Effects of Localized Micro-blowing on a Spatially Developing Flat Turbulent Boundary Layer
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Effects of Localized Micro‑blowing on a Spatially Developing Flat Turbulent Boundary Layer Lan Xie1 · Yao Zheng1 · Yang Zhang1 · Zhi‑xian Ye1 · Jian‑feng Zou1 Received: 22 January 2020 / Accepted: 21 September 2020 © Springer Nature B.V. 2020
Abstract Direct numerical simulation (DNS) is used to investigate the turbulent flat-plate boundary layer with localized micro-blowing. The 32 × 32 array of micro-holes is arranged in a staggered pattern on the solid wall, located in the developed turbulent region. The porosity of the porous wall is 23%, and the blowing fraction is 0.0015. The Reynolds number based on the inflow velocity is set to be 50,000. The structures of the turbulent boundary layer are carefully analyzed to understand the effects of micro-blowing and its drag reduction mechanism. The DNS results show that the drag reduction is efficient, and the local maximum rate of drag reduction achieves 40%. A low-speed “turbulent spot” near the microblowing region thickens the boundary layer. Some turbulent properties, such as the mean velocity profile, stream-wise vorticity and stream-wise velocity fluctuation are lifted up. Particularly, the tilting term of vorticity transport is significantly increased. Meanwhile, the visualization of 3-dimensional vortex displays several concave marks on the surface of the near-wall vortices, which is caused by the micro-jets, leading to more broken vortices and isotropic small scales. This impact travels downstream with a small distance due to the accumulation of the micro-jets, while the uplift effect will gradually disappear. In addition, FIK identity reveals that the spatial development term and mean wall-normal convection term play opposite roles in the contribution to the skin friction drag. Keywords Drag reduction · Turbulent boundary layer · Micro-blowing · Vorticity
1 Introduction The techniques of drag reduction via the flow control have caught huge attention of the aviation industry. To a civil or commercial aircraft, about 40–50% of the whole drag during cruising comes from the skin friction in the turbulent boundary layer. It is believed that 1% drag reduction of an aircraft such as A340 can possibly save about 400,000 L of fuel per year (Kornilov and Boiko 2014; Kornilov 2015). Many ideas of skin-friction drag reduction have been proposed, such as riblets (Choi et al. 1993), permeable coatings * Yang Zhang [email protected] 1
Center for Engineering and Scientific Computation, and School of Aeronautics and Astronautics, Zhejiang University, Hangzhou 310027, China
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Flow, Turbulence and Combustion
(Abderrahaman-Elena and García-Mayoral 2017), span-wise wall oscillation (Lardeau and Leschziner 2013), and travelling wave control (Du and Karniadakis 2000). As an effective drag reduction strategy, blowing control, which has already been stimulated, exerted on the wall surface with vertical injection air, has shown a wide range of research (Sumitani and Kasagi 1995; Park and Choi 1999; Krogstad and Kourakine 2000; Chung and Sung 2001;
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