• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.26 no.2
• /
• pp.362-373
• /
• 2002

A stereoscopic PIV (SPIV) measurement system based on the translation configuration was developed and applied to the flow behind a forward-swept axial-fan. Measurement of three orthogonal velocity components is essential for flow analysis of three-dimensional flows such as flow around a fan or propeller. In this study, the translation configuration was adopted to calculate the out-of-plane velocity component from 2-D PIV data obtained from two CCD cameras. The error caused by the out-of-plane motion was estimated by direct comparison of the 2-D PIV and 3-D SPIV results that measured from the particle images captured simultaneously. The comparison shows that the error ratio is relatively high in the region of higher out-of-plane motion near the axial fan blade. The turbulence intensity measured by the 2-D PIV method is bigger by about 5.8% in maximum compared with that of the 3-D SPIV method. The phase-averaged velocity field results show that the wake behind an axial fan has a periodic flow structure with respect to the blade phase and the characteristic flow structure is shifted downstream in the next phase.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.18 no.3
• /
• pp.279-285
• /
• 2012

It is necessary to install the inert gas system(IGS) for preventing fire and explosion in LNGC main diesel engine crankcase besides oil mist detector(OMD) unit with $CO_2$ gas injector. Therefore, to design the liquid nitrogen IGS, analytical work is conducted for predicting the heat input load of liquid nitrogen heater with two-phase stratified flow model. This paper also presents the effects of changes in pipe diameter, saturated pressure, and inclination angle by ship's movement on cryogenic two-phase stratified flows. It is found that the stratified model gives reasonable predictions, and the model is effective to predict the heat input load of liquid nitrogen IGS.

• Journal of Advanced Marine Engineering and Technology
• /
• v.39 no.7
• /
• pp.696-701
• /
• 2015

Two-phase flow boiling experiments were conducted in 15 micro-channels with a depth of 0.2 mm, width of 0.45 mm, and length of 60 mm. FC-72 was used as the working fluid, and the mass fluxes ranged from 200 to $400kg/m^2s$. Tests were performed over a heat flux range of $5-40kW/m^2$ and vapor quality range of 0.1-0.9. The heat transfer coefficient sharply decreased at a lower heat flux and then was kept approximately constant as the heat flux is increased. Based on the measured heat transfer data, the flow pattern was simply classified into bubbly, slug, churn, and wavy/annular flows using the existing method. In addition, these classified results were compared to the transition criterion to wavy/annular regime. However, it was found that the existing transition criterion did not satisfactorily predict the transition criterion to annular regime for the present data.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.24 no.9 s.180
• /
• pp.2159-2166
• /
• 2000

Recently, high performance machining center requires special type of sealing mechanism that prevent a leakage of oil jet or oil mist lubrication system. Sealing of oil-air mixture plays important r oles to have an enhanced lubrication for performance machining center. Current work emphasizes on investigations of the air jet effect on the protective collar type labyrinth seal. To improve sealing capabilities of conventional labyrinth seals, air jet is injected against the leakage flow. In this study, an adapted model is introduced to improve sealing capability of conventional non-contact type seals. It has a combined geometry of a protective collar type and an air jet type. Both of a numerical analysis by CFD (Computational Fluid Dynamics) and experimental measurements are carried out to verify sealing improvement. The sealing effects of the leakage clearance and the air jet magnitude aic studied in various parameters. Gas or liquid has been used as a working fluid for most of nori-contact types seals including the labyrinth seal. However, it is more reasonable to regard two-phase flows because oil mist or oil jet are used for high performance spindle's lubrication. In this study, working fluid is regarded as two phases that are mixed flow of oil and air phase. Both of turbulence and compressible flow model are also introduced in a CFD analysis to represent an isentropic process. Estimation of non-leaking property is determined by amount of pressure drop in the leakage path. Results of pressure drop in the experiment match reasonably to those of the simulation by introducing a flow coefficient. Effect of the sealing improvement is explained as decreasing of leakage clearance by air jetting. Thus, sealing effect is improved by amount of air jetting even though clearance becomes larger

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.2B
• /
• pp.175-185
• /
• 2011

This study investigates tsunami force acting on a group of onshore structures numerically by using three-dimensional one-field model for immiscible multi-phase flows, which is based on Navier-Stokes solver. In particular, we studied on the characteristics of tsunami with respect to the arrangement of onshore structures and the distance from seawall trough numerical experiments. For validation of the numerical method used in this study to calculate tsunami force, numerical results for tsunami force on the structures in coastal area are compared with available experimental data. Furthermore, a detail study on the efficiency of the numerical method is performed for the estimation of tsunami force based on the hydrostatic and hydrodynamic methods in which the numerical results are used. The obtained results are compared to the previous experimental one and design criteria. Considering both experimental results and numerical analysis results, semi-empirical formula by regression analysis is proposed. As a result, it was confirmed that the numerical analysis is effective to estimate on tsunami force acting on onshore structures.

