A Round Jet Normal to a Crossflow

Abstract

Measurements of the velocity characteristics of a jet in crossflow are reported and encompass the entire mixing region. Laser-Doppler anemometry was used in the upstream region (x/D ≤ 6) where the turbulence intensities were larger and hot-wire anemometry in the downstream region. The scalar field, stemming from the injection of a trace gas in the jet flow, was also determined. Jet to cross-flow velocities of 2.3 and 1.15 were used. The results confirm and quantify the double-vortex characteristics of the downstream flow and demonstrate that this is associated with fluid emanating from the jet. The velocity maximum observed further from the wall than the double vortex is shown to correspond to freestream fluid accelerated by the pressure field. The mean-velocity profiles in the plane of the jet exit are shown to be far from uniform and the developing jet to be characterised by strong anisotropy associated with the acceleration of the freestream around the jet and into its wake. Probability distributions of velocity together with values of the Reynolds stresses, allow a detailed interpretation of the double vortex in the downstream region and indicate, for example, the larger magnitude of the crossstream fluctuations. The flow in the downstream region is also characterised by very different magnitudes of the shear stress and the non-coexistence of zero shear stress and zero gradients of mean velocity and turbulence energy.