Turbulent Length Scales and Anisotropy in Submerged Turbulent Plane Offset Jets

Abstract

Characteristics of turbulent length scales and anisotropy in different regions of a submerged turbulent plane offset jet are analyzed. The manifestation of the preattachment, impingement, and wall jet regions, including the outer and inner layers of the jet, recirculatory bubble, and circulatory flow zones are demonstrated by the velocity vector diagram. The results of the turbulent length scales (the Taylor microscale and the Kolmogorov length scale) show that the jet layer is characterized by a reduction in the length scales as compared with the recirculatory bubble and circulatory flow zones. To analyze the turbulence anisotropy, at first, the terminologies used for the axisymmetric limits of the Lumley triangle based on the Reynolds stress tensor are revisited and explained through an improved conceptual illustration. In the Reynolds stress anisotropy analysis, the anisotropic invariant maps formed by the data plots suggest that in the preattachment region, starting from the wall, the anisotropy tends to reduce toward the three-dimensional isotropy along the left-curved boundary of the Lumley triangle up to the half-depth of the recirculatory bubble zone. Then, the data plots take a turn toward the left vertex of the triangle with a further increase in vertical distance up to the inner separation line of the offset jet, exhibiting an affinity toward the two-dimensional isotropy. Within the jet layer, the data plots form a looping trend. By contrast, in the circulatory flow zone, the data plots belong close to the left-curved boundary of the Lumley triangle, moving slightly toward the left vertex of the triangle.