• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.7
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• pp.883-892
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• 2003

The experiment using three-dimensional laser Dopperr velocimetery (LDV) measurements and the computation using the Reynolds stress model of the commercial code, FLUENT, were conducted to give a clear understanding on the structure of tip leakage flow in a forward-swept axial-flow fan operating at the maximum efficiency condition. The tip leakage vortex was generated near the position of the minimum wall static pressure, which was located at approximately 12% chord downstream from the leading edge of blade suction side, and developed along the centerline of the pressure trough within the blade passages. A reverse flow between the blade tip region and the casing, induced by tip leakage vortex, acted as a blockage on the through-flow. As a result, high momentum flux was observed below the tip leakage vortex. As the tip leakage vortex proceeded to the aft part of the blade passage, the strength of tip leakage vortex decreased due to the strong interaction with the through-flow and casing boundary layer, and the diffusion of tip leakage vortex caused by high turbulence. In comparison with LDV measurement data, the computed results predicted the complex viscous flow patterns inside the tip region, including the locus of tip leakage vortex center, in a reliable level.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.10
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• pp.1384-1391
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• 2001

Three-dimensional flow analysis is implemented to investigate the flow through transonic axial-flow compressor rotor(NASA R67) and to evaluate the performances of Abid's low-Reynolds-number k-$\omega$ and Baldwin-Lomax turbulence models. A finite volume method is used fur spatial discretization. The equations are solved implicitly in time by the use of approximate factorization. The upwind difference scheme is used for inviscid terms and viscous terms are approximated with central difference. The flux-difference-splitting method of Roe is used to obtain fluxes at the cell faces. Numerical analysis is performed near peak efficiency and near stall. The results are compared with the experimental data for NASA R67 rotor. Blade-to-Blade Mach number distributions are compared to confirm the accuracy of the code. From the results, it is concluded that Abid'k-$\omega$ model is better for the calculation of flow rate and efficiency than Baldwin-Lomax model. But, the predictions for Mach number and shock structure are almost the same.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.11
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• pp.1509-1520
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• 1998

An experiment was carried out for the fully developed turbulent flow of water in tube coils on the condition of uniform heat flux. The present work was conducted for various ranges for Dean number(1794~1321), Prandtl number (2.5~4.5), curvature ratio parameters (22~60). Heat transfer to steady viscous flow in coiled tubes of circular cross section was studied for fully developed velocity and temperature fields under the thermal boundary condition of uniform heat flux. The peripherally local Nusselt number correlated as a function of Dean and Prandtl numbers. We studied the flow in heat coiled tubes under the influence of both centrifugal and buoyancy forces in order to gain insight into the flow pattern. In the present study, we obtained three emperical formulas, $Nu_v=0.0231Re^{0.84}Pr^{0.4}(a/R)^{0.13}$ (vertical) $Nu_c=0.0241Re^{0.86}Pr^{0.4}(a/R)^{0.08}$ (corrugated) $Nu_h=0.0227Re^{0.84}Pr^{0.4}(a/R)^{0.09}$ (horizontal).

• International Journal of Aeronautical and Space Sciences
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• v.2 no.1
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• pp.12-19
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• 2001

Study of turbulent mixing layers has been a popular subject from the point of view of both practical application and phenomenological importance in engineering field. Turbulent mixing layers can be applied in many fields where rapid transition to turbulence is desirable in order to prevent boundary layer separation or to enhance mixing. The ability to control mixing, structure and growth of the shear flow would obviously have a considerable impact on many engineering applications. In addition to practical applications, free shear flows are one of the simplest flows to understand the fundamental mechanism in the transition process to turbulence. After the discovery of large-scale vortical structure in free shear flows many researchers have investigated the physical mechanism of generation and dissipation processes of the vortical structure. This study investigated the role of the large-scale vortical structures in the turbulent mixing layer using LES(Large-Eddy Simulation). The result shows that the pairing interaction of the vortical structure plays an important role in the growth rate of a mixing layer. It is found that the turbulence quantities depend strongly on the velocity ratio. It is also found that the vorticity in the high-velocity-side can extract energy from the mean flow, while the vorticity in the low-velocity-side lose energy by the viscous dissipation. Finally the results suggest the guideline to obtain the desired flow by control of the velocity ratio.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.793-802
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• 2006

