• Journal of KSNVE
• /
• v.9 no.4
• /
• pp.693-702
• /
• 1999

We study the characteristics of airflow and sound noise induced by disk rotation in optical disk drives. The characteristics of airflow around a rotating disk surrounded by various tray structures are numerically investigated using a commercial CFD program and then compared with experimental results. Sound pressure and intensity caused by the fluid-structure interactions in the CD/DVD-ROM drive are measured, and the effect of the ariflow on the sound noise and disk vibration is discussed. In order to reduce airflow-induced noise and vibration around the rotating disk, tray geometry is modified. Both numerical and experimental studies implemented with different tray models show that the improved tray model alters the characteristics of the disk-induced airflow, causing the reduction of the airflow-induced sound level.

• 유체기계공업학회:학술대회논문집
• /
• 2001.11a
• /
• pp.293-299
• /
• 2001

Since the previous cut-and-try design algorithm require much cost and time, it has recently been concerned the automatic design technique using the CFD and optimum design algorithm. In this study, the Navier-Stokes equations is solved to consider the more detail viscous flow informations of cascade interaction and O-H multiblock grid system is generated to impose an accurate boundary condition. The cubic-spline interpolation is applied to handle a relative motion of a rotor to the stator. To validate present procedure, the time averaged aerodynamic loads are compared with experiment and good agreement obtained. Once the N-S equations have been solved, the computed aerodynamic loads may be used to computed the sensitivities of the aerodynamic objective function. The Modified Method of feasible Direction(MMFD) is usef to compute the

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2009.04a
• /
• pp.645-645
• /
• 2009

In many practical applications of the centrifugal fan, the impeller-diffuser interaction noise is considered as a main source of fan noise. The housing for an electric motor is also expected to play an important role on noise propagation because of its complicated configuration. This study investigates the impeller-diffuser interaction noise and its sources by computing three-dimensional, incompressible flow field of the centrifugal fan in motor housing. The effect of motor case on fan noise characteristic is then investigated using the Brinkman penalization method, while the noise source associated with impeller-diffuser interaction is mathematically modeled. It is found that the present methodology combined with mathematical description of noise source provides a fairly good agreement with the experimental results, indicating that the motor housing has significant effect on noise characteristics. Finally, aeroacoustic noise prediction for various impeller-diffuser blade count ratios is conducted for noise reduction.

• 한국전산유체공학회:학술대회논문집
• /
• 2005.04a
• /
• pp.159-168
• /
• 2005

Noise generated by the blunt trailing edge of lifting surfaces is investigated in this study using fluid structure interaction theory. First, through the eddy modeling, noise generation doe to the flow instability on the rigid trailing edge is surveyed. Then the behavior of elastic cantileverd beam is investigated. Parametric study based on various material properties is employed to analyze the motion of the beam. Moreover, each eigenmode approach of cantilevered beam is used to find when flow induced vibration is resonant. To analyze elastic behavior of cantilever beam efficiently, moving grid generation technique based on non-conservative form of Navier-Stokes equation is used. Equation of the motion associated with the cantilever beam is discretized by the Galerkin procedure with forced vibration. As a consequence, behavior of the elastic cantilevered beam is stable when the first mode natural frequency of the material is relatively higher than that of flow induced pressure fluctuation.

• 한국전산유체공학회:학술대회논문집
• /
• 1999.05a
• /
• pp.73-78
• /
• 1999

극초음속 유동장의 정확한 해석을 위해 AUSMPW+ 수치기법과 충격파 포착시 생기는 수치오차를 제거하기 위해 충격파 정렬 기법(Shock-Aligned Grid Technique)을 개발하였다. AUSMPW+ 수치기법은 자체 수치점성이 적은 수치기법으로 점성 경계층 계산시 정확한 계산결과를 보여주며 기존의 AUSM 계열이 가지는 문제점인 물성치의 진동 현상을 제거한 수치기법이다. 원통형과 무딘 물체 주위의 극초음속 유동장 해석을 통해 공력이 진동현상 없이 정확하게 계산됨을 확인하였다. 그리고 충격파 정렬 기법의 특성을 파악하기 위해 충격파 반사문제와 충격파-충격파 상호작용 문제를 해석하여 수치오차 없이 충격파를 포착할 수 있음을 보였다. 또한 화학적 평형 비평형 유동 영역까지 충격파 정렬 격자 기법을 확장하였다.

