• Journal of computational fluids engineering
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• v.1 no.1
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• pp.26-34
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• 1996

The performance of the SIMPLE, SIMPLE-C and PISO algorithms for the treatment of the pressure-velocity coupling in fluid flow problems were examined by comparing the computational effort required to obtain the same level of the convergence. Example problems are circular duct and 90-degree bent square-duct. For circular duct case, laminar and turbulent flow were computed. For 90-degree bent square-duct case, laminar flow was simulated by the time-marching method as well as the iterative method. The convergence speed of the other two algorithms are not always superior to SIMPLE algorithm. SIMPLE algorithm is faster than SIMPLE-C algorithm in the simple laminar flow calculations. The application of the PISO algorithm in three dimensional general coordinates is not so effective as in two-dimensional ones. Since computational time of PISO algorithm is increased at each time step(or iterative step) in three dimension, the total convergence speed is not decreased. But PISO algorithm is stable for large time step by using time marching method,.

• Journal of computational fluids engineering
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• v.14 no.1
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• pp.35-44
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• 2009

To adequately analyze flows in pipe or duct network system, traditional node-based junction coupling methods require the junction loss which is specified by empirical or analytic correlations. In this paper, a new finite volume junction coupling method using a ghost junction cell is developed by considering the interchange of linear momentum as well as the important wall-effect at junction without requiring any correlation on the junction loss. Also, boundary treatment is modified to preserve the stagnation enthalpy across boundaries, such as pipe-end and the interface between junction and branch. Also, the computational accuracy and efficiency of the Godunov-type finite volume schemes are investigated by tracing the total mechanical energy of rapid transients due to sudden closure of valve at downstream end.

• Journal of computational fluids engineering
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• v.2 no.1
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• pp.1-7
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• 1997

A FA-FD hybrid method, developed for solving three-dimensional incompressible Navier-Stokes equations, is applied to calculate three-dimensional laminar flows through a square duct with a 90° bend. The method discretizes the convective terms in the primary flow direction with 3rd-order upwind finite-differences and the convective and diffusive terms in the transverse directions with the two-dimensional finite analytic method. The non-staggered grid system is used and the pressure-velocity coupling is achieved by a global iteration procedure based on the PISO algorithm. Detailed comparisons between the computed solutions and the available experimental data are given mainly for the velocity distributions at cross-sections in a 90° bend of a square duct with both fully developed and developing entry flows. Although the computational result shows generally a good agreement with the experimental data, there are some significant discrepancies underlining the necessity of more accurate numerical methods as well as reliable experimental data for their validation.

• Journal of Korean Tunnelling and Underground Space Association
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• v.19 no.2
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• pp.319-333
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• 2017

The construction of long sub-sea tunnel does not provide the favorable condition for the installation of ventilation system to be used during construction due to the constrained construction space. For the ventilation system required during construction, the artificial island where ventilation shaft is located is constructed at some location along the sub-sea tunnel route, which requires a high construction cost. Therefore, it is intended, as much as possible technically, to minimize the construction of artificial island. However, this requires a longer distance between ventilation shafts, there-by causing increased air leakage at the ventilation duct connection points due to the higher fan pressure being required to deliver ventilation air. Previously the air leakage was studied as an important issue. In this study experiments were carried out to develop the improved duct connection method considering various conditions such as, tunnel length, etc. Additionally, its performance results with leakage rates are shown and compared to the "S" class leakage rate of SIA. As a result, the new duct coupling type of improved method is analyzed as applicable to such a 30 km long tunnel with the leakage rate of $1.46mm^2/m^2$, which is better performance than SIA leakage rates.

• Nuclear Engineering and Technology
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• v.32 no.2
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• pp.169-179
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• 2000

A detailed numerical analysis of the evolution of thermal stratification in a curved piping system in a nuclear power plant is performed. A finite volume based thermal-hydraulic computer code has been developed employing a body-fitted, non-orthogonal curvilinear coordinate for this purpose. The cell-centered, non-staggered grid arrangement is adopted and the resulting checkerboard pressure oscillation is prevented by the application of momentum interpolation method. The SIMPLE algorithm is employed for the pressure and velocity coupling, and the convection terms are approximated by a higher-order bounded scheme. The thermal-hydraulic computer code developed in the present study has been applied to the analysis of thermal stratification in a curved duct and some of the predicted results are compared with the available experimental data. It is shown that the predicted results agree fairly well with the experimental measurements and the transient formation of thermal stratification in a curved duct is also well predicted.

• Journal of KSNVE
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• v.9 no.1
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• pp.184-188
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• 1999

Noise regulation of heavy construction machinery is getting stricter： 3 dB per every 4 year in European community. To meet this requirement many engineers have adopted the enclosing structures with thick absorbing materials and small opening, This increases internal temperature of the enclosure which have engine systems such as electric equipment that are vulnerable to heat, and engine block and muffler that can be regarded as heat sources. So noise control engineers have to consider a coupling problem: combining heat balance and noise reduction. This paper describes this approach by introducing simple heat transfer theory and SEA. The enclosing system of the loader whose enclosing structure consists of two rooms is investigated to show the validity of this method. The results represent that the simple heat transfer theory can be useful to estimate cooling performance when it is linked together by the back pressure theory in duct system. and the radiated noise can also be estimated by the SEA. Therefore a designer can use these approaches to define the opening ratio of an enclosure and the mass flow rate of air considering radiating noise.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.1
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• pp.145-160
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• 2018

Long subsea tunnel is subject to many restrictions in terms of spatial limitation when vertical or inclined shafts are built for tunnel ventilation. So, the construction of some artificial island is required to provide ventilation. But, because of construction difficulty and cost increase, it is necessary to minimize the artificial island construction. As a result, ventilation distance become longer and supply airflow becomes excessive due to air leakage, So, duct mounting for temporary ventilation is impossible or fan pressure and power increase exponentially. Therefore, in order to build a long subsea tunnel, it is necessary to overcome these practical problems and to develop technical solution that can keep the comfortable condition of tunnel environment during construction. In previous study, we have found that air leakage is the key factor in solving these problems and experimental results show that the new connection method has a leakage rate of about $1.46mm^2/m^2$ (Jo et al., 2017). In this study, we present the experimental results of the measurement of the leakage rate of the prototype with the new connection method, and analyze experimentally the improvement of the leakage rate when applying the flexible cover inside the duct to improve the leakage performance of the existing connection method.

• 한국전산유체공학회:학술대회논문집
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• 2008.03b
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• pp.626-629
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• 2008

Numerical predictions on flow phenomena in pipe network systems have been considered as playing an important role in both designing and operating various facilities of piping or duct systems, such as water supply, tunnel or mine ventilation, hydraulic systems of automobile or aircraft, and etc. Traditionally, coupling conditions between junction and connected branches are assumed to satisfy conservation law of mass and to share an equal pressure at junction node. However, the conventional methodology cannot reflect momentum interactions between pipes sufficiently. Thus, a new finite volume junction treatment is proposed both to reflect the interchanges of linear momentums between neighbor branches at junction and to include the effect of wall at junction in present work.