In this study, a fluid/structure coupled analysis system for simulating complex flow-induced vibration (FIV) phenomenon of cascades has been developed. The flow is modeled using Euler and Wavier-Stokes equations with different turbulent models. The fluid domains are modeled using the unstructured grid system with dynamic deformations due to the motion of structural boundary. The Spalart-Allmaras (S-A) and the SST ${\kappa}-{\omega}$ turbulent models are used to predict the transonic turbulent flows. A fully implicit time marching scheme based on the Newmark direct integration method is used in order to solve the coupled governing equations for viscous flow-induced vibration phenomena. For the purpose of validation for the developed FIV analysis system, comparison results for computational analyses of steady and unsteady aerodynamics and flutter analyses are presented in the transonic flow region. In addition, flow-induced vibration analyses for the isolated cascade and multi-blades cascade models have been conducted to show the physical fluid-structure interaction effects in the time domain.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.32 no.9
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• pp.12-26
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• 2004

A new treatment of cell-interface flux in AUSM-type methods is introduced to reduce the numerical dissipation. Through analysis of TVD limiters, a criterion for the more accurate prediction of cell-interface state is found out and M-AUSMPW+ is developed by determining the transferred property newly and appropriately within the criterion. The superiority of M-AUSMPW+ is clearly revealed in multi-dimensional flow problems. It can eliminate numerical dissipation effectively in a non-flow aligned grid system. As a result, M-AUSMPW+ is shown to be much more accurate and effective than other previous schemes in multi-dimensional problems. Through a stationary contact discontinuity, a vortex flow, a shock wave/boundary layer interactions and viscous shock tube problems, it is verified that accuracy of M-AUSMPW+ is improved.

• Journal of the Korean Society for Industrial and Applied Mathematics
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• v.20 no.4
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• pp.333-354
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• 2016

The present investigation deals, heat and mass transfer characteristics with the effect of slip on the hydromagnetic pulsatile flow through a parallel plate channel filled with saturated porous medium. Based on the pulsatile flow nature, exact solution of the governing equations for the fluid velocity, temperature and concentration are obtained by using two term perturbation technique subject to physically appropriate boundary conditions. The expressions of skin friction, Nusselt number and Sherwood number are also derived. The numerical values of the fluid velocity, temperature and concentration are displayed graphically whereas those of shear stress, rate of heat transfer and rate of mass transfer at the plate are presented in tabular form for various values of pertinent flow parameters. By increasing the slip parameter at the cold wall the velocity increases whereas the effect is totally reversed in the case of shear stress at the cold wall.

• Journal of the Society of Naval Architects of Korea
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• v.44 no.3 s.153
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• pp.258-266
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• 2007

CFD calculations are performed for KRISO 3600TEU container ship(KCS) models with different Reynolds numbers. Numerical calculations of the turbulent flows with the free surface around KCS have been carried out at $Re=0.791{\times}106\;and\;Re=1.4{\times}107$ using a standard Fluent package. In both cases, Froude number is fixed with 0.26 and wave elevation is simulated by using the VOF method. The calculated results at $Re=1.4{\times}107\;and\;Re=0.791{\times}106$ are compared with the experiment data of KRISO towing tank test and RIMS CWC test, respectively. Boundary layer thickness and wake field shows Reynolds number differences. There are some changes in wave pattern behind transom stern.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.22 no.11
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• pp.767-772
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• 2010

The incompressible viscous flow past a sphere under forced oscillation is numerically investigated at a Reynolds number of 300. The immersed boundary method is used to handle the sphere oscillating vertically to the streamwise direction. There are two important variables to characterize the oscillating state of a sphere. One is an oscillating amplitude normalized by the sphere diameter is set as a fixed number of 0.2. Another is the frequency ratio which is defined by $f_e/f_o$, where fe and fo are the excited frequency and the natural frequency of vortex shedding for the stationary sphere. In this study, three different frequency ratios of 0.8, 1.0 and 1.2 are considered. The results show a periodic flow with hairpin vortices shedding from upper and lower positions as well as vortical legs obliquely extended by oscillating motion of sphere. The enveloping vortical structure experience rupture twice in one period of oscillation. As the frequency of oscillation is increased, the vortical legs are getting shorter and eventually the hairpin vortices are much closer to the adjacent one.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.6
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• pp.1407-1414
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• 1988

Deviation angles are predicted by numerical calculation of three-dimensional compressible flow through the rotating blade row in axial flow compressor. Three-dimensional flow fields are analyzed by the quasi three-dimensional combination of blade-to blade surfaces and hub-to shroud stream surfaces and calculated by the finite element method in the cyclic calculation of both stream surfaces. In the blade-to blade calculations the method of boundary stream line correction is used and in the hub-to shroud calculations the loss effects due to viscous flow are included. The computational results are compared with the available experimental one. It is shown that the computational results from blade-to-blade flow calculation are correct for incompressible, compressible low subsonic and high subsonic flow at the inlet, and the loss effects on the deviation angle can be neglected in the range of the subsonic flow less than the critical Mach number for the axisymmetric flow and even for 3-D non-axisymmetric flow with loss. And it is found that the present results are better agreed with the experimental data than Lieblein's one.