• Proceedings of the KSME Conference
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• 2001.11b
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• pp.517-522
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• 2001

The exit edges of a diffuser are smoothly rounded, and a wall is located perpendicularly to a diffuser exit. The fluid is discharged towards the radial direction of a diffuser after impinging against a wall from a diffuser. In this flow path, pressure loss coefficients have been calculated by the variables of Reynolds number at a diffuser inlet, distance between a diffuser exit and a wall, and turbulence models. As a result, it was calculated that $h/D_0$ ratio between $0.35\sim0.4$ has the minimum pressure loss coefficient regardless of Reynolds number and turbulence models. It was also found that in case of the flow with relatively high Reynolds number at a diffuser inlet, the pressure loss coefficients by RNG $k-\varepsilon$ model have a tendency to be near to those by standard $k-\varepsilon$ model at small ratio of $h/D_0$, but to those by RSM at large ratio.

• Journal of the Korean Society of Visualization
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• v.14 no.3
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• pp.46-50
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• 2016

The objective of the present study is to perform experiments for water filled cavity heated and cooled from the side at $Ra=8.5{\times}108$. This experiment can provide validation database of the standard k-${\varepsilon}$ turbulence model for single-phase turbulent natural convection which has been regarded as one of the important phenomena in nuclear safety. For the natural convection inside a cavity, temperature and velocity were obtained by thermometry and PIV (Particle Image Velocimetry) methods. These results would be used for validation of standard k-${\varepsilon}$ turbulence model.

• 한국전산유체공학회:학술대회논문집
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• 1998.11a
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• pp.55-61
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• 1998

The purpose of this study is to compare the predictive behaviors of the extended $k-{\varepsilon}$ turbulence model and the standard $k-{\varepsilon}$ turbulence model. Grid dependency is tested with the H-type grid and the O-type grid. Computations have been performed for a circular-to-rectangular transition duct. Numerical results for several sections along the streamwise have been obtained to compare with experimental results. The Reynolds number is 390,000 based on the bulk velocity at the inlet. The computed axial velocity contours, transverse velocity profiles, static pressure contours, peripheral skin friction coefficient, and peripheral wall static pressure distributions have been compared with experimental results. The computed results obtained with the extended $k-{\varepsilon}$ turbulence model show better agreement with experimental results than those obtained with the standard $k-{\varepsilon}$ turbulence model. Comparing to the computed results obtained with the H-type grid and O-type grid, those with H-type grid agree well with experimental results.

• Proceedings of the KSME Conference
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• 2008.11b
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• pp.2816-2821
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• 2008

This paper investigates the flow field and organism concentration in a UV disinfection channel in which vertical ultraviolet lamps are arranged in a staggered configuration. Turbulence is described by low Reynolds number ${\kappa}-{\varepsilon}$ turbulence model and standard ${\kappa}-{\varepsilon}$ turbulence model, respectively. P-1 method has been employed to solve the radiative transfer equation. The obtained incident radiation is used to compute the inactivation term in the species equation. The CFD results are in good agreement with the existing experimental data for the UV channel. For the flow field, the low-Reynolds number ${\kappa}-{\varepsilon}$ model is superior to the standard ${\kappa}-{\varepsilon}$ model. The approach velocity has a significant effect on the disinfection efficiency. The organism concentration at the outlet decreases fast to a low inlet velocity.

• Journal of Bio-Environment Control
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• v.3 no.1
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• pp.10-19
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• 1994

Wind load is known to be one of major forces to influence the stability of agricultural structures. General flow fields were calculated to determine flow characteristics over the envelop of the following three types of greenhouses with arched roof : single span, twin span greenhouses, and two single span greenhouses apart 3m inbetween. Pressure coefficients along the envelop of greenhouse were numerically calculated by the k-$\varepsilon$ turbulence model, which lead to determine wind forces on it. Curvilinear coordinate for an arched roof and the upwind scheme were adopted for the study. The calculated pressure coefficients were validated with the avaliable data of Japanese Standard and NGAM Standard. The Magnitude of calculated forces over the envelop was not in good accordance with data except the windward wall. Even tile data of Japanese and NGAM Standard for validation deviated a lot from each other in quantity and quality. Such discrepancy may be attributed to different geometric and/or flow configuration conditions for experiments, or the insenstivity of the k-$\varepsilon$ turbulence model to recirculation flow.

