Presence of the quiescent core (QC) in a turbulent channel flow is examined using turbulent kinetic energy (TKE) and vorticity techniques. The performed analysis is based on direct numerical simulation (DNS) data at friction Reynolds numbers \(\hbox{Re}_{\tau }\) = 179 and 381. The algorithm presented in this paper enables the determination of the QC by thresholding the TKE and vorticity fields of turbulent channel flow. The threshold values, upon which detection of the turbulent region depends, are estimated via Otsu’s method. In both techniques, when a lower threshold value is chosen, new turbulent regions are detected, some of which merge with the previously identified ones. The comparison between the predictions of the two techniques demonstrates a reasonable agreement in the positions of the QC boundaries. Additionally, the TKE technique aligns well with the conventional uniform momentum zone technique. The DNS data shows sharp gradients at the boundaries of the QC for the conditionally averaged TKE and vorticity. These findings confirm the existence of a low-turbulence core region around the channel center and a boundary similar to the turbulent/non-turbulent interface (TNTI) observed in other shear layers. Increasing the Reynolds number leads to a significant enhancement in the core discontinuity. This challenges the common view of channel flows as “fully turbulent.” In addition, the introduced visualization techniques have shown strong potential for the detection of TNTI in other turbulent shear layer flows.
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