• Ocean and Polar Research
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• v.36 no.4
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• pp.475-485
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• 2014

Seawater flow characteristics around a manganese nodule mining device in deep sea were analyzed through numerical investigation. The mining device influences the seawater flow field with complicated velocity distributions, and they are largely dependent on the seawater flow speed, device moving speed, and injection velocity from the collecting part. The flow velocity and turbulent kinetic energy distributions are compared at several positions from the device rear, side, and top, and it is possible to predict the distance from which the mining device affects the seawater flow field through the variation of turbulent kinetic energy. With the operation of the collecting device the turbulent kinetic energy remarkably increases, and it gradually decreases along the seawater flow direction. Turbulent kinetic energy behind the mining system increases with the seawater flow velocity. The transient behavior of nodule particles, which are not collected, is also predicted. This study will be helpful in creating an optimal design for a manganese nodule collecting device that can operate efficiently and which is eco-friendly.

• Nuclear Engineering and Technology
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• v.26 no.3
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• pp.345-354
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• 1994

Numerical Predictions including secondary flows have been Performed for fully developed turbulent single-phase rod bundle flows. The k-$\varepsilon$ turbulence model(two equation model) for the isotropic eddy viscosity, together with an algebraic stress model for generating secondary velocities, enabled the prediction of mean axial velocities, secondary velocities, and turbulent kinetic energy and turbulent stresses. Comparisons with experiment hate shown that the influence of secondary motion on mean flow and turbulence is dearly evident. The convective transport effects of secondary flow on the velocity field have been identified.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.1
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• pp.42-53
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• 2008

The two dimensional PIV (particle image velocimetry) measurement technique is applied to water flow in a narrow cavitation tunnel. The nearly homogeneous and isotropic turbulent flows are generated by the honeycomb installed in the tunnel and visualized with a PIV technique. The velocities in the measurement plane at the tunnel centerline 184cm downward from the honeycomb were measured and calculated by an image correlation technique. The turbulent properties are evaluated and each term in the turbulent kinetic energy equation is calculated for the conditions with different internal pressures. Lowering the internal pressure gives an effect on the turbulent flow due to growing bubbles which are resolved in the water. The turbulent kinetic energy in the measurement plane is decayed much slower than those of other research results carried out with wind tunnels. With decreasing the tunnel internal pressures the turbulent intensities are increased about 1.5 times and the anisotropic tendency is also increased.

• Journal of the Korean Society of Propulsion Engineers
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• v.9 no.2
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• pp.97-104
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• 2005

A simple but efficient grid generation technique by using the modified compressible form of stream function has been formulated. Transformation of a physical plane to a streamline plane, the Von Mises Transformation, has been widely used to solve the differential equations governing flow phenomena, however, limitation arises in low velocity region of boundary layer, mixing layer and wake region where the relatively large grid spacing is inevitable. Modified Von Mises Transformation with simple mathematical adjustment for the stream function is suggested and applied to solve the confined coaxial turbulent jet mixing with simple $\kappa-\epsilon$ turbulence model. Comparison with several experimental data of axial mean velocity, turbulent kinetic energy, and Reynolds shear stress distribution shows quite good agreement in the mixing layer except in the centerline where the turbulent kinetic energy distributions were somewhat under estimated. This formulation is strongly suggested to be utilized specially for free turbulent mixing layers in axisymmetric flow conditions such as the investigation of mixing behavior, jet noise production and reduction for Turbofan engines.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.9
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• pp.2294-2303
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• 1993

This paper investigated the characteristics of the turbulent incompressible flow past the orifice ring in an axi-symmetric pipe. The flow field was the turbulent pulsatile flow for Reynolds number of $2{\times}10^{5}$ which was defined based on the maximum velocity and the pipe diameter at the inlet, with oscillating frequence $(f_{os})=1/4{\pi}$ which was considered as quasi-steady state frequence. In the present investigation, finite analytic method was used to solve the governing equations in Navier Stokes and turbulent transport formulations. Particularly at high Reynolds number and low oscillation frequency, the effects of orifice ring on the flow were numerically investigated. The separation zone behind the orifice ring during the acceleration phase was found to be decreased. However, during the deceleration phase, the separation behind the orifice ring for pulsatile flow continuously grow to a size even larger than that in steady flow. The pressure drop in steady flow was found to be constant and always positive while for pulsatile flow the pressure drop change with time. And large turbulent kinetic energy, dissipation rate were found to be located in the region where the flow passes through the orifics ring. The maximum turbulent kinetic energy, generally occurs along the shear layer where the velocity gradient is large.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.1
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• pp.41-51
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• 2004

