Download or read book The Effects of Viscoelasticity on the Transitioning Cylinder Wake written by David Hastings Richter and published by Stanford University. This book was released on 2011 with total page 166 pages. Available in PDF, EPUB and Kindle. Book excerpt: Using a newly developed three dimensional, time dependent finite volume code designed to compute non-Newtonian flows over a large range of Reynolds number (Re), we performed simulations of viscoelastic flow past a circular cylinder. Our goal was to elucidate elastic effects during transition to turbulence in a bluff body wake. Based on its ability to capture essential physical processes in turbulent drag reduction studies, the FENE-P rheological model was employed in the calculation, and the numerical method utilized was such that a large range of rheological parameters (polymer length L, dimensionless Weissenberg number (Wi), and polymer concentration (beta) in the FENE-P model) could be probed. Simulations were performed for Reynolds numbers ranging from Re = 100 to Re = 3900. Within this range, the Newtonian cylinder wake first undergoes a series of secondary instabilities, transitioning the wake structure from a two-dimensional, laminar vortex shedding state to one exhibiting three-dimensional motion. This transition is characterized first by the mode A instability, which develops in the region of primary vortex development at a Reynolds number of Re = 190. The mode B instability then follows at Re = 260, resulting from unstable perturbation growth in the braid region between primary vortices. At still higher Reynolds numbers, Re = O(1000), the separated shear layer immediately behind the cylinder begins to transition prior to primary vortex shedding. Through nonlinear simulations as well as a Floquet linear stability analysis, viscoelasticity was observed to stabilize both regimes of three-dimensional transition. Full nonlinear simulations revealed that for high enough polymer extensibility L at Re = 300, where mode B instability structures dominate for Newtonian flow, the wake could be reverted back to a state resembling two-dimensional, laminar vortex shedding. This was then confirmed using a Floquet stability analysis, showing significantly suppressed growth rates for both the mode A and mode B instabilities in the linear regime of their development. Mechanisms of this stabilization are presented. At Re = 3900, viscoelasticity again stabilizes the flow, though at this point through a suppression of the Kelvin-Helmoltz rollup instability present in the separated shear layer for Newtonian flows. Once a primary Karman vortex is allowed to form without the influence of a transitioned shear layer, the wake then reverts back to one resembling the mode B instabilities. Confirming this, a study was then performed at the same Reynolds number but allowing for an inhomogeneous polymer concentration throughout the flow field. By injecting polymer additives on the upstream side of the cylinder, it was found that stabilization of the shear layer and of the subsequent wake could be achieved without the presence of polymeric stresses in all downstream locations of the flow.

Download or read book The Effects of Viscoelasticity on the Transitioning Cylinder Wake written by David Hastings Richter and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Using a newly developed three dimensional, time dependent finite volume code designed to compute non-Newtonian flows over a large range of Reynolds number (Re), we performed simulations of viscoelastic flow past a circular cylinder. Our goal was to elucidate elastic effects during transition to turbulence in a bluff body wake. Based on its ability to capture essential physical processes in turbulent drag reduction studies, the FENE-P rheological model was employed in the calculation, and the numerical method utilized was such that a large range of rheological parameters (polymer length L, dimensionless Weissenberg number (Wi), and polymer concentration (beta) in the FENE-P model) could be probed. Simulations were performed for Reynolds numbers ranging from Re = 100 to Re = 3900. Within this range, the Newtonian cylinder wake first undergoes a series of secondary instabilities, transitioning the wake structure from a two-dimensional, laminar vortex shedding state to one exhibiting three-dimensional motion. This transition is characterized first by the mode A instability, which develops in the region of primary vortex development at a Reynolds number of Re = 190. The mode B instability then follows at Re = 260, resulting from unstable perturbation growth in the braid region between primary vortices. At still higher Reynolds numbers, Re = O(1000), the separated shear layer immediately behind the cylinder begins to transition prior to primary vortex shedding. Through nonlinear simulations as well as a Floquet linear stability analysis, viscoelasticity was observed to stabilize both regimes of three-dimensional transition. Full nonlinear simulations revealed that for high enough polymer extensibility L at Re = 300, where mode B instability structures dominate for Newtonian flow, the wake could be reverted back to a state resembling two-dimensional, laminar vortex shedding. This was then confirmed using a Floquet stability analysis, showing significantly suppressed growth rates for both the mode A and mode B instabilities in the linear regime of their development. Mechanisms of this stabilization are presented. At Re = 3900, viscoelasticity again stabilizes the flow, though at this point through a suppression of the Kelvin-Helmoltz rollup instability present in the separated shear layer for Newtonian flows. Once a primary Karman vortex is allowed to form without the influence of a transitioned shear layer, the wake then reverts back to one resembling the mode B instabilities. Confirming this, a study was then performed at the same Reynolds number but allowing for an inhomogeneous polymer concentration throughout the flow field. By injecting polymer additives on the upstream side of the cylinder, it was found that stabilization of the shear layer and of the subsequent wake could be achieved without the presence of polymeric stresses in all downstream locations of the flow.