• Advances in aircraft and spacecraft science
• /
• v.9 no.5
• /
• pp.415-431
• /
• 2022

Secondary flows have a huge impact on losses generation in modern low pressure gas turbines (LPTs). At design point, the interaction of the blade profile with the end-wall boundary layer is responsible for up to 40% of total losses. Therefore, predicting accurately the end-wall flow field in a LPT is extremely important in the industrial design phase. Since the inlet boundary layer profile is one of the factors which most affects the evolution of secondary flows, the first main objective of the present work is to investigate the impact of two different inlet conditions on the end-wall flow field of the T106A, a well known LPT cascade. The first condition, labeled in the paper as C1, is represented by uniform conditions at the inlet plane and the second, C2, by a flow characterized by a defined inlet boundary layer profile. The code used for the simulations is based on the Discontinuous Galerkin (DG) formulation and solves the Reynolds-averaged Navier-Stokes (RANS) equations coupled with the Spalart Allmaras turbulence model. Secondly, this work aims at estimating the influence of viscosity and turbulence on the T106A end-wall flow field. In order to do so, RANS results are compared with those obtained from an inviscid simulation with a prescribed inlet total pressure profile, which mimics a boundary layer. A comparison between C1 and C2 results highlights an influence of secondary flows on the flow field up to a significant distance from the end-wall. In particular, the C2 end-wall flow field appears to be characterized by greater over turning and under turning angles and higher total pressure losses. Furthermore, the C2 simulated flow field shows good agreement with experimental and numerical data available in literature. The C2 and inviscid Euler computed flow fields, although globally comparable, present evident differences. The cascade passage simulated with inviscid flow is mainly dominated by a single large and homogeneous vortex structure, less stretched in the spanwise direction and closer to the end-wall than vortical structures computed by compressible flow simulation. It is reasonable, then, asserting that for the chosen test case a great part of the secondary flows details is strongly dependent on viscous phenomena and turbulence.

• Journal of the Society of Naval Architects of Korea
• /
• v.54 no.3
• /
• pp.215-226
• /
• 2017

This paper presents numerical results of the performance of a marin propeller in cavitating and non-cavitating flow conditions. The geometry and experimental validation data of the propeller are provided in Potsdam Propeller Test Case(PPTC) in the framework of the second International Symposium on Marine Propulsors 2011(SMP'11) workshop. The PPTC includes open water tests, velocity field measurements and cavitation tests. The present numerical analysis was carried out by using the Reynolds averaged Navier-Stokes(RANS) method on a wall-resolved grid ensuring a y+=1, where the SST k-${\omega}$ model was mainly used for turbulence closure. The influence of the turbulence model was investigated in the prediction of the wake field under a non-cavitating flow condition. The propeller tip vortex flows in both cavitating and non-cavitating conditions were captured through adaptation of additional grids. For the cavitation flows at three operation points, Schnerr-Sauer's cavitation model was used with a Volume-Of Fluid(VOF) approach to capture the two-phase flows. The present numerical results for the propeller wake and cavitation predictions including the open water performance showed a qualitatively reasonable agreement with the model test results.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.36 no.7
• /
• pp.721-730
• /
• 2012

The present paper presents a numerical study on multiphase flows induced by wall adhesion. The continuum surface force (CSF) model with the wall adhesion boundary condition model is used for calculating the surface tension force; this model is implemented in an in-house solution code (PowerCFD). The present method (code) employs an unstructured cell-centered method based on a conservative pressure-based finite-volume method with a volume capturing method (CICSAM) in a volume of fluid (VOF) scheme for phase interface capturing. The effects of wall adhesion are then numerically simulated by using the present method for a shallow pool of water located at the bottom of a cylindrical tank with no external forces such as gravity. Two different cases are computed, one in which the water wets the wall and one in which the water does not wet the wall. It is found that the present method efficiently simulates the surface tension-dominant multiphase flows induced by wall adhesion.

• Structural Engineering and Mechanics
• /
• v.81 no.4
• /
• pp.523-527
• /
• 2022

The objective of this study is to simulate the flow in pipes with various boundary conditions. Free-pressure fluid model, is used in the pipe based on Navier-Stokes equation. The models are solved by using the numerical method. A problem called "stability of pipes" is used in order to compare frequency and critical fluid velocity. When the initial conditions of problem satisfied the instability conditions, the free-pressure model could accurately predict discontinuities in the solution field. Employing nonlinear strains-displacements, stress-strain energy method the governing equations were derived using Hamilton's principal. Differential quadrature method (DQM) is used for obtaining the frequency and critical fluid velocity. The results of this paper are analyzed by hyperbolic numerical method. Results show that the level of numerical diffusion in the solution field and the range of well-posedness are two important criteria for selecting the two-fluid models. The solutions for predicting the flow variables is approximately equal to the two-pressure model 2. Therefore, the predicted pressure changes profile in the two-pressure model is more consistent with actual physics. Therefore, in numerical modeling of gas-liquid two-phase flows in the vertical pipe, the present model can be applied.

• Journal of Energy Engineering
• /
• v.22 no.4
• /
• pp.362-369
• /
• 2013

Two-phase flow is frequently observed in many industries such as nuclear power plants and oil transportation. Two-phase flow regime depends on the flow rates, the fluid properties and the structure of flow channels. Since the identification of the flow regime is of great importance in the system design and the safety analysis, a number of theoretical and experimental investigations have been performed. This paper presents a basic research on the characteristics of each flow regime and transition boundary in the two-phase flows. The flow regime of the upward air-water flow in the vertical tube, 30 mm in the inner diameter, is distinguished by using the high-speed camera and the Wire-mesh sensor(WMS). The identified experimental data are compared with the flow regime maps proposed by Taitel et al, Mishima and Ishii. Even though there is slight difference in the transition boundary, the experimental data show general agreement with these flow regime maps.