Flow visualization and mass transfer (naphthalene sublimation) experiments were performed on acoustically excited annular air jet with diameter ratio D-i/D-o = 0.95. Two different regimes of the time-mean flow field were found, differing in the size of the central recirculation zone, with either the single stagnation point or the stagnation circle. The switching between the two regimes is accomplished by acoustic excitation, under identical geometry conditions. An effective stabilization of the large recirculation zone, as well as remarkable augmentation of average heat/mass transfer by 23%, have been achieved at the excitation Strouhal number St = 0.94. (C) 2003 Elsevier Ltd. All rights reserved.