• Journal of the Society of Naval Architects of Korea
• /
• v.44 no.1 s.151
• /
• pp.8-15
• /
• 2007

In this paper, numerical calculations are performed to analyze the unsteady flow of NACA airfoil sections. In order to ease the flow computation for the fluid region changing in time, improve the quality of solution and simplify the grid generation for the oscillating foil flow, the computational method adopts a moving and deforming mesh with the multi-block grid topology. The multi-block, structured-unstructured hybrid grid is generated using the commercial meshing software Gridgen V15. The MDM (Moving & Deforming Mesh) and the UDF (User Define function) function of FLUENT 6 are adopted for computing turbulent flows of the foil in pitching motion. Computed unsteady lift and drag forces are compared with experimental data. in general, the characteristics of unsteady lift and drag of the experiments are reproduced well in the numerical analysis.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.24 no.3
• /
• pp.247-255
• /
• 2012

Numerical calculations are carried out for the natural convection in a square enclosure with two hot cylinders induced by temperature difference between a cold outer rectangular cylinder and two hot circular cylinders. A two-dimensional solution for unsteady natural convection is obtained, using the immersed boundary method (IBM) to model two inner circular cylinders based on finite volume method, for different Rayleigh numbers varying over the range of $10^3$ to $10^5$. The study goes further to investigate the effect of the location of two cylinders on the heat transfer and fluid flow. The location of inner circular cylinders is changed vertically along the center-line of square enclosure. The changes of heat transfer quantities have been presented.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.27 no.8
• /
• pp.1071-1080
• /
• 2003

A national standard system was developed in order to calibrate and test the oil flowmeters for the petroleum field. A stop valve and a gyroscopic weighing scale were employed for the primary standard of the flow quantity. It is operated by the standing start and finish mode and the static weighing method. The model equation for uncertainty evaluation was based on the calibration principle of standard system. The sources of the uncertainties were quantified and combined according to the GUM(Guide to the Expression of Uncertainty in Measurement). It was found that the standard system had the relative expanded uncertainty of 0.04 % in the range of 18 - 350 ㎥/ｈ. According to the uncertainty budget, the uncertainties of the fluid density and the volume of pipeline, which were temperature dependent, contributed 92% of final uncertainty in the oil flow standard system.

• 유체기계공업학회:학술대회논문집
• /
• 2002.12a
• /
• pp.337-345
• /
• 2002

The present study addresses a computational result of unsteady gas flow through a critical nozzle. The axisymmetric, unsteady, compressible, Wavier-Stokes equations are solved using a finite volume method that makes use of the second order upwind scheme for spatial derivatives and the multi-stage Runge-Kutta integral scheme for time derivatives. The steady solutions of the governing equation system are validated with the previous experimental data to ensure that the present computational method is valid to predict the critical nozzle flows. In order to simulate the effects of back pressure fluctuations on the critical nozzle flows, an excited pressure oscillation with an amplitude and frequency is assumed downstream of the exit of the critical nozzle. The results obtained show that for low Reynolds numbers, the unsteady effects of the pressure fluctuations can propagate upstream of the throat of critical nozzle, and thus giving rise to the applicable fluctuations in mass flow rate through the critical nozzle, while for high Reynolds numbers, the pressure signals occurring at the exit of the critical nozzle do not propagate upstream beyond the nozzle throat. For very low Reynolds number, it is found that the sonic line near the throat of the critical nozzle remarkably fluctuateswith time, providing an important mechanism for pressure signals to propagate upstream of the nozzle throat, even in choked flow conditions. The present study is the first investigation to clarify the unsteady effects on the critical nozzle flows.

• Journal of computational fluids engineering
• /
• v.20 no.2
• /
• pp.96-102
• /
• 2015

In this study, the green water phenomena on rectangular shaped structure is numerically simulated by STAR-CCM+ to investigate the flow pattern including the velocity profiles in bubbly water flow. 5 phases of the formation of green water in front of and over the rectangular shaped structure is simulated at the design condition which is scaled down by 1:125 from FPSO operating in GOM. All numerical results are compared with the experimental results performed in a two dimensional wave flume. The water deformation due to the green water are obtained by the high speed CCD camera with employing the shadow graphy technique, which is allowed to take the bubbly water flow into images. A series of image taken by shadow graphy technique is analyzed with MQD method to calculate the velocity in bubbly water flow.

