• Tribology and Lubricants
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• 제19권3호
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• pp.139-145
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• 2003

In this paper, static characteristics of a cryogenic hydrostatic journal bearing which has 2-rows staggered recesses are numerically analyzed. The regime of operation of this bearing is fully turbulent with large fluid inertia effects. The turbulent lubrication equation is solved under the assumption that turbulence parameters are decided by the Reynolds numbers. Pressure drop caused by inertia effect at the recess edge is considered in this analysis. Also density and viscosity of working fluid are considered as function of only pressure. Numerical results for a cryogenic Hydrostatic journal bearing show pressure distribution, load capacity, flow rate, and recess pressure. The effects of turbulent flow, pressure drop and variable liquid properties are discussed.

• Journal of Advanced Marine Engineering and Technology
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• 제24권1호
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• pp.31-40
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• 2000

This paper describes the numerical computations of the interaction between the streamwise vortex and a flat plate 3-D turbulent boundary layer. In the present study, the main interest is in the behavior of the streamwise vortices introduced in turbulent boundary layers. The flow behind a vortex generator is modeled by the information that is avilable from studies on the dalta winglet. An algorithm of the solution of the incompressible Navier-Stokes equations for three-dimensional turbulent flows, together with a two layer turbulent model to resolve the near-wall flow, is based on the method of artificial compressibility. The present results show boundary layer distortion due to vortices, such as strong spanwise flow divergence and boundary thinning, and have a good agreement with the experimental data.

• 한국가시화정보학회지
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• 제3권1호
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• pp.71-77
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• 2005

Information on temporal evolution of whole velocity fields are essential for physical understanding of a complicated turbulent flow. Due to advances of high-speed imaging technique, laser and electronics, high-speed digital cameras and high-repetition pulse lasers are commercially available in nowadays. A dynamic PIV system that can measure consecutive instantaneous velocity field with 1K$\times$ 1K pixels resolution at 1 fps was developed. It consists of a high-speed CMOS camera and a high-repetition Nd:YLF pulse laser. Theoretically, it can capture velocity fields at 20 fps with a reduced spatial resolution. In order to validate its performance, the dynamic PIV system was applied to a turbulent jet of which Reynolds number is about 3000. The particle images of 1024$\times$512 pixels were captured at a sampling rate of 4 KHz. The dynamic PIV system measured successfully the temporal evolution of instantaneous velocity fields of the turbulent jet, from which spectral analysis of turbulent structure was also feasible.

• 한국연소학회지
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• 제8권4호
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• pp.15-23
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• 2003

The zone conditional two-fluid equations are derived and validated against DNS database of a premixed turbulent flame. The conditional statistics of major flow variables are investigated to understand the mechanism of flame generated turbulence. The flow field in burned zone shows substantially increased turbulent kinetic energy, which is highly anisotropic due to reaction kinematics across thin f1amelets. The transverse component may be larger than the axial component for a distributed pdf of the flamelet orientation angle, while the opposite occurs due to redistribution of turbulent kinetic energy and flamelet orientation normal to the flow at the end of a flame brush. The major source or sink terms of turbulent kinetic energy are the interfacial transfer by the mean reaction rate and the work terms by fluctuating pressure and velocity on a flame surface. Ad hoc modeling of some interfacial terms may be required for further application of the two-fluid model in turbulent combustion simulations.

• Journal of Advanced Marine Engineering and Technology
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• 제31권6호
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• pp.681-686
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• 2007

The flow analysis was made by applying the turbulent models in the scroll volume of centrifugal compressor. The $k-{\varepsilon}.\;k-{\omega}$, Spalart-Allmaras and reynolds stress models are used in which the hybrid grid is applied for the simulation. The velocity vector the Pressure contour. the change of residual along the iteration number. and the dynamic head are simulated by solving the Navier-Stokes equations for the comparison of four example cases.

