A novel and robust method for the turbulent/non-turbulent interface detection

Detecting the small-scale details of the turbulent/non-turbulent interface (TNTI) is challenging for experimental data due to noise disturbance. To shed new light on this issue, a robust TNTI detection method is proposed in the present paper. This method is based on tracking the Lagrangian trajectories of fluid particles which are bound to fluctuate violently in turbulent regions. The duration of tracking is restricted to avoid the accumulating errors introduced by the entrainment process, the noise and the spanwise velocity. The TNTI is then recognized as the isoline of the velocity fluctuation along trajectories with a threshold identified by the plateau in the curve of TNTI-mean-height against threshold. Comparisons with existing approaches show that the proposed method is able to capture more detailed small-scale structures of the TNTI, while being robust with a noise level of the free stream velocity up to 1.6%. Thus, more detailed geometric and dynamic characteristics of the interface could be explored with experiments. Graphic abstract: [Figure not available: see fulltext.]