Structure of the linearized problem for compressible parallel fluid flows

We consider the linearized compressible Navier-Stokes equation near a parallel flow in a cylindrical domain restricting our study to perturbations periodic in the generatrix direction. For any parameter values, we show that the initial value linear evolution problem is solved by the direct sum of a (strictly) contraction semi-group and an analytic semi-group. Any unbounded in time solution of this linear problem comes from isolated eigenvalues with finite multiplicities, which have non negative real part, and whose imaginary part is bounded. In addition, we precise the structure of the spectrum of the generator of the semi-group, locating the essential spectrum stricly on the left side of the complex plane. © 1997 Università degli Studi di Ferrara.