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박용 중속 디젤 엔진 밸브트레인의 이상 소음 원인 규명
김원현(Won Hyun Kim),김훈석(Hoon Suk Kim),이수목(Soo Mok Lee) 대한기계학회 2010 대한기계학회 춘추학술대회 Vol.2010 No.11
An abnormal noise was detected in the valve train of newly developed medium speed diesel engine during the shop test. The valve train system and cam profiles were designed based on the kinetic and kinematic analyses. And the vibration characteristics of camshaft were also considered. Nevertheless, the impulse noise was generated and it was confirmed that this is due to the crashing of intake valve in closing timing at the initial test. To investigate the root causes, the dynamic behaviors of valve train system and the torsional vibration of camshaft were measured. From these experiments and the additional analysis, it was concluded that the one of the cause of crashing is coincidence of intake valve closing timing and the fuel cam timing. The other one is the maximum acceleration of intake cam which close to maximum operating speed of valve train. In this work, the intake cam profile was modified to reduce the maximum valve acceleration and then the abnormal noise was disappeared.
난류모델을 이용한 기체수소-액체산소 화염에 대한 수치해석
김원현(Won Hyun Kim),박태선(Tae Seon Park) 한국추진공학회 2012 한국추진공학회 학술대회논문집 Vol.2012 No.11
초임계조건의 기체수소/액체산소 화염의 난류유동 및 온도장에 대해 난류모델을 이용한 해석이 수행되었다. 실제유체의 연소유동을 해석하기 위하여 화염편모델에 SRK 상태방정식이 도입되었다. 수정된 압력-속도-밀도 연계알고리듬이 초임계유동에 적용되었다. 실험결과를 참조로 6개의 대류항 차분법과 4개의 난류모델의 성능비교가 이루어졌다. 결과로부터 대류항차분법과 난류모델에 대한 예측성이 조사되었다. 선택된 난류모델들은 실제유체 연소유동의 다양한 특징을 고려하기 위해서 수정이 필요함을 나타내었다. Turbulent flow and thermal fields of gaseous hydrogen/liquid oxygen flames at supercritical pressure are investigated by turbulence models. The modified Soave-Redlich-Kwong (SRK) EOS is implemented into the flamelet model to realize real-fluid combustions. For supercritical fluid flows, the modified pressure-velocity-density coupling are introduced. The relative performance of six convection schemes and the predictions of four turbulence models are compared. From the results, the capability of conventional convection schemes for real-fluid combustions and the predictability for each turbulence model are examined. The selected turbulence models are needed to be modified to consider various characteristics of real-fluid combustions.
배플이 부착된 마이크로 연소기의 난류유동 및 연소에 대한 수치해석 연구
김원현(Won Hyun Kim),박태선(Tae Seon Park) 한국추진공학회 2013 한국추진공학회 학술대회논문집 Vol.2013 No.5
배플이 있는 마이크로 연소기의 난류유동 및 연소특성이 레이놀즈 응력 모형에 의하여 조사되었다. 형상변화에 따른 난류유동 및 연소에 대한 영향을 살펴보기 위하여, 여러 개의 배플형상이 선택되었다. 유동구조와 온도장의 상관관계가 재순환 영역, 화염크기, 열손실 변화에 의해 조사되었다. 유체간의 혼합은 공기유입구의 직경이 감소하는 경우가 연료유입구의 직경이 감소하는 경우보다 더 빠르게 나타났다. 연료 또는 공기유입구의 직경이 감소함에 따라 연소효율은 증가하였고, 화염길이는 감소하였다. 또한, 공기유입구의 직경이 감소함에 따라 연소온도와 열손실이 증가하고, 반면에 연료유입구의 직경이 감소함에 따라 연소온도와 열손실은 감소되었다. Turbulent flow and combustion characteristics in a micro can combustor with a baffle plate are investigated by a Reynolds Stress Model. In order to examine the geometric effects on the flow and combustion, several configurations are selected for different baffles. The interrelation between the flow structure and the thermal field are inspected by the variation of recirculation region, flame length and heat loss. The flow mixing is faster in case of air hole diameter decreases than fuel hole diameter decreases. As the fuel or air hole diameter decreases, combustion efficiency is enhanced and flame length is decreased. Additionally, as the diameter of air hole decreases, the heat loss and combustion temperature are increased, while the heat loss and combustion temperature are reduced with decreasing the diameter of fuel hole.
