Ultrasonic velocity profiler applied to explore viscosity–pressure fields and their coupling in inelastic shear-thinning vortex streets

A method for simultaneous estimation of viscosity and pressure fields in inelastic shear-thinning fluids is developed by means of ultrasound velocity profiling technique (UVP). In the method, equation of continuity, rheological model and pressure Poisson equation are incorporated as data processing sequences for measured velocity distributions. The proposed method is applied to study the vortex street structure formed behind a circular cylinder, which shows viscosity–pressure coupling due to shear-thinning property of fluid. For demonstration, aqueous solution of CMC (carboxy methyl cellulose) of weight concentration of 0.1% is chosen as the working fluid with shear-thinning property. An alternating staggered pattern of low-pressure spots is successfully reconstructed for zero-shear-based Reynolds number, Re = 50–300. We have found that increasing Re resulted in decrease in vortex shedding Strouhal number because of vortex sustainability supported by shear-thinning property. Graphical abstract

Inelastic Deformable Image Registration (i-DIR): Capturing Sliding Motion through Automatic Detection of Discontinuities

Deformable image registration (DIR) is an image-analysis method with a broad range of applications in biomedical sciences. Current applications of DIR on computed-tomography (CT) images of the lung and other organs under deformation suffer from large errors and artifacts due to the inability of standard DIR methods to capture sliding between interfaces, as standard transformation models cannot adequately handle discontinuities. In this work, we aim at creating a novel inelastic deformable image registration (i-DIR) method that automatically detects sliding surfaces and that is capable of handling sliding discontinuous motion. Our method relies on the introduction of an inelastic regularization term in the DIR formulation, where sliding is characterized as an inelastic shear strain. We validate the i-DIR by studying synthetic image datasets with strong sliding motion, and compare its results against two other elastic DIR formulations using landmark analysis. Further, we demonstrate the applicability of the i-DIR method to medical CT images by registering lung CT images. Our results show that the i-DIR method delivers accurate estimates of a local lung strain that are similar to fields reported in the literature, and that do not exhibit spurious oscillatory patterns typically observed in elastic DIR methods. We conclude that the i-DIR method automatically locates regions of sliding that arise in the dorsal pleural cavity, delivering significantly smaller errors than traditional elastic DIR methods.

Numerical investigation of the performance of perforated baffles in a plate-fin heat exchanger

The present paper is a numerical investigation on the performance of perforated baffles in a plate-fin heat exchanger. Two types of perforations are studied, namely the circular and elliptical shapes. Values of heat transfer coefficient, pressure drop and thermal performance factor are determined for both cases and compared with those for a smooth channel. Also, the flow fields and heat transfer characteristics are determined for different fluids and various Reynolds numbers. The working fluids are complex, non-Newtonian and have an inelastic shear thinning behavior. The obtained results showed a good enhancement in the thermal performance factor by the suggested design in baffles. In the case of low viscous fluids, the elliptical perforated baffle performs better (by about 63.4%) than the circular one for all values of Re. But for highly viscous fluids, the elliptical perforation shows higher thermal performance than the circular hole by about 25% for low Re and 27% for high Re. The overall thermal performance factors are about 1.55 and 1.74 for the circular and elliptical perforations, respectively.

Undulatory swimming in non-Newtonian fluids

We numerically investigate the effects of non-Newtonian fluid properties, including shear thinning and elasticity, on the locomotion of Taylor’s swimming sheet with arbitrary amplitude. Our results show that elasticity hinders the swimming speed, but a shear-thinning viscosity in the absence of elasticity enhances the speed. The combination of the two effects, modelled using a Giesekus constitutive equation, hinders the swimming speed. We find that the swimming speed of an infinitely long waving sheet in an inelastic shear-thinning fluid has a maximum, whose value depends on the sheet undulation amplitude and the fluid rheological properties. The power consumption, on the other hand, follows a universal scaling law.

Shear Deformation Behavior of Copper Nanocrystals Under Imposed Hydrostatic Stress

In this research, we have employed molecular dynamics (MD) simulations to computationally explore the effects of hydrostatic stress on the shear deformation behavior of nanocrystalline (NC) Cu, over a range of grain size (5–20 nm) and temperature (10–500 K). Simulated nanocrystals were deformed under shear with superimposed isotropic tensile/compressive hydrostatic stress σ∧ of magnitude up to 5 GPa. The results suggest that the shear strength increases under imposed compressive σ∧, and decreases under imposed tensile σ∧, by around 0.05–0.09 GPa for every GPa of imposed hydrostatic pressure. At 300 K, we computed activation volumes (3.5–9 b3) and activation energies (0.2–0.3 eV), with values agreeing with those reported in previous experimental and theoretical work, notwithstanding the extreme deformation rates imposed in MD simulations. Additionally, we observed that shear deformation under an imposed compressive hydrostatic stress tends to slightly increase both the activation volumes and the energy activation barrier. Finally, no discernible pressure effect could be observed on the distribution of inelastic shear strain.