• Proceedings of the KSME Conference
• /
• 2004.11a
• /
• pp.1389-1394
• /
• 2004

Experiments were done for the unsteady flow in a counter rotating axial flow fan near peak efficiency and stall point. Flow fields in a counter rotating axial flow fan were measured at cross-sectional planes of the upstream and downstream of each rotor. Cross sectional passage flow patterns were investigated through the acquired data by the $45^{\circ}$ inclined hot-wire. Comparison of flow characteristics between two different operating conditions such as tip vortex, secondary flow and turbulence intensity were performed through the analyses of axial, radial and tangential velocity distributions. As a result, tip vortex and secondary flows are enforced and measured obviously at stall point.

• The KSFM Journal of Fluid Machinery
• /
• v.11 no.4
• /
• pp.45-51
• /
• 2008

The purpose of this study is to examine the effect of nozzle shape on the performance and internal flow of a cross-flow hydro turbine. CFD analysis for three kinds of nozzle shape is conducted to simulate the effect of nozzle shape. The results reveal that relatively narrow nozzle width is effective to increase the turbine efficiency and output power. Almost output power is achieved at Stage 1. Therefore, optimum design of the nozzle shape is necessary to improve the turbine performance. Recirculation flow in the runner passage decreases the turbine efficiency and output power because the flow make hydraulic loss and collision loss in the region. Air should be put into the runner passage and the recirculating flow should be suppressed by the air layer in the runner.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.25 no.11
• /
• pp.1640-1649
• /
• 2001

The present study investigates the effects of various rib arrangements on heat/mass transfer in the cooling passage of gas turbine blades. A complex flow structure occurs in the cooling passage with rib turbulators which promote heat transfer on the wall. It is important to increase not only the heat transfer rates but also the uniformity of heat transfer in the cooling passage. A numerical computation is performed using a commercial code to calculate the flow structures and experiments are conducted to measure heat/mass transfer coefficients using a naphthalene sublimation technique. A square channel (50 mm $\times$ 50 mm) with rectangular ribs (4 mm $\times$ 5 mm) is used fur the stationary duct test. The experiments focus on the effects of rib arrangements and gap positions in the discrete ribs on the heat/mass transfer on the duct wall. The rib angle of attack is 60°and the rib-to-rib pitch is 32 mm, that is 8 times of the rib height. With the inclined rib angle of attack (60°), the parallel rib arrangements make a pair of counter rotating secondary flows in the cross section, but the cross rib arrangements make a single large secondary flow including a small secondary vortex. These secondary flow patterns affect significantly the heat/mass transfer on the ribbed wall. The heat/mass transfer in the parallel arrangements is 1.5 ∼2 times higher than that in the cross arrangements. However, the shifted rib arrangements change little the heat/mass transfer from the inline rib arrangements. The gap position in the discrete rib affects significantly the heat/mass transfer because a strong flow acceleration occurs locally through the gap.

• Magazine of korean Tunnelling and Underground Space Association
• /
• v.26 no.1
• /
• pp.46-62
• /
• 2024

• Transactions of the Korean Society of Automotive Engineers
• /
• v.3 no.5
• /
• pp.17-23
• /
• 1995

A numerical analysis on engine coolant is made by the use of FVM based general purpose 3 dimensional Navier-Stokes solver, TURB-3D. Numerical solutions are verified by comparison with the experimental data of Lotus model. The results show a good qualitative as well as quantitative comparison. Coolant flow rate control is attempted through adjusting the cross section area of passage base on the results of an original coolant passage. It is concluded from the results that the flow rate control is possible as attempted, and thus can be used in the real engine design.

• Journal of ILASS-Korea
• /
• v.10 no.2
• /
• pp.1-9
• /
• 2005

An experimental study was carried out to obtain the fundamental data about the effects of radical ignition on premixture combustion. A CVC(constant volume combustor) divided into the sub-chamber and the main chamber was used. Numerous narrow passage holes are arranged between the main chamber and the sub-chamber. The products including radicals generated by spark ignition in tile sub-chamber derives the simultaneous multi-point ignition in the main chamber. We have examined the effects of the sub-chamber volume, the diameter and number of passage holes, and the equivalence $ratio({\Phi})$ on the combustion characteristics by means of burning pressure measurement and flame visualization. In a CVC, the overall burning time including the ignition delay became very short and the maximum burning pressure was slightly increased by the radical ignition(RI) method in comparison with those by the conventional spark ignition(SI) method. Combustible lean limit by RI method is extended by ${\Phi}=0.25$ compared with that by SI method. Also, In cases of charging the number and the diameter for the fixed total cross section of the passage holes, combustion period increased significantly at a sub-chamber with a single hole, but those of the other conditions had almost a similar tendency in the sub-chamber with 4 or more holes. regardless of equivalence ratio. Therefore, it was Proved that a critical cross section exists with the number of passage holes.

