Rheology is the study of the flow of matter, primarily in a fluid state, but also as "soft solids" or solids under conditions in which they respond with plastic flow rather than deforming elastically in response to an applied force. Rheology is a branch of physics, and it is the science that deals with the deformation and flow of materials, both solids and liquids.
A non-Newtonian fluid is a fluid that does not follow Newton's law of viscosity, that is, it has variable viscosity dependent on stress. In non-Newtonian fluids, viscosity can change when under force to either more liquid or more solid. Ketchup, for example, becomes runnier when shaken and is thus a non-Newtonian fluid. Many salt solutions and molten polymers are non-Newtonian fluids, as are many commonly found substances such as custard, toothpaste, starch suspensions, corn starch, paint, blood, melted butter, and shampoo.
In continuum mechanics, a power-law fluid, or the Ostwald–de Waele relationship, is a type of generalized Newtonian fluid for which the shear stress, τ, is given by
Hemorheology, also spelled haemorheology, or blood rheology, is the study of flow properties of blood and its elements of plasma and cells. Proper tissue perfusion can occur only when blood's rheological properties are within certain levels. Alterations of these properties play significant roles in disease processes. Blood viscosity is determined by plasma viscosity, hematocrit and mechanical properties of red blood cells. Red blood cells have unique mechanical behavior, which can be discussed under the terms erythrocyte deformability and erythrocyte aggregation. Because of that, blood behaves as a non-Newtonian fluid. As such, the viscosity of blood varies with shear rate. Blood becomes less viscous at high shear rates like those experienced with increased flow such as during exercise or in peak-systole. Therefore, blood is a shear-thinning fluid. Contrarily, blood viscosity increases when shear rate goes down with increased vessel diameters or with low flow, such as downstream from an obstruction or in diastole. Blood viscosity also increases with increases in red cell aggregability.
In materials science and continuum mechanics, viscoelasticity is the property of materials that exhibit both viscous and elastic characteristics when undergoing deformation. Viscous materials, like water, resist shear flow and strain linearly with time when a stress is applied. Elastic materials strain when stretched and immediately return to their original state once the stress is removed.
A generalized Newtonian fluid is an idealized fluid for which the shear stress is a function of shear rate at the particular time, but not dependent upon the history of deformation. Although this type of fluid is non-Newtonian in nature, its constitutive equation is a generalised form of the Newtonian fluid. Generalised Newtonian fluids satisfy the following rheological equation:
A rheometer is a laboratory device used to measure the way in which a viscous fluid flows in response to applied forces. It is used for those fluids which cannot be defined by a single value of viscosity and therefore require more parameters to be set and measured than is the case for a viscometer. It measures the rheology of the fluid.
Rheometry generically refers to the experimental techniques used to determine the rheological properties of materials, that is the qualitative and quantitative relationships between stresses and strains and their derivatives. The techniques used are experimental. Rheometry investigates materials in relatively simple flows like steady shear flow, small amplitude oscillatory shear, and extensional flow.
Fluid mechanics is the branch of physics concerned with the mechanics of fluids and the forces on them. It has applications in a wide range of disciplines, including mechanical, aerospace, civil, chemical, and biomedical engineering, as well as geophysics, oceanography, meteorology, astrophysics, and biology.
Manfred Hermann Wagner is the author of Wagner model and the molecular stress function theory for polymer rheology. He is a Professor for Polymer engineering and Polymer physics at the Technical University of Berlin.
Subhasish Dey is a hydraulician and educator. He is known for his research on the hydrodynamics and acclaimed for his contributions in developing theories and solution methodologies of various problems on hydrodynamics, turbulence, boundary layer, sediment transport and open channel flow. He is currently a distinguished professor of Indian Institute of Technology Jodhpur (2023–). Before, he worked as a professor of the department of civil engineering, Indian Institute of Technology Kharagpur (1998–2023), where he served as the head of the department during 2013–15 and held the position of Brahmaputra Chair Professor during 2009–14 and 2015. He also held the adjunct professor position in the Physics and Applied Mathematics Unit at Indian Statistical Institute Kolkata during 2014–19. Besides he has been named a distinguished visiting professor at the Tsinghua University in Beijing, China.
