• Journal of Korea Water Resources Association
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• v.37 no.11
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• pp.949-958
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• 2004

A combined experimental and numerical effort is presented for investigation of reflection of irregular waves due to rectangular submerged breakwaters. In the numerical model, the Reynolds equations are solved by a finite difference method and k-$\varepsilon$ model is employed for the turbulence analysis. To track the free surface displacement, the volume of fluid method is employed. Numerical predictions of transmission and reflection coefficients are verified by comparing to laboratory measurements. Very reasonable agreements are observed. The reflection coefficients become stronger in proportion to numbers of submerged breakwaters.

• International Journal of Fluid Machinery and Systems
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• v.10 no.1
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• pp.76-85
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• 2017

Wall pressure measurements and flow visualization were conducted for a 90 degree elbow with an axis curvature radius the same as its inner diameter (125 mm). Reynolds numbers 320,000 and 500,000, based on the inner diameter and bulk velocity, were examined. A deflected inflow, having an almost constant velocity slope and a faster velocity at the inside, was introduced. Ensemble averaged pressure distributions showed that no difference of normalized pressure could be found in both the Reynolds number cases. Power spectral density functions of pressures exhibited that the fluctuation having the Strouhal number (based on the inner diameter and bulk velocity) of 0.6 existed in the downstream region of the elbow, which was 0.1 larger than that of the uniform inflow case [1]. Results of numerical calculations qualitatively coincided with the experimental ones.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.5
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• pp.888-905
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• 2015

For Super-Cavitating Underwater Vehicles (SCUV), the numerical analyses and experiments in a large cavitation tunnel are carried out at relatively large Reynolds numbers. The numerical results agree well with experiments and the drag coefficient of SCUV is rarely changed by the Reynolds number. As the cavitation number is decreased, the cavity occurs and grows, the cavitator drag decreases and the body drag is affected by the degree of covering the body with the cavity. The tunnel effects, i.e. the blockage and the friction pressure drop of the tunnel, on the drag and the cavitation of SCUV are examined from the numerical results in between the tunnel and unbounded flows. In the tunnel, a minimum cavitation number exists and the drag of SCUV appears larger than that in unbounded flow. When the super-cavity covers the entire body, the friction drag almost disappears and the total drag of SCUV can be regarded as the pressure drag of cavitator.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.1
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• pp.137-151
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• 1988

Thurbulent thermal convection between two plates, bottom plate is at higher temperature $T_{h}$ and the upper plate is at lower temperature $T_{i}$ is numerically investigated. Model equations are abridged Reynolds stress equations; full Reynolds stress equations are simplified to yield algebraic relations in case of mean square velocity fluctuations in vertical and horizontal directions. Boundary conditions for turbulent kinetic energy k and mean square temperature variance .thera.$^{2}$oner bar at the plate surfaces are set to be zero and those of dissipation rate of turbulent kinetic energy .epsilon. and dissipation rate of mean square temperature variance .epsilon.$_{\theta}$ are assumed at first grid point nearest to the boundary surfaces, whose values are approximated by inviscid estimates. Results show that temperature profiles are in good agreement with experimental data except transition region, in which temperature is over-predicted. Such discrepancy becomes larger as the Rayleigh number becomes smaller. Nusselt numbers, which are calculated from the temperature gradients at the boundary surfaces, are also in good agreement with experimental data.a.a.

• International Journal of Naval Architecture and Ocean Engineering
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• v.7 no.1
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• pp.195-211
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• 2015

Flat plate friction lines have been used in the process to estimate speed performance of full-scale ships in model tests. The results of the previous studies showed considerable differences in determining form factors depending on changes in plate friction lines and Reynolds numbers. These differences had a great influence on estimation of speed performance of full-scale ships. This study was conducted in two parts. In the first part, the scale effect of the form factor depending on change in the Reynolds number was studied based on CFD, in connection with three kinds of friction resistance curves: the ITTC-1957, the curve proposed by Grigson (1993; 1996), and the curve developed by Katsui et al. (2005). In the second part, change in the form factor by three kinds of friction resistance curves was investtigated based on model tests, and then the brake power and the revolution that were finally determined by expansion processes of full-scale ships. When three kinds of friction resistance curves were applied to each kind of ships, these were investigated: differences between resistance and self-propulsion components induced in the expansion processes of full-scale ships, correlation of effects between these components, and tendency of each kind of ships. Finally, what friction resistance curve was well consistent with results of test operation was examined per each kind of ships.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.6
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• pp.407-412
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• 2008

