• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.10
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• pp.2724-2737
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• 1994

The swirl effect on an axisymmetric turbulence has been investigated along its centerline by the hot wire anemometry. Flow facility to generate and conrol the swirl has been built by using the rotating honeycomb and grid. For the case of internal flows, as the strength of the swirl increases the flow tends to be locally isotropic by modifying the radial and the rotational components mainly. In comparison with those of the plain free jet, the decay of the centerline turbulences seems to be delayed substantially even with a slight swirl component.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.4
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• pp.50-56
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• 2012

Vent mixer can provide main flow directly into a recirculation region downstream of the mixer to enhance fuel-air mixing efficiency. Based on experimental results of three-dimensional velocity, vorticity and turbulent kinetic energy obtained by a stereoscopic PIV method, the performance of the vent mixer was compared with that of the step mixer which was used as a basic model. Thick shear layers of the vent mixer induced the increase of the penetration height. The turbulent kinetic energy mainly distributed along a boundary layer between the main flow and the jet plume. This turbulent field activates mass transfer in a mixing region, leading to the mixing enhancement.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.807-812
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• 2001

The effects of casing shapes on the interaction of the impeller and volute in a small-size turbo-compressor are investigated. Numerical analysis is conducted for the compressor with circular and single volute casings from inlet to discharge nozzle. In order to predict the flow pattern inside the entire impeller, vaneless diffuser, and casing, calculations with a multiple frame of reference method between the rotating and stationery parts of the domain are carried out. For incompressible turbulent flow fields, the continuity and three-dimensional time-averaged Navier-Stokes equations are employed. To predict the performance of two types of casings, the static pressure and loss coefficients are obtained with various flow rates. Also, static pressure distributions around casings are studied for different casing shapes, which are very important to predict the distribution of radial load.

• 한국전산유체공학회:학술대회논문집
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• 2011.05a
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• pp.488-493
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• 2011

The object of this study is to develope the program for analyzing the fluid flow and heat transfer of PMSM electric motor. The program will be mainly used for inexperienced users of CFD analysis. So it has to be performed using the geometry data and the heat source of each part only. Interface program for converting the given data to the instruction of pre-processor is developed. The conjugate heat transfer between a flow passage of the motor and inner parts consisting of rotor and stator is regarded. In order to reduce the computational time and memory storage, cyclic boundary condition is applied. For the numerical simulation, MRF(Multi-Reference Frame) method is used to consider rotating operation of the rotor and heat source is applied to the copper, wire, and magnetic parts in the motor. On the screen of computer, the users can show the velocity distributions and the contours such as pressure, turbulent kinetic energy, turbulent dissipation rate and temperature.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.1
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• pp.125-132
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• 2002

An experimental study on the characteristics of stability of propane turbulent nonpremixed jet flames discharged normal to air free-streams with uniform velocity profile is conducted. Experimental observations are focused on the flame shape, the stability considering two kinds of flame, lift-off distance, and the flame length according to velocity ratio. In order to investigate the mixing structure of the flame base at the lower limit, we employ the RMS technique and measure the species concentration by a gas chromatography. In the results of the stability curve and lifted flame, it is fecund that the dependency of nozzle diameter is closely related to the large-scale vortical structure representing counter-rotating vortices pair. Also, the detailed discussion on the phenomenon of blowout due to this large vortical motion, is provided.

• Journal of the Society of Naval Architects of Korea
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• v.55 no.2
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• pp.169-177
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• 2018

Twisted rudder, twisted rudder with bulb, and twisted rudder with bulb and fin have been developed computationally for 3,000 TEU container ship through parametric study. The objective function is to minimize delivered power in model scale. Design variables are twisted angle, rudder bulb diameter and fin angle. The governing equation is Reynolds averaged Navier-Stokes equations in an unsteady turbulent flow and the Reynolds stress model applied for the turbulent closure. A double body model is used for the treatment of free-surface. The calculation was carried out in towing and self-propulsion conditions at design speed. The sliding mesh technique was employed to simulate the flow around the propeller. Form factor is obtained from the towing computation. Self-propulsion point is obtained from the self-propelled computations at two propeller rotating speeds. The delivered power due to the designed twisted rudder, twisted rudder with bulb, and twisted rudder with bulb and fin are reduced by 1.1%, 1.6%, and 2.0%, respectively.

