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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.
김원현(Won-Hyun Kim),이수목(Soo-Mok Lee),배종국(Jong-Gug Bae),김도중(Do-Joong Kim) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
A valve train dynamics of newly developed medium speed diesel engine was measured and analyzed. OHV-type valve train is represented by 7-DOF lumped mass model and distributed parameter model for the dynamic simulation. Analysis results with the given cam profiles were compared with the measured valve displacements, accelerations and acting forces. Based on these results, dynamic characteristics of valve train were investigated and the performance and safety were also evaluated. To improve the analysis accuracy, contributions of design parameters(mass and stiffness) to the dynamic behavior were investigated with the natural vibration analysis and sensitivity analysis. In addition, model tuning and optimization were performed from the measurement results.
Air-Air, CO₂-Air, He-Air 난류 제트유동의 입구단면 형상변화에 따른 혼합 특성변화에 대한 수치해석 연구
김원현(W. H. Kim),박태선(T. S. Park) 대한기계학회 2012 대한기계학회 춘추학술대회 Vol.2012 No.11
Spatially developing flow structure and mixing characteristics in turbulent jets issuing from a fully developed turbulent flow, with a weakly confined in an Air coflow, three different nozzle geometries and variable densities are investigated by using Reynolds Stress Models(RSM). In order to analyse the geometric effects on the flow mixing, round, square and equilateral triangular shape of nozzle exit plane are selected at a constant Reynolds number based on identical equivalent diameters. Also, variable density are selected that the density ratio(S=<SUB>pc/pco</SUB>) is 0.14 for He-Air and 1.52 for CO2-Air with a comparison of unity density ratio case for Air-Air with a constant momentum flux and mass flow rate. The variance of the mean velocity decay, a passive scalar mixedness, entrainment rates and turbulent intensity of square and equilateral triangular jet are compared with turbulent round jet. From the result, equilateral triangular jet is the highest mixing efficiency among three different inlet nozzle geometries and variable densities. Furthermore, mixing efficiency is increased by decreasing S with the same geometric conditions.
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.
다공배플 두께가 마이크로 연소기의 유동 및 혼합특성에 미치는 영향
김원현(Won Hyun Kim),박태선(Tae Seon Park) 대한기계학회 2017 大韓機械學會論文集B Vol.41 No.9
다공배플을 가진 마이크로연소기에 레이놀즈응력 난류모형을 이용하여 난류유동 및 혼합특성에 대한 수치해석 연구를 수행하였다. 다공배플은 연소실 내부에 다수의 3차원 와유동을 발생시키는 기하학적 특징을 가지고 있다. 그러한 형상특징 중에서 배플두께를 변화시킬 경우 와유동구조의 다양한 변화가 얻어졌다. 여러 와유동중에서 연료유동으로부터 생성된 와유동은 혼합도 증가에 결정적 역할을 하였다. 연소실 내부의 3차원 와유동구조는 배플두께 변화에 따른 유동의 발달상태에 의존하였다. 특히, 배플두께가 연료유입구 직경보다 작을수록 배플구멍 제트유동의 속도분포는 포물선형태에서 안장모양의 형태로 변하였다. 연소실내부의 재순환영역크기 및 혼합도는 이러한 제트유동구조에 밀접한 상관관계를 가졌다. Flow structure and mixing characteristics in a micro combustor with a multi-hole baffle were numerically studied using the Reynolds stress model. The multi-hole baffle has geometrical features to produce multiple three-dimensional vortices inside combustion chamber. When the thickness of the baffle"s geometrical factors changes, variations of vortical structures occur variously. Among these vortices, the vortex generated from the fuel stream exerts a critical influence on the mixing enhancement. The three-dimensional vortical structure, in its development state, was strongly dependent on the baffle thickness. In particular, as the baffle thickness decreases to values less than the diameter of the fuel hole, the jet stream in baffle holes changes from the parabolic to saddleback profile type. The sizes of recirculation zones inside combustion chamber and the mixing state were closely affected by the structure of the jet streams.
입구유동 가진이 있는 층류 후향계단 유동에서 열전달에 대한 프란틀수 효과해석
김원현(Won Hyun Kim),박태선(Tae Seon Park) 대한기계학회 2012 大韓機械學會論文集B Vol.36 No.9
입구유동 가진이 있는 층류 후향계단 유동에서 Pr수의 변화에 따른 열전달 특성변화를 조사하기 위하여 비정상 수치해석을 수행하였다. 입구는 가진주파수와 가진진폭의 변화에 따른 교란이 주어졌고, 온도함수의 물성치가 적용되었다. 열전달 변화에 대한 다양한 특징들이 열경계층 변화에 의해서 설명되 었다. 물성치가 일정한 경우와 비교하였을 때, 물성치가 온도의 함수성이 있는 경우 Pr < 1인 조건에서 열전달은 감소하였고, 반대로 Pr < 1인 조건에서 열전달은 증가하였다. 또한 가진진폭이 증가함에 따라 계단 후류 바닥면에서 열전달도 증가하였다. 그렇지만 가진주파수 변화의 경우 St < 0.2 조건에서 열전달이 크게 증가하는 특정주파수 영역이 존재하였다. 특히, 열전달의 증가는 재부착 길이의 rms값의 변동정도와 밀접한 관련이 있음을 보여주었다. The wall heat transfer of backward-facing step laminar flows with different Prandtl numbers and a pulsating inlet is investigated by unsteady simulations. The inlet is perturbed by the variation of frequency and amplitude. Temperature-dependent transport properties are adopted. Various characteristics of the wall heat transfer are explained by the variation of the thermal boundary layer. For Pr < 1, the wall heat transfer of temperature-dependent properties is decreased compared to that of constant properties, whereas it increases for Pr < 1. In addition, the wall heat transfer increases depending on the pulsating amplitude. However, the results of frequency variation for St < 0.2 show that the heat transfer is strongly enhanced at a specific frequency. In particular, the increase in the wall heat transfer is strongly related to the root mean square of the fluctuations of the reattachment length.
김원현(Won-Hyun Kim),정건화(Kun-Hwa Jung),이수목(Soo-Mok Lee),류영석(Young-Seok Ryoo) 한국마린엔지니어링학회 2006 한국마린엔지니어링학회 학술대회 논문집 Vol.2006 No.-
Diesel power plant(DPP) with the medium speed diesel engine is operated under the very severe condition in aspect of load and operating time as compared with the marine diesel generator set. So, minimized vibration level have to be insured for the more stable operation of engine and generator. The vibration of generator set mainly comes from the resonance between the rigid modes by resilient mount or distortion modes by structural stiffness and the excitation forces of engine. Then, avoidance of resonance with structural modification is generally well known. In this paper, the first order vibration in non-resonance range and local vibration modes were investigated by impact test, response /ODS(operational deflection shape) measurement and 3D finite element analysis for the additional reduction of vibration. The proposed countermeasures were actually applied and their final effects were verified through the in-situ measurement.