• The KSFM Journal of Fluid Machinery
• /
• v.11 no.3
• /
• pp.30-35
• /
• 2008

The purpose of this study is to examine the effect of nozzle shapes on the performance and internal flow characteristics of a cross-flow type hydro turbine for wave power generation. The performance of the turbine is calculated with the variation of rotational speed for 4 types of the nozzle shape using a commercial CFD code. The results show that nozzle shape should be designed considering available head of the turbine. Best efficiencies of the turbine by 4 types of the nozzle shape do not change largely but overall performances varies mainly by the nozzle width. The output power of the cross-flow type hydro turbine changes considerably by the nozzle shape and a partial region of stage 2 in the runner blade passage produces maximum regional output power in comparison with the other runner blade passage areas.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.26 no.9
• /
• pp.1249-1259
• /
• 2002

The present study investigates the convective heat/mass transfer inside a cooling passage of rotating gas-turbine blades. The rotating duct has various configurations made of ribs with 70。 attack angle, which are attached on leading and trailing surfaces. A naphthalene sublimation technique is employed to determine detailed local heat transfer coefficients using the heat and mass transfer analogy. The present experiments employ two-surface heating conditions in the rotating duct because the surfaces, exposed to hot gas stream, are pressure and suction side surfaces in the middle passages of an actual gas-turbine blade. In the stationary conditions, the parallel rib arrangement presents higher heat/mass transfer characteristics in the first pass, however, these characteristics disappear in the second pass due to the turning effects. In the rotating conditions, the cross rib present less heat/mass transfer discrepancy between the leading and the trailing surfaces in the first pass. In the second pass, the heat/mass transfer characteristics are much more complex due to the combined effects of the angled ribs, the sharp fuming and the rotation.

• Proceedings of the KSME Conference
• /
• 2001.11b
• /
• pp.22-29
• /
• 2001

The present study investigates the effects of various rib arrangements and rotating on heat/mass transfer in the cooling passage of gas turbine blades. The cooling passage has very complex flow structure, because of the rib turbulator and rotating effect. Experiments and numerical calculation are conducted to investigate the complex flow structures and heat transfer characteristics; the numerical computation is performed using a commercial code, FLUENT ver.5, to calculate the flow structures and the experiments are conducted to measure heat/mass transfer coefficients using a naphthalene sublimation technique. For the rotating duct tests, the test duct, which is the cross section of is $20mm\times40mm$ (the hydraulic diameter, $D_h$, of 26.7 mm, has two-pass with $180^{\circ}$ turning and the rectangular ribs on the wall. The rib angle of attack is $70^{\circ}$ and the maximum radius of rotation is $21.63D_h$. The partition wall has 10 mm thickness, which is 0.5 times to the channel width, and the distance between the tip of the partition wall and the outer wall of the turning region is 26.7 mm $(1D_h)$. The turning effect of duct flow makes the very complex flow structure including Dean type vortex and high turbulence, so that the heat/mass transfer increases in the turning region and at the entrance of the second pass. The Coriolis effect deflects the flow to the trailing surface, resulting in enhancement of the heat/mass transfer on the trailing surface and reduction on the leading surface in the first pass. However, the opposite phenomena are observed in the second pass. The each rib arrangement makes different secondary flow patterns. The complex heat/mass transfer characteristics are observed by the combined effects of the rib arrangements, duct rotation and flow turning.

• Journal of Korean Tunnelling and Underground Space Association
• /
• v.12 no.3
• /
• pp.201-213
• /
• 2010

Recently, plans of tunnel and construction have increased. Unfortunately, the more we have tunnels, the more we have accidents in there. Because an accident or a fire in the tunnel is fatal to user safety, social concerns are focusing on the disaster prevention facilities. Cross passage tunnel is regarded as one of the useful disaster prevention facilities, which is increasing, while there were only few studies about the support system. This study tried to verify whether the support system is appropriate or not with empirical methods-theoretical methods and back analysis using measurement data. Additionally, we also looked into the range of reinforcement in accordance with strength/stress ratio of rock mass.