• 한국유체기계학회 논문집
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• 제13권2호
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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.

• 대한기계학회논문집B
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• 제41권8호
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• pp.521-529
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• 2017

본 연구에서는 항공기 추진용 가스터빈 엔진의 고증속 터빈 제1단 정익 익렬을 새로이 구축하고, 이 정익의 기본 유동 특성에 대하여 연구하였다. 그 결과 본 연구에서 도입된 정익의 압력면에는 강한 순압력구배가 존재하는 반면, 흡입면에는 앞전에서 미드코드 근처까지 압력면보다 훨씬 더 심한 순압력구배가 존재하고 그 이후 역압력구배가 존재하였다. 두 종류의 유막법을 적용한 유동의 가시화 실험을 통하여, 정익 앞전 상류 영역에 4와류모델 말발굽와류 시스템이 존재함을 확인하였고, 입구 경계층 유동의 박리선과 재부착 유동의 박리선을 정확히 파악하였다. 이와 함께 이 고증속 정익 익렬 하류에서의 2차유동, 압력손실, 선회각, 등에 대한 데이터를 확보하였다.

• 한국전산유체공학회지
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• 제17권3호
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• pp.53-58
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• 2012

Steady flow simulations through a high pressure turbine guide vanes were carried out. The main objective of the present work is to study the performance of turbulence models on the steady flow prediction from aerodynamic and aerothermal points of view. Three turbulence models were compared, namely SST, k-${\omega}$ and ${\omega}$-Reynolds stress models. The laminar results were also compared. The comparison was done with emphasis on the isentropic Mach number and heat transfer coefficient along the blade, and total pressure loss in the wake region. The calculated isentropic Mach number showed reasonable agreement with experimental data along the blade surface for all three turbulent models. For the total pressure loss in the wake region, ${\omega}$-Reynolds stress model showed the best agreement with the experimental data. However, unless using an appropriate transition model, the heat transfer coefficients of all three turbulent models showed poor agreement with experimental data.

• 대한기계학회논문집
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• 제18권12호
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• pp.3404-3412
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• 1994

The present study was undertaken to investigate the dry wear process and wear mechanism of the alumina ceramics in the purity variation which are used for the mechanical seal, roll, liner and dies. The wear test was carried out under different experimental condition using the wear testing device and in which the annular surface rubbed on dry sliding condition various sliding speed, contact pressure and sliding distance. In case of alumina purity 95%, there was speed range which wear loss increased rapidly owing to enlargement of heat impact force and temperature rise of wear surface. According as the alumina purity increased, wear loss decreased but alumina purity 85% with much void and defect had the most wear loss than any other alumina purity. The friction coefficient of sliding initial stage of wear curves has a large value but according to increase of sliding distance, it decreased owing to drop of the shear strength of wear surfaces.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2004년도 춘계학술대회논문집
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• pp.718-723
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• 2004

The insertion loss of a noise barrier comes from the effects of diffraction, transmission loss, absorption coefficient and attenuation by direct propagation. The noise level after the noise barrier, differs reatly from the diffraction on the upper part of the barrier. Maekawa, furze and Anderson presented a empirical formula for calculating the diffraction of a semi infinte screen shaped noise barrier. In this syudy, Noise reduction performance software was developed for the proper design and assessment of new plastic barrier . Predicted sound pressure level from using the software is compared with the site-measurement results to verify the noise reduction performance and feasibility of prediction software for insertion loss of noise barrier.

• 한국추진공학회지
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• 제21권4호
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• pp.89-95
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• 2017

본 논문에서 극저온 추진제를 사용하는 액체추진기관의 재순환예냉 시스템 설계의 유연성을 확보하기 위한 연소기 산화제 개폐밸브 재순환예냉 유로의 유량계수 개선 내용을 소개하였다. 밸브의 재순환 예냉 출구 포트 크기와 밸브 내부 유로 형상 변경에 의한 재순환예냉 유로의 유량계수 값을 예측하기 위해서 기존 밸브에서 측정한 재순환예냉 유로의 유량계수 값들을 활용하였으며, 액체질소를 운용유체로 사용하여 측정한 유량계수와 예측값과의 비교를 통해 밸브 내부 형상 변경에 의한 유량계수 개선정도를 확인하였다. 연소기 산화제 개폐밸브의 재순환예냉 유로의 유량계수는 기존 밸브에 비해 2배가량 향상되었으며, 결과적으로 연소기 산화제 개폐밸브에 할당되었던 설계 요구 차압의 75%가량을 재순환예냉 시스템에서 추가적으로 소요될 수 있는 잠재적인 차압과 재순환예냉 시스템의 다른 구성품의 추가 차압으로 활용될 수 있을 것으로 기대된다.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2006년도 하계학술발표대회 논문집
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• pp.590-595
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• 2006

