Turbulence of a non-buoyant jet in a wave environment

This paper presents experimental results of a turbulent non-buoyant jet vertically discharged in a stagnant ambient and of the same jet discharged in a flow field of regular waves. The study was carried out in the wave channel of the laboratory of the Department of Water Engineering of Bari Polytechnic (Italy). Jet velocities were measured with a backscatter four-beam two-component fiber-optic LDA system. Results indicate that oscillating velocity components (obtained by phase-averaging the horizontal and vertical velocity components acquired by LDA system) cannot be described by classic wave motion theories. Amplitudes, particularly for the vertical oscillating velocity components, are larger than those obtainable through these theories. This result may be justified by both the effect of pressure variation on the nozzle due to wave motion, and nonlinear jet-wave interaction. Comparison of the root-mean square of turbulent velocity components indicates the effect of wave presence. For cross sections further from the nozzle, the experimental values of shear turbulent Reynolds stresses indicate that for configurations with the presence of wave motion, an inversion occurs of the sign compared to the jet issued in quiescent ambient. The cross sectional profiles of the shear wave Reynolds stresses are similar to those of the shear turbulent Reynolds stresses, but their magnitude is smaller. Comparison of the wave Reynolds stress in each cross section indicates that the lower the stress the smaller the wave period.