Heat transfer from three-dimensional heat-generating modules was investigated. Simulated electronic module in an array configured with dummy module elements were used to measure the average heat transfer coefficients. Various module arrangements were tested using module spacings of 0.85 and 1.15 cm for six Reynolds numbers ranging from 500 to 975. The results show that a module placed in-line with and upstream of a heated module results in the heat transfer enhancement due to high turbulence intensity prompted by upstream modules. The highest enhancement occurs when the separation distance between modules is close to the module length in the flow direction. The laminar flow was observed on the front of the first module, slow recirculation regions on the sides parallel to the airstream, and turbulent flow on the back side. It appears that the first module serves to trip the air stream and produce a high level of turbulence, which enhances the heat transfer rate downstream.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.32 no.10
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• pp.791-799
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• 2008

We investigate the flow characteristics around a series of rectangular bodies ($40^d{\times}80^w{\times}80^h$, $80^d{\times}80^w{\times}80^h$ and $160^d{\times}80^w{\times}80^h$) placed in a deep turbulent boundary layer. The study is aiming to understand the surface pressure distribution around the bodies such as the suction pressure in the leading edge, when the flow is normal, which is responsible for producing extreme suction pressures on the roof. The experiment includes wind tunnel work by using HWA (Hot-Wire anemometry) and pressure transducers. The experiments are carried out at three different Reynolds numbers, based on the velocity U at the body height h, of $2.4{\times}10^4$, $4.6{\times}10^4$ and $6.7{\times}10^4$, and large enough that the mean flow is effectively Reynolds number independent. The results include the measurements of the growth of the turbulent boundary layer in the wind tunnel and the surface pressure around the bodies.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.4
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• pp.622-632
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• 1995

The present numerical study is aimed to investigate time-dependent characteristics of a two-dimensional lid-driven square cavity flow of three high Reynolds numbers, $7.5{\times}10^3$, $10^4$ and $3{\times}10^4$. A conservative convection term on irregular grids was adopted by renewing the MAC type difference schemes on regular grids. Relaxation of velocity and pressure is implemented by SOLA algorithm. In case of $Re=7.5{\times}10^3$, flow behavior converges to steady state after a transient period. But for $Re=10^4$, periodic unsteady sinusoidal fluctuation of local velocity and kinetic energy is found and continuous movements of small eddies in the secondary flow regions are also discovered. Random generation of eddies and their active migrating behavior are detected for $Re=3{\times}10^4$, resulting in complete unsteady and non-linear flow characteristics. And, an organized structure similar to a Moffat vortex is also observed from the time-mean flow patterns. Furthermore, a typoon-like vortex(TLV) appears intemittently and rotates along the separation regions and boundary layers.

• Proceedings of the SAREK Conference
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• 2008.11a
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• pp.215-220
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• 2008

A microchannel PCHE is manufactured by the two technologies of micro photo-etching and diffusion bonding. In this paper, heat transfer and pressure drop characteristics by applying various configuration for the flow channel in the microchannel PCHE is experimentally investigated. The flow channel configurations are designed three types such as straight, wavy and offset strip channels. The performance experiment of each configuration is performed for Reynolds numbers in ranges of $100{\sim}700$ under various flow conditions for the hot side and the Reynolds number of cold side is fixed at 350. The inlet temperatures of the hot side and cold side are conducted as $40^{\circ}C$ and $20^{\circ}C$, respectively. The heat transfer performance of wavy channel, which was similar to that of offset strip channel, was much higher than that of straight channel. The effectiveness of wavy channel and offset strip channel was evaluated as about $0.5{\sim}0.9$. The pressure drop of wavy channel was highest among configurations and that of offset strip channel was lower than that of straight channel because the round curved surface of each strip edge was reduced the pressure loss.

• International Journal of Aeronautical and Space Sciences
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• v.18 no.3
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• pp.395-402
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• 2017

The local heat transfer and total pressure drops of developed turbulent flows in the ribbed rectangular convergent/divergent channels with ${\Lambda}/V-shaped$ ribs have been investigated experimentally. The channels have the exit hydraulic diameter ($D_{ho}$) to inlet hydraulic diameter ($D_{hi}$) ratios of 0.67 for convergence and 1.49 for divergence, respectively. The ${\Lambda}/V-shaped$ ribs with three different flow attack angles of $30^{\circ}$, $45^{\circ}$, and $60^{\circ}$ are manufactured with a fixed rib height (e) of 10 mm and the ratio of rib spacing (S) to height (e) of 10 on the walls. Thermal performances of the ribbed rectangular convergent/divergent channels are compared with the smooth straight tube under identical pumping power. The results show that the flow attack angle of $45^{\circ}$ with ${\Lambda}-shaped$ rib has the greatest thermal performance at all the Reynolds numbers studied in the convergent channel; whereas, the flow attack angle of $60^{\circ}$ with V-shaped rib has the greatest thermal performance over Reynolds number of 30,000 in the divergent channel.