• Journal of the Korean Society of Visualization
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• v.9 no.4
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• pp.22-27
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• 2011

In this study, we present methods of coupling a commercial code, ANSYS CFX, and the user Fortran codes for solving an unsteady electro-osmotic flow around a pair of electrodes, receiving DC, attached to the top and the bottom walls of a two-dimensional cavity. We developed a module of Fortran programs for solving the ion-transport equations as well as the Poisson equations for the potential to be used in coupling with the CFX. We present how the developed codes are applied to solving the transient DC electro-osmotic flow problem within a simple cavity. We also address various problems encountered during the development process and explain why such problems are raised.

• 유체기계공업학회:학술대회논문집
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• 2004.12a
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• pp.705-710
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• 2004

In the present study, a transient incompressible viscous turbulent flow is simulated for the automotive torque converter with moving mesh technique. For the analysis, entire torque converter flow passages are modeled. Computed torque ratio, capacity factor and efficiency show a good agreement with the experiment data. The flow instabilities characterized by back-flow and wake etc. appeared in some cascade passages are shown to be Propagating along tangential direction. These flow patterns are mainly influenced by the pump and turbine blade passing and can't be predicted through conventional steady simulation with a mixing plane approach. The understanding of the unsteady flow characteristics in a torque converter achieved in the present study may lead to the optimal design of a torque converter.

• The KSFM Journal of Fluid Machinery
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• v.9 no.5 s.38
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• pp.36-41
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• 2006

In the present study, a transient incompressible viscous turbulent flow is simulated for the automotive torque converter with moving mesh technique. For the analysis, entire torque converter flow passages are modeled. Computed torque ratio, capacity factor and efficiency show a good agreement with the experiment data. The flow instabilities characterized by back-flow and wake etc. appeared in some cascade passages are shown to be propagating along tangential direction. These flow patterns are mainly influenced by the pump and turbine blade passing and can't be predicted through conventional steady simulation with a mixing plane approach. The understanding of the unsteady flow characteristics in a torque converter achieved in the present study may lead to the optimal design of a torque converter.

• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.517-518
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• 2006

Transient and asymmetric density distributions have been investigated by three-dimensional digital speckle tomography with a novel integration method. Multiple CCD images captured movements of speckles in three angles of view simultaneously because the flows were asymmetric and unsteady. The speckle movements which have been formed by a ground glass between no flow and downward butane flow from a circular half opening have been calculated by a cross-correlation tracking method so that those distances can be transferred to deflection angles of laser rays for density gradients. A novel integration method has been developed to obtain projection data from the deflection angles for the speckle tomography.'The three-dimensional density fields have been reconstructed from the accurate projection values by a real-time multiplicative algebraic reconstruction technique (MART) with the developed integration method.

• Transactions of the Korean Society of Automotive Engineers
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• v.18 no.5
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• pp.108-114
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• 2010

The injection nozzle of an electro-hydraulic injector is being opened and closed by movement of a injector's needle which is balanced by pressure at the nozzle seat and at the needle control chamber, at the opposite end of the needle. In this study, the effects of needle movement in a piezo-driven injector on unsteady cavitating flows behavior inside nozzle were investigated by cavitation numerical model based on the Eulerian-Lagrangian approach. Aimed at simulating the 3-D two-phase flow behavior, the three dimensional geometry model along the central cross-section regarding of one injection hole with real design data of a piezo-driven diesel injector has been used to simulate the cavitating flows for injection time by at fully transient simulation with cavitation model. The cavitation model incorporates many of the fundamental physical processes assumed to take place in cavitating flows. The simulations performed were both fully transient and 'pseudo' steady state, even if under steady state boundary conditions. As this research results, we found that it could analyze the effect the pressure drop to the sudden acceleration of fuel, which is due to the fastest response of needle, on the degree of cavitation existed in piezo-driven injector nozzle.

