Fold-Over, Intermittency and Crossing Frequency of a Plane Jet Interface with and without an Acoustic Disturbance.

摘要

The following conclusions are made based on this work: The sign of the slope of the interface can be deduced from the types of fold-over events; The presence of fold-over, especially at the back of the interface edge, is consistent with the hypothesis that one of the entrainment mechanisms is large scale engulfment of the nonturbulent ambient fluid by the turbulent fluid. However, the presence of fold-over is inconsistent with the Gaussian interface model. This model assumes that there are no fold-over events at the fronts and backs of the interface. An acoustic disturbance at a frequency corresponding to the first sensitive frequency was found to reduce the mean interface locations, for the intermittency, crossing frequency and fold-over frequency curves. The percent reductions were on the order of the percent increase in the widening rate of the jet. In detecting the turbulent-nonturbulent interface by this method, it was convenient to select a fixed hold time and vary the threshold level.