• International Journal of Fluid Machinery and Systems
• /
• v.4 no.1
• /
• pp.209-216
• /
• 2011

The flow upstream of a centrifugal pump impeller has been investigated by both experimental test and numerical simulation. For experimental study, the flow field at four sections in the pump suction is measured by using PIV method. For calculation, the three dimensional turbulent flow for the full flow passage of the pump is simulated based on RANS equations combined with RNG k-$\varepsilon$ turbulence model. From those results, it is noted that at both design lo ad and quarter load condition, the pre-swirl flow whose direction is the same as the impeller rotation exists at all four sections in suction pipe of the pump, and at each section, the pre-swirl velocity becomes obviously larger at higher rotational speed. It is also indicated that at quarter load condition, the low pressure region at suction surface of the vane is large because of the unfavorable flow upstream of the pump impeller.

• Journal of the Korean Society of Safety
• /
• v.10 no.3
• /
• pp.68-80
• /
• 1995

A series of parametric calculations have been performed in order to investigate the short-term and short-range plume and puff behavior of toxic gaseous and solid pollutant dispersion in an open atmosphere. The simulation is made by the use of the computer program developed by this laboratory, in which a control-volume based finite-difference method is used together with the SIMPLEC algorithm for the resolution of the pressure-velocity coupling appeared In Wavier-Stokes equation. The Reynolds stresses are solved by the standard two-equation k-$\varepsilon$ model modified for buoyancy together with the RNG(Renormalization Group) k-$\varepsilon$ model. The major parameters considered in this calculation are pollutant gas density and temperature, the relative velocity of pollutants to that of the surrounding atmospheric air, and particulate size and density together with the height released. The flow field is typically characterized by the formation of a strong recirculation region for the case of the low density gases such as $CH_4$ and air due to the strong buoyancy, while the flow is simply declining pattern toward the downstream ground for the case of heavy molecule like the $CH_2C1_2$and $CCl_4$, even for the high temperature, $200^{\circ}C$. The effect of gas temperature and velocity on the flow field together with the particle trajectory are presented and discussed in detail. In general, the results are physically acceptable and consistent.

• International Journal of Naval Architecture and Ocean Engineering
• /
• v.11 no.1
• /
• pp.314-328
• /
• 2019

This paper attempts to combine the pneumatic breakwater and submerged breakwater to increase the effectiveness of wave damping for long-period waves. A series of physical experiments concerning pneumatic breakwater, submerged breakwater and their joint breakwater was conducted and used to validate a mathematical model based on Reynolds-averaged Navier-Stokes equations, the RNG $k-{\varepsilon}$ turbulence model and the VOF method. In addition, the mathematical model was used to investigate the wave transmission coefficients of three breakwaters. The nonlinear wave propagation behaviors and the energy transfer from lower frequencies to higher frequencies after the submerged breakwater were investigated in detail. Furthermore, an optimal arrangement between pneumatic breakwater and submerged breakwater was obtained for damping longer-period waves that cannot be damped effectively by the pneumatic breakwater alone. In addition, the reason for the appearance of the combination effect is that part of the energy of the transmitted waves over the submerged breakwater transfers to shorter-period waves. Finally, the impact of the joint breakwater on the wave field during wave propagation process was investigated.

• International Journal of Aeronautical and Space Sciences
• /
• v.17 no.1
• /
• pp.8-19
• /
• 2016

