Modulating flow and mixing characteristics of an inclined jet in crossflow at a large backward inclination angle by acoustic excitation

Abstract

Previous investigations revealed that the backward-inclined jet in crossflow exhibits seemingly lower transverse velocity and turbulence intensity at inclination angles higher than a critical value about 25°, thus resulting in significantly low jet fluid dispersion properties. In this article, the acoustic excitations were applied to a backward-inclined jet in crossflow at an inclination angle higher than the critical value to examine experimentally whether the flow and dispersion characteristics could be improved or not. The flow in the test section of an open-loop wind tunnel was used as the crossflow. A profiled nozzle assembly with a loudspeaker installed in the lower part of it was used to generate the pulsating jet. The instantaneous and time-averaged smoke flow patterns were obtained by the laser-light-sheet assisted flow visualization method. The binary edge detection method was employed to the long-exposure smoke flow images to measure the jet spread width. The turbulence intensities, as well as the Lagrangian integral turbulence time and length scales, were obtained using a hotwire anemometer. The jet-fluid dispersion characteristics were examined using the tracer-gas detection technique. The results revealed that in the domain of jet pulsation intensity and excitation Strouhal number, the pulsed backward-inclined jet in crossflow presented three characteristic flow modes: synchronized oscillating jet, transition, and synchronized shear-layer vortices. The synchronized oscillating jet exhibited violent transverse oscillations due to the high axial jet pulsations induced by the acoustic excitation. The transverse jet width and jet penetration height were enlarged. The turbulence intensities were significantly increased, and the turbulence time and length scales were decreased, therefore led to a significant enhancement in the jet-fluid dispersions and mixing capabilities.