PHYSICS OF THE AMPLIFICATION OF VORTEX DISTURBANCES IN SHEAR FLOWS

The physics of the linear mechanism of the amplification of vortex dis turbances in shear flows, which is due to the nonorthogonality of the eigenfunctions of the problem in the linear dynamics, is described. To obtain the dearest and simplest picture, a parallel flow with a linea r velocity shear is studied, and the vortex disturbances are represent ed in the form of plane waves - spatial Fourier harmonics. On this lev el our physical approach is consonant with the nonmodal mathematical a nalysis of linear processes in shear flows, which has been actively cu ltivated in the last few years. The physics presented explains the non monotonic growth of vortex disturbances in time at the linear stage of evolution. Moreover, being universal, the ''language'' employed in th is work can also be used to describe the amplification of potential (a coustic) disturbances. (C) 1996 American Institute of Physics.