A direct numerical simulation is performed to analyze the effects of a localized time-periodic blowing on a turbulent boundary layer flow at R $e_{+}$=300. Main emphasis is placed on the blowing frequency effect on near-wall turbulent flow structures at downstream. Wall-normal velocity on a spanwise slot is varied periodically at different frequencies (0.004$\leq$ $f^{＋}$$\leq$0.080). The amplitude of periodic blowing is $A^{＋}$=0.5 in wall nit, which corresponds to the value of $v_{rms}$ at $y^{＋}$=15 without blowing. The frequency responses are scrutinized by examining the phase or time-averaged turbulent statistics. The optimal frequency ( $f^{＋}$=0.03) is observed, where maximum increase in Reynolds shear stress, streamwise vorticity fluctuations and energy redistribution occurs. The phase-averaged stretching and tilting term are investigated to analyze the increase of streamwise vorticity fluctuations which are closely related to turbulent coherent structures. It is found that the difference between PB and SB at a high blowing frequencies is negligible.e.e.

• Journal of the Society of Naval Architects of Korea
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• v.47 no.4
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• pp.517-524
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• 2010

This paper covers the numerical studies performed to investigate the characteristics of turbulent wake generated by a submarine, SUBOFF model. A SUBOFF model assumed as an axial-symmetric body was used to generate wake. The numerical simulation was performed by using a commercial S/W, FLUENT, with the same condition as the experiments by Shin et al.(2009). Mainly the cross-sectional distribution of the time-averaged mean wake and turbulent kinetic energy was compared with the experiments. Both results are agreed well with each other in the propeller wake section, but the agreement between both is not so satisfied in the far wake field. It means that more numerous number of grid points and their concentration should be required in that field.

• Journal of Mechanical Science and Technology
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• v.20 no.11
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• pp.1993-2001
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• 2006

The piezoelectric bimorph film, which, as an actuator, can generate more effective displacement than the usual PVDF film, is used to control the turbulent boundary-layer flow. The change of wall pressures inside the turbulent boundary layer is observed by using the multi-channel microphone array flush-mounted on the surface when actuation at the non-dimensional frequency $f_b^+$:=0.008 and 0.028 is applied to the turbulent boundary layer. The wall pressure characteristics by the actuation to produce local displacement are more dominantly influenced by the size of the actuator module than the actuation frequency. The movement of large-scale turbulent structures to the upper layer is found to be the main mechanism of the reduction in the wall- pressure energy spectrum when the 700$700{\nu}/u_{\tau}$-long bimorph film is periodically actuated at the non- dimensional frequency $f_b^+$:=0.008 and 0.028. The biomorph actuator is triggered with the time delay for the active forcing at a single frequency when a 1/8' pressure-type, pin-holed microphone sensor detects the large-amplitude pressure event by the turbulent spot. The wall-pressure energy in the late-transitional boundary layer is partially reduced near the convection wavenumber by the open-loop control based on the large amplitude event.

• Journal of Mechanical Science and Technology
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• v.15 no.1
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• pp.117-124
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• 2001

This paper presents turbulent characteristics of an impinging F-O-O-F type injector in which fuel ad oxidizer impinge on each other to atomize under the different momentum ratio. Water was used as an inert simulant liquid instead of fuel and oxidizer. The droplet size and velocity in the impinging spray flow field were measured using a PDPA. The gradient of the spray half-width(b$_2$) along the long-axis direction declined throughout the entire spray flow field with increasing the momentum ratio from 1.19 to 6.48. However, the gradient of the half-width(b$_1$) along the short-axis direction decreased with increasing the momentum ratio. The turbulence intensity and turbulent kinetic energy were converged into the center of the center of the initial region with increasing the momentum ratio. As the momentum ratio increased from MR=1.19 to MR=6.48, the turbulent shear stress decreased. The results of this study can be used for the design of an impinging type injector for liquid rackets.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2000.06a
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• pp.93-98
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• 2000

Turbulence on the journal bearing operation is examined. And the thermal variability is studied for isothermal, convective and adiabatic conditions on the walls within some degree of journal misalignment. An efficient algorithm for the solution of the coupled turbulent Reynolds and energy equations is used to examine the effects of the various factors. The calculation data of turbulent analysis are compared with the ones of laminar analysis. Heat convection is found to play but a small role in determining friction and load. The friction distribution patterns through inside a journal bearing now appear different with high values at the front part of the bearing due to the high speed and low temperature, and a sudden decrease past the pressure maximum.