This paper investigates the effects of inlet turbulence conditions and near-wall treatment methods on the heat transfer prediction of gas turbine vanes within the range of engine relevant turbulence conditions. The two near-wall treatment methods, the wall-function and low-Reynolds number method, were combined with the SST and ${\omega}RSM$ turbulence model. Additionally, the RNG $k-{\varepsilon}$, SSG RSM, and $SST_+{\gamma}-Re_{\theta}$ transition model were adopted for the purpose of comparison. All computations were conducted using a commercial CFD code, CFX, considering a three-dimensional, steady, compressible flow. The conjugate heat transfer method was applied to all simulation cases with internally cooled NASA turbine vanes. The CFD results at mid-span were compared with the measured data under different inlet turbulence conditions. In the SST solutions, on the pressure side, both the wall-function and low-Reynolds number method exhibited a reasonable agreement with the measured data. On the suction side, however, both wall-function and low-Reynolds number method failed to predict the variations of heat transfer coefficient and temperature caused by boundary layer flow transition. In the ${\omega}RSM$ results, the wall-function showed reasonable predictions for both the heat transfer coefficient and temperature variations including flow transition onset on suction side, but, low-Reynolds methods did not properly capture the variation of the heat transfer coefficient. The $SST_+{\gamma}-Re_{\theta}$ transition model showed variation of the heat transfer coefficient on the transition regions, but did not capture the proper transition onset location, and was found to be much more sensitive to the inlet turbulence length scale. Overall, the Reynolds stress model and wall function configuration showed the reasonable predictions in presented cases.

• 한국전산유체공학회:학술대회논문집
• /
• 1996.05a
• /
• pp.58-67
• /
• 1996

This paper describes some computational results of various energy and environmental systems using Patankar's SIMPLE method. The specific topics handled in this study are jet bubbling reactor for flue gas desulfurization, cyclone-type afterburner for incineration, 200m tall stack for 500 MW electric power generation, double skin and heat storage systems of building energy saving for the utilization of solar heating, finally turbulent combustion systems with liquid droplet or pulverized coal particle. A control-volume based finite-difference method with the power-law scheme is employed for discretization. The pressure-velocity coupling is resolved by the use of the revised version of SIMPLE, that is, SIMPLEC. Reynolds stresses are closed using the standard $k-{\varepsilon}$ and RNG $k-{\varepsilon}$ models. Two-phase turbulent combustion of liquid drop or pulverized coal particle is modeled using locally-homogeneous, gas-phase, eddy breakup model. However simple approximate models are incorporated for the modeling of the second phase slip and retardation of ignition without consideration of any detailed particle behavior. Some important results are presented and discussed in a brief note. Especially, in order to make uniform exit flow for the jet bubbling reactor, a well-designed structure of distributor is needed. Further, the aspect ratio in the double skin system appears to be one of important factors to give rise to the visible change of the induced air flow rate. The computational tool employed in this study, in general, appears as a viable method for the design of various engineering system of interest.

• Korean Journal of Optics and Photonics
• /
• v.22 no.2
• /
• pp.83-89
• /
• 2011

In order to improve the calculation speed of an integrating-sphere simulator based on a ray-tracing method, parallel processing with OpenMP directive was implemented into the simulator and the randomness of Monte Carlo method was guaranteed by utilizing a parallel random number generator. It was confirmed that simulation results obtained with more than $10^7$ rays showed good agreement with theoretical results within the error range of 0.5%, and that the calculation speed improved as the number of threads increased. Finally, the spatial response distribution functions of a real integrating sphere were simulated and compared with previous results.

• Journal of Pharmacopuncture
• /
• v.3 no.2
• /
• pp.153-168
• /
• 2000

This study was designed to study on major components of various Bee Venom(Bee Venom by electrical stimulation in Korea; K-BV I, Bee Venom by Microwave stimulation in Korea; K -BV II, 0.5rng/ml, Fu Yu Pharmaceutical Factory, China; C-BV, 1mg /ml, Monmouth Pain Institute, Inc., U.S.A.; A-BV) using Electrophoresis. The results were summarized as follows: 1. In 1:4000 Bee Venom solution rate, the band was not displayed distinctly usmg Electrophoresis. But in 1: 1000, the band showed clearly. 2. The results of Electrophoresis at solution rate 1:1000, K-BV I and K-BVII showed similar band. 3. The molecular weight of Phospholipase $A_2$ was known as 19,000 but its band was seen at 17,000 in Electrophoresis. 4. Protein concentration of Bee Venom by Lowry method was different at solution rate 1:4000 ; C-BV was $250{wmu}g/ml,\;K-BV\;I\;was\;190{wmu}g/ml,\;K-BVII\;was\;160{wmu}/ml\;and\;C-BV\;was\;45{wmu}/ml5$. Electrophoresis method was unuseful for analysis of Bee Venom when solution rate is above 1:4000 but Protein concentration of Bee Venom by Lowry method was possible. These data from the study can be applied to establish the standard measurement of Bee Venom and prevent pure bee venom from mixing of another components. I think it is desirable to study more about safety of Bee Venom as time goes by.

