• 한국전산유체공학회:학술대회논문집
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• 2005.10a
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• pp.179-182
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• 2005

We have developed a numerical scheme to reproduce the unsteady flows with cavitation by the finite-difference method. The evolution of cavitation is represented by the source/sink of vapor phase in the incompressible liquid flow. The pressure-velocity coupling is based on the fractional-step method for incompressible fluid flows, in which the compressibility is taken into account through the low Mach number assumption. We applied our method for the cavitating flows in a two-dimensional cascade, which approximates the portion near the tip of inducer in liquid-fuel engine. Particular attention was focused on the influence of turbulence model in this report. Using an eddy viscosity model, although it was not an optimized one for our purpose, the agreement with the experimental observation was improved.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.572-578
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• 2011

The vane type air-motor hand-piece is used widely in the dental services. There are a lot of experimental studies about air-motor but eccentrically off not many numerical studies by using Computational Fluid Dynamics. An air-motor has rotor which rotates at the center of inner housing. The retractable vanes are installed on the rotor. As the rotor of the air-motor rotates, vanes move up and down straightly in the radial direction along the guide. Therefore we have to analyze the unsteady flow field by accurate time dependent marching technique. ANSYS 12.0 CFX is used to analyze unsteady vane-motor flow field Analysis of the changing control volume inside air-motor is implemented by user-defined functions and moving mesh options. Rotational speed of the rotor is approximately 23,000rpm.

• Journal of Mechanical Science and Technology
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• v.15 no.1
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• pp.125-138
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• 2001

An efficient correction storage scheme on a structured grid is applied to a sequence of approximate Jacobian systems arising at each time step from a linearization of the discrete nonlenear system of equations, obtained by the implicit time discretization of the conservation laws for unsteady fluid flows. The contribution of freezing the Jacobian matrix to computing costs is investigated within the correction storage scheme. The performance of the procedure is exhibited by measuring CPU time required to obtain a fully developed laminar vortex shedding flow past a circular cylinder, and is compared with that of a collective iterative method on a single grid. In addition, some computed results of the flow are presented in terms of some functionals along with measured data. The computational test shows that the computing costs may be saved in favor of the correction storage scheme with the frozen Jacobian matrix, to a great extent.

• 유체기계공업학회:학술대회논문집
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• 1999.12a
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• pp.69-77
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• 1999

The aim of this paper is to understand the unsteady flow phenomena in a high speed centrifugal compressor channel diffuser. Instantaneous pressures are measured at six locations in the diffuser using fast-response pressure transducers. Instantaneous pressure ratio decomposition was applied to analyze the pressure signal. In vaneless space where impeller-vaned diffuser interaction is strong, aperiodic unsteadiness is high and periodic pressure waveforms by blade passing are not clear at low flow rates, especially near vane suction side. High aperiodic unsteadiness decreases downstream of diffuser. The blade-to-blade pressure wave does not disappear in surge flow condition. In surge there exist not only large scale periodic surge wave but also blade-to-blade pressure wave.

• International Journal of Fluid Machinery and Systems
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• v.8 no.3
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• pp.193-201
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• 2015

This paper deals with the influence of leakage flow existing in SHF pump model on the analysis of internal flow behaviour inside the vane diffuser of the pump model performance using both experiments and calculations. PIV measurements have been performed at different hub to shroud planes inside one diffuser channel passage for a given speed of rotation and various flow rates. For each operating condition, the PIV measurements have been trigged with different angular impeller positions. The performances and the static pressure rise of the diffuser were also measured using a three-hole probe. The numerical simulations were carried out with Star CCM+ 9.06 code (RANS frozen and unsteady calculations). Some results were already presented at the XXth IAHR Symposium for three flowrates for RANS frozen and URANS calculations. In the present paper, comparisons between URANS calculations with and without leakages and experimental results are presented and discussed for these flow rates. The performances of the diffuser obtained by numerical calculations are compared to those obtained by the three-holes probe measurements. The comparisons show the influence of fluid leakages on global performances and a real improvement concerning the efficiency of the diffuser, the pump and the velocity distributions. These results show that leakage is an important parameter that has to be taken into account in order to make improved comparisons between numerical approaches and experiments in such a specific model set up.

