Experimental study of self-sustained spanwise streaks and turbulent mixing in separated shear flow
Experimental study of self-sustained spanwise streaks and turbulent mixing in separated shear flow
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DOI：
10.1016/j.ijheatfluidflow.2022.109012
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发表时间：
2022
期刊：
影响因子：
--
通讯作者：
Nan Jiang
中科院分区：
文献类型：
--
作者：
Xingyu Ma;Zhanqi Tang;Nan Jiang
The self-sustained streaks in turbulent backward-facing step flow are experimentally studied at a step height.Reynolds number of 1.0 × 103. As one of the featured dynamic behaviors, evolution of the spanwise streaks plays.an important role in the large-scale, aperiodic and vertical flapping motions of the separated/reattaching shear.layer. By time-resolved particle image velocimetry, we measure the velocity vector fields in the streamwisespanwise and streamwise-vertical planes downstream of a two-dimensional backward-facing step. The two.cross-sectional velocity fields show that the shear layer remains two-dimensional along the span in the initial half.of the shear layer, and then three-dimensional structures start to evolve in the latter half, leading to an unsteady.reattaching shear layer and a shifting reattachment point on the downstream wall. By analyzing the finite-time.Lyapunov exponent in the spanwise field of view, we find that low-speed fluid elements are vertically entrained.upwards into the shear layer. As a result, the entrained fluid elements produce transient and localized low-speed.fluid patches in the streamwise-spanwise plane, which move and decay downstream with strong straining and.stretching motions along their boundaries. Furthermore, the large-scale streak-type and flap-type flows are.clearly extracted and reconstructed by the energy-containing proper orthogonal decomposition modes.
