• Water for future
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• v.29 no.2
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• pp.153-165
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• 1996

One-dimensional unsteady flow model including weir flow simulation is studied. Applicabilities of both the single channel model with local treatment of the weir overflow, and the looped-network model are studied using a test problem. It is shown that various type of weir flows including reverse flows are successfully simulated. Flow discontinuity due to the high crest elevation can also be simulated. The reverse free-flowing overflow can be simulated by the single-channel model as well as by the looped-network model.

• 한국전산유체공학회:학술대회논문집
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• 2003.08a
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• pp.126-131
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• 2003

A series of computational simulations have been carried out for supersonic flows in a scram jet engine with and without a cavity. Transverse injection of hydrogen, a simplest form of fuel supply, is considered in the present study with the injection pressure varying from 0.5 to 1.5 MPa. The corresponding equivalence ratios are 0.167 - 0.50. The work features detailed resolution of the flow dynamics in the combustor, which was not typically available in most of the Previous studies. In particular, oscillatory flow characteristics are captured at a scale sufficient to identify the underlying physical mechanisms. Much of the flow unsteadiness is related not only to the cavity, but also to the intrinsic unsteadiness in the flowfield. The interactions between shock waves and shear layer may cause a large excursion of flow oscillation. The role of the cavity and injection pressure are examined systematically.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.11
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• pp.864-872
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• 2002

In this study, the effect of planform curvature on the stability of coupled flow/structure vibration is examined in transonic and supersonic flow regions. The aeroelastic analysis for the frequency and time domain is performed to obtain the flutter solution. The doublet lattice method(DLM) in subsonic flow is used to calculate unsteady aerodynamics in the frequency domain. For all speed range, the time domain nonlinear unsteady transonic small disturbance code has been incorporated into the coupled-time integration aeroelastic analysis (CTIA). Two curved wings with experimental data have been considered in this paper MSC/NASTRAN is used for natural free vibration analyses of wing models. Predicted flutter dynamic pressures and frequencies are compared with experimental data in subsonic and transonic flow regions.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.22 no.4
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• pp.241-251
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• 2018

The present study is carried out to examine the combined effect of heat absorption on flow model. The model consists of unsteady flow of a viscous, incompressible and electrically conducting fluid. The flow is along an impulsively started oscillating vertical plate with variable mass diffusion. The magnetic field is applied perpendicular to the plate. The fluid model under consideration has been solved by Laplace transform technique. The numerical data obtained is discussed with the help of graphs and table. The numerical values obtained for skin-friction have been tabulated. To shorten the lengthy equations in the solution some symbols have been assumed, which are mentioned in appendix. The appendix is included in the article as the last section of the manuscript.

• 한국전산유체공학회:학술대회논문집
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• 1997.10a
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• pp.10-15
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• 1997

Unsteady natural convection of an enclosed fluid has been one of the fundamental thermo-fluid problems, of which dynamic relevance is found in many engineering applications. Together with the inherent coupling between the boundary layers and the interior core, and strong interaction between flow and temperature fields, the unsteadiness poses serious hurdles for analytical and experimental approaches. With the recent development of computers and solution algorithms, computational fluid dynamics has become the prevailing tool to tackle the underlying problems. In this presentation, a few examples of numerical studies are introduced. The usefulness and potential of numerical simulations in investigating unsteady natural convection are elaborated.

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.252-268
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• 2009

In the present study, a grid deformation technique has been incorporated into the unsteady compressible and incompressible viscous flow solvers on unstructured hybrid meshes. An algebraic method based on the basis decomposition of normal edge vector was used for the deformation of viscous elements, and a ball-vertex spring analogy was adopted for inviscid elements among several spring analogy methods due to its robustness. The present method was validated by comparing the results obtained from the grid deformation and the rigid motion of entire grids. Fish swimming motion of an NACA0012 airfoil and flapping wing motion of a generic fighter were simulated to demonstrate the robustness of the present grid deformation technique.

• Journal of computational fluids engineering
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• v.9 no.2
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• pp.52-61
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• 2004

In the present study, a solution algorithm for the computation of unsteady flows on unstructured meshes is presented. Dual time stepping is incorporated to achieve the second-order temporal accuracy while reducing errors associated with linearization and factorization. This allows any time step size, which is suitable for considering physical phenomena of interest. The Gauss-Seidel scheme is used to solve the linear system of equations. A special treatment based on spring analogy is made to handle meshes with high aspect-ratio cells. The present method was validated by comparing the results with experimental data and those obtained from rigid motion.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.2
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• pp.202-212
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• 1997

In this study, performance of the multi-stage explicit methods for numerical computation of the unsteady Navier-Stokes equations is investigated. Three methods under consideration are 1 st-, 2 nd-, and 4 th-order Runge-Kutta (R-K) methods. Compared in this estimation is stability, accuracy, and CPU time of each method. The computational codes developed are applied to the two-dimensional flow in a square cavity driven by an oscillating lid. It turned out that at Reynolds number 400, the 1 st-order R-K method is the best, while at 3200 the 2 nd-order R-K is recommended. At higher Reynolds numbers, it is conjectured that the 4 th-order R-K method will be the best algorithm among three due to its highest stability.

• Journal of computational fluids engineering
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• v.10 no.1
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• pp.24-30
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• 2005

Unstructured grid system is suitable for flows of complex geometries. For problems with moving boundary walls, the grid system must be time-dependently changing and deforming according to the movement of the boundaries when we use a body fitted grid system. In this paper, a new moving-grid finite-volume method on unstructured grid system is proposed and developed for unsteady compressible flows with shock waves. To assure geometric conservation laws on moving grid system, a control volume on the space-time unified domain is adopted for estimating numerical flux. The method is described and applied for two-dimensional flows.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.662-665
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• 2011

Pintle technology, which is one of the thrust control method for solid rocket motor, can control the thrust by the control of nozzle throat area through the pintle moving. For studying the unsteady flow characteristics of pintle nozzle by needle type pintle moving, cold flow test and numerical analysis were performed. The pressure distribution on the pintle tip was varied for pintle moving and stopping and thrust was varied by this effects.