The profile of shear stress in the liquid at turbulent flow

Abstract

Abstract:The article describes the theory of cavitation at high values of shear stress in a viscous liquid. For this purpose, a spatial model of two cylindrical shells imposed concentrically was designed. In the narrow gap between the cylinders the temperature, density and viscosity of liquid is constant. Shear stress is induced by the rotary motion of the inner cylinder, resulting in a change of velocity and pressure fields. Due to the pressure drop between the cylinders there is a precondition to the formation of cavitation bubbles at the point of the lowest static pressure. To verify the assumption was made CFD model based on simplified physical model, through which cavitation was qualitatively and quantitatively assessed. In this paper the results of the numerical solution will be presented alongside with basic form of experimental device for physical generation of cavitation at high values of shear stress.

Accelerating Fluid Development on a Chip for Renewable Energy

“…In a bulk flow with the same emulsion, these shear rates are reached only in the laminar viscous shear layer at the wall in an otherwise turbulent flow (e.g., a pipe diameter at 10 –1 m with Re = 10 5 –10 6 ). The experimental results of fluid behaviors from laminar flow tests can thus recreate the maximum shear rate conditions expected in large-scale applications . In addition, the microfluidic device could also provide data to capture the local flow behaviors around a PCM droplet (i.e., Stokes flow) for bulk scale applications.…”

“…The experimental results of fluid behaviors from laminar flow tests can thus recreate the maximum shear rate conditions expected in large-scale applications. 51 In addition, the microfluidic device could also provide data to capture the local flow behaviors around a PCM droplet (i.e., Stokes flow) for bulk scale applications. A full scan of the magnitudes of bulk shear rate conditions in the microfluidic chip provides a complete characterization of emulsion fluid mechanical stability expected in the larger systems of interest.…”

Estimation of Drag Reduction by Polymer Additives at High Reynolds Numbers Using Rheological Measurements

“…Re asymptote m,p s m,s p (33) Note that this limit also holds true when using the shear stress (i.e., eq 32). The significance of this ratio comes from the wide use of DR applications at very high Re, and by performing a simple data fitting of the shear stress profile of a rheology test, an indication of the performance of the polymer solution can be obtained.…”

“…As for shear stress, the expression is dependent on the region. For Laminar–Newtonian flow, shear stress takes the form τ normalw ( γ̇ ) = η γ̇ where the viscosity profile η(γ̇) can be given in an empirical form, as we shall see in Section . Until this point, the DR expression in eq , in the laminar region, can be fully expressed in terms of γ̇.…”

“…Finally, for the unstable region, we write the shear stress as the sum of a viscous shear stress τ wν (γ̇) and a turbulent shear stress τ wt (γ̇) τ wu ( γ̇ ) = τ normalw ν ( γ̇ ) + τ wt ( γ̇ ) For simplicity, the viscous shear stress is assumed to have the same form of laminar shear stress in eq . As for the turbulent shear stress, the viscous shear stress can also be written in terms of fitting parameters as τ wt ( γ̇ ) = L normalm γ̇ 2 where L m is a fitting parameter.…”