• International Journal of Fluid Machinery and Systems
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• v.4 no.3
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• pp.349-359
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• 2011

An unsteady numerical analysis has been carried out to study the strong impeller volute interaction of a centrifugal pump with six backward swept blades shrouded impeller. The numerical analysis is done by solving the three-dimensional Reynolds Averaged Navier-Stokes codes with standard k-${\varepsilon}$ two-equations turbulence model and wall regions are modeled with a scalable log-law wall function. The flow within the impeller passage is very smooth and following the curvature of the blade in stream-wise direction. However, the analysis shows that there is a recirculation zone near the leading edge even at design point. When the flow is discharged into volute casing circumferentially from the impeller outlet, the high velocity flow is severely distorted and formed a spiraling vortex flow within the volute casing. A spatial and temporal wake flow core development is captured dynamically and shows how the wake core diffuses. Near volute tongue region, the impeller/volute tongue strong interaction is observed based on the periodically fluctuating pressure at outlet. The results of existing analysis also proved that the pressure fluctuation periodically is due to the position of impeller blade relative to tongue.

• Polymer(Korea)
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• v.38 no.4
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• pp.449-456
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• 2014

Ternary blends of poly(L-lactic acid) (PLLA), poly(${\varepsilon}$-caprolactone) (PCL) and polyethylene oxide (PEO) were produced with different concentrations of components via melt blending. By leaching the PEO from the samples by water, porous materials were obtained with potential application for bio scaffolds. Sample porosity was evaluated by calculating the ratio of porous scaffold density (${\rho}^*$) to the non-porous material density (${\rho}_s$). Highest porosity (51.42%) was related to the samples containing 50 wt%. of PEO. Scanning electron microscopy (SEM) studies showed the best porosity resulted by decreasing PLLA/PCL ratio at constant concentration of PEO. Crystallization behavior of the ternary blend samples was studied using differential scanning calorimetry (DSC). Results revealed that the crystallinity of PLLA was improved by addition of PEO and PCL to the samples. The porosity plays a key role in governing the compression properties. Mechanical properties are presented by Gibson-Ashby model.

• The KSFM Journal of Fluid Machinery
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• v.19 no.5
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• pp.42-49
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• 2016

Aerodynamic analysis of a low-voltage electric motor has been performed with various inlet vent shapes. Effects of inlet vent shape on aerodynamic performance of a motor cooling fan have been investigated numerically using three-dimensional Reynolds-averaged Navier-Stokes equations. The k-${\varepsilon}$ turbulence model was used for the analysis of turbulence. The finite volume method and unstructured tetrahedral grids were used in the numerical analysis. Optimal grid system in the computational domain was selected through a grid-dependency test. From the results of the flow analysis, considerable energy loss by flow separation was observed in the flow passage. It was found that mass flow rate through the cooling fan in the low-voltage motor can be increased by modifying the inlet vent shape. And, some inlet vent shapes were suggested to improve the aerodynamic performance of the motor cooling fan.

• Journal of Ocean Engineering and Technology
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• v.24 no.4
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• pp.38-46
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• 2010

The wall thinning phenomenon of pipes was simulated as metal loss due to erosion and corrosion. Such wall thinning defects in the pipes of power plants are a very important safety consideration. In this study, we analyzed wall thinning defects that occurred by weld bead of weld zone of boost pump recirculation pipe. From the results of the analysis of pipe failures, numerical analysis was performed by Fluent v6.3.26 using the standard k-$\varepsilon$ model of the weld bead shape, such as an elliptical or a spherical shape, on the inner wall of the pipe. Using the results obtained, we showed the overlap effect by cavitations corrosion and erosion-corrosion at the bottom of the wall-thinning defect.

• Wind and Structures
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• v.11 no.6
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• pp.479-496
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• 2008

In this paper, computer simulation of wind flow around a single cooling tower with louver support at the base in the KAZERUN power station in south part of IRAN is presented as a case study. ANSYS FLOTRAN, an unstructured finite element incompressible flow solver, is used for numerical investigation of wind induced pressure load on a single cooling tower. Since the effects of the wind ribs on external surface of the cooling tower shell which plays important role in formation of turbulent flow field, an innovative relation is introduced for modeling the effects of wind ribs on computation of wind pressure on cooling tower's shell. The introduced relation which follows the concept of equivalent sand roughness for the wall function is used in conjunction with two equations ${\kappa}-{\varepsilon}$ turbulent model. In this work, the effects of variation in the height/spacing ratio of external wind ribs are numerically investigated. Conclusions are made by comparison between computed pressure loads on external surface of cooling tower and the VGB (German guideline for cooling tower design) suggestions.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.520-524
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• 2000

A ejector system is one of the fluid machinery, which has been mainly used as an exhaust pump or a vacuum pump. The ejector system has often been pointed out to have only a limited efficiency because it is driven by pure shear action and the mixing action between primary and secondary streams. In the present work, numerical simulations were conducted to investigate the effects of the geometry and the mass flow ratio of supersonic ejector-diffuser systems on their mixing performance. A fully implicit finite volume scheme was applied to solve the axisymmetric Navier-Stokes equations, and the standard ${\kappa}-{\varepsilon}$ turbulence model was used to close the governing equations. The flow fields of the supersonic ejector-diffuser systems were investigated by changing the ejector throat area ratio and the mass flow ratio. The existence of the second throat strongly affected the shock wave structure inside the mixing tube as well as the spreading of the under-expanded jet discharging from the primary nozzle, and served to enhance the mixing performance.

