Kunt Atalık - Academia.edu (original) (raw)

Papers by Kunt Atalık

Research paper thumbnail of Effects of blood viscoelasticity on pulsatile hemodynamics in arterial aneurysms

Journal of Non-Newtonian Fluid Mechanics

Research paper thumbnail of Thermomagnetic effects on the stability of Taylor-Couette flow of a ferrofluid in the presence of azimuthal magnetic field

Journal of Magnetism and Magnetic Materials

Research paper thumbnail of Effects of polymer/surfactant additives on forced convective heat transfer in vortex shedding flow past a circular cylinder

International Journal of Thermal Sciences

Research paper thumbnail of Numerical investigation of the effects of blood rheology and wall elasticity in abdominal aortic aneurysm under pulsatile flow conditions

Research paper thumbnail of Comparison of Inelastic and Elastic Non-Newtonian Effects on the Flow Around a Circular Cylinder in Periodic Vortex Shedding

Journal of Non-Newtonian Fluid Mechanics

Research paper thumbnail of Magnetic field effects on Newtonian and non-Newtonian ferrofluid flow past a circular cylinder

Applied Mathematical Modelling, 2016

Research paper thumbnail of Non-linear temporal stability analysis of viscoelastic plane channel flows using a fully-spectral method

A non-linear analysis of the temporal evolution of finite, two-dimensional disturbances is conduc... more A non-linear analysis of the temporal evolution of finite, two-dimensional disturbances is conducted for plane Poiseuille and Couette flows of viscoelastic fluids. A fully-spectral method of solution is used with a stream-function formulation of the problem. The upper-convected Maxwell (UCM), Oldroyd-B and Giesekus models are considered. The bifurcation of solutions for increasing elasticity is investigated both in the high and low Reynolds number regimes. The transition mechanism is discussed in terms of both the transient linear growth of misfit disturbances due to non-normality, and their possible saturation into finite-amplitude periodic solutions due to non-linear effects.

Research paper thumbnail of Synthesis and Experimental Characterization of Rheological Behavior of EG and Water Based hBN Nanofluids

In this study, salicylic and izonicotinic acid hydrazide was converted into 4-amino 5-substituted... more In this study, salicylic and izonicotinic acid hydrazide was converted into 4-amino 5-substituted-4H-1,2,4-triazole-3-thiol 1a,b. A series of [1,2,4]triazolo[3,4-b] [1,3,4]thiadiazole-6(5H)-thione 2a,b were prepared from aminomercaptotriazoles. The reaction of aminomercaptotriazole compounds 2a,b with aromatic carboxylic acid and phosphorus oxychloride afforded the newly synthesized 3-substituted-[1,2,4]triazolo[3,4-b] [1,3,4]thiadiazole derivatives 3a-h in good yields. In addition, the structures of synthesized compounds were confirmed by IR, 1 H-NMR and 13 C-NMR spectra.

Research paper thumbnail of Prediction of Thermal Conductivity and Shear Viscosity of Water-Cu Nanofluids Using Equilibrium Molecular Dynamics

Volume 8C: Heat Transfer and Thermal Engineering, 2013

ABSTRACT Nanofluids are new class of fluids which can be used for many engineering applications d... more ABSTRACT Nanofluids are new class of fluids which can be used for many engineering applications due to their enhanced thermal properties. The macroscopic modeling tools used for flow simulations usually rely on effective thermal and rheological properties of the nanofluids that can be predicted through various effective medium theories. As these theories significantly under-predict, using correlations based on experimental data is considered as the only reliable means for prediction of these effective properties. However, the behavior might change significantly once the particle material or base fluid change due to different particle fluid interactions in the molecular level. One of the most promising means of modeling effective properties of the nanofluids is the molecular dynamics simulations where all the intermolecular effects can be modeled. This study investigates equilibrium molecular dynamics simulation of the water-Cu nanofluids to predict the thermal and rheological properties. The molecular dynamics simulation is carried out to achieve a thermodynamic equilibrium, based on a state that is defined by targeted thermodynamic properties of the system. The Green-Kubo method is used to predict the thermal conductivity and viscosity of the system. The study considers the use of different combining rules such as Lorentz-Berthelot and sixth-power rules for defining the inter-atomic potentials for water modeled by SPC/E and nanoparticles modeled by Lennard-Jones potential. The predicted effective properties that are thermal conductivity and shear viscosity are then compared with experimental data from literature. The predicted transport properties at different temperatures and particle concentrations are compared to experimental data from literature for model validation.

