FLUIDS BULK VISCOSITY: CURRENT PHYSICAL AND ANALYTICAL CONCEPTIONS AND PROSPECTS OF THEIR DEVELOPMENT

Taking note of bulk viscosity is especially important at the description of high-intensity processes, such as explosion, a flow with high speeds, the acoustic phenomena, and also in characteristic points of a condition of substance. Bulk viscosity characterizes ability of substance to transformation of mechanical energy in thermal at nonequilibrium volume deformation. In the work the main theoretical directions of bulk viscosity influence studying are considered: physical acoustics, hydrodynamics, molecular and kinetic theory of gases and liquids. It is established that the molecular mechanism of the bulk viscosity emergence described in Landau's Enskog, Kramer works allows more deep understanding of the physical processes which are taking place at change of volume in the compressed liquid. Special interest is submitted to the theory of relaxation proposed by Mandelstam and Leontovich where the equation of a state includes the parameter defining internal structure of liquid that allows to consider effects of acoustic waves distribution. Expediency of Green-Kubo formula application which connects bulk viscosity with autocorrelation function of pressure microscopic fluctuations is noted. The existing methods of bulk viscosity coefficient experimental determination such as acoustic spectroscopy and Brillouin-Mandelstam scattering are analyzed. Problems of bulk viscosity near a critical point liquid-gas determination are considered.