• The Journal of the Acoustical Society of Korea
• /
• v.37 no.2
• /
• pp.92-98
• /
• 2018

This paper is a study on the generation mechanism of propeller singing based on the cavitation tunnel test, underwater impact test, finite element analysis and computational flow analysis for the model propeller. A wire screen mesh, a propeller and a rudder were installed to simulate ship stern flow, and occurrence and disappearance of propeller singing phenomenon were measured by hydrophone and accelerometer. The natural frequencies of propeller blades were predicted through finite element analysis and verified by contact and non-contact impact tests. The flow velocity and effective angle of attack for each section of the propeller blades were calculated using RANS (Reynolds Averaged Navier-Stokes) equation-based computational fluid analysis. Using the high resolution analysis based on detached eddy simulation, the vortex shedding frequency calculation was performed. The numerical predicted vortex shedding frequency was confirmed to be consistent with the singing frequency and blade natural frequency measured by the model test.

• Journal of the Society of Naval Architects of Korea
• /
• v.51 no.6
• /
• pp.480-488
• /
• 2014

Vortex shedding which is the dominant feature of body wakes and of direct relevance to practical engineering problems, has been intensively studied for flows past a circular cylinder. In contrast, vortex shedding from a hydrofoil trailing edge has been studied to much less extent despite numerous practical applications. The physics of the problem is still poorly understood. The present study deals with $K{\acute{a}}rm{\acute{a}}n$ vortex shedding from a truncated trailing-edge hydrofoil in relatively high Reynolds number flows. The objectives of this paper are twofold. First, we aim to simulate unsteady turbulent flows past a two dimensional hydrofoil through a hybrid particle-mesh method and penalization method. The vortex-in-cell (VIC) method offers a highly efficient particle-mesh algorithm that combines Lagrangian and Eulerian schemes, and the penalization method enables to enforce body boundary conditions by adding a penalty term to the momentum equation. The second purpose is to investigate shedding frequencies of vortices behind a NACA 0009 hydrofoil operating at a zero angle of attack.

• Proceedings of the Korean Society of Propulsion Engineers Conference
• /
• 2011.11a
• /
• pp.31-37
• /
• 2011

Detail flow structure in a large solid rocket motor with two inhibitors has been investigated using 3D Large Eddy Simulation and Proper Orthogonal Decomposition(POD) analysis. Vortex shedding frequencies periodically occurred by inhibitors are coupled with flow acoustics induced by the impinging of vorticity on nozzle head. As a result of 3D analysis, it was observed that the nozzle exit flow causes roll-torques from the vortex being decomposed in unbalanced shape for the impinging of vorticity on the nozzle head.

• Journal of the Society of Naval Architects of Korea
• /
• v.49 no.2
• /
• pp.151-157
• /
• 2012

The present study explored the possibilities of the applications of open source libraries to shipbuilding and marine engineering industries. A computational fluid dynamics (CFD) code, termed SNUFOAM, was developed and tested for turbulent flow around a ship, free surface flow around a hull, cavitating flow, and vortex shedding dynamics around a cylinder. The results using the developed CFD codes were compared against existing experimental data and solution of commercial CFD codes. SNUFOAM showed the nearly same results as commercial CFD codes and proved to be an alternative to commercial CFD codes for shipbuilding and marine engineering industries.

• Journal of the Society of Naval Architects of Korea
• /
• v.48 no.5
• /
• pp.414-420
• /
• 2011

Decades of studies of geophysical flow have unveiled that the flow downstream of obstacles in stratified flow consists of attached wake and strong gravity waves, or separated, fluctuating wake and persistent late wakes. Among unique and interesting characteristics of the stratified flow past obstacles is the generation of coherent vortex in the late wake far downstream of the object. Unlike in homogeneous fluid, the flow field downstream self-develops coherent vortex even after diminishing of the near wake, no matter how small the stratification is. This paper present a computational approach to simulate the generation of the coherent vortex structure in the late wake of a moving sphere submerged in weakly stratified fluid. The results are in consistent with several experimental observations and the vortex stretching mechanism is employed to explain the process of coherence.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2006.05a
• /
• pp.1007-1010
• /
• 2006

In order to optimize the rotating angle of the auto louver, the air-cleaner with turbo fan was numerical and experimentally analyzed . The noise generated from the auto louver was changed by modifying the installation angle of the louver. Flow field and flow noise were analyzed numerically by commercial tool SC/Tetra and FlowNoise S/W. Experiment was also done at anechoic chamber. From the numerical and experimental data, we can find the optimal rotating angle for auto louver of the air-cleaner.

• Proceeding of EDISON Challenge
• /
• 2014.03a
• /
• pp.579-584
• /
• 2014

고속 열차의 속도가 점점 빨라짐에 따라 고속 열차 주행 시 발생하는 여러 공력적인 문제가 대두되고 있다. 그 중 고속 열차와 전력선을 이어주는 판토그래프에서의 소음 발생과 압상력 불안정 문제가 중요시 되어왔고 이에 대한 여러 선행연구가 진행되고 있다. 지금까지의 선행 연구는 원형, 사각형, 에어포일과 같이 기본적인 형상을 이용한 판토그래프 팬헤드의 최적 단면 형상을 찾는 데에 초점을 맞추고 있다. 본 연구는 이러한 주류의 접근 방식에서 벗어나 팬헤드에 구멍을 추가하여 그 효과를 보는 다양한 시도를 해보았고 구멍이 소음 발생과 압상력 불안정에 미치는 영향에 대하여 연구하였다.

• Journal of computational fluids engineering
• /
• v.7 no.1
• /
• pp.20-27
• /
• 2002

Flow over a circular cylinder is studied numerically using a turbulence model. Based on the κ-ε-f/sub μ/ model of Park and Sung[6], a new damping function is used. The efficiency of the strain dependent damping function is addressed for vortex-shedding flows past a circular cylinder. The mean velocity and Reynolds stresses are compared with available experimental data at Re/sub D/= 3900. Also, the computational results for the Strouhal number are evaluated at several Reynolds number. The predictions by κ-ε-f/sub μ/ model are in good agreement with the experiments.

• Journal of computational fluids engineering
• /
• v.16 no.3
• /
• pp.22-28
• /
• 2011

Laminar Flow over an equilateral triangular cylinder is studied for several inflow angles. Under an uniform flow of $Re_d$=50,75,100,125,150, the triangular cylinder is rotated by ${\theta}$=$0^{\circ}$,$15^{\circ}$,$30^{\circ}$,$45^{\circ}$,$60^{\circ}$,$75^{\circ}$,$90^{\circ}$,$105^{\circ}$. The governing equations are solved by the PISO algorithm based on the finite volume method of the unstructured grid system. The effects of the inflow angle on the vortex-shedding flows are investigated. The Strouhal number shows a minimum at ${\theta}$=$60^{\circ}$. It is closely related to the variation of pressure and flow structure induced by the movement of separation points.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.44 no.5
• /
• pp.381-390
• /
• 2016

In this study, aeroacoustic characteristics of combined fan are investigated and noise was reduced by applying Serrated Trailing Edge which is known as the method to reduce fan noises. Unsteady CFD (Computational Fluid Dynamics) analysis was carried out using Lattice Boltzmann Method(LBM) to figure out the combined fan's aeroacoustics and experimental results was used to verify simulation results. Results show that different BPFs are generated at the each inner fan and outer fan on the different frequency while Blade Passing Frequency(BPF) of general fans is constant on the entire frequency range. Boundary vortex and vortex shedding are suppressed or dispersed by applying the Serrated Trailing Edge to the inner fan. Furthermore, broadband noise and fan's torque are reduced.