Research paper thumbnail of Applications of the nonlinear galerkin methods to some flow problems

Lecture Notes in Physics, 1999

ABSTRACT

Research paper thumbnail of Investigation of Single Phase Models for Predicting Pressure Drop in Nanofluid Flow in Circular Pipes

Volume 8A: Heat Transfer and Thermal Engineering, 2013

ABSTRACT Macroscopic modeling of hydrodynamic behavior of nanofluid flow in a uniformly heated ci... more ABSTRACT Macroscopic modeling of hydrodynamic behavior of nanofluid flow in a uniformly heated circular pipe is considered. Single-phase models with Brownian and dispersion viscosity models are evaluated by comparing predicted pressure drop and apparent friction factor with experimental and two-phase Eulerian-Eulerian model results from literature. Single-phase models are capable of predicting heat transfer of nanofluids better when dispersion models are used. However, they fail to accurately predict pressure drop when used with standard viscosity models. Two-phase models on the other hand, can accurately predict both thermodynamic and hydrodynamic field at the expense of computational time. A new viscosity model, which is based on dispersion viscosity, is proposed to increase accuracy of single-phase models in predicting hydrodynamic field of nanofluid flow. Results suggest that single-phase dispersion viscosity model is the most accurate single-phase model.

Research paper thumbnail of Assessment of Single and Two-Phase Models for Nanofluid Flow at the Entrance Region of a Uniformly Heated Tube

Volume 7: Fluids and Heat Transfer, Parts A, B, C, and D, 2012

ABSTRACT Hydrodynamic and thermal characteristics of Al 2 O 3 − water nanofluid flow at entry reg... more ABSTRACT Hydrodynamic and thermal characteristics of Al 2 O 3 − water nanofluid flow at entry region of a uniformly heated pipe are studied applying finite control volume method (FCV). Single phase and Eulerian-Eulerian two-phase models were used in modelling of nanofluid flow and heat transfer. The two methods are evaluated by comparing predicted convective heat transfer coefficients and friction factor with experimental results from literature. Solutions with two different velocity pressure coupling algorithms, Full Multiphase Coupled, and Phase Coupled Semi-Implicit Method for Pressure Linked Equations are also compared in terms of accuracy and computational cost. Two-phase model predicts convective heat transfer coefficient and friction factor more accurately at the entry region. More-over, computational cost can be reduced by implementing Full Multiphase Coupled scheme. INTRODUCTION Nanofluids are engineered fluids made of a base fluid and nano sized particles, which offer superior heat transfer character-istics over that of the base fluid. CuO, Al 2 O 3 , and TiO 2 are most common particles added to water or ethylene glycol (EG) [1] to

Research paper thumbnail of Spectral Analysis of the Stress Response of Viscoelastic Fluids in Large Amplitude Oscillatory Shear Flow

Research paper thumbnail of Small and Large Amplitude Oscillatory Shear Response in Non-Isothermal Flow of a PTT Fluid in Lid-Driven Polar Cavity

Research paper thumbnail of Rotating-surface-driven non-Newtonian flow in a cylindrical enclosure

Research paper thumbnail of Isothermal and Non-Isothermal Flow of PTT Fluid in Lid-Driven Polar Cavity

Research paper thumbnail of Symmetry groups and similarity analysis for boundary layer control over a wedge using electric forces

International Journal of Non-Linear Mechanics, 2009

ABSTRACT

Research paper thumbnail of Computational parametric analysis of rotating surface flow

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2009

The flow due to rotating surfaces in a cylindrical enclosure is commonly used in many application... more The flow due to rotating surfaces in a cylindrical enclosure is commonly used in many applications such as rheometry, electronic cooling, and turbomachinery, and has drawn scientists’ attention for many years. The main objective of this study is to solve the problem with a robust and efficient code. It is achieved by using the ‘Portable, Extensible Toolkit for Scientific computation’ (PETSc), which is a computational tool for the parallel solution of scientific problems. By keeping the Newton's method as the non-linear solver, different linear solvers, preconditioning techniques, and numbers of processors are tested for the performance. In addition to computational parameters such as the performance of the linear solver, performance of the preconditioner, parallel performance, and grid dependence, the effects of some physical parameters such as the Reynolds number, aspect ratio, and altering of the rotating surface are investigated. The results indicate that the core of the circ...

