• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 추계학술대회 논문집
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• pp.711-716
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• 2011

Today, high-speed trains enjoy wide acceptance as fast, convenient and environment-friendly means of transportation. However, increase in the speed of the train entails a concomitant increase in the aerodynamic noise, adversely affecting the passenger comfort. At the train speed exceeding 300 km/h, the effects of turbulent flows and vortex sheddding are greatly amplified, contributing to a significant increase in the aerodynamic noise. Drawing a biomimetic analogy from low-noise flight of owl, a method to reduce aerodynamic noise at inter-coach space of high-speed trains is investigated. The proposed method attempts to achieve the noise reduction by modifying the turbulent flow and vortex shedding characteristics at the inter-coach space. To determine the aerodynamic noise at various train speeds, wind tunnel testing and numerical CFD (Computational Fluid Dynamics) simulation for the basic inter-coach spacing model are carried out, and their results compared. The simulation and experimental results reveal that there are discrete frequency components associated with turbulent air flow at constant intervals in the frequency domain

• 국제초고층학회논문집
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• 제11권4호
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• pp.287-300
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• 2022

Unconventional structures are getting more popular in recent days. Large-span roofs are used for many structures, such as airports, stadiums, and conventional halls. Identifying the pressure distribution and wind load acting on those structures is essential. This paper offers a collaborative study of computational fluid dynamics (CFD) simulations and wind tunnel tests for assessing wind pressure distribution for a building with a combined slender curved roof. The hybrid turbulence model, Improved Delayed Detached Eddy Simulation (IDDES), simulates the open terrain turbulent flow field. The wind-induced local pressure coefficients on complex roof structures and the turbulent flow field around the structure were thus calculated based upon open terrain wind flow simulated with the FLUENT software. Local pressure measurements were investigated in a boundary layer wind tunnel simultaneous to the simulation to determine the pressure coefficient distributions. The results predicted by CFD were found to be consistent with the wind tunnel test results. The comparative study validated that the recommended IDDES model and the vortex method associated with CFD simulation are suitable tools for structural engineers to evaluate wind effects on long-span complex roofs and plan irregular buildings during the design stage.

• 한국전산유체공학회지
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• 제21권4호
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• pp.61-70
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• 2016

Dong-tan Station, shared by high-speed railway and urban express railway, is a very complicated underground station having 6 tracks together with barrier and shafts between them, therefore it seems very hard to investigate the aerodynamic effects including the pressure variation and train gust in the station when a high-speed train runs through it. In this study, the aerodynamic effects on the structures and platform passengers when a high-speed train runs through an underground station have been studied using Computational Fluid Dynamics. STAR-CCM+ has been employed for numerical simulation based on Navier-Stokes equation and 2-equation turbulence model and moving mesh scheme supported by STAR-CCM+ has also been used to represent the relative motion between a train and station. Based on the simulation results, the unsteady flow fields in the underground station induced by the high-speed train have been analyzed and the pressures on the PSDs and pressure variation at the platform have quantitatively assessed.

• International Journal of Aeronautical and Space Sciences
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• 제14권1호
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• pp.30-45
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• 2013

The present work focuses on the unsteady aerodynamics and aeroelastic properties of a small-medium sized wind-turbine blade operating under ideal conditions. A tapered/twisted blade representative of commercial blades used in an experiment setup at the National Renewable Energy Laboratory is considered. The aerodynamic loads are computed using Computational Fluid Dynamics (CFD) techniques. For this purpose, FLUENT$^{(R)}$, a commercial finite-volume code that solves the Navier-Stokes and the Reynolds-Averaged Navier-Stokes (RANS) equations, is used. Turbulence effects in the 2D simulations are modeled using the Wilcox k-w model for validation of the CFD approach. For the 3D aerodynamic simulations, in a first approximation, and considering that the intent is to present a methodology and workflow philosophy more than highly accurate turbulent simulations, the unsteady laminar Navier-Stokes equations were used to determine the unsteady loads acting on the blades. Five different blade pitch angles were considered and their aerodynamic performance compared. The structural dynamics of the flexible wind-turbine blade undergoing significant elastic displacements has been described by a nonlinear flap-lag-torsion slender-beam differential model. The aerodynamic quasi-steady forcing terms needed for the aeroelastic governing equations have been predicted through a strip-theory based on a simple 2D model, and the pertinent aerodynamic coefficients and the distribution over the blade span of the induced velocity derived using CFD. The resulting unsteady hub loads are achieved by a first space integration of the aeroelastic equations by applying the Galerkin's approach and by a time integration using a harmonic balance scheme. Comparison among two- and three- dimensional computations for the unsteady aerodynamic load, the flap, lag and torsional deflections, forces and moments are presented in the paper. Results, discussions and pertinent conclusions are outlined.

