Browsing by Subject "Non-Newtonian"
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Item A Comparative Study between Newtonian and Non-Newtonian Models in a Stenosis of a Carotid Artery(2013-12-10) Khambhampati, Tejasvi KrishnaBlood, the most significant biological fluids plays a very vital role in the human mechanism, in terms of supplying the required nutrients to different parts of the human body, removing waste products and defending the body against infection through the action of antibodies. Therefore, it is imperative that blood flow must be studied in great detail. Hemodynamic analysis of blood flow in vascular beds and prosthetic devices requires the rheological behavior of blood to be characterized through appropriate constitutive equations relating the stress to deformation and rate of deformation. Numerical simulations, although not very accurate, provide an excellent alternative around this difficulty. As part of the preliminary studies, the Newtonian model of blood was assumed, and wall shear stresses have been plotted at certain critical points. Profiles of wall shear stress were then compared with the experimental results of Ku and Giddens. A numerical investigation of blood flow in stenosed carotid artery of the human body is presented in this thesis. Using a three-dimensional computational model of the stenosis, simulations were performed to capture the Non-Newtonian behavior of blood. The flow is considered as being pulsatile, with appropriate realistic boundary conditions. A shear thinning model (Carreau?s) and a visco-elastic model (Yeleswarapu?s Olydroyd-B model) have been employed to predict wall shear stress for the case of a healthy carotid artery and two cases of stenosed carotid artery models (50% and 90% stenosed carotid artery). From these simulation results, it was observed that wall shear stresses predicted by the models at certain critical points are different. Recirculation zones, flow separation and associated negative wall shear stress were observed in certain cases.Item An investigation of the effectiveness of block preconditioners on a non-Newtonian blood flow model(2011-05) Fuchs, Ashlee; Howle, Victoria E.; Kirby, Robert C.; Long, KevinNewtonian and non-Newtonian fluid flow can be modeled by the steady-state incompressible Navier-Stokes equations. Developing a non-Newtonian blood flow model is the particular problem of interest for this thesis. The process of solving this problem involves utilizing iterative solvers which can perform with higher accuracy and efficiency if properly preconditioned. Physics-based preconditioners have been developed for solving the steady-state incompressible Navier-Stokes equations. The primary aim of this thesis is to apply the pressure convection-diffusion (PCD) preconditioner to a non-Newtonian flow model in order to investigate effectiveness.Item CFD-based representation of non-Newtonian polymer injectivity for a horizontal well with coupled formation-wellbore hydraulics(2010-12) Jackson, Gregory Thomas, 1983-; Balhoff, Matthew T.; Huh, ChunDuring injection of a high-viscosity, non-Newtonian polymer into a long horizontal well, a significant pressure drop occurs along the well length. Computational Fluid Dynamics (CFD) modeling of the shear-thinning flow of polymer in the wellbore, coupled with the viscoelastic flow in composite gravel-pack/near-well formation zone, was carried out to develop convenient correlations for axial pressure values of both Newtonian and non-Newtonian fluids along the well length, for use in chemical EOR simulations. The detailed CFD modeling of the non-Newtonian flow behavior of polymer within the horizontal wellbore, completion zone and the near-well formation, not only allows accurate accounting of pressure distribution along the long horizontal well, but also can be employed for screening diagnosis for possible injectivity inefficiencies resulting from non-uniform pressure values. At both high and low injection rates, CFD modeling predicts non-uniform pressure distributions for highly viscous fluids. The inclusive pressure correlation was implemented into UTCHEM, a University of Texas at Austin research simulator, to determine the importance of including pressure drop in polymer injections. Early times (i.e., less than 100 days) yielded a significant oil recovery deviation from a uniform pressure wellbore. However, at later times the recovery loss generated by the pressure decrease was deemed negligible; therefore, the traditional assumption regarding uniform pressure in horizontal wellbores was still reasonable for highly viscous non-Newtonian flow. This CFD study is the first mechanistic investigation of the polymer injectivity with detailed description of the wellbore, completion zone and near-well formation, and with full accounting of the shear-thinning rheology for pipe flow and the viscoelastic rheology of polymer in porous media. With increased use of very high molecular-weight polymers for chemical EOR processes for mobility control, the latter mechanism is known to be critical.