• International Journal of Fluid Machinery and Systems
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• v.8 no.4
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• pp.274-282
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• 2015

This paper deals with the influence of leakage flow existing in SHF pump model on the analysis of internal flow behaviour inside the vane diffuser of the pump model performance using both experiments and calculations. PIV measurements have been performed at different hub to shroud planes inside one diffuser channel passage for a given speed of rotation and various flow rates. For each operating condition, the PIV measurements have been trigged with different angular impeller positions. The performances and the static pressure rise of the diffuser were also measured using a three-hole probe. The numerical simulations were carried out with Star CCM+ 9.06 code (RANS frozen and unsteady calculations). Some results were already presented at the XXth IAHR Symposium for three flowrates for RANS frozen and URANS calculations. In the present paper, comparisons between URANS calculations with and without leakages and experimental results are presented and discussed for these flow rates. The performances of the diffuser obtained by numerical calculations are compared to those obtained by the three-holes probe measurements. The comparisons show the influence of fluid leakages on global performances and a real improvement concerning the efficiency of the diffuser, the pump and the velocity distributions. These results show that leakage is an important parameter that has to be taken into account in order to make improved comparisons between numerical approaches and experiments in such a specific model set up.

• International Journal of Fluid Machinery and Systems
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• v.4 no.3
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• pp.349-359
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• 2011

An unsteady numerical analysis has been carried out to study the strong impeller volute interaction of a centrifugal pump with six backward swept blades shrouded impeller. The numerical analysis is done by solving the three-dimensional Reynolds Averaged Navier-Stokes codes with standard k-${\varepsilon}$ two-equations turbulence model and wall regions are modeled with a scalable log-law wall function. The flow within the impeller passage is very smooth and following the curvature of the blade in stream-wise direction. However, the analysis shows that there is a recirculation zone near the leading edge even at design point. When the flow is discharged into volute casing circumferentially from the impeller outlet, the high velocity flow is severely distorted and formed a spiraling vortex flow within the volute casing. A spatial and temporal wake flow core development is captured dynamically and shows how the wake core diffuses. Near volute tongue region, the impeller/volute tongue strong interaction is observed based on the periodically fluctuating pressure at outlet. The results of existing analysis also proved that the pressure fluctuation periodically is due to the position of impeller blade relative to tongue.

• 유체기계공업학회:학술대회논문집
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• 2000.12a
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• pp.3-8
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• 2000

The new development of turbo-compressor and fan in China is introduced here. For improving the performance of compressor and fan, we have studied the design method, numerical simulation, unsteady flow and the strategy for anti-surge control, got some achievement.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.1 s.151
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• pp.8-15
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• 2007

In this paper, numerical calculations are performed to analyze the unsteady flow of NACA airfoil sections. In order to ease the flow computation for the fluid region changing in time, improve the quality of solution and simplify the grid generation for the oscillating foil flow, the computational method adopts a moving and deforming mesh with the multi-block grid topology. The multi-block, structured-unstructured hybrid grid is generated using the commercial meshing software Gridgen V15. The MDM (Moving & Deforming Mesh) and the UDF (User Define function) function of FLUENT 6 are adopted for computing turbulent flows of the foil in pitching motion. Computed unsteady lift and drag forces are compared with experimental data. in general, the characteristics of unsteady lift and drag of the experiments are reproduced well in the numerical analysis.

• Journal of computational fluids engineering
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• v.16 no.1
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• pp.53-59
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• 2011

In this study, steady and unsteady aerodynamic analyses of a huge rocket configuration have been conducted in a transonic flow region. The launch vehicle structural response are coupled with the transonic flow state transitions at the nose of the payload fairing. Before performing the coupled fluid-structure transonic aeroealstic simulations transonic aerodynamic characteristics are investigated for the pitching motions of the rocket at finite angle-of-attack. An unsteady CFD analysis method with a moving grid technique based on the Reynolds-averaged Navier-Stokes equations with the k-w SST transition turbulence model is applied to accurately predict the transonic loads of the rocket at pitching motion. It is shown that the fluctuating amplitude of the lateral aerodynamic loads imposed on the rocket due to the pitching motion can be significantly increased in the transonic flow region.