입구유동 가진이 있는 층류 후향계단 유동에서 열전달에 대한 Prandtl 효과해석
김원현(Won Hyun Kim),박태선(Tae Seon Park) 대한기계학회 2011 대한기계학회 춘추학술대회 Vol.2011 No.10
This study the effect on Prandtl numbers on heat transfer of backward-facing step laminar flow with a pulsating inlet. The characteristics of laminar backward-facing step flow with pulsating inlet are investigated using temperature dependent function of dynamic viscosity and thermal conductivity with unsteady flow simulation. In order to analyze the effect of Prandtl numbers on heat transfer are selected for various values of Prandtl numbers, the dimensionless pulsating frequency and amplitude. The result showed that, an improvement in Nusselt number observed for the increasing pulsating amplitude and both heat transfer enhancement and reduction were detected depending on pulsating frequency
원형/비원형 난류 제트 유동의 혼합 특성 변화에 대한 수치 해석 연구
김원현(Won Hyun Kim),박태선(Tae Seon Park) 대한기계학회 2020 대한기계학회 논문집. Transactions of the KSME. C, 산업기술과 혁신 Vol.8 No.1
난류 제트 유동에서 입구 노즐 단면 형상 변화에 따른 혼합 특성 변화를 살펴보기 위해 레이놀즈 응력 모형(RSM)을 사용한 수치 해석을 수행하였다. 유동 혼합에 대한 형상 효과를 분석하기 위해, 원형 노즐과 동일한 입구 단면적을 가지는 정사각형과 정삼각형의 비원형 제트를 선택하였다. 원형 및 비원형 제트에 대해 축 방향 속도, 와유동 크기, 혼합도, 정압 및 난류 강도 변화를 통해 입구 노즐의 형상 변화가 혼합 특성에 미치는 영향을 살펴보았다. 그러한 결과로부터, 원형 제트에 비해 비원형 제트의 혼합 성능이 크게 향상되었고, 정사각형 제트보다 정삼각형 제트에 대해 상대적으로 높은 혼합성능을 얻을 수 있음을 확인하였다. Numerical analysis using Reynolds stress model (RSM) are performed to examine the variation of mixing characteristics according to the change in cross-sectional shape of nozzle inlet in turbulent jets. To analyze the geometric effects on the flow mixing, non-circular jets of square and equilateral triangular shapes having the inlet area of the same magnitude as the circular jet are selected. For the circular and noncircular jets, the shape effect of nozzle inlet on the mixing characteristics is investigated by the variations of axial velocity, vorticity magnitude, mixedness, static pressure and turbulence intensity. From such results, it is confirmed that the mixing performance of the non-circular jet is significantly improved in comparison of the circular jet, and relatively higher mixing performance is obtained for the equilateral triangular jet than the square jet.
배플이 부착된 마이크로 연소기의 난류유동 및 연소에 대한 수치해석 연구
김원현(Won Hyun Kim),박태선(Tae Seon Park) 한국추진공학회 2013 한국추진공학회지 Vol.17 No.6
Turbulent flow and combustion characteristics in a micro can combustor with a baffle plate are investigated by a Reynolds Stress Model. In order to examine the geometric effects on the turbulent combusting flow, several baffle configurations are selected. The interrelation between the flow structure and the thermal field are investigated by examing the variation of recirculation region, flame length and heat loss. For the flow mixing, the decreasing air hole is more efficient than the decrease of the fuel hole. As the fuel or air hole diameter decreases, combustion efficiency is enhanced and flame length is decreased. Additionally, as the diameter of air hole decreases, the heat loss and combustion temperature are increased, while they are reduced with decreasing the diameter of fuel hole.