Intermittency in the process of turbulence evolution in a free jet flow

Turbulence characteristics in the process of turbulence evolution in an air-in-air jet flow are explored in a constant velocity region (CVR), a transitional turbulence region (TTR), and a preservative turbulence region (PTR). Swift velocity variations (i.e., turbulent velocities), which are caused by entrainment due to the viscous shear of the fluid motion, occur intermittently in the CVR and the TTR. The probability density function (PDF) of the turbulent velocity departs largely in the TTR from a Gaussian PDF. The scaling property in the inertial subrange (ISR) begins to appear in the TTR, where the turbulent velocity is intermittent even in the ISR, Fully developed turbulence established in the PTR exhibits a nearly Gaussian PDF, and is basically intermittent at viscous subrange (VSR) frequencies. The intermittency effects are inherent in the VSR throughout the process of turbulence evolution. The scaling property is the attribute of the scaling transformation invariance of the Navier-Stokes equation for an incompressible fluid in the inviscid limit. The intermittency effects are attributed to the instability of flow motion. The intermittency is not directly related to the scaling property.