Laminar Jet Characteristics in a Loudspeaker Induced Standing Wave

In this paper, the acoustic excitation effects on the flow characteristics of a laminar jet inside an air-filled cylindrical tube have been presented and discussed. It is observed that the acoustic excitation has a strong effect on the jet velocity and its flow structure. Under excitation, the velocity is observed to increase more than seven times. Comparisons and investigations of the velocity characteristics with and without excitation, at different position above the nozzle exit have been carried out in detail. An important observation is that the acoustic excitation could induce a static pressure in the cylindrical tube. As a result, an increase of air flow rate could be measured if the air nozzle is positioned in the negative static pressure zone. When under acoustic excitation and the air jet is replaced by a propane fuel jet, the laminar jet propane diffusion flame was observed to change colour, shorter in height, and lifting off at different acoustic regimes of the standing wave. These observations indicate that acoustic excitation have changed the flow and flame properties significantly. It is observed that acoustic excitation does not accelerate the flow field uniformly. The high velocity region is found to increase in value much more than in the low velocity region. To investigate the effect of acoustic excitation on flow characteristics in a confined space is of great importance.