Physical Review Fluids publishes a collection of papers associated with the invited talks presented at the 76th Annual Meeting of the APS Division of Fluid Dynamics in Washington, D.C. in November 2023.
Physical Review Fluids publishes a collection of papers associated with the invited talks presented at the 76th Annual Meeting of the APS Division of Fluid Dynamics in Washington, D.C. in November 2023.
The objective of this work is to establish a unified theoretical framework for the rheology of dense granular suspensions across different flow regimes. By conducting rheological measurements at imposed volume fractions or at imposed values of particle normal stress, a unified granular rheology can be proposed across the viscous to inertial flow regime. This granular rheology, identified for suspensions of hard spheres, can be extended to a soft granular rheology for soft particles.
This paper explores the intricate dynamics of interfacial flows, focusing on the dual role of surface tension in shaping and destabilizing interfaces within solidifying polymer melts. It reviews recent developments in the experimental characterization and rationalization of these complex flows, emphasizing key challenges and opportunities. The insights presented aim to inform the strategic harnessing of interfacial effects to advance soft material technologies.
A nematic liquid crystal, a phase of matter composed of rod-like molecules, exhibits a tendency towards uniform molecular alignment. Bodies inserted into such a fluid can disturb this orientational order, resulting in elastic stresses in the bulk fluid, which may be relaxed by body repositioning or deformation. We review classical work on rigid particles and their interactions in nematic liquid crystals, and more recent work on the shapes and interactions of deformable bodies in this complex fluid medium.
This paper discusses the transformative potential of self-exploring automated experiments for the discovery, optimization, and control of unsteady vortex-dominated flow phenomena. By minimizing experimentalists’ input in the actual performance of fluid experiments, the potential for scientific discovery is maximized.
The movement and placement of cellular components is crucial for the proper development of egg cells and embryos. These transport processes take place within the fluidic interior of the cell and can yield surprisingly complex fluid-structure interactions. Fortunately, advances in mathematical modeling, multiscale coarse-graining, and the large-scale simulation of fluid-structure interactions have all helped in the understanding of this fundamental cellular biology. This paper discusses how simulations of immersed mobile structures and load-bearing biopolymers within cells helped show how the mitotic spindle finds its proper place inside an embryo approaching its very first cell division. Also discussed is the role played by coarse-grained porous medium models, stability analyses, and large-scale fluid-structure simulation, in revealing the self-organized processes that may underlie large-scale transport flows in developing egg cells.
Echocardiography and cardiac MRI have helped expand understanding of complex fluid dynamics within the heart’s chambers. However, many of the advances have yet to be fully used in clinical practice. We explore the role of fluid mechanics in intracardiac flow analysis and in assessing cardiac function and diagnosing diseases. Emerging trends include a shift from pressure-based assessments to more detailed analyses of flow energy and vortex dynamics, and the use of machine learning. Reproducibility and standardization remain challenging. Critical research needs are identified, including validating fluid mechanics measurements and developing a unified framework for intracardiac flow analysis.
Observations of ultrasound interacting with coated microbubbles has become an important biomedical tool for diagnostic imaging and therapeutics. This paper presents a perspective which highlights the underlying linear and nonlinear bubble dynamics. Mathematical modeling of contrast microbubbles, including an interfacial rheological model, and model building and improvement using attenuation and scattering experiments are presented. A method of noninvasive organ-level blood pressure monitoring is described. Microbubbles together with low-intensity pulsed ultrasound are also demonstrated to be an effective tool in tissue engineering.
When a wetting drop is deposited on a fibrous material, such as water on paper or fabric, its spreading is coupled with absorption between and inside the fibers, which often causes swelling and large deformations of the fiber network. Using experimental model systems and simple modeling, we describe the coupled effects of perfect wetting, capillary forces, and liquid absorption/swelling in assemblies of fibers.
