Bursting process of large- and small-scale structures in turbulent boundary layer perturbed by a cylinder roughness element

• DOI: 10.1007/s00348-016-2174-0
• Publication Date: 2016-05-03T05:58:48Z
• Authors: Zhanqi Tang; Nan Jiang; Xiaobo Zheng; Yanhua Wu
• Keywords: 0103 physical sciences; 01 natural sciences

Hot-wire measurements on a turbulent boundary layer flow perturbed by a wall-mounted cylinder roughness element (CRE) are carried out in this study. The cylindrical element protrudes into the logarithmic layer, which is similar to those employed in turbulent boundary layers by Ryan et al. (AIAA J 49:2210–2220, 2011. doi: 10.2514/1.j051012 ) and Zheng and Longmire (J Fluid Mech 748:368–398, 2014. doi: 10.1017/jfm.2014.185 ) and in turbulent channel flow by Pathikonda and Christensen (AIAA J 53:1–10, 2014. doi: 10.2514/1.j053407 ). The similar effects on both the mean velocity and Reynolds stress are observed downstream of the CRE perturbation. The series of hot-wire data are decomposed into large- and small-scale fluctuations, and the characteristics of large- and small-scale bursting process are observed, by comparing the bursting duration, period and frequency between CRE-perturbed case and unperturbed case. It is indicated that the CRE perturbation performs the significant impact on the large- and small-scale structures, but within the different impact scenario. Moreover, the large-scale bursting process imposes a modulation on the bursting events of small-scale fluctuations and the overall trend of modulation is not essentially sensitive to the present CRE perturbation, even the modulation extent is modified. The conditionally averaging fluctuations are also plotted, which further confirms the robustness of the bursting modulation in the present experiments.