• Journal of the Society of Naval Architects of Korea
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• v.41 no.2
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• pp.90-97
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• 2004

Flow mechanism of contractive and dilative motion is numerically investigated to obtain a propulsive force in highly viscous fluid. An axisymmetric code is developed with unstructured grid system based on cell-centered scheme. It is validated by comparing with the results of Stokes approximation for the problem of uniform flow past a sphere in low Reynolds number(R$_{n}$=1). The validated code is applied to the simulation of contractive and dilative periodic motion of body whose results are quantitatively compared with the two dimensional case. In order to investigate the grid dependency, two different grids are applied to the present computations. The present study provides key information for the development of an axisymmetric Micro-hydro-robot.t.

• Journal of Mechanical Science and Technology
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• v.19 no.5
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• pp.1148-1157
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• 2005

In the present study, the unsteady Hartmann flow of a dusty viscous incompressible electrically conducting fluid under the influence of an exponentially decreasing pressure gradient is studied without neglecting the ion slip. The parallel plates are assumed to be porous and subjected to a uniform suction from above and injection from below. The fluid is acted upon by an external uniform magnetic field which is applied perpendicular to the plates. An analytical solution for the governing equations of motion is obtained to yield the velocity distributions for both the fluid and dust particles.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.695-696
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• 2002

Three-dimensional blood flow in the sac of the KTAH(Korean total artificial heart) is simulated using fluid-structure interaction model. The aim of this study is to delineate the three-dimensional unsteady-blood flow in the sac of KTAH. Incompressible viscous flow is assumed for blood using the assumption of Newtonian fluid. The numerical method employed in this study is the finite element software called ADINA. Fluid-structure interaction model between blood and sac is utilized to represent the deformation of the sac by the rigid moving actuator. Three-dimensional geometry of cactus type KTAH is chosen for numerical model with prescribed pressure boundary condition on the sac surface. Blood flow is generated by the motion of moving actuator and strongly interacts with the solid material surrounding blood. High shear stress is observed mainly near the inlet and outlet of the sac.

• Journal of the Korean Mathematical Society
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• v.43 no.4
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• pp.733-763
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• 2006

We study quasi-stationary Stokes flow in a dihedral domain arising from a study of a free boundary problem of viscous fluid in a container. We construct an exact solution of quasi-stationary Stokes equations and derive its estimates with norm in a weighted Sobolev spaces.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.9
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• pp.1208-1216
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• 1998

The present numerical study investigates the effect of a secondary flow on the heat transfer in order to delineate the mechanism of laminar heat transfer enhancement of a viscoelastic fluid in rectangular ducts. The second normal stress generating a secondary flow is modeled by adopting the Reiner-Rivlin constitutive equation and the calculated secondary flow showed good agreement with experiments. The primary velocity U as well as the pressure drop were not affected by the secondary flow in rectangular ducts, whose order of magnitude is less than 0.1% of the primary velocity. The small magnitude of the secondary flow, however, affect moderately the temperature fields. The calculated Nusselt numbers with secondary flow show 50% heat transfer enhancement over those of a purely viscous non-Newtonian fluid, which are considerably lower than the experimental values. Therefore, we conclude that there should be an additional heat transfer enhancement mechanism involved in the viscoelastic fluid such as temperature-dependence.

• Journal of Ocean Engineering and Technology
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• v.4 no.2
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• pp.73-84
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• 1990

A circular cylinder is oscillated in th otherwise quiescent viscous fluid. Numerical analysis performed for this problem by using the fourth-order Runge-kutta method for the unsteady Navier-stokes equations. For K(Kelegan-Carpenter's No.)=5, the flow developed symmetrically, while for K=10, it revealed random patterns. The coefficient of the rms force is overestimated by 20-30% compared with the experimental result.

• The KSFM Journal of Fluid Machinery
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• v.17 no.3
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• pp.46-51
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• 2014

In this study, a numerical analysis methodology is studied to predict thermal and flow characteristics of C3X vane with internal cooling. Effects of turbulence models, transition models and viscous work term on temperature and pressure distributions on the vane surface are investigated. These optional terms have few effects on the pressure distributions over the vane surface. However, they have great influence on prediction of the temperature distributions on the vane surface. The combination of k-${\omega}$ based SST turbulence model, ${\gamma}$ transition model and viscous work term are better than RSM turbulence model on prediction of the surface temperature. The average temperature difference between CFD results and experimental results is calculated 2 % at the pressure side and 1 % at the suction side. Furthermore computing time of this combination is half of the RSM turbulence model. When k-${\omega}$ based SST turbulence model and ${\gamma}$ transition model with viscous work term are applied, more accurate predictions of thermal and internal flow characteristics of high pressure turbine are expected.

• Journal of Mechanical Science and Technology
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• v.18 no.3
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• pp.491-498
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• 2004

An analysis of the plane Couette flow between two parallel plates of a viscous, incompressible, micropolar fluid is presented. Especially, the effects of non-zero values of the micro-gyration boundary condition coefficient and pressure gradient on the flow fields are studied. Numerical results show that the micro polar parameter was found to have much more of an impact on the flow behaviors. It is also observed that the micro-gyration boundary condition coefficient influenced on the coefficients of skin friction and couple stress due to its different effect on the surface stress.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.1
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• pp.214-224
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• 1990

A "two-fluid" model using thermal eddy diffusivity concept and Lumley's drag reduction theory, is proposed to analyze heat transfer of the turbulent dilute gas-particle flow in a vertical pipe with constant wall heat flux. The thermal eddy diffusivity is derived to be a function of the ratio of the heat capacity-density products .rho. over bar $C_{p}$ of the gaseous phase and the particulate phase and also of the ratio of thermal relaxation time scale to that of turbulence. The Lumley's theory dictates the variation of the viscous sublayer thickness depending on the particle loading ratio Z and the relative particle size $d_{p}$/D. At low loading ratio, the size of viscous sublayer thickness is important for suspension heat transfer, while at higher loading, the effect of the ratio .rho. $_{p}$ over bar $C_{p}$$_{p}$/ .rho. $_{f}$ over bar $C_{p}$$_{f}$ is dominant. The major cause of decrease in the suspension Nusselt number at lower loading ratio is found to be due to the increase of the viscous sublayer thickness caused by the suppression of turbulence near the wall by the presence of solid particles. Predicted Nusselt numbers using the present model are in satisfactory agreements with available experimental data both in pipe entrance and the fully developed regions.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.13 no.2
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• pp.73-86
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• 2009

The problem of thermal stability of an exothermic reactive viscous fluid between two parallel walls in the plane Poiseuille and Couette flow configurations is investigated for different thermal boundary conditions. Neglecting reactant consumption, the closed-form solutions obtained from the momentum equation was inserted into the energy equation due to dissipative effect of viscosity. The resulting energy equation was analyzed for criticality using the variational method technique. The problem is characterized by two parameters: the Nusselt number(N) and the dynamic parameter($\Lambda$). We observed that the thermal and dynamical boundary conditions of the wall have led to a significant departure from known results. The influence of the variable pre-exponential factor, due to the numerical exponent m, also give further insight into the behavior of the system and the results expressed graphically and in tabular forms.