Research paper thumbnail of Isothermal and non-isothermal viscoelastic flow of PTT fluid in lid-driven polar cavity

Korea-Australia Rheology Journal, 2012

ABSTRACT

Research paper thumbnail of On the occurrence of even harmonics in the shear stress response of viscoelastic fluids in large amplitude oscillatory shear

Journal of Non-Newtonian Fluid Mechanics, 2004

The non-linear response of polymeric liquids observed experimentally in large amplitude oscillato... more The non-linear response of polymeric liquids observed experimentally in large amplitude oscillatory shear (LAOS) is generally characterized by the presence of odd harmonics of the excitation frequency in the Fourier spectrum for the shear stress. Even harmonics of relatively smaller amplitude have also been observed, whose appearance is usually attributed to wall slip phenomena. In the present work, we show that wall slip is not a necessary condition for the occurrence of even harmonics. To this end, we perform a non-linear study of planar LAOS flow between two infinite parallel plates using either a monotone or non-monotone viscoelastic constitutive equation (i.e., respectively, the Giesekus and Johnson-Segalman models). The analysis allows for spatially non-homogeneous velocity and stress fields. We assume no-slip boundary conditions, and investigate the combined effects of inertia, elasticity, and shear thinning by means of spectral methods. A regular perturbation analysis is also conducted in the inertialess monotone case. Results for the Giesekus model show that combination of elasticity and shear thinning yields transient even harmonics in shear stress whose life span and intensity are considerably increased by inertia. Furthermore, the one-dimensional flow is unstable to finite two-dimensional perturbations under inertia and at high elasticity. This results in the development of secondary flows and saturation of even harmonics into small but finite values. Simulations for the non-monotone Johnson-Segalman model predict even harmonics of relatively larger amplitude that settle in dynamic equilibrium. Furthermore, the fluid's response is quasi-periodic with the appearance of incommensurate frequencies.

Research paper thumbnail of Effects of blood viscoelasticity on pulsatile hemodynamics in arterial aneurysms

Journal of Non-Newtonian Fluid Mechanics

Research paper thumbnail of Thermomagnetic effects on the stability of Taylor-Couette flow of a ferrofluid in the presence of azimuthal magnetic field

Journal of Magnetism and Magnetic Materials

Research paper thumbnail of Effects of polymer/surfactant additives on forced convective heat transfer in vortex shedding flow past a circular cylinder

International Journal of Thermal Sciences

Research paper thumbnail of Numerical investigation of the effects of blood rheology and wall elasticity in abdominal aortic aneurysm under pulsatile flow conditions

Research paper thumbnail of Comparison of Inelastic and Elastic Non-Newtonian Effects on the Flow Around a Circular Cylinder in Periodic Vortex Shedding

Journal of Non-Newtonian Fluid Mechanics

Research paper thumbnail of Magnetic field effects on Newtonian and non-Newtonian ferrofluid flow past a circular cylinder

Applied Mathematical Modelling, 2016

Research paper thumbnail of Non-linear temporal stability analysis of viscoelastic plane channel flows using a fully-spectral method

A non-linear analysis of the temporal evolution of finite, two-dimensional disturbances is conduc... more A non-linear analysis of the temporal evolution of finite, two-dimensional disturbances is conducted for plane Poiseuille and Couette flows of viscoelastic fluids. A fully-spectral method of solution is used with a stream-function formulation of the problem. The upper-convected Maxwell (UCM), Oldroyd-B and Giesekus models are considered. The bifurcation of solutions for increasing elasticity is investigated both in the high and low Reynolds number regimes. The transition mechanism is discussed in terms of both the transient linear growth of misfit disturbances due to non-normality, and their possible saturation into finite-amplitude periodic solutions due to non-linear effects.

