刘瑶瑶, 潘翀, 郭辉, 等. 水下航行体边界层转捩流动结构实验研究[J]. 实验流体力学, 2024, 38(2): 1-9. DOI: 10.11729/syltlx20230107
引用本文: 刘瑶瑶, 潘翀, 郭辉, 等. 水下航行体边界层转捩流动结构实验研究[J]. 实验流体力学, 2024, 38(2): 1-9. DOI: 10.11729/syltlx20230107
LIU Y Y, PAN C, GUO H, et al. Experimental study on flow structure of transition boundary layer of the underwater vehicles[J]. Journal of Experiments in Fluid Mechanics, 2024, 38(2): 1-9. DOI: 10.11729/syltlx20230107
Citation: LIU Y Y, PAN C, GUO H, et al. Experimental study on flow structure of transition boundary layer of the underwater vehicles[J]. Journal of Experiments in Fluid Mechanics, 2024, 38(2): 1-9. DOI: 10.11729/syltlx20230107

水下航行体边界层转捩流动结构实验研究

Experimental study on flow structure of transition boundary layer of the underwater vehicles

  • 摘要: 采用激光诱导荧光(Laser Induced Fluorescence,LIF)和粒子图像测速(Particle Image Velocimetry,PIV)技术,对自由湍流条件下SUBOFF模型转捩边界层中的流动结构进行精细测量。实验在北京航空航天大学大型低速回流水洞中进行,SUBOFF模型长度为1.436 m,基于模型长度和来流速度的实验雷诺数为3.35 × 105。采用流动显示灰度场和有限时间李雅普诺夫指数(Finite-Time Lyapunov Exponents,FTLEs)对转捩边界层中的涡结构进行识别,并对转捩过程中发卡涡、二次涡等典型拟序结构的生成演化过程进行分析。采用两点相关方法提取转捩区拟序结构,同时采用椭圆拟合方法计算相干结构倾角,计算结果表明,结构倾角沿法向先增大后减小,在边界层附近达到最大值。为深入研究转捩流动结构特性,发展了基于流动显示的湍流/非湍流界面(T/NT)识别方法,并对界面几何特性进行了研究。研究结果表明,在转捩过程中,界面的法向高度和分形维数沿程增长。

     

    Abstract: Laser induced fluorescence (LIF) and particle image velocimetry (PIV) are used to measure the flow field of the transition boundary layer of the SUBOFF model subject to the free-stream turbulence (FST). The experiment is conducted in the water tunnel at Beihang University. The length of the SUBOFF model is L = 1.436 m, and the Reynolds number is ReL = 3.35 × 105 based on the length of the model and the free-stream velocity. The vortex structures during the transition process are identified using the grayscale field of laser-induced fluorescence and Finite-Time Lyapunov Exponents methods, which illustrate the generation and evolution process of typical structures, such as hairpin vortices and the induced secondary vortices. The coherent structures of the transition boundary layer are extracted using two-point correlation. Simultaneously, the elliptical fitting method is used to calculate the inclination angle of coherent structures. The inclination angle increases initially, and then decreases along the normal direction, reaching its maximum near the boundary layer. The visualization-based method is proposed for identifying turbulent/non-turbulent interfaces, with a focus on studying the geometric characteris-tics of the interface during the transition process. It is shown that the height and the fractal dimension of the interface increase along the transition.

     

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