Identification of Turbulent/Non-turbulent Interface in a Turbulent Boundary Layer Using Uniform Momentum Zone Concept

This presentation develops and applies a threshold-free method for identifying the turbulent/non-turbulent interface (TNTI) in a zero-pressure-gradient turbulent boundary layer using the outermost uniform momentum zone boundary. Using the Sillero et al. DNS dataset over Reτ ≈ 1000–2000, each instantaneous streamwise velocity plane is analysed with a moving-window velocity histogram to determine a local edge velocity, from which the TNTI is extracted. The resulting interface height follows an approximately Gaussian distribution and scales with local boundary-layer thickness, with geometric statistics consistent with previous experimental studies. Conditional statistics relative to the TNTI show a sharp mean-velocity jump across the interface, higher Reynolds stresses below the interface than above it, and a peak in conditioned spanwise vorticity within the TNTI. The collapse of Reynolds-stress and vorticity profiles under local TNTI scaling supports the robustness of the UMZ-based identification method.