• Journal of the Semiconductor & Display Technology
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• v.7 no.3
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• pp.55-58
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• 2008

The objective of this research is to design, manufacture and test a mass flow controller capable of measuring compressible as well as incompressible fluid flows based on a 'bucket and stop-watch' method. The basic principle behind such a system is the measurement of time, where the time taken to fill and empty a bucket of known volume is measured. This device should be able to handle fluid flows in the range of 0.1 ml/min to 10 ml/min within an accuracy of ${\pm}$1%. For the flow meter to be able to compete with established designs, it must be not only comparable in cost and robustness, but also very accurate and reliable as well.

• The KSFM Journal of Fluid Machinery
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• v.6 no.3 s.20
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• pp.58-63
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• 2003

The performance of turbo pump drops rapidly and it gets into break-down when the void fraction reaches above the threshold value because the impeller flow passage is choked up with air bubbles. Phenomenological understanding of break-down and pumping recovery mechanisms under air-water two-phase flow conditions are therefore important for pump designers and essential assignment for researchers. In this paper, we investigated the characteristics of break-down and pumping recovery due to entrained air occurring inside a screw-type centrifugal pump which has a wide flow passage mainly through the findings of suction and discharge pressures, rotational speed, flow rate measurements and visualization.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.1
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• pp.13-19
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• 1995

An experimental investigation has been made for flow in a circular cylinder with a rotating bottom disk. Flow system considered in this paper is a characteristic model of interior flows of an electric washing machine. Flows in a tub of an electric washing machine are driven by a rotating bottom disk called a pulsator. The simple and characteristic model was composed of a circular cylinder with impulsively rotating endwall disk and a viscous fluid in it. Rotational motion of the pulsator is periodic and alternative in rotation direction. The flow field in the interior region is governed by a horizontal boundary layer forms on the impulsively rotating disk. Experimental approach was accomplished by adopting an image processing technique for velocity measurements. Comprehensive details of the flow structure are presented. Also a meridional circulation is obtained by tracking image particles suspended in the fluid. Flow structure and data are successfully procured for this complex rotating flow field.

• Wind and Structures
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• v.4 no.4
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• pp.279-298
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• 2001

The greatest suction on the cladding of flat roof low-rise buildings is known to occur beneath the conical vortices that form along the roof edges for cornering winds. In a companion paper, a model of the vortex flow mechanism has been developed which can be used to connect the surface pressure beneath the vortex to adjacent flow conditions. The flow model is experimentally validated in this paper using simultaneous velocity and surface pressure measurement on a 1 : 50 model of the Texas Tech University experimental building in a wind tunnel simulated atmospheric boundary layer. Flow visualization gives further insight into the nature of peak suction events. The flow model is shown to account for the increase in suction towards the roof corner as well as the presence of the highest suction at wind angles of $60^{\circ}$. It includes a parameter describing vortex suction strength, which is shown to be related to the nature of the reattachment, and also suggests how different components of upstream turbulence could influence the surface pressure.

• International Journal of Fluid Machinery and Systems
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• v.9 no.1
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• pp.66-74
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• 2016

Concerning the numerical simulation of high-speed water jet with intensive cavitation this paper presents a practical compressible mixture flow method by coupling a simplified estimation of bubble cavitation and a compressible mixture flow computation. The mean flow of two-phase mixture is calculated by URANS for compressible fluid. The intensity of cavitation in a local field is evaluated by the volume fraction of gas phase varying with the mean flow, and the effect of cavitation on the flow turbulence is considered by applying a density correction to the evaluation of eddy viscosity. High-speed submerged water jets issuing from a sheathed sharp-edge orifice nozzle are treated when the cavitation number, ${\sigma}=0.1$, and the computation result is compared with experimental data The result reveals that cavitation occurs initially at the entrance of orifice and bubble cloud develops gradually while flowing downstream along the shear layer. Developed bubble cloud breaks up and then sheds downstream periodically near the sheath exit. The pattern of cavitation cloud shedding evaluated by simulation agrees experimental one, and the possibility to capture the unsteadily shedding of cavitation clouds is demonstrated. The decay of core velocity in cavitating jet is delayed greatly compared to that in no-activation jet, and the effect of the nozzle sheath is demonstrated.