This paper presents the friction and anti-wear characteristics of nano-oil with a mixture of a refrigerant oil and carbon nano-particles in the thrust slide-bearing of scroll compressors. Frictional loss in the thrust slide-bearing occupies a large part of total mechanical loss in scroll compressors. The characteristics of friction and anti-wear using nano-oil are evaluated using the thrust bearing tester for measuring friction surface temperature and the coefficient of friction at the thrust slide-bearing as a function of normal loads up to 4,000 N and orbiting speed up to 3,200 rpm. It is found that the coefficient of friction increases with decreasing orbiting speed and normal force. The friction coefficient of carbon nano-oil is 0.015, while that of pure oil is 0.023 under the conditions of refrigerant gas R-22 at the pressure of 5 bars. It is believed that carbon nano-particles can be coated on the friction surfaces and the interaction of nano-particles between surfaces can be improved the lubrication in the friction surfaces. Carbon nano-oil enhances the characteristics of the anti-wear and friction at the thrust slide-bearing of scroll compressors.

• 한국항공우주학회지
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• 제44권12호
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• pp.1062-1070
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• 2016

본 연구에서는 전산해석을 통해 냉각 터빈 블레이드 팁 간극의 유동 및 열전달 특성을 연구하였다. 1단 고압터빈 노즐 출구에서 획득한 속도, 온도 프로파일을 로터의 입구에 적용하여 로터 도메인을 대상으로 전산해석을 하였다. 스퀼러 팁이 적용된 블레이드의 팁 간극을 스팬의 1%부터 2.5%로 조절하여 팁 간극의 공력 손실, 열전달 계수와 막냉각 효율의 영향을 고찰했다. 팁 간극이 커질수록 출구에서 공력 손실과 블레이드 끝단 표면에서 열전달 계수는 증가하였다. 특히 팁 간극이 스팬의 2%일 때 평균 열전달 계수가 급격히 증가하였다. 팁 영역의 막냉각 효율은 팁 간극이 작을수록 높았고, 캐비티 내부 냉각 홀 근처의 막냉각 효율이 높았다.

• Journal of the Korean Data and Information Science Society
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• 제22권2호
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• pp.287-296
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• 2011

36명의 여대생을 대상으로 체 지방 감소효과에 대한 실험을 실시하였다. 이 실험에서 처리는 매일 섭취하는 식사종류 및 양에 대한 식사일지 작성과 카메라 폰으로 찍어 실험관리자에게 전송하여 매주상담을 받는 것이다. 실험관리자는 체 지방 및 관련된 자료를 일주일마다 측정하여 8주간의 반복측정자료를 얻었다. 이 실험자료를 이용하여 혼합모형의 일종인 변량계수모형을 이용하여 추정 및 유의성 검정을 실시한 결과, 유의한 고정인자들은 처리 전체지방 값, 비만지수, 확장기 혈압, 총 콜레스테롤 및 시간이다. 처리 후 시간에 따른 체 지방 감소는 2차 함수의 관계가 성립된다. 변량인자인 개체효과와 개체와 시간과의 교호작용에서 1차 함수의 관계가 존재한다. 처리 후 시간이 지남에 따라 체 지방 량은 점점 감소하였으며, 실험실시 8주 후에는 평균 2.1kg 감소한 효과가 있음을 보여주었다.

• Wind and Structures
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• 제16권1호
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• pp.1-23
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• 2013

The wind-induced transient response of internal pressure following the creation of a sudden dominant opening during the occurrence of high external pressure, in low-rise residential and industrial buildings was numerically investigated. The values of the ill-defined parameters namely the flow contraction coefficient, loss coefficient and the effective slug length were calibrated by matching the analytical response with the computational fluid dynamics predictions. The effect of a sudden i.e., "instantaneously created" windward opening in the Texas Technical University (TTU) test building envelope was studied for two different envelope flexibility-leakage combinations namely: (1) a quasi-statically flexible and non-porous envelope and (2) a quasi-statically flexible and porous envelope. The responses forced by creating the openings at different time leads/lags with respect to the occurrence of the peak external pressure showed that for cases where the openings are created in close temporal proximity to the peak pressure, the transient overshoot values of internal pressure could be higher than the peak values of internal pressure in the pre-sequent or subsequent resonant response. In addition, the influence of time taken for opening creation on the level of overshoot was also investigated for the TTU building for the two different envelope characteristics. Non-dimensional overshoot factors are presented for a variety of cavity volume-opening area combinations for (1) buildings with rigid/quasi-statically flexible non-porous envelope, and (2) buildings with rigid/quasi-statically flexible and porous envelope (representing most low rise residential and industrial buildings). While the factors appear slightly on the high side due to conservative assumptions made in the analysis, a careful consideration regarding the implication of the timing and magnitude of such overshoots during strong gusts, in relation to the steady state internal pressure response in cyclonic regions, is warranted.