• Journal of the Korean Mathematical Society
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• v.54 no.2
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• pp.563-574
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• 2017

Let $\mathcal{A}$ be a unital real standard Jordan operator algebra acting on a Hilbert space H of dimension at least 2. We show that every bijection ${\phi}$ on $\mathcal{A}$ satisfying ${\phi}(A^2{\circ}B)={\phi}(A)^2{\circ}{\phi}(B)$ is of the form ${\phi}={\varepsilon}{\psi}$ where ${\psi}$ is an automorphism on $\mathcal{A}$ and ${\varepsilon}{\in}\{-1,1\}$. As a consequence if $\mathcal{A}$ is the real algebra of all self-adjoint operators on a Hilbert space H, then there exists a unitary or conjugate unitary operator U on H such that ${\phi}(A)={\varepsilon}UAU^*$ for all $A{\in}\mathcal{A}$.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.9
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• pp.1183-1192
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• 2001

The numerical simulation has been conducted for the investigation of flow and heat transfer characteristics of an oblique impingement jet injected to a flat plate. The finite volume method was used to discretize the governing equations based on the non-orthogonal coordinate with non-staggered variable arrangement. The $textsc{k}$-$\varepsilon$-ν(sup)'2 turbulence model was employed to consider the consider the anisotropic flow characteristics generated by the impingement jet flow. The predicted results were compared with the experimental data and those of the standard $textsc{k}$-$\varepsilon$ turbulence model. The results of the $textsc{k}$-$\varepsilon$-ν(sup)'2 model showed better agreement with the experimental data than those of the standard $textsc{k}$-$\varepsilon$ model. In order to get the optimum condition, the flow and temperature fields were calculated with a variation of inclined angle($\alpha$=30$^{\circ}$~90$^{\circ}$) and the distance between the jet exit and impingement plate-to-diameter (L/D=4~10) at a fixed Reynolds number(Re=20,000). For a small L/D, the near-peak Nusselt numbers were not significantly effected by the inclined angle. The near-peak Nusselt numbers were not significantly affected by the L/D in the case of a large $\alpha$. The overall shape of the local Nusselt numbers was influenced by both the jet orifice-to-plate spacing and the jet angle.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.9
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• pp.1149-1164
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• 1997

In this study, the applicability of the RNG k-.epsilon. model to the analysis of the complex flows is studied. The governing equations based on a non-orthogonal coordinate formulation with Cartesian velocity components are used and discretized by the finite volume method with non-staggered variable arrangements. The predicted results using the RNG k-.epsilon. model of three complex flows, i.e., the flow over a backward-facing step and a blunt flat plate, the flow around a 2D model car are compared to these from the standard k-.epsilon. model and experimental data. That of the unsteady axisymmetric turbulent flow within a cylinder of reciprocating model engine including port/valve assembly and the spray characteristics within a chamber of direct injection model engine are compared to these from the standard k-.epsilon. model and experimental data. The results of reattachment length, separated eddy size, average surface pressure distribution using the RNG k-.epsilon. model show more reasonable trends comparing with the experimental data than those using the modified k-.epsilon. model. Although the predicted rms velocity using the modified k-.epsilon. model is lower considerably than the experimental data in incylinder flow with poppet valve, predicted axial and radial velocity distributions at the valve exit and in-cylinder region show good agreements with the experimental data. The spray tip penetration predicted using the RNG k-.epsilon. model is more close to the experimental data than that using the modified k-.epsilon. model. The application of the RNG k-.epsilon. model seems to have some potential for the simulations of the unsteady turbulent flow within a port/valve-cylinder assembly and the spray characteristics over the modified k-.epsilon. model.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.21 no.7
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• pp.911-918
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• 1997

The turbulent viscous wake flows behind a single airfoil, two-dimensional stationary blade row and three-dimensional rotating blade row were calculated, and the numerical results were compared with experimental ones. The numerical technique was based on the SIMPLE algorithm using three turbulent closure models, standard k-.epsilon. model(WFM), low Reynolds number k-.epsilon. model(LRN) and Reynolds stress model (RSM). In the case of a single airfoil, WFM, LRN and RSM presented fairly good velocity distributions in the wake compared with experimental data. In the case of the stationary blade row, LRN and RSM presented better results than WFM for wake velocity distribution, and especially LRN showed best results among these three turbulent models. In the case of the rotating blade row, WFM and LRN showed fairly good agreement with experimental data of the three-dimensional velocity component distributions in the range from hub to mid span region. LRN was also superior to WFM in accuracy of prediction for the wake velocity distribution as same with the cases of a airfoil and the stationary blade row.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.8
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• pp.1114-1121
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• 2003

A mathematical model considering the air side and the frost layer is presented to predict the frost layer growth. The standard k-$\varepsilon$ model for the air flow and the diffusion and energy equations for the frost layer are employed. The numerical results are compared with experimental data to validate the present model, and agree well with experimental data within a maximum error of 10%. The present model predicts well the frost properties and heat and mass transfer with respect to the frosting time. The variation of total heat transfer strongly depends on the operating condition, and has a similar trend to that of the sensible heat transfer. The frost properties along the flow direction are also investigated.