Large eddy simulation on the effect of free-stream turbulence on bypass transition |
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Institution: | 1. Department of Thermal Science and Energy Engineering, University of Science and Technology of China, Hefei, Anhui 230026, China;2. Institute of Engineering Thermophysics, Chinese Academy of Sciences, Beijing 100190, China;3. Key Laboratory of Light-Duty Gas-Turbine, Chinese Academy of Sciences, Beijing 100190, China;1. Faculty of Aeronautics and Astronautics, Istanbul Technical University, 34469 Maslak, Istanbul, Turkey;2. School of Aeronautics, Universidad Politécnica de Madrid, 28040 Madrid, Spain;1. School of Software Engineering, Tongji University, Shanghai, China;2. Department of Electronics and Information Engineering, Huazhong University of Science and Technology, 1037 Luoyu Road, Wuhan, Hubei 430074, China;1. ONERA, DMPE, Universite de Toulouse, 31055 Toulouse, France;2. ISAE-SUPAERO, Universite de Toulouse, 31055 Toulouse, France |
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Abstract: | The effect of free-stream turbulence (FST) on bypass transition in a zero-pressure-gradient boundary layer is investigated by means of Large Eddy Simulation (LES). The broadband turbulent inflow is synthesized to validate the feasibility of LES. Both a zero-thickness plate and one with super-ellipse leading-edge are addressed. The calculated Reynolds-averaged fields are compared with experimental data and decent agreement is achieved. Instantaneous fields show the instability occurs in the lifted low-speed streaks similar to earlier DNS results, which can be ascribed to outer mode. Various inflows with bi-/tri-mode interaction are specified to analyze effects of particular frequency mode on the instability pattern and multifarious transition or non-transition scenarios are obtained. Outer instability is observed in the cases with one low-frequency mode and one high-frequency mode inflow as reported by Zaki and Durbin (2005), and with one more high-frequency mode appended. Inner instability is observed in the case with a low-frequency dominant inflow, while the high-frequency mode is indispensable to induce the secondary instability. Furthermore, the results show that the transition onset is highly sensitive to low-frequency mode while the transition rate is highly sensitive to high-frequency mode. Finally, the formational frequency of turbulent spot (FFTS) is counted and the frequency of laminar streaks is demonstrated by spectral analysis. |
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Keywords: | Boundary layer Bypass transition Large eddy simulation Receptivity |
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