Dr. Hongna Zhang

School of Mechanical Engineering of Tianjin University, China

E-mail: hongna@tju.edu.cn

Bio

Dr.Hongna Zhang is an associate professor in School of Mechanical Engineering, Tianjin University. She received her Master’s degree in Fluid Machinery and Engineering at Harbin Institute of Technology, and Ph.D. in Nuclear Engineering in Kyoto University. She carried out post-doctoral research at Kyoto University and Harbin Institute of Technology. Currently, she is working on viscoelastic fluid turbulence, heat transfer enhancement, microfluidics and computational fluid dynamics.

Title

Direct numerical simulations of two-dimensional elasto-inertial turbulence in channel flows

Abstract

Recent studies have confirmed that, the novel turbulence type, namely elasto-inertial turbulence (EIT), can exist in two-dimensional channels. Now, the research on EIT has reached the stage of identifying the minimal flow unit (MFU). On this issue, direct numerical simulations (DNSs) of FENE-P fluid flow in two-dimensional channels with variable sizes are conducted in this study. In my talk, we demonstrate with the increase of channel length, the simulated flow experiences several different flow patterns and there exists a MFU for EIT to be self-sustained. Through capturing the onset process of EIT, we observed that EIT originates from the sheet-like extension structure located near the wall which maybe related with the wall mode rather than the center mode. The fracture and regeneration of this sheet-like structure is the key mechanism for the self-sustaining of EIT. Moreover, we also qualitatively analyzes the statistical characteristics and dynamic mechanisms of two-dimensional flow and explores its similarities and differences with three-dimensional flow. We find that the parametric effects on the statistical characteristics show an opposite trends in two-dimensional EIT versus three-dimensional EIT and drag-reducing turbulence (DRT). In addition, we also identify the anomalous Reynolds stress that contributes negatively to the flow resistance in two-dimensional EIT by quadrant analysis. The anomalous phenomenon can be attributed to the motions in the first and third quadrants are closely associated with the polymer sheet-like extension structures, which incline from the near-wall region towards the channel centre.