The length scale which, combined with the fluid’s kinematic viscosity $\nu$, defines the local average speed of the turbulent-nonturbulent interface has been postulated to be the smallest (Kolmogorov) length scale $\eta$ of the turbulence Corrsin and Kistler, [NACA Report No. 1244, 1955, p. 1033.]. This is indeed the case when the turbulence dissipation rate obeys the Kolmogorov equilibrium cascade scaling, but in the presence of the nonequilibrium turbulence dissipation scaling the average local turbulent-nonturbulent interface speed scales as $\nu /\lambda$, instead of $\nu /\eta$, where $\lambda$ is the Taylor length. We derive this theoretically and confirm it experimentally in the range of distances between 20 and 50 nozzle widths of a turbulent planar jet.

• Received 2 June 2020
• Accepted 7 September 2020
• Corrected 18 November 2020

DOI:https://doi.org/10.1103/PhysRevLett.125.174501