• Advances in aircraft and spacecraft science
• /
• v.3 no.4
• /
• pp.367-378
• /
• 2016

Thrust Vectoring is a dynamic feature that offers many benefits in terms of maneuverability and control effectiveness. Thrust vectoring capabilities make the satisfaction of take-off and landing requirements easier. Moreover, it can be a valuable control effector at low dynamic pressures, where traditional aerodynamic controls are less effective. A numerical investigation of Fluidic Thrust Vectoring (FTV) is completed to evaluate the use of fluidic injection to manipulate flow separation and cause thrust vectoring of the primary jet thrust. The methodology presented is general and can be used to study different techniques of fluidic thrust vectoring like shock-vector control, sonic-plane skewing and counterflow methods. For validation purposes the method will focus on the dual-throat nozzle concept. Internal nozzle performances and thrust vector angles were computed for several range of nozzle pressure ratios and fluidic injection flow rate. The numerical results obtained are compared with the analogues experimental data reported in the scientific literature. The model is integrated using a finite volume discretization of the compressible URANS equations coupled with a Spalart-Allmaras turbulence model. Second order accuracy in space and time is achieved using an ENO scheme.

• Wind and Structures
• /
• v.13 no.6
• /
• pp.519-528
• /
• 2010

A meteorological model, RAMS, and a commercial computational fluid dynamics (CFD) model, FLUENT are combined as a one-way off-line nested modeling system, namely, RAMS/FLUENT system. The system is experimentally applied in the wind simulation over a complex terrain, with which numerical simulations of wind field over Foyeding weather station located in the northwest mountainous area of Beijing metropolis are performed. The results show that the method of combining a meteorological model and a CFD model as a modeling system is reasonable. In RAMS/FLUENT system, more realistic boundary conditions are provided for FLUENT rather than idealized vertical wind profiles, and the finite volume method (FVM) of FLUENT ensures the capability of the modeling system on describing complex terrain in the simulation. Thus, RAMS/FLUENT can provide fine-scale realistic wind data over complex terrains.

• Journal of Korea Water Resources Association
• /
• v.36 no.5
• /
• pp.741-749
• /
• 2003

This study presents a combined experimental and numerical effort to investigate experimentally and numerically the Bragg reflection of sinusoidal waves due to trapezoidal submerged porous breakwaters. Numerical predictions of the study are verified by comparing to laboratory measurements. In the numerical model, the flow in porous structures is described by the spatially averaged Navier-Stokes equations and the volume of fluid method is employed to track the free surface displacements. Numerical solutions are agree well with laboratory measurements. The reflection coefficients of porous structures are smaller than those of non-porous structures and become stronger in proportion to the increase of number of submerged breakwaters.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.30 no.9 s.252
• /
• pp.834-841
• /
• 2006

In the present wort the Laser-induced Fluorescence (LIF) technique and Confocal Laser Scanning Microscopy (CLSM) have been combined to measure the temperature distribution across a micro-scale liquid layer as a direct and non-invasive method. Only the fluorescent light emitted from a very thin volume around a focal plane can be selectively detected, and it enables us to measure the liquid temperatures even at the close vicinity of the walls. As an experimental verification, a test section consists of two flat plates (for heating and cooling, respectively) separated by about 240 microns was made, and the methanol mixed with a temperature-sensitive dye, Rhodamine B, was filled in the gap between them. The measured temperature distribution across the gap showed good linearity, which is a typical characteristic of conduction heat transfer through a thin liquid layer. In result, the CLSM-LIF technique proposed in the present study was found to be a promising method to measure the local temperatures in the liquid flow field in microfluidic devices.

• Journal of Chest Surgery
• /
• v.33 no.5
• /
• pp.398-406
• /
• 2000

Background: Cardiac atrium is an endocrine gland secreting a family of natriuretic peptides. The secretion of atrial natriuretic peptide(ANP) had been shown to be controlled by variable factors. The change in atrial dynamics have been considered as one of the most prominent stimuli for the stimulation of ANP secretion. Hypoxic stress has been shown to increase cardiac ANP secretion. However, the mechanism by which hypoxia increases ANP secretion cardiac ANP secretions. However, the mechanism by which hypoxia increases ANP secretion has not to be defined. Therefore, the purpose of the present study was tow-fold: to develop a protocol to defined the effect of hypoxia on ANP secretion in perfused beating rabbit atria and to clarify the mechanism responsible for the accentuation by hypoxia of ANP secretion. Material and Method: Experiments have been done in perfused beating rabbit atria. ANP was measured by radioimmunoassay. Result: Hypoxic stimulus with nitrogen decreased atrial stroke volume. The decrease in atrial stroke volume recovered basal level during the period of recovery with oxygen. ANP secretion and the concentration of perfusate ANP in terms of extracellular fluid(ECF) translocation which reflects the rate of myocytic release of ANP were increased by hypoxia and returned to basal levels during the recovery. Changes in ECF translocation paralleled by hypoxia and returned to basal levels during the recovery. Changes in ECF translocation paralleled to that of atrial stroke volume. At the start of recovery in atrial storke volume, ECF tranalocation incrased for several minutes. The above responses were stable and reproducible. Glibenclamide treatment prevented the recovery in atrial stroke volume. Increments by hypoxia of ANP secretion and ANP concentration were suppressed by glibenclamide. Conclusion: These results indicate that hypoxia incrased atrial myocytic ANP release and that the mechanism responsible for the accentuation is partially related to the change in K+ATP channel activity.