• Resources Recycling
• /
• v.10 no.4
• /
• pp.18-23
• /
• 2001

Air pollutants, phenol was generated in case of thermal regeneration of used activated carbon loaded with phenol and because of this problem, removal process of phenol were studied. Electrolytic oxidation of samples, used S.company granular activated carbon (WS-GAC), used C.company granular activated carbon (WC-GAC) and used L.company granular activated carbon (WL-GAC) loaded with phenol carried out by potentiostatic method in this study. In case of experiment was to come into operation in condition of samples containing 100 mg/g phenol, supporting electrolyte was 1.0% sodium chloride solution, Ti-Ir (10$\times$10$\textrm{cm}^2$) electrode and electrode distance was 2 cm, current density was $1.25 A/dm^2$, Obtained from the results of electrolytic oxidation experiments were not detected residual phenol. And then we knew about reaction time of electrolytic oxidation, current density, concentration of supporting electrolyte and electrode and electrode distance were 60 minutes, 1.25 A/dm$^2$, 1.0%, 2 cm.

• Journal of Advanced Research in Ocean Engineering
• /
• v.4 no.2
• /
• pp.86-95
• /
• 2018

The fluid flow over structures has been widely investigated by many researchers because its extensive application in offshore structures, skyscrapers, chimneys and cooling towers, brides. In the viewpoint of reducing the drag for offshore structure, it becomes challenging problem in the field of hydrodynamic of offshore structure. The purpose of this study is to investigate a flow over a square cylinder with an attached splitter plate using RANS method. First, RANS turbulent models such as a standard $k-{\omega}$ model, SST $k-{\omega}$ model, RNG $k-{\varepsilon}$ model, realizable $k-{\varepsilon}$ model, standard $k-{\varepsilon}$ model were used for choosing suitable turbulent model which has the best agreement with available experimental result. Drag of single cylinder estimated by using standard $k-{\omega}$ has a good agreement with published experimental result. Therefore, the stand $k-{\omega}$ was selected for simulation for flow over a square cylinder with an attached plate. Second, the numerical results of drag of square cylinder with an attached splitter plate in various length of an attached plate were performed using RANS method in ANSYS Fluent. In this paper, the numerical simulations were conducted at a Reynolds number of 485 and the thickness of the splitter plate is chosen as a constant value about 10% of cylinder width. The numerical results of drag coefficient of square cylinder are compared with experimental result published by other researchers. Finally, the effect of the splitter plate attached to the rear side of the square cylinder has been investigated numerically with a focus on the drag coefficient and flow characteristic. As a result, the drag coefficient decreases with an increase in splitter plate length.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.7 no.4
• /
• pp.33-38
• /
• 2003

The Physics of the Plume-induced shock and separation Particularly at a high Plume to exit pressure ratio and supersonic speeds up to Mach 3.0 with and without a passive control method, porous extension, were studied using computational techniques. Mass-averaged Navier-Stokes equations with the RNG $\kappa$-$\varepsilon$ turbulence model were solved using a fully implicit finite volume scheme and a 4-stage Runge-Kutta method. The control methodology for plume-afterbody interactions is to use a perforated wall attached at either the nozzle exit or the edge of the missile base. The Effect of porous wall length on plume interference is also investigated The computational results show the main effect of the porous extension on plume-afterbody interactions is to restrain the plume from strongly underexpanding during a change in flight conditions. With control, a change in porous extension length has no significant effect rut plume interference.