• Proceeding of EDISON Challenge
• /
• 2013.04a
• /
• pp.349-353
• /
• 2013

공동주위의 유동에 대한 연구결과를 보면 개방형 공동(L/D<10)과 밀폐형 공동(L/D>13)으로 구별하는 데 개방형 공동은 앞전에서 발생한 자유전단층이 뒷전 부근에 재부착하여 공동을 완전히 연결하므로, 자유전단층과 외부유동과의 상호작용으로 발생하는 심한 압력변화에 의해 진동현상이 나타나게 된다. 이것은 큰 소음을 유발하고, 구조물의 고장 혹은 파괴의 원인이 되기도 하고, 공력 성능 및 안정성에 해를 주고 민감한 계기를 손상 시킬 수도 있다. 본 논문에서는 공동을 연구하기 위해 EDISON_CFD를 사용하여 공동의 시뮬레이션하기 위해 격자를 구성하고 세장비를 각각 1/5, 1/3, 1/2, 1, 2, 5 로 변화를 주어 M=1.5 일 때 밀도, 압력, 마하수와 유동구조를 세장비에 따라 결과를 비교, 분석한다.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.16 no.3 s.108
• /
• pp.263-269
• /
• 2006

The objective of the present work is to develop a time-domain numerical method of broadband noise in a cascade of airfoils. This paper focuses on dipolar broadband noise sources, resulting from the interaction of turbulent inflows with the flat-plate airfoil cascade. The turbulence response of a two-dimensional cascade is studied by solving both of the linearised and the full nonlinear Euler equations employing accurate higher order spatial differencing, time stepping techniques and non-reflecting inflow/outflow boundary condition. The time-domain result using the linearised Euler equations shows good agreement with the analytical solution using the modified LINSUB code. Through the comparison of the nonlinear time-domain result using the full nonlinear Euler equations with the linear, it is found that the acoustic mode amplitude of the nonlinear response is less than that of the linear response due to the energy cascade from low frequency components to the high frequency ones. Considering the merits of the time-domain methods over the typical time-linearised frequency-domain analysis, the current method is expected to be promising tools for analyzing the effects of the airfoil shapes, non-uniform background flow, linear-nonliear regimes on the broadband noise due to turbulence-cascade interaction.

• Aerospace Engineering and Technology
• /
• v.7 no.2
• /
• pp.46-52
• /
• 2008

The instrumentation was studied in order to measure aerodynamic performance and efficiency of a compressor as a component of a 5MW-class gas turbine for power generation. In case of an axial compressor, the distributions of static pressure on a casing can be obtained by averaging at each stage and those of total pressure and temperature in the flow field of the compressor can be measured with a Kiel temperature probe. In case of a centrifugal compressor, the static pressures at the hub and the tip, respectively, of an impeller exit are considerably different, so the pressures need to be measured at both positions and thereafter averaged. The distributions of static pressures in a diffuser and a deswirler are measured at ten positions along five streamlines in one pitch. In addition the flow field can be measured in detail by 5-hole Pitot tube in order to analyze the flow characteristics of the core flow region and wake region and the rotor-stator interaction of the compressor.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.39 no.8
• /
• pp.693-702
• /
• 2015

This paper presents the performance characteristics of a Darrieus-type vertical-axis wind turbine (VAWT) with National Advisory Committee for Aeronautics (NACA) airfoil blades. To estimate the optimum shape of the Darrieus-type wind turbine in accordance with various design parameters, we examine the aerodynamic characteristics and separated flow occurring in the vicinity of the blade, the interaction between the flow and blade, and the torque and power characteristics that are derived from it. We consider several parameters (chord length, rotor diameter, pitch angle, and helical angle) to determine the optimum shape design and characteristics of the interaction with the ambient flow. From our results, rotors with high solidity have a high power coefficient in the low tip-speed ratio (TSR) range. On the contrary, in the low TSR range, rotors with low solidity have a high power coefficient. When the pitch angle at which the airfoil is directed inward equals $-2^{\circ}$ and the helical angle equals $0^{\circ}$, the Darrieus-type VAWT generates maximum power.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2012.04a
• /
• pp.521-526
• /
• 2012

It is essential for the accurate time-domain prediction of broadband noise due to turbulence-cascade interaction to develop inflow/outflow boundary conditions to satisfy the following three requirements: to maintain the back ground mean flow, to nonreflect the outgoing disturbances and to generate the specified input gust. The preceding study(1) showed that Perfectly Matched Layer (PML) boundary condition was successfully applied to absorb the outgoing disturbances and to generate the specified gust in the time-domain computations of broadband noise due to interaction of incident gust with a cascade of flat-plates. In present study, PML boundary condition is extended in order to predict steady mean flow that is needed for the computation of noise due to interaction of incident gust with a cascade of airfoils. PML boundary condition is originally designed to absorb flow disturbances superimposed on the steady meanflow in the buffer zone. However, the steady meanflow must be computed before PML boundary condition is applied on the flow computation. In the present paper, PML equations are extended by introducing source term to maintain desired mean flow conditions. The extended boundary condition is applied to the benchmark problem where the meanflow around a cascade of airfoils is predicted. These illustrative computations reveal that the extended PML equations can effectively provide and maintain the target meanflow.