• Journal of the Korean Society of Visualization
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• v.6 no.1
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• pp.34-40
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• 2008

The flow characteristics in a confined slot jet impinging on a flat plate were investigated in low Reynolds number regime (Re$\leq$1,000) by using time-resolved particle image velocimetry technique. The jet Reynolds number was varied from 404 to 1026, where it is presumed that the transient regime exists. It is found that the vortical structures in the shear layer are developed with increasing Reynolds number and that the jet remains steady at the Reynolds number of 404. Vortical structures and their temporal evolution are verified and the results were compared with previous numerical studies.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.4
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• pp.395-405
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• 2004

The filling pattern and an adaptive grid refinement based on the finite element method and Eulerian mesh advancement approach have been developed to analyze incompressible transient viscous flow with free surfaces. The governing equation for flow analysis is Navier-Stokes equation including inertia and gravity effects. The mixed FE formulation and predictor-corrector method are used effectively for unsteady numerical simulation. The flow front surface and the volume inflow rate are calculated using the filling pattern technique to select an adequate pattern among four filling patterns at each triangular control volume. By adaptive grid refinement, the new flow field that renders better prediction in flow surface shape is generated and the velocity field at the flow front part is calculated more exactly. In this domain the elements in the surface region are made finer than those in the remaining regions for more efficient computation. Using the proposed numerical technique, the collapse of a water dam has been analyzed to predict flow phenomenon of fluid and the predicted front positions with respect to time have been compared with the reported experimental results.

• Journal of the Korean Society of Propulsion Engineers
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• v.4 no.1
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• pp.74-92
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• 2000

A numerical analysis has been conducted to study the transient flowfield during the transition from the booster to sustainer phase in an integrated rocket ramjet (IRR) propulsion system. Emphasis is placed on the unsteady inlet aerodynamics, fuel/air mixing in an entire ramjet engine during the flow transient phase. The computational geometry consists of the entire IRR engine, including the inlet, the combustion chamber, and the exhaust nozzle. Turbulence closure is achieved using a low-Reynolds-number two-equation model. The governing equations are solved numerically by means of a finite-volume, preconditioned flux-differencing scheme over a wide range of Mach umber. Various important physical processes are investigated systemically, including terminal shock train.

• Journal of ILASS-Korea
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• v.9 no.4
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• pp.38-45
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• 2004

This study describes the analysis results of unsteady cavitating flows behavior inside nozzle of the prototype piezo-driven injector. This piezo-driven injector has been recognised as one of the next generation diesel injector due to a higher driven efficiency than the conventional solenoid-driven injector. The three dimensional geometry model along the central cross-section regarding of one injection hole has been used to simulate the cavitating flows for injection time by at fully transient simulation with cavitation model. The cavitation model incorporates many of the fundamental physical processes assumed to take place in cavitating flows. The simulations performed were both fully transient and 'pseudo' steady state, even if under steady state boundary conditions. We could analyze the effect the pressure drop to the sudden acceleration of fuel, which is due to the fastest response of needle, on the degree of cavitation existed in piezo-driven injector nozzle

• Journal of the Korean Society of Propulsion Engineers
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• v.14 no.6
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• pp.38-44
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• 2010

The shock wave and boundary layer interaction patterns in an over-expanded rocket nozzle are associated with the production of undesirable side-forces during the start-up and shut-down processes of the engine. In the present work, a computational study is carried out to investigate the effect of the transient nozzle pressure ratio (NPR) on the flow fields inside the nozzle. The unsteady, compressible, axisymmetric, Navier-Stocks equations with SST k-${\omega}$ turbulence model are solved using a fully implicit finite volume scheme. NPR is varied from 2.0 to 10.0, in order to simulate the start-up and shut-down processes of the rocket engine. It is observed that the interaction patterns and the hysteresis phenomenon strongly depend on the time variation of NPR, leading to significantly different characteristics in the lateral forces.