• Journal of Mechanical Science and Technology
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• v.20 no.2
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• pp.262-270
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• 2006

Direct numerical simulations (DNS) of turbulent channel flows up to $Re_{\tau}=1270$ are performed to investigate an elliptic feature and strain rate field on cross sections of coherent fine scale eddies (CFSEs) in wall turbulence. From DNS results, the CFSEs are educed and the strain rate field around the eddy is analyzed statistically. The principal strain rates (i.e. eigenvalues of the strain rate tensor) at the CFSE centers are scaled by the Kolmogorov length $\eta$ and velocity $U_k$. The most expected maximum (stretching) and minimum (compressing) eigenvalues at the CFSE centers are independent of the Reynolds number in each $y^+$ region (i. e. near-wall, logarithmic and wake regions). The elliptic feature of the CFSE is observed in the distribution of phase-averaged azimuthal velocity on a plane perpendicular to the rotating axis of the CFSE $(\omega_c)$. Except near the wall, phase-averaged maximum $(\gamma^{\ast}/\gamma_c^{\ast})$ and minimum $(\alpha^{\ast}/\alpha_c^{\ast})$ an eigenvalues show maxima on the major axis around the CFSE and minima on the minor axis near the CFSE center. This results in high energy dissipation rate around the CFSE.

• The KSFM Journal of Fluid Machinery
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• v.3 no.4 s.9
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• pp.22-29
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• 2000

Numerical analysis using three dimensional finite volume method for the discretization, adaptive grid method for the numerical accuracy, multiple rotating frame method for the rotating body and the standard $k-{\epsilon}$ model for the turbulent flow was performed to understand the heat transfer phenomena and to improve the efficiency of the scroll compressor. The temperature measurement was carried out under ARI condition. It was found that the fluid temperature in the compressor was predicted accurately while the temperature of the motor coil showed large discrepancy between the calculation and experiment due to the large anisotropy of the conductivity and non homogeneity. We found that the efficiency of the compressor depends on the inlet temperature of the compressing part and the flow pattern around the inlet region of the compressing part influences the inlet temperature due to high surface temperature of the main frame. The efficiency of the compressor using Coanda effect is higher than the previous one because the smooth suction at the inlet region of the compressing part leads to low heat transfer to the refrigerant of the compressor.

• Journal of Mechanical Science and Technology
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• v.16 no.9
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• pp.1121-1136
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• 2002

The flow characteristics of film coolant issuing into turbulent boundary layer developing on a convex surface have been investigated by means of flow visualization and three-dimensional velocity measurement. The Schlieren optical system with a spark light source was adopted to visualize the jet trajectory injected at 35° and 90° inclination angles. A five-hole directional pressure probe was used to measure three-dimensional mean velocity components at the injection angle of 35°. Flow visualization shows that at the 90° injection, the jet flow is greatly changed near the jet exit due to strong interaction with the crossflow. On the other hand, the balance between radial pressure gradient and centrifugal force plays an important role to govern the jet flow at the 35° injection. The velocity measurement shows that at a velocity ratio of 0.5, the curvature stabilizes downstream flow, which results in weakening of the bound vortex structure. However, the injectant flow is separated from the convex wall gradually, and the bound vortex maintains its structure far downstream at a velocity ratio of 1.98 with two pairs of counter rotating vortices.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.12
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• pp.1655-1666
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• 2003

It is experimentally well-known that high anisotropies of the turbulent flow field are dominant inside the tip leakage vortex, which is attributable to a substantial proportion of the total loss and constitutes one of the dominant mechanisms of the noise generation. This anisotropic nature of turbulence invalidates the use of the conventional isotropic eddy viscosity turbulence models based on the Boussinesq assumption. In this study, to check whether an anisotropic turbulence model is superior to the isotropic ones or not, the results obtained from the steady-state Reynolds averaged Navier-Stokes simulations based on the RNG k-$\varepsilon$ model and the Reynolds stress model (RSM) are compared with experimental data for two test cases: a linear compressor cascade and a forward-swept axial-flow fan. Through this comparative study of turbulence models, it is clearly shown that the RSM, which can express the production term and body-force term induced by system rotation without introducing any modeling, should be used to predict quantitatively the complex tip leakage flow, especially in the rotating environment.