• 한국자동차공학회논문집
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• 제20권5호
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• pp.26-35
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• 2012

This paper investigates the influence on the aerodynamic performance of a passenger cruising very fast by some specific car body parts such as side mirrors, wheel arches and wheels designed hardly regarding aerodynamics. The magnitude of the contribution of each part is analyzed via on the CFD simulations. YF SONATA, a sedan of Hyundai Motors Company, plays a major role as the baseline car in this research, representing all passenger car. The CFD analysis condition consists of 6 different cases depending on whether each part exists or not. According to the CFD results, there were confirmed that additionally to the body parts' own drag, the car body went through somewhat the consequential increment of the drag by them. Among the 3 parts, wheel is the magnate that not only has the maximal drag but drives the drag of the passenger car to increase most steeply and the next is the side mirror.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 춘계학술대회논문집
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• pp.39-42
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• 2009

The aerodynamic characteristics of aircraft winglet with structural deformation was investigated using the static FSI(Fluid-Structure Interaction) system. The system, comprised of CAD, CFD, CSD, VSI, and grid regeneration modules, was constructed. In the process VSI, grid regeneration, and integration modules were developed to combine CSD and CFD modules. As a test model, KC-135A, the double winglet suggested by Whitcomb, was selected and its aerodynamic characteristics for the rigid and deformable models was calculated by applying the static FSI system. As a result, the lift and drag coefficients of test models were reduced to 11% and 1.3%, respectively.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2000년도 추계 학술대회논문집
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• pp.15-24
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• 2000

The transient response of an airfoil to a rapidly deploying spoiler is numerically investigated using the turbulent compressible Navier-Stokes equations in two dimensions. Algebraic Baldwin-Lomax model, Wilcox $\kappa-\omega$ model, and SST $\kappa-\omega$ turbulence model are used to calculate the unsteady separated flow due to the rapid spoiler deployment. The spoiler motion relative to a stationary airfoil is treated by an overset grid hounded by a Dynamic Domain-Dividing Line which has been devised by the authors. The adverse effects of the spoiler influenced by the spoiler location and the hinge gap are expounded. The numerical results are in reasonably good agreement with the existing experimental data.

• Wind and Structures
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• 제20권6호
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• pp.811-827
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• 2015

This study presents experimental and numerical aerodynamic investigation of a prototype vehicle. Aerodynamics forces examined which exerted on a prototype. This experimental study was implemented in a wind tunnel for the Reynolds number between $10^5-3.1{\times}10^5$. Numerical aerodynamic analysis of the vehicle is conducted for different Reynolds number by using FLUENT CFD software, with the k-$\varepsilon$ realizable turbulence model. The studied model aims at verifying the aerodynamic forces between experimental and numerical results. After the Reynolds number of $2.8{\times}10^5$, the drag coefficient obtained experimentally becomes independent of Reynolds number and has a value of 0.25.

• 한국유체기계학회 논문집
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• 제13권2호
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• pp.18-23
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• 2010

This paper presents a procedure for the aerodynamic and aeroacoustic characteristics of a sirocco fan. For the aerodynamic and aeroacoustic analyses of the sirocco fan, three-dimensional steady and unsteady Reynolds-averaged Navier-Stokes equations are solved with a shear stress transport turbulence model for turbulence closure. The flow analyses were performed on a hexahedral grid using a finite-volume solver. The validation of the numerical results is performed by comparing with experimental data for the pressure, efficiency and power. The internal flow analyses of the sirocco fan are performed to understand the unstable flow phenomenon on the casing for the wall pressure and internal flow characteristics at each position. It was found that fluctuation of pressure and locally concentrated noise source are observed near the cut-off and expansion regions of the casing.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 추계 학술대회논문집
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• pp.77-81
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• 2007

In this paper, helicopter aerodynamics is simulated in hovering and forwarding flighst. The governing equation is the unsteady Euler equation. To consider the blade motion and moving effects, an overset grid technique is applied in this simulation. At the boundary, the Riemann invariants condition is used for inflow and outflow. To validate this method, the result is compared with Caradonna-Tung's experimental data.