• Journal of the Korean Society of Industry Convergence
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• v.4 no.4
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• pp.387-393
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• 2001

The flow characteristics on the centerline in case of free jet, sudden expansion jet and impinging jet have been investigated. Centerline flow behaviors and similaritis with mean velocities, turbulent intensities, shear stresses, isotropic structures and turbulent kinetic energies on the streamwise direction were looked into and compared with three jets, The results show that mean velocities have represented potential core and decayed with similar gradients. The turbulent intensities and shear stresses were presented peak values in the self-preserving region, and then they were in decay. Aeolotropy in the initial region were possible returned to isotropy patterns with asymptotic approach in the downstream region. It has been found that the turbulent kinetic energies for the three cases of jet existed in the similarity and they coincided with Gaussian profile.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.14 no.3
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• pp.206-213
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• 2002

In this paper, the flow characteristics of an axial fan spraying isothermal compact jet in a confined space were investigated by the experimental methods, the numerical method, and the free jet theory According to the results, the numerical result and the experimental result are agreed well qualitatively and different quantitatively within $\pm1.0%$ for the centerline velocity, the entrainment ratio, and the maximum throw. However, the free jet theory can reasonably predict the centerline velocity except the entrainment ratio and the maximum throw. In other words, the entrainment ratio and the maximum throw by 1.he free jet theory are hard to estimate the characteristics of jet because of restriction of c confined space.

• Transactions of the Korean Society of Mechanical Engineers
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• v.18 no.12
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• pp.3335-3344
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• 1994

The initial flow characteristics of the turbulent circular jet discharging into the sudden expansion pipes have been investigated by the hot wire anemometry. Evolutions of similarity, centerline behavior, jet boundary and typical turbulent quantities were looked into for the expansion ratios. The results show that the spreading rates of discharging jet seem not to be dependent of the expansion ratio and that the velocity profiles in the radial directions exhibit the similarity in the regions, 2-5d, 2-6d and 3-8d for the corresponding expansion rations of 2, 3 and 5, respectively. With the increase of expansion ratio the centerline velocity decays rather slowly. The anisotropic behaviors of the discharging jets into the sudden expansion pipe look stronger than those of the free jet.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.26 no.4
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• pp.531-538
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• 2002

Flow characteristics of a round jet with swirl number of 0.17 have been investigated using a hot -wire anemometry in the initial region within 10D(exit diameter). Swirl effects were observed by comparing centerline flow characteristics, similarities and turbulent budgets of a swirl jet and a free jet, respectively. To obtain similarity of the radial profiles mean velocity and higher moments were measured at the vertical pl anes, located at 2.5, 5.0, 7.5D, 10D, respectively. The centerline velocity characteristics were also measured. It is turned out that similarities of mean and Reynolds stress are established. The jet boundary has wider width than that of a free jet and the shear stress also becomes stronger. In addition the centerline decay becomes faster than that of the free jet, indicating that the swirl induces more entrainment in the initial region of the swirl Jet by transferring the axial mean kinetic energy into the swirl energy and, therefore, has wider boundary, compared with that of free jet.

• 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.

• Transactions of the Korean Society of Mechanical Engineers
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• v.17 no.12
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• pp.3166-3178
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• 1993

The turbulent flow characteristics of impinging jet have been investigated by the hot wire anemometry with a movable impinging wall. Turbulences were generated by the meshed jet as well as the typical round jet and their characteristics were compared, of mean velocity profiles, turbulent intensities. Reynolds stresses, similarities and their centerline flow behaviors. The meshed jet tends to make shear layer wider than the normal one in the initial region and the velocity profiles of the normal jet is rather contractive being compared with those of the meshed one near the wall. The effect of meshed exit appears only within 4D at the begining of jets and the cascading process of the meshed one marches more rapidly than that of the normal jet. The wall effects appear in the downstream of about 0.85 H to the impinging wall for every case of wall positions in both nozzles.

