• Fire Science and Engineering
• /
• v.5 no.2
• /
• pp.11-20
• /
• 1991

Dilute polymer solutions were injected into turbulent pipe flow of a Newtonian fluid. The local drag reduction for injection of polymer solution at the pipe wall was larger than that at centerline. From the above result we may conclude that the polymer additives were found to influence the flow in the neighborhood of the wall. The effects of the injection apparatus on the local drag reduction are small compared to the drag-reducing effects. The extent of drag reduction increased with polymer concentration and injection flow rate, and the maximum drag reduction obtained were 47% for Polyox Coagulant and 35% for Separan AP-273. In respect to polymer degradation, the polyacrylamide showed better shear stability than the polyethyleneoxide and thus the former expected to have a sharper molecular weight distribution.

• Proceedings of the KSME Conference
• /
• 2001.06e
• /
• pp.783-788
• /
• 2001

Choosing the most suitable mathematical model and relating this to turbulent tangential tensions model are very important in the investigations of turbulent two-phase flow. This paper considers two-fluid scheme. According to it, two phases have their own densities, velocities, and temperatures at any spatial point and at any moment. The equations of motion and heat transfer for each phase are linked with the forces of interaction between two phases. These forces are considered as predominant for the flow. As a closure in the system of motion equations, one modification of $K - {\epsilon}$ turbulent model is worked out. The modification uses two equations for turbulent kinetic energy of the phases and one - for the turbulent energy loss of main phase. This model can be set as a $K_g - K_p -{\epsilon}$ model. The modified model has been tested for both a two-phase non-isothermal flat jet and axially symmetrical jet. The numerical results are compared with the reference data revealing a good agreement between them.

• Journal of The Korean Astronomical Society
• /
• v.37 no.5
• /
• pp.557-562
• /
• 2004

We discuss diffusion of particles in turbulent flows. In hydrodynamic turbulence, it is well known that distance between two particles imbedded in a turbulent flow exhibits a random walk behavior. The corresponding diffusion coefficient is ${\~}$ ${\upsilon}_{inj}{\iota}_{turb}$, where ${\upsilon}_{inj}$ is the amplitude of the turbulent velocity and ${\iota}_{turb}$ is the scale of the turbulent motions. It Is not clear whether or not we can use a similar expression for magnetohydrodynamic turbulence. However, numerical simulations show that mixing motions perpendicular to the local magnetic field are, up to high degree, hydrodynamical. This suggests that turbulent heat transport in magnetized turbulent fluid should be similar to that in non-magnetized one, which should have a diffusion coefficient ${\upsilon}_{inj}{\iota}_{turb}$. We review numerical simulations that support this conclusion. The application of this idea to thermal conductivity in clusters of galaxies shows that this mechanism may dominate the diffusion of heat and may be efficient enough to prevent cooling flow formation when turbulence is vigorous.

• Proceedings of the Korean Society of Marine Engineers Conference
• /
• 2005.06a
• /
• pp.1149-1154
• /
• 2005

The finite difference lattice Boltzmann method(FDLBM) is a quite recent approach for simulating fluid flow, which has been proven as a valid and efficient tool in a variety of complex flow problems. It is considered an attractive alternative to conventional FDM and FVM, because it recovers the Navier-Stokes equations and is computationally more stable, and easily parallelizable to simulate for various laminar flows and a direct simulation of aerodynamics sounds. However, the research of a numerical simulation of turbulent flow by FDLBM, which is important to analyze the structure of turbulent flow in engineering fields, is not carried out. In this research, the FDLBM built in the turbulent model is applied, and a flowfield around 2-dimensional square to validate the applied model with 2D9V is simulated. Besides, 2D computation of the cavity noise generated by flow over a cavity at a Mach number of 0.1 and a Reynolds number based on cavity depth of 5000 is calculated. The computation result is well presented a understanding of the physical phenomenon of tonal noise occurred primarily by well-jet shear layer and vortex shedding and an aeroacoustic feedback loop.

