Mixing of an acoustically pulsed air jet with a confined crossflow

Mean velocity and turbulence profiles, downstream of the jet orifice, in a 10 m/s crossflow have been measured over a range of Strouhal numbers and excitation powers for a jet/crossflow velocity ratio range of 1.3 to 4.6. This showed that acoustically exciting a jet flow causes significant increases in jet spread, penetration (up to 92% increase), and mixing. The jet mixing length was strongly reduced. Toroidal vortices were shown to be shedding from the jet orifice and produced profound changes in the jet structure. Increase of jet penetration and turbulence (hence mixing) began to saturate by about 80-W driving power, thus only small further gains were possible up to the maximum power used of 160 W. The jet turbulence and penetration data showed that the response appeared to be optimum at about a Strouhal number of 0.22. Overall, the jet mixing processes were significantly improved, in a controllable manner, by pulsating the jet flow.