Large eddy simulations of a turbulent mixing layer periodically excited with fundamental and third harmonic frequency

A better understanding of the mixing behavior of excited turbulent mixing layers is critical to a number of aerospace applications. Previous studies of excited turbulent mixing layers focused on single frequency excitation or the excitation with fundamental and its second har-monic frequency. There is a lack of detailed studies on applying low and higher frequency exci-tation. In this study, we have performed large-eddy simulations of periodically excited turbulent mixing layers. The excitation consists of a fundamental frequency and its third harmonic. We have used phase-averaging to identify the vortex structure and strength in the mixing layer, and we have studied the vortex dynamics. Two different vortex paring mechanisms are observed depending on the phase shift between the two excitation frequencies. The influence of these two mechanisms on the mixing of a passive scalar is also studied. It is found that exciting the mixing layer with these low and high frequencies has initially an adverse influence on the mixing process; however, it improves the mixing further downstream of the splitter plate with the excitation using a phase shift of D/ 1/4 p showing the best mixing performance. The present works shed lights on the fundamental vortex dynamics, and has great potential for aeronautical, automotive and com-bustion engineering applications.& COPY; 2023 Production and hosting by Elsevier Ltd. on behalf of Chinese Society of Aeronautics and Astronautics. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).

Automated summary

A better understanding of the mixing behavior of excited turbulent mixing layers is crucial for aerospace applications. This study focuses on the mixing effects of low and high frequency excitation in turbulent mixing layers. Two different vortex pairing mechanisms are observed depending on the phase shift between the two excitation frequencies. The influence of these mechanisms on mixing a passive scalar is studied, and the results show that a phase shift of D/1/4 p yields the best mixing performance.