Effect of finite Weissenberg number on turbulent channel flows of an elastoviscoplastic fluid

Direct numerical simulations are carried out to study the effect of finite Weissenberg number up to $Wi=16$ on laminar and turbulent channel flows of an elastoviscoplastic (EVP) fluid, at a fixed bulk Reynolds number of $2800$ . The incompressible flow equations are coupled with the evolution equation for the EVP stress tensor by a modified Saramito model that extends both the Bingham viscoplastic and the finite extensible nonlinear elastic-Peterlin (FENE-P) viscoelastic models. In turbulent flow, we find that drag decreases with both the Bingham and Weissenberg numbers, until the flow laminarises at high enough elastic and yield stresses. Hence, a higher drag reduction is achieved than in the viscoelastic flow at the same Weissenberg number. The drag reduction persists at Bingham numbers up to 20, in contrast to viscoplastic flow, where the drag increases in the laminar regime compared with a Newtonian flow. Moreover, elasticity affects the laminarisation of an EVP flow in a non-monotonic fashion, delaying it at lower and promoting it at higher Weissenberg numbers. A hibernation phenomenon is observed in the EVP flow, leading to large changes in the unyielded regions. Finally, plasticity is observed to affect both low- and high-speed streaks equally, attenuating the turbulent dissipation and the fragmentation of turbulent structures.

Viscoplastic flow of functional cellular materials with use of peridynamics

The subject of the study is the deformation of the oxygen-free high conductivity copper. The copper sample is given in the form of a foam. The sample undergoes an impact into an elastic wall. The strain rate hardening effect is investigated. The numerical model of the open-cell foam skeleton is prepared in the framework of the peridynamics method. The dynamic process of compression with different impact velocities is simulated. It has been found that the strain rate hardening effect is essential for the load-carrying capacity of the material under study. Taylor impact test of solid cylinder analysis precedes the analysis of the metallic foam.

Development of constitutive equations for hot working of titanium matrix composites

This research is devoted to modelling the viscoplastic deformation behaviour and microstructure evolution of particle reinforced titanium matrix composites (TMCs) at hot working conditions. A series of Gleeble hot compression tests were conducted to obtain the stress-strain curves. According to the dominant mechanisms of TMCs during deformation, a set of mechanism-based constitutive equations was developed and fitted based on the experiment data. Lamellar alpha globularisation, dynamic recrystallization and damage were considered and incorporated into the constitutive equations to describe the viscoplastic flow behaviour.

MODELING OF EXTERNAL FRICTION COEFFICIENTS OF OILSEED MATERIAL IN THE EXTRUSION IN THE AUGER PRESS

Исследовано внешнее трение масличного материала процесса экструдирования в шнековом прессе. Использован метод математического моделирования вязкопластичного течения для описания процесса экструдирования. Определены коэффициенты внешнего трения масличного материала процесса экструдирования по каналу В от 0,342 до 0,349 и по корпусу З от 0,384 до 0,377 при частоте вращения шнека NВ от 1,571 до 2,827 Гц соответственно. Установлена необходимость использования теоретически обоснованной модели вязкопластичного течения в канале экструдера. Показана возможность использования этих параметров процесса экструдирования для увеличения пропускной способности загрузочных витков маслоотжимных агрегатов. The external friction of the oilseed material of the extrusion process in the screw press is investigated. The method of mathematical modeling of viscoplastic flow is used to describe the extrusion process. The coefficients of external friction of the oilseed material of the extrusion process along the channel В from 0,342 to 0,349 and the body Z from 0,384 to 0,377 at the speed of rotation of the screw NВ from 1,571 to 2,827 Hz, respectively. The necessity of using a theoretically grounded model of viscoplastic flow in the extruder channel is established. The possibility of using these parameters of the extrusion process to increase the capacity of the loading coils of oilpumping units is shown.