• Ocean and Polar Research
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• 제36권4호
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• pp.475-485
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• 2014

Seawater flow characteristics around a manganese nodule mining device in deep sea were analyzed through numerical investigation. The mining device influences the seawater flow field with complicated velocity distributions, and they are largely dependent on the seawater flow speed, device moving speed, and injection velocity from the collecting part. The flow velocity and turbulent kinetic energy distributions are compared at several positions from the device rear, side, and top, and it is possible to predict the distance from which the mining device affects the seawater flow field through the variation of turbulent kinetic energy. With the operation of the collecting device the turbulent kinetic energy remarkably increases, and it gradually decreases along the seawater flow direction. Turbulent kinetic energy behind the mining system increases with the seawater flow velocity. The transient behavior of nodule particles, which are not collected, is also predicted. This study will be helpful in creating an optimal design for a manganese nodule collecting device that can operate efficiently and which is eco-friendly.

• 동력기계공학회지
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• 제18권3호
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• pp.59-65
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• 2014

The computational fluid dynamics was carried out to evaluate turbulent models on the swirling flow of a gun-type gas burner(GTGB) according to the mesh size. The commercial SC/Tetra software was used for a steady-state, incompressible and three-dimensional numerical analysis. In consequence, the velocity magnitude from the exit of a GTGB and the flowrate predicted by the turbulent models of MP k-${\varepsilon}$, Realizable k-${\varepsilon}$ and RNG k-${\varepsilon}$ agree with the results measured by an experiment very well. Moreover, the turbulent kinetic energy predicted by the turbulent model of standard k-${\varepsilon}$ with mesh type C only agrees with the experimental result very well along the radial distance. On the other hand, the detailed prediction of the information of swirling flow field near the exit of a GTGB at least needs a CFD analysis using a fairly large-sized mesh such as a mesh type C.

• 한국자동차공학회논문집
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• 제1권1호
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• pp.1-13
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• 1993

The three-dimensional numerical analysis for in-cylinder flow of four-valve engine without intake port has been successfully computed. These computations have been performed using technique of the general coordinate transformation based on the finite-volume method and body-fitted non-orthogenal grids using staggered control volume and covariant variable as dependent one. Computations are started at intake valve opening and are carried through top-dead-center of compression. A k-$\varepsilon$model is used to represent turbulent transport of momentum. The principal study is the evolution of interaction between mean flow and turbulence and of the role of swirl and tumble in generating near TDC turbulence. Results for three different inlet flow configuration are presented. From these results, complex flow pattern may be effective for promoting combustion in spark-ignition engines and kinetic energy of mean flow near TDC is well converted into turbulent kinetic energy.

• Nuclear Engineering and Technology
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• 제55권9호
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• pp.3367-3382
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• 2023

Smoothed Particle Hydrodynamics (SPH) is a Lagrangian computational fluid dynamics method that has been widely used in the analysis of physical phenomena characterized by large deformation or multi-phase flow analysis, including free surface. Despite the recent implementation of eddy-viscosity models in SPH methodology, sophisticated turbulent analysis using Lagrangian methodology has been limited due to the lack of computational performance and numerical consistency. In this study, we implement the standard and dynamic Smagorinsky model and dynamic Vreman model as sub-particle scale models based on a weakly compressible SPH solver. The large eddy simulation method is numerically identical to the spatial discretization method of smoothed particle dynamics, enabling the intuitive implementation of the turbulence model. Furthermore, there is no additional filtering process required for physical variables since the sub-grid scale filtering is inherently processed in the kernel interpolation. We simulate lid-driven flow under transition and turbulent conditions as a benchmark. The simulation results show that the dynamic Vreman model produces consistent results with experimental and numerical research regarding Reynolds averaged physical quantities and flow structure. Spectral analysis also confirms that it is possible to analyze turbulent eddies with a smaller length scale using the dynamic Vreman model with the same particle size.

• 열처리공학회지
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• 제37권2호
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• pp.73-78
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• 2024

This study presents a real-time method that uses Laser Absorption Spectroscopy (LAS) to measure exhaust gas temperatures in turbulent flow fields. It was possible to measure temperature by passing a laser beam through the exhaust gas in a grid pattern, and obtain a temperature distribution image through time series analysis at 0.1 second intervals. Temperature image resolution has been improved with CT reconstruction algorithms. Estimating maximum temperature values and locations enabled 2D temperature analysis, surpassing single-point methods like thermocouples. The accuracy of LAS measurements was evaluated by comparison with thermocouple measurements. This approach will contribute to automotive technology and environmental protection by providing reliable temperature data for interpreting turbulent temperature distributions.