Research paper thumbnail of Synthesis and Experimental Characterization of Rheological Behavior of EG and Water Based hBN Nanofluids

In this study, salicylic and izonicotinic acid hydrazide was converted into 4-amino 5-substituted... more In this study, salicylic and izonicotinic acid hydrazide was converted into 4-amino 5-substituted-4H-1,2,4-triazole-3-thiol 1a,b. A series of [1,2,4]triazolo[3,4-b] [1,3,4]thiadiazole-6(5H)-thione 2a,b were prepared from aminomercaptotriazoles. The reaction of aminomercaptotriazole compounds 2a,b with aromatic carboxylic acid and phosphorus oxychloride afforded the newly synthesized 3-substituted-[1,2,4]triazolo[3,4-b] [1,3,4]thiadiazole derivatives 3a-h in good yields. In addition, the structures of synthesized compounds were confirmed by IR, 1 H-NMR and 13 C-NMR spectra.

Research paper thumbnail of Prediction of Thermal Conductivity and Shear Viscosity of Water-Cu Nanofluids Using Equilibrium Molecular Dynamics

Volume 8C: Heat Transfer and Thermal Engineering, 2013

ABSTRACT Nanofluids are new class of fluids which can be used for many engineering applications d... more ABSTRACT Nanofluids are new class of fluids which can be used for many engineering applications due to their enhanced thermal properties. The macroscopic modeling tools used for flow simulations usually rely on effective thermal and rheological properties of the nanofluids that can be predicted through various effective medium theories. As these theories significantly under-predict, using correlations based on experimental data is considered as the only reliable means for prediction of these effective properties. However, the behavior might change significantly once the particle material or base fluid change due to different particle fluid interactions in the molecular level. One of the most promising means of modeling effective properties of the nanofluids is the molecular dynamics simulations where all the intermolecular effects can be modeled. This study investigates equilibrium molecular dynamics simulation of the water-Cu nanofluids to predict the thermal and rheological properties. The molecular dynamics simulation is carried out to achieve a thermodynamic equilibrium, based on a state that is defined by targeted thermodynamic properties of the system. The Green-Kubo method is used to predict the thermal conductivity and viscosity of the system. The study considers the use of different combining rules such as Lorentz-Berthelot and sixth-power rules for defining the inter-atomic potentials for water modeled by SPC/E and nanoparticles modeled by Lennard-Jones potential. The predicted effective properties that are thermal conductivity and shear viscosity are then compared with experimental data from literature. The predicted transport properties at different temperatures and particle concentrations are compared to experimental data from literature for model validation.

Research paper thumbnail of Applications of the nonlinear galerkin methods to some flow problems

Lecture Notes in Physics, 1999

ABSTRACT

Research paper thumbnail of Investigation of Single Phase Models for Predicting Pressure Drop in Nanofluid Flow in Circular Pipes

Volume 8A: Heat Transfer and Thermal Engineering, 2013

ABSTRACT Macroscopic modeling of hydrodynamic behavior of nanofluid flow in a uniformly heated ci... more ABSTRACT Macroscopic modeling of hydrodynamic behavior of nanofluid flow in a uniformly heated circular pipe is considered. Single-phase models with Brownian and dispersion viscosity models are evaluated by comparing predicted pressure drop and apparent friction factor with experimental and two-phase Eulerian-Eulerian model results from literature. Single-phase models are capable of predicting heat transfer of nanofluids better when dispersion models are used. However, they fail to accurately predict pressure drop when used with standard viscosity models. Two-phase models on the other hand, can accurately predict both thermodynamic and hydrodynamic field at the expense of computational time. A new viscosity model, which is based on dispersion viscosity, is proposed to increase accuracy of single-phase models in predicting hydrodynamic field of nanofluid flow. Results suggest that single-phase dispersion viscosity model is the most accurate single-phase model.

Research paper thumbnail of Assessment of Single and Two-Phase Models for Nanofluid Flow at the Entrance Region of a Uniformly Heated Tube