• Water Engineering Research
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• v.3 no.2
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• pp.93-111
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• 2002

In this paper, mixing characteristics and dilution of the merging buoyant discharges from array of multiple jets has been extensively studied in the hydraulic model experiments. New equations for dilution, which include the merging effects correctly, were derived. Experiments were constructed in a 20-m long, 4.9-m wide and 0.6-m deep flume, and the model diffuser was manufactured to indicate the typical characteristics of the existing ocean wastewater outfall in South Korea. Buoyant discharge from the diffuser was reproduced using heated water. Water temperature was measured using CC-Type thermocouple sensors, which were connected to a 40-channel data logger. Experimental results show that merging between ports in a particular riser is dependent upon the discharge densimetric Froude number, whereas merging between two ports which are facing each other at 90$\circ$ at the adjacent risers is dependent upon the discharge densimetric Froude number and distance from the port and port spacing. Centerline dilution increase with distance from the port outlet until two plumes has merged. However, after merging occurs, increase of the centerline dilution almost stops. Further distance from the position where merging occurs, centerline dilution increases again.

• Nuclear Engineering and Technology
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• v.22 no.1
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• pp.66-74
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• 1990

The thermal-hydraulic characteristics of the 17$\times$17 OFA (Optimized Fuel Assembly) used in the KNU 7&8 are analyzed and compared with that of the 17$\times$17 SFA (Standard Fuel Assembly) loaded in the KNU 5&6. The thermal-hydraulic characteristics analyzed are minimum DNBR, fuel centerline temperature and exit void fraction at normal operation and design over power transient. Additionally, local linear rod power, which will cause fuel centerline melting, is calculated. The DNBR sensitivity calculations are performed with respect to the reactor operating parameters. COBRA-IV-I code is used for these calculations. The modified W-3 correltion and the drift-flux model are applied for the critical heat flux calculation and the void fraction calculation, respectively. From the calculated results, it has been found that the possibility of DNB occurrence is higher in the OFA than in the SFA. The other hand, the local linear power resulting in fuel centerline moiling of the OFA is nearly equal to that of the SFA.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.22 no.2
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• pp.221-228
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• 1998

In order to look into the comparative flow characteristics between a circular contraction duct and a circular expansion duct the both centerline turbulent structures have been investigated by the hot wire anemometry. Both of the contraction and the expansion have Morel type contours. Means, turbulences, and triple moments have been measured for the turbulent kinetic energy budgets along their centerlines. It is resulted that mean velocities of both have much deviated from theoretical values calculated by one-dimensional continuity considerations, and that for the same upstream condition, the expansion maintains the isotropy in general while the contraction maintains a severe anisotropy through the whole duct. The mean transport of the TKE along the expansion is willing to balance mostly with the dissipation in the TKE budgets while that along the contraction is balanced with the production in the turbulent kinetic energy equation.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2002.05a
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• pp.48-53
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• 2002

Sheet or plate bending is one of the most important industrial metal forming processes. And considerable attention has been focused on gaining a better understanding of many of bending characteristics. One of defaults in bending process is the springback. In this study, the springback characteristics of tailor-welded strips in U-bending process was investigated. Furthermore, not only the relationships between the springback and the process variables such as the geometry of the tools and thickness combination of workpiece but also the heat effect which affects the springback due to welding process was experimentally considered. First, tailor-welded strips are joined by the laser welding process and consisted of two types of thickness combinations of the SCPI sheet, 0.8t${\times}$1.2t and 0.8${\times}$1.6t to investigate the effect of different thickness combination on the springback. Secondly, two different directionally welded strips, one was welded along the centerline of the strip-width and the other was along the centerline of strip-length, were adopted to compare the effects of the location of weld line on the springback. And three punch profile radii of 3, 9, and 15 m were used. Some cases of the experimental results were simulated by using a commercial FEM code, PAM-STAMP to compare the experimental results to the analytical ones.