• Journal of the Society of Naval Architects of Korea
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• v.36 no.3
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• pp.8-14
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• 1999

The flor characteristics around the KRISO 3600TEU container ship model have been experimentally investigated in a subsonic wind tunnel. The mean velocity and turbulence characteristics in the stern and wake regions were measured using an x-type hot-wire probe. The flow characteristics in the stern and near wake regions revealed a complicated three-dimensional flow pattern. The measured results showed clearly the formation of longitudinal vortices and their effect on the flow pattern in the wake region. The shear layer developed along the ship model expands showly to the downward direction. The turbulence statistics measured can be used as comparative data of numerical simulations and provide insights into development of accurate turbulence models for the ship design.

• The Journal of the Acoustical Society of Korea
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• v.9 no.6
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• pp.81-90
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• 1990

유체 동역학에서, 난류에 의해 수중 구조물에 가해지는 압력과 전단력의 측정은 중요한 문제이 다. 이러한 유체의 흐름에 의한 압력과 전단력, 나아가 유체의 흐름방향까지 시간과 거리의 함수로 측정 할 수 있는 새로운 탄성표면파 센서가 개발되었다. 센서는 압축 인장형 전단력을 받는 두 개의 표면파 와 흐르는 유체 속의 표면파의 속도차는 또한 유체흐름에 의해 가해지는 압력에 비례한다. 정지류 속의 표면파와 흐르는 유체 속의 표면파의 속도차는 또한 유체흐름에 의해 가해지는 압력에 비례한다. 이 센 서를 응력 로젯과 같이 배열하면 유체의 진행방향도 함께 측정할 수 있다. 표면파 센서는 넓은 주파수 대역에 걸쳐 사용이 가능하므로, 적절히 설계하면 유체의 흐름에 의한 표면력과 유체의 진행방향을 동 시에 거리와 시간의 함수로서 국부적으로, 광역적으로 측정할 수 있다.

• Journal of Wetlands Research
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• v.19 no.3
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• pp.303-310
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• 2017

This paper is to understand the settling properties of cohesive sediments under effects of ions in turbulent flow. The experiments were conducted using a miniature annular flume(mini flume) with a free water surface. Silica was used as sediment of experiment. The suspended concentrations were measured by using a CCD-Camera. Settling of silica($SiO_2$) was allowed to occur under various shear stresses in a concentration of 7g/L. At condition of pH 4.2 and high NaCl concentration, the floc size D of silica was larger than D at condition of pH6.8 with the bed shear stress increasing. The settling velocity $W_s$ of silica was higher at condition of 10g NaCl/L than $W_s$ at condition of pH4.2. Comparison of measured concentration-time curves and concentration-time curves calculated by this study showed similar tendency in flow under effects of ions.

• Journal of Korea Water Resources Association
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• v.33 no.5
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• pp.581-592
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• 2000

Turbulence structure and suspended sediment transport capacity in vegetated open-channel flows are investigated numerically in the present paper. The $\textsc{k}-\;\varepsilon$ model is employed for the turbulence closure. Mean velocity and turbulence characteristics including turbulence intensity, Reynolds stress, and production and dissipation of turbulence kinetic energy are evaluated and compared with measurement data available in the literature. The numerical results show that mean velocity is diminished due to the drag provided by vegetation, which results in the reduction of turbulence intensity and Reynolds stress. For submerged vegetation, the shear at the top of vegetation dominates turbulence production, and the turbulence production within vegetation is characterized by wakes. For emergent condition, it is observed that the turbulence generation is dominated by wakes within vegetation. In general, simulated profiles compares favorably to measured data. Computed values of eddy viscosity are used to solve the conservation equation for suspended sediment, yielding sediment concentration more uniform over the depth compared with the one in the plain channel. The simulation reveals that the suspended load decreases as the vegetation density increases and the suspended load increases as the particle diameter decreases for the same vegetation density.

• Journal of Power System Engineering
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• v.5 no.1
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• pp.21-26
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• 2001

This paper represents the turbulent intensity, the turbulent kinetic energy and Reynolds shear stress in the X-Y plane of cone type swirl gas burner measured by using X-probe from the hot-wire anemometer system. The experiment is carried out at flowrate 350 and $450{\ell}/min$ respectively in the test section of subsonic wind tunnel. The turbulent intensity and the turbulent kinetic energy show that the maximum value is formed in the narrow slits distributed radially on the edge of a cone type swirl burner, hence, the combustion reaction is anticipated to occur actively near this region. And the turbulent intensities ${\upsilon}\;and\;{\omega}$ are disappeared faster than the turbulent intensity u due to the inclined flow velocity ejecting from the swirl vanes of a cone type baffle plate of burner. Moreover, the Reynolds shear stress $u{\upsilon}$ is distributed about three times as large as the Reynolds shear stress $u{\omega}$ in the outer region of the cone type gas burner.

• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.6
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• pp.732-742
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• 1985

Measurements of mean velocity and turbulence characteristics are obtained with a linearized constant temperature hot-wire anemometer in a two-dimensional turbulent jet discharging parallel to a flate. Wall static pressure distribution is also measure. The Reynolds number based on the jet nozzle width (D) is about 42,000 and the step height is 2.5D. The reattachment length is found to be 7.5D by using both wool tuft and oil methods. Upstream of the reattachment point, there exist double coherent structures and mean velocity, Reynolds stresses and triple product profiles are asymmetric about jet center line due to the influence of streamline curvature and recirculating flow region. Near the reattachment point, wall static pressure and turbulence quantities change its shape rapidly because of the large eddies by the solid wall. Especially, turbulence intensity has a maximum value in the reattachment regin, then decreases slowly in the redeveloping wall jet ragion. Downstream of X/D=14, a single large scale eddy structure is formed. Far downstream affer the reattachment(X/D.geq.18) mean velocity profile, the decay of maximum velocity and the variation of jet half width are nearly similar to those of plane wall jet, but the Reynolds stresses are higher than those of the latter.

• Nuclear Engineering and Technology
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• v.24 no.3
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• pp.263-273
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• 1992

The study on the velocity distribution and the pressure drop characteristic of the nuclear fuel assembly is of importance for the thermal hydraulic design and safety analysis. The purpose of this experimental study is to investigate the hydraulic mixing behind the different kinds of spacer grids in the now or rod bundles. In this study, the detailed hydraulic characteristics in subchannels of 5$\times$5 PWR(Pressurized Water Reactor) rod bundles were measured using one-component He-Ne LDV(Laser Doppler Velocimeter). Measurements of the axial velocity, turbulent intensities and pressure drops were peformed Lateral velocity, turbulent intensities and Reynolds shear stress were also measured by adjust-ing LDV alignment. Friction factors in rod bundles and loss coefficients for spacer grids were evaluated from the measured pressure drops. Hydraulic mixing performance for different kinds of spacer grids could be investigated by estimating the turbulent cross-flow mixing rates between neighboring subchannels.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.900-907
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• 2000

The three-dimensional turbulent flow in curved pipes susceptible to flow-accelerated corrosion has been analyzed numerically to predict the pressure and shear stress distributions on the inner surface of the pipes. The analysis employs the body-fitted non-orthogonal curvilinear coordinate system and a standard $ {\kappa}-{\varepsilon}$ turbulence model with wall function method. The finite volume method is used to discretize the governing equations. The convection term is approximated by a high-resolution and bounded discretization scheme. The cell-centered, non-staggered grid arrangement is adopted and the resulting checkerboard pressure oscillation is prevented by the application of a modified version of momentum interpolation scheme. The SIMPLE algorithm is employed for the pressure and velocity coupling. The numerical calculations have been performed for two curved pipes with different bend angles and curvature radii, and discussions have been made on the distributions of the primary and secondary flow velocities, pressure and shear stress on the inner surface of the pipe to examine applicability of the present analysis method. As the result it is seen that the method is effective to predict the susceptible systems or their local areas where the fluid velocity or local turbulence is so high that the structural integrity can be threatened by wall thinning degradation due to flow-accelerated corrosion.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.3
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• pp.177-186
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• 2003

In the present study, the flow characteristics of developing turbulent flows are investigated at the exit region of a square cross-sectional 180" curved duct with dimensions of 40mm$\times$40mm$\times$4000mm (height $\times$ width $\times$length). Smoke particles produced from mosquito coils were used as seed particles for the LDV measurement. Experiments were carried out to measure axial velocity profiles, shear stress distributions and entrance lengths by using an LDV system and Rotating Machinery Resolver RMR with PHASE software. Experimental results clearly show that the time-averaged Reynolds number does not affect oscillatory flow characteristics because the turbulent components tend to balance the oscillatory components in the fully developed flow region. Also, the velocity profiles are in good agreement with 1/7power law such as the results of steady turbulent flows. The turbulent intensity linearly increases along the walls and is slightly higher, especially in the period of deceleration. On the other hand, the LDV measurements show that shear stress values in slightly higher in the period of deceleration due to the flow characteristics in the exit region. The entrance length where flows become stable appears at the point that is 40 times the length of hydraulic diameter.eter.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.11
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• pp.1481-1489
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• 1999

The sliding-belt concept introduced by Bechert et al. (AIAA J., Vol. 34, pp. 1072~1074) is numerically applied to a turbulent boundary layer flow for the skin-friction reduction. The sliding belt is moved by the shear force exerted on the exposed surface of the belt without other dynamic energy input. The boundary condition at the sliding belt is developed from the force balance. Direct numerical simulations are performed for a few cases of belt configuration. In the ideal case where the mechanical losses associated with the belt can be ignored, the belt velocity increases until the integration of the shear stress over the belt surface becomes zero, resulting in zero skin friction on the belt. From practical consideration of losses occurred In the belt device, a few different belt velocities are given to the sliding belt. It is found that the amount of drag reduction is proportional to the belt velocity.