• Journal of Mechanical Science and Technology
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• v.18 no.1
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• pp.153-166
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• 2004

This paper presents a comparative study of a fully coupled, upwind, compressible Navier-Stokes code with three two-equation models and the Baldwin-Lomax algebraic model in predicting transonic/supersonic flow. The k-$\varepsilon$ turbulence model of Abe performed well in predicting the pressure distributions and the velocity profiles near the flow separation over the axisymmetric bump, even though there were some discrepancies with the experimental data in the shear-stress distributions. Additionally, it is noted that this model has y$\^$*/ in damping functions instead of y$\^$＋/. The turbulence model of Abe and Wilcox showed better agreements in skin friction coefficient distribution with the experimental data than the other models did for a supersonic compression ramp problem. Wilcox's model seems to be more reliable than the other models in terms of numerical stability. The two-equation models revealed that the redevelopment of the boundary layer was somewhat slow downstream of the reattachment portion.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.9 no.5
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• pp.28-33
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• 2010

A computer code was developed to simulate all three stages of the injection molding process: filling, packing and cooling by finite element method. The constitutive equation used here was compressible Leonov model. The PVT relationship was assumed to follow the Tait equation. The flow-induced birefringence was related to the calculated flow stresses through the linear stress-optical law. Based on the simulation, the Taguchi method was used to investigate the influences of injection molding conditions on the birefringence of a center gate disk. In addition, the optimal processing conditions were selected to minimize the birefringence and the birefringence difference along the positions of the disk.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2005.10a
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• pp.305-309
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• 2005

A computer code was developed to simulate all three stages of the injection molding process ? filling, packing and cooling by finite element method. The constitutive equation used here was compressible Leonov model. The PVT relationship was assumed to follow the Tait equation. The flow-induced birefringence was related to the calculated flow stresses through the linear stress-optical law. Based on the simulation, the Taguchi method was used to investigate the influences of injection molding conditions on the birefringence of a center gate disk. In addition, the optimal processing conditions were selected to minimize the birefringence and the birefringence difference along the positions of the disk.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.03a
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• pp.260-265
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• 2008

A numerical scheme for solid propellant rocket has been studied using preconditioning method to research unsteady combustion processes for the double-base propellant with a converging-diverging nozzle. The Navier-Stokes equation is solved by dualtime stepping method with finite volume method. The turbulence model uses a shear stress transport modeling. The species equation follows up the method of Xinping WI, Mridul Kumar and Kenneth K. Kuo. A preconditioned algorithm is applied to solve incompressible regime inside the combustor and compressible flow at nozzle. Mass flux was evaluated using modified advective upwind splitting method. The simulated result the comparison a fully coupled implicit method and a semi implicit method in terms of accuracy and efficiency. This report shows the result of solid rocket propellant combustion.

• 한국전산유체공학회:학술대회논문집
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• 1999.11a
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• pp.139-144
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• 1999

There have been many studies for heat transfer enhancement. Particularly, the study of flow in heat exchangers which have fin device has been main theme in heat transfer area. Practically, the circular tube which has internal fins is widely used for developing heat transfer rate. In this study, flow and heat transfer analysis of the circular tube with fins are investigated. The height and the number of fins are arbitrary. The flow field is assumed to be laminar. The conformal mapping is used for analytic solution of the laminar flow field. Discretization of governing equation, namely, FDM was used for numerical analysis. The velocity field, flow rate and shear stress are calculated for some numbers of fins in circular tube and for some heights of fin. Temperature fields are plotted along the tube length. It can be shown that the numerical solution agrees with the analytical solution.

• Korean Journal of Materials Research
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• v.11 no.2
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• pp.82-87
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• 2001

The hot deformation behavior of Ti-6Al-2Sn-4Zr-6Mo(Ti6246) alloy was investigated in both the $\alpha$+$\beta$ and $\beta$-phase fields by conducting compression tests over a strain rate range of $10^{-3}s^{-1}$ to $10^0s^{-1}$. The flow stress was increased with increasing strain rate and decreasing test temperature. The flow curves obtained at temperatures below 90$0^{\circ}C$ exhibited a flow softening. However, in the $\beta$-phase field, above 95$0^{\circ}C$, the flow stress increased monotonically with plastic strain approaching steady state values. Constitutive equations for the dependence of flow stress on strain, strain rate, and temperature were developed through the analysis of the flow curves.

• Structural Engineering and Mechanics
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• v.81 no.4
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• pp.523-527
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• 2022

The objective of this study is to simulate the flow in pipes with various boundary conditions. Free-pressure fluid model, is used in the pipe based on Navier-Stokes equation. The models are solved by using the numerical method. A problem called "stability of pipes" is used in order to compare frequency and critical fluid velocity. When the initial conditions of problem satisfied the instability conditions, the free-pressure model could accurately predict discontinuities in the solution field. Employing nonlinear strains-displacements, stress-strain energy method the governing equations were derived using Hamilton's principal. Differential quadrature method (DQM) is used for obtaining the frequency and critical fluid velocity. The results of this paper are analyzed by hyperbolic numerical method. Results show that the level of numerical diffusion in the solution field and the range of well-posedness are two important criteria for selecting the two-fluid models. The solutions for predicting the flow variables is approximately equal to the two-pressure model 2. Therefore, the predicted pressure changes profile in the two-pressure model is more consistent with actual physics. Therefore, in numerical modeling of gas-liquid two-phase flows in the vertical pipe, the present model can be applied.

• Journal of the Korea Concrete Institute
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• v.20 no.3
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• pp.317-323
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• 2008

In the current study, A model for the flow analysis of fresh and highly flowable concrete has been developed using a particle method, the moving particle semi-implicit (MPS) method. The phenomena on the flow of concrete has been considered as a visco-plastic flow problem, and the basic governing equation of concrete particle dynamics has been based on the Navier-Stokes equation in Lagrangian form and the conservation of mass. In order to formulate a visco-plastic flow constitutive law of fresh concrete, concrete is modeled as a highly viscous material in the state of non-flow and as a visco-plastic material in the state of flow after reaching the yield stress of fresh concrete. A flow test of fresh concrete in the L-box was simulated and the predicted flow was well matched with the experimental result. The developed method was well showed the flow motion of concrete particles because it was formulated to be based on the motion of visco-plastic fluid dynamics.

• Journal of the Korean Society of Propulsion Engineers
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• v.20 no.5
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• pp.51-59
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• 2016

STS 321 stainless steel is generally used for a material of high-temperature and high-pressure system including liquid rocket engine. The constitutive equation for flow stress has been suggested using thermal stress component and athermal stress component based on Kocks dislocation barrier model to predict 321 stainless steel's deformation behavior at elevated temperature. The suggested model predicted well the material deformation behaviors of 321 stainless steel at the wide temperature range from room temperature to $500^{\circ}C$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.1 s.256
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• pp.29-39
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• 2007

A second-moment closure is applied to the prediction of a homogeneous turbulent shear flow laden with mono-size particles. The closure is curried out based on a 'two-fluid' methodology in which both carrier and dispersed phases are considered in the Eulerian frame. To reduce the number of coupled differential equations to be solved, Reynolds stress transport equations and algebraic stress models are judiciously combined to obtain the Reynolds stress of carrier and dispersed phases in the mean momentum equation. That is, the Reynolds stress components for carrier and dispersed phases are solved by modelled transport equations, but the fluid-particle velocity covariance tensors are treated by the algebraic models. The present predictions for all the components of Reynolds stresses are compared to the DNS data. Reasonable agreements are observed in all the components, and the effects of the coupling of carrier and dispersed phases are properly captured in every aspects.