• International Journal of Fluid Machinery and Systems
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• v.4 no.1
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• pp.199-208
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• 2011

This work presents numerical results, using OpenFOAM, of the flow in the swirl flow generator test rig developed at Politehnica University of Timisoara, Romania. The work shows results computed by solving the unsteady Reynolds Averaged Navier Stokes equations. The unsteady method couples the rotating and stationary parts using a sliding grid interface based on a GGI formulation. Turbulence is modeled using the standard k-${\varepsilon}$ model, and block structured wall function ICEM-Hexa meshes are used. The numerical results are validated against experimental LDV results, and against design velocity profiles. The investigation shows that OpenFOAM gives results that are comparable to the experimental and design profiles. The unsteady pressure fluctuations at four different positions in the draft tube is recorded. A Fourier analysis of the numerical results is compared whit that of the experimental values. The amplitude and frequency predicted by the numerical simulation are comparable to those given by the experimental results, though slightly over estimated.

• Journal of computational fluids engineering
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• v.17 no.4
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• pp.81-86
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• 2012

The objective of the present study is to investigate the effects of various turbulence models on the aerodynamic noise of an air-conditioner (AC) indoor unit. The results from URANS (unsteady Reynolds-averaged Navier-Stokes) simulations with the standard k-$\varepsilon$, k-$\omega$ shear stress transport (SST) and Spalart-Allmaras (S-A) turbulence models were analyzed and compared with the noise data from the experiments. The frequency spectra of the far-field acoustic pressure were computed using the Farrasat equation derived from the Ffowcs Williams-Hawkings (FW-H) equation based on the acoustic analogy model. Two fixed fan casings and the rotating cross-flow fan were used as the source surfaces of the dipole noise in the Farrasat equation. The result with the standard k-$\epsilon$ model showed a much better agreement with the experimental data compared to the k-w SST and S-A models. The differences in the pressure spectra from the different turbulence models were discussed based on the instantaneous vorticity fields. It was found that the over-estimated power spectra with the k-w SST and S-A models are related to the emphasized small-scale vortices produced with these models.

• Korean Journal of Agricultural Science
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• v.33 no.1
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• pp.85-95
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• 2006

A model experiment has been performed to get the heat transfer coefficient on the soil surface in the closed ecosystem. The heat flux on the soil surface was measured and the heat transfer coefficient was derived in the following two cases with 5-stepped control of inside air current speed. One case was that heat flowed from air to soil and the other case was that heat flowed from soil to air. Three dimensional CFD model has been set to simulate thermal environment in the closed ecosystem including soil layers. The standard $k-{\varepsilon}$ model of the CFD program was chosen for turbulence model and heating wire buried in the soil layers was set as heat source option to simulate the case when the temperature of soil surface was higher than that of inside air in the closed ecosystem. Between one case that heat flowed from air to soil and the other case that heat flowed from soil to air, there were big differences in the temperature distribution of soil layers and the heat transfer coefficient of the soil surface. The increasing rate of heat transfer coefficient on each case according to the increase of inside air current speed was similar to each other and it respectively increased linearly. But the heat transfer coefficient on the case that heat flowed from soil to air was much bigger than that of the other case. The model was validated by comparing simulated values of CFD model with measured values of the model experiment. Simulated and measured temperature of inside air and soil layers, and heat transfer coefficient of the soil surface were well accorded and the range of corrected $R^2$ was 0.664 to 0.875. The developed CFD model was well simulated in parts of the temperature of inside air and soil layers, the distribution of the inside air current speed, and heat transfer coefficient of the soil surface were able to be quantitatively analyzed by using this model. Therefore, the model would be applied and used for analysis of heat transfer coefficient between air and surface in various agricultural facilities.

• Journal of the Society of Naval Architects of Korea
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• v.49 no.3
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• pp.247-253
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• 2012

Dam-break flows, a type of very shallow gravity-driven flow, are substantially influenced by resistance forces due to viscous friction and turbulence. Assuming turbulent flow, the main focus of this study is to validate the increase of drag forces caused by surface roughness and especially turbulence intensity. A Reynolds Averaged Navier-Stokes(RANS) approach with the standard k-${\varepsilon}$ turbulence model is used for this study, where the free surface motion is captured by using a volume of fluid(VOF) method. Surface roughness effects are considered through the law of the wall modified for roughness, while the initial turbulence intensity which determines the lowest level of turbulence in the flow domain of interest is used for the variation of turbulence intensity. It has been found that the numerical results at higher turbulence intensities show a reasonably good agreement with the physical aspects shown by two different dam-break experiments without and with the impact of water.