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Computational investigation of hydrodynamics of viscoelastic fluids flowing around square cylinder and complex fluid rheology via magnetic resonance imaging

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2016
Tezel, Güler Bengüsu
The flow past bluff bodies, especially cylinders, have been an attraction in all kinds of fluid mechanical investigations for a long time. The analysis of external flow past a square cylinder is a key to various engineering applications such as shell and tube heat exchangers, coating processes, cooling towers, extruders and membrane processes. It involves complex phenomena like flow separation and reattachment, drag formation. In the present study, the main objective is to investigate flow of a viscoelastic fluid around a confined square obstacle computationally. Phan-Thien Tanner (PTT) and Oldroyd-B are used as constitutive viscoelastic fluid models. Finite volume method is employed to solve coupled equations of continuity, motion and constitutive model along with appropriate boundary conditions. The stress terms in the momentum and constitutive equations are approximated by a higher-order and bounded scheme of xi Convergent and Universally Bounded Interpolation Scheme for the Treatment of Advection (CUBISTA) to get accurate numerical solutions. Effects of inertia in terms of Reynolds number Re, elasticity in terms of Weissenberg number, We, and constitutive equation parameters on the recirculation length, drag coefficients, Cd and on the flow field in terms of stress and velocity fields are examined and presented in detail. Differences between the behavior of Newtonian and viscoelastic fluids flowing such over square cylinder as the normal stress effects are highlighted. In order to verify the computational methodology employed, Particle Image Velocimetry technique was used to get velocity field around the immersed cylinder in the case of Newtonian fluid. Experimental measurements and computational results compared well qualitatively. Online and offline rheological measurements on complex fluid such as Carboxylmethyl cellulose, and Carbopol solutions fluid flow is presented in detail. Magnetic Resonance Imaging (MRI) are used for online measurements.