Journal of the Indian Institute of Science最新文献

This review article traces the development of the Volume-Of-Solid immersed boundary method, referred to as VOS-IB, over the last decade. Starting from its simple beginnings inspired by the Volume-Of-Fluid method in multiphase flow, we discuss the evolution of this technique and its extensions for problems in Boussinesq and non-Boussinesq flows, conjugate heat transfer, multi-fluid flows, fluid–structure interactions, and turbulent flows. A critical assessment of the strengths and limitations of the VOS-IB technique is presented and possible directions for future research, both in terms of development of the method and its applications, are outlined.

In the human body, blood acts as a transporter of oxygen and other nutrients as well as carbon dioxide and other waste materials to and from all the organs. Therefore, continuous supply of blood to all the organs is critical for proper functioning of the human body. Blood is a complex fluid and has more than 40% flexible particles which include red blood cells, white blood cells, platelets and other proteins suspended in a water-like fluid, plasma. The dynamics of blood flow, known as haemodynamics, is critical in the development, diagnosis and treatment planning of vascular diseases and design and development of cardiovascular devices. Whilst the most advanced flow measurement techniques such as X-ray imaging, magnetic resonance imaging and ultrasound imaging are used in the diagnosis and treatment of vascular diseases, it is not possible to obtain the complete information of pressure and velocity field experimentally via in vivo methods. Therefore, in silico methods or computational modelling techniques are being increasingly employed not only to understand the haemodynamics but also for use in the clinical setting. Whilst blood is treated as a homogeneous, single-phase fluid in several studies, it is possible to capture several features of the flow of blood only by modelling it as a multiphase fluid. A number of approaches have been adopted to model multiphase flow of blood. A broad categorisation can be based on whether the cell boundary is captured explicitly, e.g. immersed boundary method, or the phases are treated as interpenetrating and two or more phases can exist simultaneously at a point, e.g. Euler–Euler method. In the literature, both the approaches have been adopted to model the flow of blood. Particle-based methods, such as smoothed particle hydrodynamics and dissipative particle dynamics have also been employed by researchers to study the complex interactions associated with the flow of blood. In this article, we discuss different multiphase modelling approaches and their application in the haemodynamics modelling.

A review of recent literature on thrust generation mechanisms by a hydrofoil, bioinspired from fish locomotion is presented. The present work considers fish-inspired periodic kinematics of three types: pitching, heaving, and undulations along with the combination of some of these motions. The pitching corresponds to the tail of the fish while heaving and undulation correspond to that of the body. The undulation also corresponds to the surface of the body; for certain fishes. Both numerical and experimental studies in this arena have been reviewed. The present review follows the classification of oscillatory and undulatory motion. We discuss oscillatory motion with emphasis on pitching, heaving, and the combination of these two motions. In undulatory motion, we cover body undulation and surface undulation motion as a propulsive mechanism. We compare and contrast wake signatures, thrust, and propulsive efficiencies for different motion types. A future outlook, which may help researchers to identify open questions, has been provided.

Efficient and accurate computational model for blood flow dynamics (hemodynamics), is essential for determining optimal treatment strategy, diagnosis, and pathology identification of cardiovascular diseases (CVDs). The focus of the present review paper is to discuss on critical aspects of hemodynamics. Various numerical methods for computational hemodynamics are examined—addressing three key modeling choices. First, the relevance of non-Newtonian hemorheological models in varying vascular conditions is presented. Second, an assessment of single-phase versus multiphase modeling’s validity, for different arterial geometries, is presented. Lastly, investigation on the impact of arterial wall elasticity on blood flow patterns is carried out and a discussion on the necessity of fluid–structure interaction (FSI) model is presented. By surveying diverse scenarios of blood flow modeling, presented in recent literature, it is observed that non-Newtonian behavior significantly impacts severely stenosed arteries or those with low diameters and Womersley numbers, while larger arteries exhibit characteristics similar to Newtonian fluids. Differences between single-phase and multiphase modeling vary with arterial configurations, showcasing notable particle migration effects in curved and branched arteries. Additionally, arterial wall elasticity’s influence varies across scenarios—highlighting the importance of FSI, particularly in diseased states. The article identifies crucial areas for future research to enhance CFD-based hemodynamic modeling, emphasizing the integration of multiphase simulation with non-linear elastic arteries, considering surrounding tissue effects in FSI, innovating patient-specific CAD geometries, and developing faster computational techniques.

