UNSTEADY PERTURBED FLOW AT LOW MACH NUMBER OF A VISCOUS COMPRESSIBLE FLUID

The problem of the unsteady perturbed two-dimensional flow at low Mach number of a viscous compressible fluid is studied taking the relation between the stress and deformation rates tensors that was obtained an d applied in [1] and [3]. It is shown that the system of equations des cribing the phenomenon is totally hyperbolic and therefore the perturb ations in any point P of the field are propagated by means of waves co rresponding to four characteristic surfaces passing through P. The dis placement and propagation velocities of these waves are determined. as well as their dependence on the orientation of their front in P; it i s shown besides that the discontinuity vector across the waves has com ponents both longitudinal and transversal. The variation laws of the f luid velocities both on the characteristic surfaces and along their bi characteristics are determined, which allows us to solve the Cauchy pr oblem with a ''step-by-step'' method.