• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.9 s.114
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• pp.937-948
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• 2006

In this study, a fluid/structure coupled analysis system for simulating complex flow-induced vibration (FIV) phenomenon of cascades has been developed. The flow is modeled using Euler and Wavier-Stokes equations with different turbulent models. The fluid domains are modeled using the unstructured grid system with dynamic deformations due to the motion of structural boundary. The Spalart-Allmaras (S-A) and the SST ${\kappa}-{\omega}$ turbulent models are used to predict the transonic turbulent flows. A fully implicit time marching scheme based on the Newmark direct integration method is used in order to solve the coupled governing equations for viscous flow-induced vibration phenomena. For the purpose of validation for the developed FIV analysis system, comparison results for computational analyses of steady and unsteady aerodynamics and flutter analyses are presented in the transonic flow region. In addition, flow-induced vibration analyses for the isolated cascade and multi-blades cascade models have been conducted to show the physical fluid-structure interaction effects in the time domain.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.6
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• pp.753-765
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• 2003

A finite element code for the numerical solution of the Navier-Stokes equation is parallelized by vertex-oriented domain decomposition. To accelerate the convergence of iterative solvers like conjugate gradient method, parallel block ILU, iterative block ILU, and distributed ILU methods are tested as parallel preconditioners. The effectiveness of the algorithms has been investigated when P1P1 finite element discretization is used for the parallel solution of the Navier-Stokes equation. Two-dimensional and three-dimensional Laplace equations are calculated to estimate the speedup of the preconditioners. Calculation domain is partitioned by one- and multi-dimensional partitioning methods in structured grid and by METIS library in unstructured grid. For the domain-decomposed parallel computation of the Navier-Stokes equation, we have solved three-dimensional lid-driven cavity and natural convection problems in a cube as benchmark problems using a parallelized fractional 4-step finite element method. The speedup for each parallel preconditioning method is to be compared using upto 64 processors.

• Journal of computational fluids engineering
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• v.18 no.1
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• pp.49-57
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• 2013

Analysis of fluid-structure interaction for two nearby underwater vehicles immersed in the sea is quite challenging because simulation of flow around them is very difficult due to the complexity of underwater vehicle shapes. The conventional approach using body-fitted or unstructured grids demands much time in dynamic grid generation, and yields slow convergence of solution. Since an analysis of fluid-structure interaction must be based on accurate simulation results, a more efficient way of simulating flow around underwater vehicles, without sacrificing accuracy, is desirable. An immersed boundary method facilitates implementation of complicated underwater-vehicle shapes on a Cartesian grid system. An LES modeling is also incorporated to resolve turbulent eddies. In this paper, we will demonstrate the effectiveness of the immersed boundary method we adopted, by presenting the simulation results on the flow around a modeled high-speed underwater vehicle interacting with a modeled low-speed one.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.16 no.10 s.115
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• pp.1082-1089
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• 2006

In this study, advanced computational analysis system has been developed in order to investigate flow-induced vibration(FIV) phenomenon for general stator-rotor cascade configurations. Relative movement of the rotor with respect to stator is reflected by modeling Independent two computational domains. Fluid domains are modeled using the unstructured grid system with dynamic moving and local deforming methods. Unsteady, Reynolds-averaged Wavier-stokes equations with one equation Spalart-Allmaras and two-equation SST ${\kappa}-{\varepsilon}$ turbulence models are solved for unsteady flow problems and also relative moving and vibration effects of the rotor cascade are fully considered. A coupled implicit time marching scheme based on the Newmark integration method is used for computing the governing equations of fluid-structure interaction problems. Detailed vibration responses for different flow conditions are presented and then vibration characteristics are physically investigated in the time domain as computational virtual tests.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2006.05a
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• pp.793-802
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• 2006

In this study, a fluid/structure coupled analysis system for simulating complex flow-induced vibration (FIV) phenomenon of cascades has been developed. The flow is modeled using Euler and Wavier-Stokes equations with different turbulent models. The fluid domains are modeled using the unstructured grid system with dynamic deformations due to the motion of structural boundary. The Spalart-Allmaras (S-A) and the SST ${\kappa}-{\omega}$ turbulent models are used to predict the transonic turbulent flows. A fully implicit time marching scheme based on the Newmark direct integration method is used in order to solve the coupled governing equations for viscous flow-induced vibration phenomena. For the purpose of validation for the developed FIV analysis system, comparison results for computational analyses of steady and unsteady aerodynamics and flutter analyses are presented in the transonic flow region. In addition, flow-induced vibration analyses for the isolated cascade and multi-blades cascade models have been conducted to show the physical fluid-structure interaction effects in the time domain.

