Turbulence Measurements of a Longitudinal Vortex Generated by an Inclined Jet in a Turbulent Boundary Layer

Abstract

A longitudinal vortex in a flat-plate turbulent boundary layer was examined in a wind tunnel experiment using Laser Doppler Anemometry. The vortex was produced by an inclined round jet (D = 14 mm) in the turbulent boundary layer (δ0.99 ≈ 25 mm). The jet nozzle was positioned at pitch and skew angles of 45 deg to the oncoming stream, and the jet speed ratios (jet speed/freestream flow speed) were 0.5, 1.0, and 1.5. The flow was characterized by embedded vortices, induced high turbulent kinetic energy peak, local areas of high primary shear stress, and negative shear stress. Two types of normal stress evolution were observed: (a) low normal stress beneath the vortex on the upwash side and high normal stress above the center of the vortex, caused by spanwise momentum transfer and local turbulent production; (b) high normal stress beneath the vortex on the upwash side and high normal stress coinciding with the center of the vortex, produced by spanwise and transverse momentum transfer of a vortex away from the wall with turbulent convection playing an important role. The study provided a database for numerical modeling effort.