Volume 7: Fluids and Heat Transfer, Parts A, B, C, and D, 2012

ABSTRACT Hydrodynamic and thermal characteristics of Al 2 O 3 − water nanofluid flow at entry reg... more ABSTRACT Hydrodynamic and thermal characteristics of Al 2 O 3 − water nanofluid flow at entry region of a uniformly heated pipe are studied applying finite control volume method (FCV). Single phase and Eulerian-Eulerian two-phase models were used in modelling of nanofluid flow and heat transfer. The two methods are evaluated by comparing predicted convective heat transfer coefficients and friction factor with experimental results from literature. Solutions with two different velocity pressure coupling algorithms, Full Multiphase Coupled, and Phase Coupled Semi-Implicit Method for Pressure Linked Equations are also compared in terms of accuracy and computational cost. Two-phase model predicts convective heat transfer coefficient and friction factor more accurately at the entry region. More-over, computational cost can be reduced by implementing Full Multiphase Coupled scheme. INTRODUCTION Nanofluids are engineered fluids made of a base fluid and nano sized particles, which offer superior heat transfer character-istics over that of the base fluid. CuO, Al 2 O 3 , and TiO 2 are most common particles added to water or ethylene glycol (EG) [1] to

Research paper thumbnail of Spectral Analysis of the Stress Response of Viscoelastic Fluids in Large Amplitude Oscillatory Shear Flow

Research paper thumbnail of Small and Large Amplitude Oscillatory Shear Response in Non-Isothermal Flow of a PTT Fluid in Lid-Driven Polar Cavity

Research paper thumbnail of Rotating-surface-driven non-Newtonian flow in a cylindrical enclosure

Research paper thumbnail of Isothermal and Non-Isothermal Flow of PTT Fluid in Lid-Driven Polar Cavity

Research paper thumbnail of Symmetry groups and similarity analysis for boundary layer control over a wedge using electric forces

International Journal of Non-Linear Mechanics, 2009

ABSTRACT

Research paper thumbnail of Computational parametric analysis of rotating surface flow

Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science, 2009

The flow due to rotating surfaces in a cylindrical enclosure is commonly used in many application... more The flow due to rotating surfaces in a cylindrical enclosure is commonly used in many applications such as rheometry, electronic cooling, and turbomachinery, and has drawn scientists’ attention for many years. The main objective of this study is to solve the problem with a robust and efficient code. It is achieved by using the ‘Portable, Extensible Toolkit for Scientific computation’ (PETSc), which is a computational tool for the parallel solution of scientific problems. By keeping the Newton's method as the non-linear solver, different linear solvers, preconditioning techniques, and numbers of processors are tested for the performance. In addition to computational parameters such as the performance of the linear solver, performance of the preconditioner, parallel performance, and grid dependence, the effects of some physical parameters such as the Reynolds number, aspect ratio, and altering of the rotating surface are investigated. The results indicate that the core of the circ...

Research paper thumbnail of Isothermal and non-isothermal viscoelastic flow of PTT fluid in lid-driven polar cavity

Korea-Australia Rheology Journal, 2012

ABSTRACT

Research paper thumbnail of On the occurrence of even harmonics in the shear stress response of viscoelastic fluids in large amplitude oscillatory shear

Journal of Non-Newtonian Fluid Mechanics, 2004

The non-linear response of polymeric liquids observed experimentally in large amplitude oscillato... more The non-linear response of polymeric liquids observed experimentally in large amplitude oscillatory shear (LAOS) is generally characterized by the presence of odd harmonics of the excitation frequency in the Fourier spectrum for the shear stress. Even harmonics of relatively smaller amplitude have also been observed, whose appearance is usually attributed to wall slip phenomena. In the present work, we show that wall slip is not a necessary condition for the occurrence of even harmonics. To this end, we perform a non-linear study of planar LAOS flow between two infinite parallel plates using either a monotone or non-monotone viscoelastic constitutive equation (i.e., respectively, the Giesekus and Johnson-Segalman models). The analysis allows for spatially non-homogeneous velocity and stress fields. We assume no-slip boundary conditions, and investigate the combined effects of inertia, elasticity, and shear thinning by means of spectral methods. A regular perturbation analysis is also conducted in the inertialess monotone case. Results for the Giesekus model show that combination of elasticity and shear thinning yields transient even harmonics in shear stress whose life span and intensity are considerably increased by inertia. Furthermore, the one-dimensional flow is unstable to finite two-dimensional perturbations under inertia and at high elasticity. This results in the development of secondary flows and saturation of even harmonics into small but finite values. Simulations for the non-monotone Johnson-Segalman model predict even harmonics of relatively larger amplitude that settle in dynamic equilibrium. Furthermore, the fluid's response is quasi-periodic with the appearance of incommensurate frequencies.