Influence of Turbulent Mechanical Stresses on Microorganisms

Many phenomena depend on the features of the fine-scale structure of turbulence, including its intermittency. This article discusses the problem of the turbulent “shear” in biotechnology including the effect of the shear stress on particles (cells, flocs, cells immobilized on microcarriers). Traditionally, the effect of intermittency has not been taken into account in the shear problem and the theory of isotropic turbulence introduced by Kolmogorov (1941) based on average values of the rate of kinetic energy dissipation, velocity fluctuactions, rates of strain, turbulent stresses etc. has been applied. In this paper a multifractal formalism is employed to describe intermittency; the results of multifractal approach are then compared with predictions of other models of intermittent and non-intermittent turbulence. The multifractal model of intermittent turbulence has been used to derive equations describing flow-particle interactions, including: equations describing turbulent stresses acting upon particles in the inertial and viscous subranges of turbulence; mass transfer to small particles suspended in turbulent fluid; turbulent rupture of flocs; particles encounters in turbulent flow including the average number of collisions per unit time in the inertial and viscous subranges of turbulence and the severity of collisions; mechanical stress generated by bubble coalescence. Generally, the article shows how the traditional approach to the shear problem in turbulence, based on the Kolmogorov theory, can be extended by including the influence of intermittency. This review article includes 47 references.