• Transactions of the Korean Society of Mechanical Engineers B
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• v.28 no.9
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• pp.1005-1014
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• 2004

Experiments were done for the three dimensional unsteady flow in a counter-rotating axial flow fan under peak efficiency operating condition. 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 flow patterns were investigated through the acquired data by the 45$^{\circ}$ inclined hot-wire. Flow characteristics such as tip vortex, secondary flow and tip leakage flow were confirmed through axial, radial and tangential velocity vector plot. It has been found that the radial and tangential velocity components disappeared, while the axial velocity component highly increased as soon as the tip vortex was generated. It has been observed that secondary flow and turbulence intensity which were increased by the front rotor were dissipated passing through the rear rotor. As the result the energy loss of the counter rotating axial flow fan decreased at the downstream of rear rotor. Also, it has been verified that tip vortex pattern of the rear rotor was dampened because the tip vortex generated by front rotor was mixed with that of the rear rotor.

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.1044-1051
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• 1989

A numerical calculation is carried out for the analysis of 3-dimensional compressible flow field in axial-flow rotating blades by using finite element method. The calculation of flow in impellers plays a dominant role in the theoretical research and design of turbomachines. Three-dimensional flow fields can be obtained by the quasi-three-dimensional iterative calculation of the flows both on blade-to-blade stream surfaces and hub-to-shroud stream surfaces with the introduction of viscous loss model in order to consider a loss due to viscosity of fluid. In devising the loss model, four primary sources of losses were identified: (1) blade profile loss (2) end wall loss (3) secondary flow loss (4) tip-leakage loss. For the consideration of an axially parabolic distribution of loss, the results of present calcullation are well agreed with the results by experiment, thus the introduction of loss model is proved to be valid.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.614-617
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• 2008

An unstructured hybrid mesh flow solver has been developed for the simulations of three dimensional steady and unsteady incompressible flow fields. The incompressible Navier-Stokes equations with an artificial compressibility method were discretized by using a node-based finite-volume method. For the unsteady time-accurate computation, a dual-time stepping method was adopted to satisfy a divergence free flow field at each physical time step. The one equation Spalart-Allmaras turbulence model has been adopted to solve the high-Reynolds number flow fields. This method has been applied to calculate the steady flow fields around submarine configurations and unsteady flow fields around a 3-D infinite cylinder.

• Proceedings of the Korea Society for Energy Engineering kosee Conference
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• 1996.10b
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• pp.34-44
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• 1996

N-machine produces more than input energy at above 3000 rpm. any space energy is absorbed when the N-machine is rotating at a very high velocity. Laws of electromagnetics verify that normal conduction is due to that electrons moves from one three-dimensional crystallizing ${\pi}-bonding$ orbital to next. The ${\pi}-far$ infrared rays are generated from the resonance and rotation of the electrons on the orbitals of three-dimensional crystallizing ${\pi}-bonding$ atoms. Material in universe is composed of ${\pi}-rays$, which have alternative outward electric field. If the alternative outward electric fields of the ${\pi}-rays$ are resonant each other they make attraction force, which is the gravity. The collection of space energy is due to a attraction force between the radially alternating electric field and the ${\pi}-far$ infrared rays in the space. Electrons flow by absorbed density difference of ${\pi}-far$ infrared rays along a conduction wire, which also verifies that normal electron conduction is due to a flow from one three-dimensional crystallizing ${\pi}-bonding$ orbital to next.

• Transactions of the Korean Society of Mechanical Engineers
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• v.12 no.6
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• pp.1407-1414
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• 1988

Deviation angles are predicted by numerical calculation of three-dimensional compressible flow through the rotating blade row in axial flow compressor. Three-dimensional flow fields are analyzed by the quasi three-dimensional combination of blade-to blade surfaces and hub-to shroud stream surfaces and calculated by the finite element method in the cyclic calculation of both stream surfaces. In the blade-to blade calculations the method of boundary stream line correction is used and in the hub-to shroud calculations the loss effects due to viscous flow are included. The computational results are compared with the available experimental one. It is shown that the computational results from blade-to-blade flow calculation are correct for incompressible, compressible low subsonic and high subsonic flow at the inlet, and the loss effects on the deviation angle can be neglected in the range of the subsonic flow less than the critical Mach number for the axisymmetric flow and even for 3-D non-axisymmetric flow with loss. And it is found that the present results are better agreed with the experimental data than Lieblein's one.

