Characteristics of the turbulent non-turbulent interface in a spatially evolving turbulent mixing layer

The effect of the geometric features of the turbulent/non-turbulent interface on the entrainment of a passive scalar into a jet

“…18,19 However, as also noted in Ref. 22, the 2D studies are unable to recover the value of the Gaussian curvature, Kg. Therefore, we evaluate the curvedness solely by substituting the mean curvature value in its expression, which results in an overestimation of the radius of the vorticity structures.…”

“…8(b), showing a non-Gaussian distribution. 21,22 The negative skewness of the distribution implies that the component of the curvature that we capture is in fact mostly the smaller principal curvature, κ 2 . The peak of the PDF is located at κIλ ≈ −0.8, indicating a predominance of concave elements at the TNTI outline.…”

“…scitation.org/journal/phf as jets, 13 wakes, 2 mixing layers, 14 and boundary layers. 15 In addition, the PDF of the TNTI curvature reveals that the boundary is dominated by smooth bulges with radii of curvature of the order of the integral length scale and λ in shear-free turbulent fronts 16 and other free turbulent flows, [17][18][19][20][21][22] respectively. Another line of active research has been the local entrainment velocity at the TNTI, vn, which is defined as the relative velocity between the surface propagation velocity, us, and the local fluid velocity at the TNTI, uI, i.e., vnn = us − uI, wheren is the local interface-normal unit vector.…”

“…Nonetheless, the current two-dimensional analysis confirms that λ-sized vorticity structures dominate the TNTI region of a round turbulent jet, similar to that found in previous studies. 11,18,19,22 The interface angle, ψI, is associated with the convolution of the TNTI outline. The time-averaged cross section of a round jet is a circle, where the radial and normal unit vectors are perfectly aligned, and thus, cos(ψI) = 1 everywhere along the curve.…”

“…According to Mandelbrot, 64 this results in a 2D fractal dimension of D 2 = 1.32 ± 0.01, which resides well inside the accepted range of D 2 = 1.3-1.4, as previously found by recent studies. 22,36,37,39,40…”