• Journal of Korean Association for Spatial Structures
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• v.15 no.1
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• pp.75-84
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• 2015

This paper presents the dimensionless wall distance, y+ effect on SST turbulent model for wind turbine blade. The National Renewable Energy Laboratory (NREL) Phase VI wind turbine was used for the study, which the wind tunnel and structural test data has publicly available. The near wall treatment and turbulent characteristics have important role for proper CFD simulation. Most of the CFD development in this area is focused on advanced turbulence model closures including second moment closure models, and so called Low-Reynolds (low-Re) number and two-layer turbulence models. However, in many cases CFD aerodynamic predictions based on these standard models still show a large degree of uncertainty, which can be attributed to the use of the $\epsilon$-equation as the turbulence scale equation and the associated limitations of the near wall treatment. The present paper demonstrates the y+ definition effect on SST (Shear Stress Transport) turbulent model with advanced automatic near wall treatment model and Gamma theta transitional model for transition from lamina to turbulent flow using commercial ANSYS-CFX. In all cases the SST model shows to be superior, as it gives more accurate predictions and is less sensitive to grid variations.

• Journal of the Society of Naval Architects of Korea
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• v.54 no.2
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• pp.132-142
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• 2017

As the International Maritime Organization (IMO) recently introduced the Energy Efficiency Design Index (EEDI) for new ships building and the Energy Efficiency Operational Indicator (EEOI) for ship operation, thus an accurate estimation of added resistance of ships advancing in waves has become necessary. In the present study, OpenFOAM, computational fluid dynamics libraries of which source codes are opened to the public, was used to calculate the added resistance and motions of the KCS. Unstructured grid using a hanging-node and cut-cell method was used to generate dense grid around a wave and KCS. A dynamic deformation mesh method was used to consider the motions of the KCS. Five wavelengths from a short wavelength (${\lambda}/LPP=0.65$) to a long wavelength (${\lambda}/LPP=1.95$) were considered. The added resistance and the heave & pitch motions calculated for various waves were compared with the results of model experiments.

• Proceedings of the KSME Conference
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• 2007.05b
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• pp.2857-2861
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• 2007

Flow and aerodynamic characteristics were analyzed numerically for a commercial passenger airplane, Boeing 747-400, flying in the cruising condition. The model geometry with 100:1 in scale was obtained by the photo scanning measurement with the maximum error of 1.4% comparing with the real airplane dimension. The three-dimensional inviscid steady compressible governing equations were solved by the finite volume method in the unstructured grid system. The convective terms were treated by the Crank-Nicholson and first-order upwind schemes. In the computational results, the strong wing-tip vortices were clearly observed and the pressure contours on the airplane surface were suggested. The lift and drag forces in the wing with engines increase by 1.49% and 3.9%, respectively compared with the case without engines. The aerodynamic forces were estimated quantitatively for each element which consists of the airplane.

• Journal of computational fluids engineering
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• v.19 no.3
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• pp.62-68
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• 2014

The aerodynamic and noise calculations were performed through the CFD-CSD loose coupling methodology. In the loose coupling process, the trimmed rotor airloads were predicted by the in-house CFD code based on unstructured overset meshes, and the trim of the rotorcraft and the aeroelastic deformation of rotor blades were accounted with the CAMRAD II rotorcraft comprehensive code. The set of codes was used to analyze the HART-II baseline test condition. The effect of grid resolution and time step was examined and the loose coupling approach was found to be stable and convergent for the case. Comparison of the resulting sectional airloads, structural deformations, the noise carpets and the wake geometry with experimentally measured data was presented and showed the good agreement.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.311-318
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• 2001

A three-dimensional numerical analysis of the flow and heat transfer characteristic of wood-flour-filled polypropylene melt in an extrusion die was carried out Used for this analysis were Finite Concept Method based on FVM, unstructured grid and non-Newtonian fluid viscosity model. Temperature and flow fields are closely coupled through temperature dependent viscosity and viscous dissipation. With large Peclet, Nahme, Brinkman numbers, viscous heating caused high temperature belt near die housing, Changing taper plate thickness and examining some predefined parameters at die exit investigated the effect of taper plate on velocity and temperature uniformities. In the presence of taper plate, uniformity at die exit could be improved and there existed an optimum thickness to maximize it.