• International Journal of Air-Conditioning and Refrigeration
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• v.9 no.2
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• pp.8-18
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• 2001

The direct simulation Monte Carlo Method is applied to investigate the two-dimensional flow fields of a turbomolecular pump(TMP) in both molecular and transition flow regions. The pumping characteristics of the TMP are investigated for a wide range of the Knudsen number. The maximum of compression ratio and of pumping speed strongly depend on the Knudsen number in transition region, while they weakly depend on the Knudsen number in free molecular flow region. The present numerical results show good agreement with the previously known experimental data. Finally. the results of the single blade row in both molecular and transition regions are used to predict the overall performance of a TMP, which has three kinds of blade with 24-rows.

• The KSFM Journal of Fluid Machinery
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• v.15 no.5
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• pp.48-53
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• 2012

This paper presents a systematic procedure for three-dimensional noise analysis of an axial-flow fan by using computational aero-acoustics based on Ffowcs Williams-Hawkings equation. Flow-fields of a basic fan model are simulated by solving three-dimensional, unsteady, Reynolds-averaged Navier-Stokes equations using the commercial code ANSYS CFX 11.0. Starting with steady flow results, unsteady flow analysis is performed to extract the fluctuating pressures in the time domain at specified local points on the blade surface of the axial flow fan. The perturbed density wave by rotating blades reaches at the observer position, which is simulated by an in-house noise prediction software based on Ffowcs Williams-Hawkings equation. The detailed far-field noise signatures from the axial-flow fan are analyzed in terms of source types, field characteristics, and interpolation schemes.

• Journal of Mechanical Science and Technology
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• v.15 no.7
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• pp.906-920
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• 2001

This paper presents three-dimensional mean velocities, turbulent intensities and Reynolds shear stresses measured in the Y-Z plane of the gas swirl burner with a cone type baffle plate by using an X-type hot-wire probe. This experiments is carried out at the flow rate of 450ℓ/min which is equivalent to the combustion air flow rate necessary to heat release 15,000 kcal/hr in a gas furnace. Mean velocities and turbulent intensities etc. show that their maximum values exist around the narrow slits situated radially on the edge of and in front of a burner. According to downstream regions, they have a peculiar shape like a starfish because the flows going out of the narrow slits and the swirl vanes of an inclined baffle plate diffuse and develop into inward and outward of a burner. The rotational flow due to the inclined flow velocity going out of swirl vanes of a cone type baffle plate seems to decrease the magnitudes of mean velocities V and W respectively by about 30% smaller than those of mean velocity U. The turbulent intensities have large values of 50%∼210% within the range of 0.5

• Nuclear Engineering and Technology
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• v.54 no.1
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• pp.97-109
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• 2022

Multi-dimensional coupling analysis is a research hot spot in nuclear reactor thermal hydraulic study and both the full-scale system transient response and local key three-dimensional thermal hydraulic phenomenon could be obtained simultaneously, which can achieve the balance between efficiency and accuracy in the numerical simulation of nuclear reactor. A one-dimensional to three-dimensional (1D-3D) coupling platform for the nuclear reactor multi-dimensional analysis is developed by XJTU-NuTheL (Nuclear Thermal-hydraulic Laboratory at Xi'an Jiaotong University) based on the CFD code Fluent and system code RELAP5 through the Dynamic Link Library (DLL) technology and Fluent user-defined functions (UDF). In this paper, the International Standard Problem (ISP) No. 43 is selected as the benchmark and the rapid boron dilution transient in the nuclear reactor is studied with the coupling code. The code validation is conducted first and the numerical simulation results show good agreement with the experimental data. The three-dimensional flow and temperature fields in the downcomer are analyzed in detail during the transient scenarios. The strong reverse flow is observed beneath the inlet cold leg, causing the de-borated water slug to mainly diffuse in the circumferential direction. The deviations between the experimental data and the transients predicted by the coupling code are also discussed.

• Journal of computational fluids engineering
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• v.10 no.1
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• pp.45-50
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• 2005

A fundamental understanding of the flow around the wind turbine is important to investigate the performance of new type of wind turbine. This study presents the simulation of three dimensional flow fields around the Darius wind turbine as an example. Incompressible Navier-Stokes equations are used for this simulation. The rotating coordinate system that rotates in the same speed of the turbine is used in order to simplify the boundary condition on the blades. Additionally, the boundary fitted coordinate system is employed in order to express the shape of the blades precisely. Fractional step method is used to solve the basic equations. Third order upwind scheme is chosen for the approximation of the non-linear terms since it can compute the flow field stably even at high Reynolds number without any turbulence models. The flow fields obtained in this study are highly complex due to the three dimensionality and are visualized effectively by using the technique of the computer graphics.