• 한국전산유체공학회:학술대회논문집
• /
• 2003.10a
• /
• pp.200-202
• /
• 2003

In this paper, Gauss filter function is used to filter the N-S equation and the subgrid-scale Reynold stresses model is introduced to deduce the practical form of LES equation for 2-D case for flow calculation of hydraulic machine. Then the LES equation and its discrete form in computational field are obtained in the body-fitted coordinate system and the numerical calculation program is built. The incompressible turbulent flow in double-flow-conduits-sewage pump impeller is computed by using the abovementioned program, and then the distribution rules of velocity and pressure in flow field are obtained. Based on this, the designs of double-flow-conduits-sewage pump impeller are optimized.

• The Journal of the Acoustical Society of Korea
• /
• v.19 no.1E
• /
• pp.27-37
• /
• 2000

This paper presents a simplified analytical formulation for computing acoustic power radiation from a rectangular plate exposed to random forces such as turbulent boundary layer pressure fluctuations and arbitrary mechanical force in a subsonic flow field. The expression for the acoustic power is derived using modal expansion method and light fluid loading is assumed on the plate. In order to simplify the formulation for acoustic power due to combined excitations of mechanical forces and turbulent pressures, it is assumed that the structural damping of the plate is small and excitations are broadband random forces having frequency spectra above the convective coincidence. Under these assumptions, an approximate solution for the broadband acoustic power radiation from a plate excited by both turbulent pressures and arbitrary mechanical forces is obtained and evaluated considering the effect of modal coupling on the radiated acoustic power. An efficient method is also suggested to compute modal acoustic impedance in a moving fluid medium by using averaged Green function.

• Journal of the Korean Society of Visualization
• /
• v.16 no.1
• /
• pp.37-41
• /
• 2018

The two-fluid model is widely used for practical applications involving multi-phase flows in chemical reactor, nuclear reactor, desalination systems, boilers, and internal combustion engine. There are several modeling terms in the two-fluid model, which must be determined properly. This study suggests the best models for turbulent vertical bubbly flow.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.33 no.7
• /
• pp.541-551
• /
• 2009

Configuration of the inlet transition square duct (hereinafter referred to as "transition duct") for heat recovery steam generator (hereinafter referred to as "HRSG") in combined cycle power plant is limited by the construction type of HRSG and plant site condition. The main purpose of the present study is to analyze the effect of a variation in turbulent flow pattern by roof slop angle change of transition duct for horizontal HRSG, which is influencing heat flux in heat transfer structure to the finned tube bank. In this study, a computational fluid dynamics(CFD) is applied to predict turbulent flow pattern and comparisons are made to 1/12th scale cold model test data for verification. Re-normalization group theory (RNG) based k-$\epsilon$ turbulent model, which improves the accuracy for rapidly strained flow and swirling flow in comparison with standard k-$\epsilon$ model, is used for the results cited in this study. To reduce the amount of computer resources required for modeling the finned tube bank, a porous media model is used.

• The KSFM Journal of Fluid Machinery
• /
• v.18 no.1
• /
• pp.44-50
• /
• 2015

Labyrinth seals are commonly used in various kinds of turbomachinery to reduce leakage flow. In the present 3D CFD analysis of see-through-type labyrinth air seal, the methodology of determining leakage and rotordynamic coefficients is suggested with the relative coordinate system for steady-state simulation. The leakage flow and rotordynamic forces predicted by using different solvers and turbulent models of FLUENT are compared with the results of the existing bulk-flow analysis code LABYSEAL.FOR and experiment. The present CFD result of direct stiffness(K) shows only improvement in prediction. The results of leakage and rotordynamic coefficients as well as computing time are sensitive against the used solver and turbulent model.

• Tunnel and Underground Space
• /
• v.6 no.1
• /
• pp.64-68
• /
• 1996

Analyzed in this paper is fluid flow in the region near the exhaust and blower ports of the ventilation ducts inside a vehicle tunnel. Theoretical analysis shows that prediction of the energy loss in this region is important for designing the ventilation system. A finite-difference numerical model for the two-dimensional turbulent flow field was used to obtain the flow solution as well as the energy loss. It was shown that the blower-nozzle angle ($\beta$) had an important role in establishing both the pressure gradient and the energy loss, while the effect of the distance between two ports on them was not so significant.