische Universität Berlin, 10623 Berlin, Germany;3. Fachbereich 3, Mathematik, Numerische Mathematik u. Funktionalanalysis, Technische Universität Berlin, 10623 Berlin, Germany;1. Department of Physics, Hooghly Mohsin College, Hooghly-Chinsurah 712101, West Bengal, India;2. Department of Physics, University of Burdwan, Burdwan 713104, West Bengal, India;1. Department of Mechanical Engineering, Celal Bayar University, 45140 Manisa, Turkey;2. Department of Mechanical Engineering, Technology Faculty, Fırat University, 23119 Elazığ, Turkey;1. School of Mechanical Engineering, Shanghai Jiao Tong University, Shanghai 200240, China;2. School of Mechanical Engineering, Nantong University, Nantong 226019, China;1. Mechanical Engineering Department, College of Engineering, Universiti Tenaga Nasional, Jalan IKRAM-UNITEN, 43000 Kajang, Selangor, Malaysia;2. Department of Environmental Engineering, College of Engineering, Komar University of Science and Technology (KUST), King Mahmud Circle, Sulaymani-Kurdistan Region, Iraq;3. FABE, Limkokwing University of Creative Technology, Jalan Teknokrat 1/1, 63000 Cyberjaya, Selangor, Malaysia;4. Department of Mechanical Engineering, University of Anbar, 31001 Anbar, Iraq;5. Shanghai Key Lab of Vehicle Aerodynamics and Vehicle Thermal Management Systems, 4800 Cao An Rd., Jiading, Shanghai 201804, China;1. Institute of Aerodynamics and Chair of Fluid Mechanics, RWTH Aachen University, Wüllnerstrae 5a, 52062 Aachen, Germany;2. Institute of Fluid Mechanics and Aerodynamics, Bundeswehr University Munich, Werner-Heisenberg-Weg 39, 85577 Neubiberg, Germany |
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| Abstract: | Results from a joint experimental and direct numerical simulation (DNS) investigation are presented for the flow over a backward-facing step manipulated by low-amplitude time-periodic (harmonic) blowing/suction excitation through a narrow slot at the edge of the step. For a Reynolds number of Reh=3000 (based on step height, h, and inflow velocity, Uo) and for laminar inflow, a 33% reduction of the mean recirculation length (in comparison to the non-manipulated reference case) could be obtained with a forcing amplitude of the order of one per cent of Uo. Based on the momentum thickness, θ, of the incoming laminar boundary layer (at the edge of the step), the corresponding optimum Strouhal number is Stθ=foptθ/Uo=0.012. From the experimental data it can be concluded that, in our flow case, the optimum frequency, fopt=50 Hz , was the most amplified frequency in the transition-to-turbulence process of the separated laminar shear layer. Detailed comparison of the experimental data with data from the numerical simulation shows that DNS and experimental data agree up to second-order statistics. The joint experimental and numerical investigations exhibit a complementary nature in the sense that, on the one hand, the main advantage of the experiment was the relative ease with which a wide range of forcing parameters could be tested and, on the other hand, DNS could provide spatio-temporal details of the flow which could not be so easily obtained in the experiment. |
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