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RISS 인기검색어
- 검색키워드
- 저자 : Kerim Yapici (검색결과 4 건)
- 무료
- 기관 내 무료
- 유료
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Yapici, Kerim 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.1
In this computational study, the convergence, stability and order of accuracy of several different numerical schemes are assessed and compared. All of the schemes considered were developed using a normalized variable diagram. Two test cases are considered: (1) two-dimensional steady incompressible laminar flow of a Newtonian fluid in a square lid-driven cavity; and (2) creeping flow of a PTT-linear fluid in a lid-driven square cavity. The governing equations are discretized to varying degrees of refinement using uniform grids, and solved by using the finite volume technique. The momentum interpolation method (MIM) is employed to evaluate the face velocity. Coupled mass and momentum conservation equations are solved through an iterative SIMPLE (Semi-Implicit Method for Pressure-Linked Equation) algorithm. Among the higher-order and bounded schemes considered in the present study, only the CLAM, COPLA, CUBISTA, NOTABLE, SMART and WACEB schemes provide a steady converged solution to the prescribed tolerance of $1{ \times}10^{-5}$ at all studied Weissenberg ($We$) numbers, using a very fine mesh structure. It is found that the CLAM, COPLA, CUBISTA, SMART and WACEB schemes provide about the same order of accuracy that is slightly higher than that of the NOTABLE scheme at low and high Weissenberg numbers. Moreover, flow structures formed in the cavity, $i.e.$ primary vortex, are captured accurately up to $We$ = 5 by all converged schemes.
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Kerim Yapici 한국유변학회 2012 Korea-Australia rheology journal Vol.24 No.1
In this computational study, the convergence, stability and order of accuracy of several different numerical schemes are assessed and compared. All of the schemes considered were developed using a normalized variable diagram. Two test cases are considered: (1) two-dimensional steady incompressible laminar flow of a Newtonian fluid in a square lid-driven cavity; and (2) creeping flow of a PTT-linear fluid in a lid-driven square cavity. The governing equations are discretized to varying degrees of refinement using uniform grids, and solved by using the finite volume technique. The momentum interpolation method (MIM) is employed to evaluate the face velocity. Coupled mass and momentum conservation equations are solved through an iterative SIMPLE (Semi-Implicit Method for Pressure-Linked Equation) algorithm. Among the higher-order and bounded schemes considered in the present study, only the CLAM, COPLA, CUBISTA, NOTABLE, SMART and WACEB schemes provide a steady converged solution to the prescribed tolerance of 110-5 at all studied Weissenberg (We) numbers, using a very fine mesh structure. It is found that the CLAM, COPLA, CUBISTA, SMART and WACEB schemes provide about the same order of accuracy that is slightly higher than that of the NOTABLE scheme at low and high Weissenberg numbers. Moreover, flow structures formed in the cavity, i.e. primary vortex, are captured accurately up to We = 5 by all converged schemes.
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Rheological characterization of polyethylene glycol based TiO2 nanofluids
Kerim Yapici,Nese K. Cakmak,Naciye Ilhan,Yusuf Uludag 한국유변학회 2014 Korea-Australia rheology journal Vol.26 No.4
Rheological characterization of TiO2 nanoparticle dispersions in polyethylene glycol (PEG 200) is presentedover 1-10 wt% particle mass fraction range in terms of shear viscosity, thixotropy and linear viscoelasticity. A stress controlled rheometer fitted by a cone-and-plate system was employed for the rheologicalmeasurements between –10oC and 40oC. The non-linear viscoelastic experiments revealed that TiO2-PEG200 nanofluid exhibits a shear thinning behavior when particle mass fraction exceeds 1%. No appreciablechange in the shear viscosity versus shear rate behavior was detected over the course of four days ofdispersion storage. At high particle concentrations the dispersions had a yield stress that was determined byfitting the results through Herschel-Bukley model. Within the studied range of particle concentration, noevidence of thixotropic behavior was observed. In addition, relative viscosity measured at high shear regionwas found to be independent of the temperature. On the other hand, strong temperature dependency wasobserved at low shear region particularly at high temperatures. Storage and loss moduli of the TiO2-PEG200 nanofluid were determined by frequency sweep measurements with applied stresses in the linearviscoelastic region. It was found that when the applied stress is lower than the corresponding yield stressTiO2-PEG 200 nanofluid showed a gel structure especially at high particle mass concentration.
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Kerim Yapici,Yusuf Uludag 한국유변학회 2013 Korea-Australia rheology journal Vol.25 No.4
Computational results for steady laminar flow of three different shear thinning fluids lid-driven square cavity are presented. The viscoelastic nature of the fluids is represented by linear and exponential Phan-Thien Tanner (PTT) and Giesekus constitutive models. Computations are based on finite volume technique incorporating non-uniform collocated grids. The stress terms in the constitutive equations are approximated by higher-order and bounded scheme of Convergent and Universally Bounded Interpolation Scheme for the Treatment of Advection (CUBISTA). Effects of the elasticity, inertia as well as constitutive model parameters on the stress and velocity fields, size and intensity of the primary and secondary vortexes are investigated and discussed in detail. Moreover highly accurate benchmark numerical solutions are provided for each considered constitutive model.
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