INFLUENCE OF UNSTEADY FORCES ACTING ON A PARTICLE IN A SUSPENSION APPLICATION TO THE SOUND-PROPAGATION

First, the influence of the unsteady forces (the pressure gradient, th e virtual mass effect and the Basset history term) on the complex velo cities ratio of the fluid and of the dispersed phases has been studied . To this end, the particle momentum equation is linearized for small oscillating motion of the two phases which are at rest in the referenc e state. It is shown that the unsteady terms are of great importance w hen the coefficient chi, mass density of the particle divided by the m ass density of the fluid, becomes small. A particular study of the Bas set history term is also investigated. Then, a two fluids theory, incl uding viscous and thermal losses effects, is developed for calculating the velocity and the damping of the sound propagating in a two-phase flow. As the former treatment, the classical equations of the multipha se flows are linearized and the dispersion equation of the acoustical wave is obtained. Several tendencies and the special part played by th e Basset history term in acoustics are pointed out.