Annual Review of Fluid Mechanics is a peer-reviewed scientific journal covering research on fluid mechanics. It is published once a year by Annual Reviews and the editors are Parviz Moin and Howard Stone. As of 2023, Annual Review of Fluid Mechanics is being published as open access, under the Subscribe to Open model. As of 2023, Journal Citation Reports gives the journal a 2022 impact factor of 27.7, ranking it first out of 34 journals in "Physics, Fluids and Plasmas" and first out of 137 journals in the category "Mechanics".
Viswanathan Kumaran is an Indian chemical engineer, rheologist and a professor at the Department of Chemical Engineering of the Indian Institute of Science. He is known for his studies on stability of flow past flexible surfaces and is an elected fellow of the Indian Academy of Sciences, Indian National Science Academy and the Indian National Academy of Engineering. The Council of Scientific and Industrial Research, the apex agency of the Government of India for scientific research, awarded him the Shanti Swarup Bhatnagar Prize for Science and Technology, one of the highest Indian science awards for his contributions to Engineering Sciences in 2000. A recipient of the TWAS Prize in 2014 and the Infosys Prize 2016 in the Engineering and Computer Science category, Kumaran was listed in the Asian Scientist 100, a list of top 100 scientists from Asia, by the Asian Scientist magazine.
Alan Jeffrey Giacomin is a professor of chemical engineering at Queen's University in Kingston, Ontario, and cross-appointed in the Department of Mechanical & Materials Engineering, and of Physics, Engineering Physics, and Astronomy. He has been editor-in-chief of Physics of Fluids since 2016. He holds the Tier 1 Canada Research Chair in Rheology from the Canadian government's Natural Sciences and Engineering Research Council. Since 2017, Giacomin has been President of the Canadian Society of Rheology.
Capillary breakup rheometry is an experimental technique used to assess the extensional rheological response of low viscous fluids. Unlike most shear and extensional rheometers, this technique does not involve active stretch or measurement of stress or strain but exploits only surface tension to create a uniaxial extensional flow. Hence, although it is common practice to use the name rheometer, capillary breakup techniques should be better addressed to as indexers.
Nhan Phan-Thien, Fellow of the Australian Academy of Science, is a professor of mechanical engineering at the National University of Singapore, Singapore. He has been an associate editor of Physics of Fluids since 2016, and an editorial board member of Journal Non-Newtonian Fluid Mechanics. He held a Personal Chair at University of Sydney [1991-02] and head of the Mechanical Engineering Department National University of Singapore [2016–19]. His contribution to the rheology field includes the PPT model for viscoelastic fluid and its variant. He is the author and co-author of several books in rheology
Gareth Huw McKinley is Professor of Teaching Innovation in the Department of Mechanical Engineering at Massachusetts Institute of Technology (MIT).
Ronald G. Larson is George G. Brown Professor of Chemical Engineering and Alfred H. White Distinguished University Professor at the University of Michigan, where he holds joint appointments in macromolecular science and engineering, biomedical engineering, and mechanical engineering. He is internationally recognized for his research contributions to the fields of polymer physics and complex fluid rheology, especially in the development of theory and computational simulations. Notably, Larson and collaborators discovered new types of viscoelastic instabilities for polymer molecules and developed predictive theories for their flow behavior. He has written numerous scientific papers and two books on these subjects, including a 1998 textbook, “The Structure and Rheology of Complex Fluids”.
Rachel (Raya) Takserman-Krozer [] was a theoretical physicist and professor of rheology. Takserman-Krozer worked on diverse aspects of theoretical physics ranging from theory of relativity to studies of polymers and their flow. Her scientific work includes contributions to behaviour of polymers and polymers solutions in velocity fields, theory of spinnability, problems of phenomenological rheology, and molecular-statistical theory of polymer networks. Takserman-Krozer worked across several countries including Russia, Poland, Israel, and Germany.
Lynn Walker is a professor of chemical engineering at Carnegie Mellon University. Her research considers the rheology of complex fluids and how nanostructure impacts the behavior of complex systems. She is a Fellow of the American Institute of Chemical Engineers, the Society of Rheology, and the American Physical Society.