Hydrodynamics of slender flexible filaments plays an important role in biology, human physiology, locomotion of organisms, as well as biomedical devices. It is, therefore, important to utilize efficient and accurate numerical models for capturing fluid–structure interaction involving flexible slender structures for numerically simulating such biological systems. In this review article, several computational techniques for evolving the hydrodynamics of slender flexible filaments have been discussed. Special emphasis has been placed on continuous forcing immersed boundary method and slender body theory due to their utility in efficient simulation of thin rod-like filaments.

Numerical methods for the simulation of cavitation processes have been developed for more than 50 years. The rich variety of physical phenomena triggered by the collapse of a bubble has several applications in medicine and environmental science but requires the development of sophisticated numerical methods able to capture the presence of sharp interfaces between fluids and solid/elastic materials, the generation of shock waves and the development of non-spherical modes. One important challenge faced by numerical methods is the important temporal and scale separation inherent to the process of bubble collapse, where many effects become predominant during very short time lapses around the instant of minimum radius when the simulations are hardly resolved. In this manuscript, we provide a detailed discussion of the parameters controlling the accuracy of direct numerical simulation in general non-spherical cases, where a new theoretical analysis is presented to generalize existing theories on the prediction of the peak pressures reached inside the bubble during the bubble collapse. We show that the ratio between the gridsize and the minimum radius allows us to scale the numerical errors introduced by the numerical method in the estimation of different relevant quantities for a variety of initial conditions.

In the last 2 decades, the interest in developing computational fluid dynamics (CFD) models of the stomach has grown steadily. This bean-shaped organ plays a key role in our digestive system by chemically and physically processing food before emptying it into the intestines. The stomach walls drive the flow of the contents to achieve mixing, grinding, and emptying of the contents. Most computational models prescribe the motion of the walls and solve for the flow field inside the lumen, but some recent models also incorporate fluid–structure interaction between the muscles and the contents. Some models employ a simplified two-dimensional or axisymmetric geometry, while others use anatomically realistic stomach shapes. The emptying mechanism employed by the model and the inclusion, or lack thereof, of the pylorus further add to the nonconformity among the different models. In this review, we summarise these different CFD models of the stomach available in the literature. A comparison between these models with regard to their complexity, validation, and specificity is presented. While there has been rapid progress in the past few years, computational models are still far behind their other physiological counterparts, such as cardiovascular flows.

Understanding and predicting multiphase flows is of great relevance due to the ubiquitous nature of such flows in both nature and in many industrial applications. Rapid development of high speed computers and problem-specific algorithms in the last 2 decades has enabled the study of multiphase flows through numerical simulations. In this paper, we give a brief overview of different methods used in direct numerical simulations of two-phase flows. In particular, we focus on the volume of fluid (VOF) method used for locating and advecting the interface. VOF method is a mesh based interface capturing method in which a scalar function called void fraction field (which is the ratio of tracked fluid to the cell volume) is advected in order to track the interface position. A geometric VOF algorithm is detailed in this work. which strikes a balance between accuracy, ease of implementation and volume conservation on a structured grid. Another challenge in two-phase flow simulations is the inclusion of surface tension forces accurately. Here, we give a brief overview of Eulerian surface tension models and detail an approach balancing computational cost, curvature estimation and imposed timestep restriction. Finally, we discuss the most recent advances in VOF methods and outline the various numerical challenges we expect to encounter.

The design of micro aerial vehicles has been long inspired by biological flyers such as birds and insects. The aerodynamic principles of flapping wing flights are complex due to the rapid wing motion and the inherent complex vortex dynamics. Several experimental and numerical investigations have been carried out in the past decades to uncover the mechanisms responsible for the improved aerodynamic capability of flapping wings. This paper provides an overview of the aerodynamics of flapping insect wings. After providing a brief overview of the aerodynamics of a single wing, we discuss how the vortex dynamics are altered in the case of tandem wings. A significant challenge to designing a stable MAV is the environmental effects stemming from the gust and ground presence. In this paper, we present how the force generation is altered due to such effects. Moreover, we point out unsolved research questions on insect flight whose answers could greatly help to improve the design of flapping wing MAVs.

In this paper, we systematically review interface-driven mesh adaptation procedures for the phase-field modeling of fluid–structure interaction problems. One of the popular ways of handling fluid–structure interaction problems involving large solid deformations is the fully Eulerian approach. In this procedure, we use a fixed computational grid over which a diffused interface description can be used to evolve the fluid–structure boundary. The Eulerian solid representation and a diffuse interface method necessitate the use of adaptive mesh refinement to achieve reasonable accuracy for the problem at hand. We explore the usage of mesh refinement techniques for such FSI problems and focus specifically on interface-driven adaptivity. We present comparisons among various error indicators for the adaptive procedure of the unstructured mesh. We finally explore some possible future directions and challenges in the field.