• Particle and aerosol research
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• v.9 no.2
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• pp.103-110
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• 2013

The electrostatic precipitator (ESP) has been used for degrading atmospheric pollutants. These devices induce the electrical forces to facilitate the removal of particulate pollutants. The ions travel from the high voltage electrode to the grounded electrode by Coulomb force induced by the electric field when a high voltage is applied between two electrodes. The ions collide with gas molecules and exchange momentum with each other thus inducing fluid motion, electrohydrodynamic (EHD) flow. In this study, for the simulation of electric field and EHD flow in ESPs, an open source EHD solver, "espFoam", has been developed using open source CFD toolbox, OpenFOAM(R) (Open Field Operation and Manipulation). The electric potential distribution and ionic space charge density distribution were obtained with the developed solver, and validated with experimental results in the literature. The comparison results showed good agreement. Turbulence model is also incorporated to simulate turbulent flow; hence the developed solver can analyze laminar and turbulent flow. In distributions of electric potential and space charge, the distributions become distorted and asymmetric as the flow velocity increases. The effect of electrical drift flow was investigated for different flow velocities and the secondary flow in a flow of low velocity is successfully predicted.

• Proceedings of the KSME Conference
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• 2001.06e
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• pp.582-587
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• 2001

A numerical method using FLUENT code was employed to investigate fluid drag and lift forces on a cylinder in a group of circular cylinders, subjected to a uniform cross flow. The cylinders can be arranged in tandem or in a staggered arrangements relative to the free stream flow. A vortex street behind the cylinder pairs or jets between the cylinders forms according to the arrangements. Vibration on a cylinder can occurs due to vortex shedding, fluid-elastic stiffness and wake galloping. The flow is first investigated and then the forces acting on the cylinder are calculated. The lift and drag forces on an elastically mounted cylinder in the wake of an upstream fixed cylinder arise from the mean flow plus velocity and pressure gradients in the wake. The analytical results of two staggered cylinder were compared with the existing experimental ones for validation of the present method. The analytical results of the forces were in good agreement with the experimental ones. The present method can be used for the analysis of the fluid induced vibration where the group of circular cylinders are subjected to a cross flow.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.24 no.9
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• pp.1227-1238
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• 2000

This study examines the effects of the discretization schemes on numerical solutions of viscoelastic fluid flows. For this purpose, a temporally evolving mixing layer, a two-dimensional vortex pair interacting with a wall, and a turbulent channel flow are selected as the test cases. We adopt a fourth-order compact scheme (COM4) for polymeric stress derivatives in the momentum equations. For convective derivatives in the constitutive equations, the first-order upwind difference scheme (UD) and artificial diffusion scheme (AD), which are commonly used in the literature, show most stable and smooth solutions even for highly extensional flows. However, the stress fields are smeared too much and the flow fields are quite different from those obtained by higher-order upwind difference schemes for the same flow parameters. Among higher-order upwind difference schemes, a third-order compact upwind difference scheme (CUD3) shows most stable and accurate solutions. Therefore, a combination of CUD3 for the convective derivatives in the constitutive equations and COM4 for the polymeric stress derivatives in the momentum equations is recommended to be used for numerical simulation of highly extensional flows.

• Journal of Ocean Engineering and Technology
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• v.25 no.2
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• pp.15-20
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• 2011

This study aimed at validating the adopted numerical methods to solve two-phase flow around a two-dimensional (2D) rectangular floating structure in regular waves. A structure with a draft equal to one half of its height was hinged at the center of gravity and free to roll with waves that had the same period as the natural roll period of a rectangular barge. In order to simulate the 2D incompressible viscous two-phase flow in a wave tank with the rectangular barge, the present study used the volume of fluid (VOF) method based on the finite volume method with a standard turbulence model. In addition, the sliding mesh technique was used to handle the motion of the rectangular barge induced by the fluid-structure interaction. Consequently, the present results for the flow field and roll motion of the structure had good agreement with those of the relevant previous experiment.

• Journal of computational fluids engineering
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• v.11 no.3 s.34
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• pp.46-51
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• 2006

This paper presents the numerical results of fluid flow and mixing in a microfluidic device for electro-osmotic flow (EOF) with an trapezoidal electrode array on the bottom wall (ETZEA). Differently from previous EOF in a channel which only transports fluid in colloidal system. ETZEA can also be utilized to mix a target liquid with a reagent. In this study we propose a method of controlling fluid flow and mixing enhancement. To obtain the flow and mixing characteristics, numerical computations are performed by using a commercial code, CFX-10, and a self-made code LBM-D. It was found that the flow near the trapezoidal electrode in the ETZEA is of 3-D complex flows due to the zeta potential difference between the trapezoidal electrode and channel walls, and as a consequence the hetrogeneous zeta potential on the electrodes plays an important role in mixing the liquid.