• Proceedings of the Korean Society of Precision Engineering Conference
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• 2004.05a
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• pp.99-99
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• 2004

CD-ROM에서 생성되는 소음은 구조소음과 공력소음의 분포비율을 생각해 볼 때 하드디스크 등의 경우와는 다소 다른 특성이 있는데, 구조적으로 차폐나 디스크의 크기 및 회전속도 등의 차이로 인해 공력소음의 비중이 매우 커진 점을 들 수 있다. 공기역학적으로 생성되는 소음은 구조소음의 경우와는 다르게 에너지 분포가 주기성을 찾아보기 어려우며 널은 주파수 대역에 고루 분포하는 특징이 있다.(중략)

• Aerospace Engineering and Technology
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• v.2 no.1
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• pp.35-43
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• 2003

In this study, a rotor planform shape with high performance and low noise has been designed and its aerodynamic and aeroacoustic characteristics are analysed. First of all, rotor blade planform with low noise characteristics, has been designed based on the paddle-shape blade by applying vane-tip concept. Finally, noise characteristics of the designed next-generation rotor blade have been investigated and the results are compared with those of BERP blade.

• Aerospace Engineering and Technology
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• v.5 no.2
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• pp.27-36
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• 2006

This paper describes the performance test procedures and results of NRSB-1M and NRSB-2M Not only aerodynamic performance test but also sound measurement test were performed for the small-scaled blades in the ground Total thrusts and torques of the rotor were measured using rotating balance for aerodynamic performance test. Sound pressure levels were measured using microphone in 1.64D distance for sound measurement test. Non-dimensionalized test data are compared and analyzed. Consequently, It was confirmed that NRSB-2 was better than NRSB-1.

• Journal of Aerospace System Engineering
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• v.17 no.2
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• pp.26-37
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• 2023

Urban air mobility (UAM) is being developed as part of the next-generation aircraft, which could be a viable solution to entrenched problems of urban traffic congestion and environmental pollution. A new airport platform called vertiport as a space where UAM can take off and land vertically is also being introduced. Noise regulations for UAM will be strict due to its operation in a highly populated urban area. Ground effects caused by vertiport can directly affect aerodynamic forces and noise characteristics of UAM. In this study, ground effects of vertiport on aerodynamic loads, vorticity field, and far-field noise were analyzed using Lattice-Boltzmann Method (LBM) simulation and Ffowcs Williams and Hawkings (FW-H) acoustic analogy with a permeable surface method.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.2
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• pp.83-91
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• 2003

Pantograph design Process must be considered in terms of stability of aerodynamics and reduction of aeroacoustics. Furthermore pantograph needs to be insensible to severe circumstance condition like typhoon, tunnel, a change of season. In this paper, robust design of panhead sections is conducted based on the Taguchi's design of experiment method. In the aeroacoustic noise analysis, an acoustic analogy using the Ffowcs Williams and Hawkings(FW-H) equation is used to calculate the flow induced sound pressure level in aeroacoustics. From the near-field CFD analysis data, the far-field noise is predicted at the positions of 25 m away from Pantograph. Based on aerodynamic(CFD) and aeroacoustic(FW-H) analysis data, the optimal sizing and Positioning of panhead elements are determined using robust design optimization method. Design parameters such as thickness, length and radius are controllable factors, while outdoor air temperature and atmospheric pressure are considered as uncontrollable factors in the context of Taguchi's approach. A number of CFD simulation and aeroacoustic analysis are performed based on orthogonal arrays. In this paper, two-step optimization method is used as a parameter design procedure. It is executed using signal to noise(S/N) ratio and analysis of means(ANOM) method. So Thus, an optimal level of design parameters Is extracted to minimize the disconnection ration between contact strips and catenary system, and reduce the far-field aeroacoustic noise.

• The KSFM Journal of Fluid Machinery
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• v.13 no.2
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• pp.59-64
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• 2010

A design method of Sirocco fan is developed for constructing 3-D impeller and scroll geometries, and for predicting both the aerodynamic performance and the noise characteristics of the designed fan. The aerodynamic blading design of fan is conducted by blade angle, camber line determinations and airfoil thickness distribution, and then the scroll geometry of fan is designed by using logarithmic spiral. The aerodynamic performance of designed fan is predicted by the meanline analysis with flow blockage, slip and pressure loss correlations. Based on the predicted performance data, fan noise is predicted by two models for cutoff frequency and broadband noise sources. The present predictions for the performance and the noise level of actual fans are well agreed with measurement results.

• Journal of the Korean Society for Railway
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• v.19 no.3
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• pp.271-279
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• 2016

Pantograph aerodynamic noise is a major cause of noise that occurs when a train is traveling at high speeds. In this study, in order to analyze the contribution of pantograph aerodynamic noise, real train tests using HEMU-430X were carried out. In order to analyze the frequency characteristic of the noise of the pantograph in an actual vehicle, a sound field visualization has been carried out using a 144-channel microphone array at train speeds of 350 and 400km/h. As a result, it was confirmed that the low frequency noise in the 250~400Hz bandwidth provides the main contribution to the pantograph noise. And, in order to estimate the noise contribution of the pantograph, the noise level difference between cases in which the pantograph is ascending and those in which it is descending were compared in single microphone experiments. The frequency analysis in the single microphone tests showed that the bands of 315~400Hz and 1000~1250Hz are the main frequency characteristics of pantograph noise. These results show quite good agreement with those of previous studies and with results of sound field visualization.

• Proceedings of the KSR Conference
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• 2008.11b
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• pp.416-421
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• 2008

Recent high-speed trains around the world have achieved remarkable improvement in speed. In Korea, the new high-speed train with maximum speed of 400km/h has been developing through the 'Future High-Speed Rail System Project'. The improvement in train speed brings numerous aerodynamic problems such as strong aerodynamic resistance, noise, drastic pressure variation due to the crosswind or passing by, micro-pressure wave at tunnel exit, and so on. Especially, the nose shape of high-speed train is closely related to the most of the aerodynamic problems. Also the pantograph has to be considered for noise prevention and detachment problems. In this paper, the project, 'Research on the Aerodynamic Technology Advancement of the High-Speed EMU' is introduced briefly, which is one of the efforts for the speed improvement of the 'HEMU400x'. Finally, two main results of train nose and pantograph will be shown. First, the optimization of the cross-sectional area distribution of the high-speed train nose to reduce tunnel micro-pressure wave, and second, robust design optimization of the panhead shape of a pantograph.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.38 no.3
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• pp.269-274
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• 2014

In this study, low noise designs for a Savonius wind turbine were numerically investigated. As was reported in our previous study, the harmonic components with a fundamental frequency higher than the BPF were identified as being dominant in the noise spectrum of a Savonius wind turbine, and these components were a result of vortex shedding. On a basis of this observation, an S-shaped blade tip is proposed as a means of reducing the noise generated by small vertical(Savonius) wind turbines. This blade induces phase differences in the shedding vortices from the blades, and thus reduces the noise from the wind turbine. The aerodynamic noise characteristics of the conventional and "S-shaped" Savonius turbines were investigated by using the Hybrid CAA method where the flow field around the turbine is computed using the CFD techniques and the radiated noise are predicted by applying acoustic analogy to the computed flow field data. The degree of noise reduction resulting from the proposed design and its reduction mechanism were confirmed by comparing the predicted noise spectrum of these turbines and the flow characteristics around them.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.815-817
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• 2012