Download or read book NBS Special Publication written by and published by . This book was released on 1976 with total page 838 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Hydraulic Research in the United States and Canada written by United States. National Bureau of Standards and published by . This book was released on 1978 with total page 384 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Hydraulic Research in the United States and Canada 1974 written by Pauline H. Gurewitz and published by . This book was released on 1976 with total page 364 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Physics Briefs written by and published by . This book was released on 1991 with total page 1240 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Hydraulic Research in the United States and Canada 1972 written by Gershon Kulin and published by . This book was released on 1974 with total page 344 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Research in Progress written by and published by . This book was released on 1963 with total page 302 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book International Aerospace Abstracts written by and published by . This book was released on 1999 with total page 974 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Applied Mechanics Reviews written by and published by . This book was released on 1970 with total page 796 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Viscoelastic Effects on a Polyetherimide Cylinder with Constant Radial Deformation written by Louis Edward Parkman III and published by . This book was released on 2015 with total page 76 pages. Available in PDF, EPUB and Kindle. Book excerpt: The relaxation of an axisymmetric radially crimped joint is analyzed with the inner component being formed from the engineering grade polymer ULTEM (Trademark) 1000 polyetherimide. Creep and Relaxation tests were performed at several temperatures in order to use Time Temperature Superposition theory to assemble a master curve for predictions at long times based on short time testing. The master curves for each test were fit to the appropriate Prony Series and all coefficients are tabulated for re-use. The elastic theory for the classic thick walled cylinder was reviewed and the conversion from elasticity to viscoelasticity was demonstrated. Strength predictions are shown and compared to their elastic counterparts. Finally, a non-dimensionalized model of strength over time is presented.

Download or read book Advances in Heat Transfer written by Young I. Cho and published by Academic Press. This book was released on 2011-11-28 with total page 459 pages. Available in PDF, EPUB and Kindle. Book excerpt: Advances in Heat Transfer fills the information gap between regularly scheduled journals and university-level textbooks by providing in-depth review articles over a broader scope than in journals or texts. The articles, which serve as a broad review for experts in the field, will also be of great interest to non-specialists who need to keep up-to-date with the results of the latest research. This serial is essential reading for all mechanical, chemical and industrial engineers working in the field of heat transfer, graduate schools or industry. Provides an overview of review articles on topics of current interest Bridges the gap between academic researchers and practitioners in industry A long-running and prestigious series

Download or read book Scientific and Technical Aerospace Reports written by and published by . This book was released on 1995 with total page 704 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Theoretical and Applied Rheology written by P. Moldenaers and published by Elsevier. This book was released on 2013-10-22 with total page 1110 pages. Available in PDF, EPUB and Kindle. Book excerpt: More than 900 authors from over 35 countries contributed to the 1992 International Congress on Rheology. These proceedings volumes comprise 17 plenary and keynote papers, 250 oral contributions and some 200 poster presentations. All relevant aspects of rheology are covered, e.g., theoretical rheology, molecular theories, fluid mechanics, rheometry, experimental methods, foams, polymer solutions, polymer melts, rubber, solids, composites, biorheology, industrial rheology, polymer processing, food rheology and electrorheology, reflecting the development of rheology into a broad, multidisciplinary field of recognized academic and industrial relevance.

Download or read book Origin of Turbulence written by Hua-Shu Dou and published by Springer Nature. This book was released on 2022-03-25 with total page 503 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents the new discovery of the origin of turbulence from Navier–Stokes equations. The fully developed turbulence is found to be composed of singularities of flow field. The mechanisms of flow stability and turbulent transition are described using the energy gradient theory, which states all the flow instability and breakdown resulted from the gradient of the total mechanical energy normal to the flow direction. This approach is universal for flow instability in Newtonian flow and non-Newtonian flow. The theory has been used to solve several problems, such as plane and pipe Poiseuille flows, plane Couette flow, Taylor–Couette flow, flows in straight coaxial annulus, flows in curved pipes and ducts, thermal convection flow, viscoelastic flow, and magnet fluid flow, etc. The theory is in agreement with results from numerical simulations and experiments. The analytical method used in this book is novel and is different from the traditional approaches. This book includes the fundamental basics of flow stability and turbulent transition, the essentials of the energy gradient theory, and the applications of the theory to several practical problems. This book is suitable for researchers and graduate students.

Download or read book A Numerical Study of the Effect of Viscoelasticity on Cavitation and Bubble Dynamics written by Steven John Lind and published by . This book was released on 2010 with total page 572 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this thesis two different models and numerical methods have been developed to investigate the dynamics of bubbles in viscoelastic fluids. In the interests of gaining crucial initial insights, a simplifed system of governing equations is first considered. The ambient fluid around the bubble is considered incompressible and the flow irrotational. Viscoelastic effects are included through the normal stress balance at the bubble surface. The governing equations are then solved using a boundary element method. With regard to spherical bubble collapse, the model captures the behaviour seen in other studies, including the damped oscillation of the bubble radius with time and the existence of an elastic-limit solution. The model is extended in order to investigate multi-bubble dynamics near a rigid wall and a free surface. It is found that viscoelastic effects can prevent jet formation, produce cusped bubble shapes, and generally prevent the catastrophic collapse that is seen in the inviscid cases. The model is then used to investigate the role of viscoelasticity in the dynamics of rising gas bubbles. The dynamics of bubbles rising in a viscoelastic liquid are characterised by three phenomena: the trailing edge cusp, negative wake, and the rise velocity jump discontinuity. The model predicts the cusp at the trailing end of a rising bubble to a high resolution. However, the irrotational assumption precludes the prediction of the negative wake. The corresponding absence of the jump discontinuity supports the hypothesis that the negative wake is primarily responsible for the jump discontinuity, as mooted in previous studies. A second model is developed with the intention of gaining further insight into the role of viscoelasticity and corroborating the finndings of the first model. This second model employs the full compressible governing equations in a two dimensional domain. The equations are solved using the spectral element method, while the two phases are represented by "marker particles". The results are in qualitative agreement with the first model and confirm that the findings presented are a faithful account of bubble dynamics in viscoelastic fluids.

Download or read book Technical Publications Announcements with Indexes written by United States. National Aeronautics and Space Administration and published by . This book was released on 1962 with total page 1556 pages. Available in PDF, EPUB and Kindle. Book excerpt: