On the mode development in the developing region of a plane jet

The development of the mode arrangement in the developing region of an acou stically excited plane jet is extensively studied using hot-wire measuremen ts. Two single-wire probes are located within the two shear layers of the j et to detect the flow structure patterns simultaneously. The jet is excited at its fundamental frequency in either varicose mode (m = 0) or sinuous mo de (m = 1) condition. Experimental results show that different excitation m ode conditions lead to different spreading rates and velocity fluctuation d istributions in the developing flow field. The frequency spectral distribut ions for the m = 1 excitation exhibit double peaks of f(a) and f(b), rather than a single subharmonic f(0)/2 for the m = 0 excitation. These three com ponents constitute a relationship of (f(a) + f(b))/2 = f(0)/2. The mode swi tching phenomenon is found to be prominent under the m = 0 case, while less pronounced for the m = 1 case. The mode development is mainly governed by the evolution of the primary instabilities in the jet shear layers. (C) 199 9 American Institute of Physics, [S1070-6631(99)03906-9].