분무액적과 벽의 상호작용에 대한 연구

양희천(H. C. Yang),유홍선(H. S. Ryou),정연태(Y. T. Jeong) 한국자동차공학회 1998 한국 자동차공학회논문집 Vol.6 No.4

The impingement of the fuel spray on the wall within the combustion chamber in compact high-pressure injection engines and on the intake port wall in port-fuel-injection type engines is unavoidable. It is important to understand the characteristics of impinging spray because it influences on the rate of fuel evaporation and droplet distribution etc. In this study, the numerical study for the characteristics of spray/wall interaction is performed to test the applicablity and reliability of spray/wall impingement models. The impingement models used are stick model, reflect model, jet model and Watkins and Park's model. The head of wall-jet eminating radilly outward from the spray impingement site contains a vortex. Small droplets are deflected away from the wall by the stagnation flow field and the gas wall-jet flow. While the larger droplets with correspondingly higher momentum are impinged on the wall surface and then are moved along the wall and are rolled up by wall-jet vortex. Using the Watkins and Park's model the predicted results show the most reasonable trend. The rate of increase of spread and the height of the developing wall-spray is predicted to decrease with increased ambient pressure (gas density).

유동장 및 분무특성에 미치는 난류모델의 영향

양희천(H. C. Yang),유홍선(H. S. Ryou) 한국자동차공학회 1997 한국 자동차공학회논문집 Vol.5 No.1

The ability of turbulence model to accurately describe the complex characteristics of the flow field and the fuel spray is of great importance in the optimum design of diesel engine. The numerical simulations of the flow field and the spray characteristics within the combustion chamber of direct injection model engine are performed to examine the applicability of turbulence model. The turbulence models used are the RNG k-e model and the modified k-?? model which included the compressibility effect due to the compression/expansion of the charges. In this study, the predicted results in the quiescent condition of direct injection model engine show reasonable trends comparing with the experimental data of spray characteristics. i. e., spray tip penetration, spray tip velocity. The results of eddy viscosity obtained using the k-?? model in the spray region is significantly larger than that obtained using the RNG k-￡ model. The spray tip penetration predicted using the RNG k-?? model is more close to the experimental data than that using the k-￡ model. The application of the RNG model seems to have some potential for the simulations of the spray characteristics, e. g., spray tip penetration, spray tip velocity, droplets distribution over the k-?? model.

희박 엔진 연소실내의 유동해석 ( I )

양희천(H. C. Yang),이준식(J. S. Lee),유정열(J. Y. Yoo),최해천(H. C. Choi) 한국자동차공학회 1995 한국 자동차공학회논문집 Vol.3 No.6

Turbulent flow characteristics of a lean-burn engine were qualitatively studied in order to obtain the optimum design parameters. 3-D lean-burn model engine was made up of an intake port, an intake valve and a cylinder. Computational grids were generated using PATRAN which was a FEM grid-generation software and numerical calculations were performed using STAR-CD. The predicted results showed that swirl and tumble structures were significantly changed by the valve lifts.

자동차 주위의 3차원 유동에 대한 수치해석적 연구

양희천(H.C.Yang),유정열(J.Y.Yoo),이준식(J.S.Lee),최해천(H.Choi) 한국자동차공학회 1995 한국자동차공학회 춘 추계 학술대회 논문집 Vol.1995 No.11_1

In this paper three-dimensional external airflow around road vehicle models was numerically studied to investigate the aerodynamic characteristics. FVM based on a general curvilinear coordinate system was used to solve the governing equations. The drag coefficients by the calculation were about 40-50% higher than the experimental values.<br/>

디젤기관 연료분무의 분열 현상에 대한 수치해석적 연구

양희천(H. C. Yang),최영기(Y. K. Choi),유홍선(H. S. Ryou) 한국자동차공학회 1995 한국 자동차공학회논문집 Vol.3 No.6

Three dimensional numerical study of non-evaporating and evaporating spray characteristics was performed in a quiescent and motoring condition of direct injection diesel engine. The calculation parameter was breakup model. The breakup models used were Reitz & Diwakar model and TAB model. The modified k-ε turbulence model considering the compressibility effect due to the compression and expansion of piston was used.<br/> The calculation results of the spray tip penetration and tip velocity using the TAB model showed similar trends comparing with the experimental data. Although the evaporation rate was not nearly affected with the breakup model at the higher injection pressure, in the low injection case, the evaporation rate result using the TAB model became higher than that of R & D model. The evaporation rate was increased with the injection pressure due to the vigorous interaction with the gas field.

[論文] 실린더 내부 유동장에 대한 흡입 밸브의 편심 효과에 관한 수치적 연구

양희천(H.C.Yang),최영기(Y.K.Choi),유홍선(H.S.Ryou),고상근(S.K.Kauh),허선무(S.M.Huh) 한국자동차공학회 1992 오토저널 Vol.14 No.4

Three dimensional numerical calculation carried out to investigate the eccentricity effect of intake valve on the in-cylinder flow fields for the intake stroke and the compression stroke.<br/> During the intake stroke, a corner vortex in the vicinity of the valve exit interacted strongly with a toroidal vortex in the case of axisymmetric valve. But a weak interaction between the corner vortex and the toroidal vortex occurred due to the eccentricity of the valve in the narrow region between valve and cylinder wall in the case of offset valve.<br/> During the compression stroke, it was found that a solid body rotation was maintained in the radial-circumferential plane in the case of axisymmetric valve. But a weak secondary vortex was formed in the radial-circumferential plane in the case of offset valve, because of the interaction between swirl flows and inward flows towards cylinder axis.<br/> The calculated turbulence intensity presented a similar trend with the experiental results but, in spite of using the modified k-ε model, it was found that the qualitative difference between the numerical results and experimental results was large in the region where the velocity gradient is substantial.

Study on turbulent flow in rectangular tunnel by using PIV

박상규(S. K. Park),양희천(H. C. Yang),임종한(J. H. Lim),Chen Gong 한국동력기계공학회 2007 한국동력기계공학회 학술대회 논문집 Vol.- No.-

Along with the development of measurement techniques to fluid mechanics, the importance of fluid flow and heat transfer has been emphasized even in the field of science and engineering. In order to determine the characteristics of smoke movement in a rectangular tunnel, Particle Image Veocimetry (PIV) measurements are used here. This paper presents the experimental results of turbulent flow in the rectangular tunnel which has four different exhaust outlets, which are respectively positioned at 0, 100, 200 and 300㎜ away from the inlet in the x-direction, The experiments have been conducted by using olive oil droplets, whose viscosity is 1.51×10?? ㎡/s, as tracer particles.

人蔘 種子形成에 對한 生理化學的 硏究 Ⅲ. 美國人蔘 및 竹節人蔘의 花器 및 種子形成 過程에 있어서의 遊離아미노酸의 消長

J. K. Hwang(黃鍾奎),H. C. Yang(梁熙天) 한국육종학회 1973 한국육종학회지 Vol.5 No.1

The changes of free amino acids throughout the formation of flower organs and seeds of two ginseng species, Panax quinquefolium (PQ) and Panax japonicus (PJ), were investigated and the changes in these two species were compared with the changes in Panax ginseng. As a result, some common characteristics of the ginseng plant, some characteristics of each Ginseng species, and the relation between the sterility of ginseng hybrid and metabolism of amino acids were studied. The results are summarized as follows: 1. Depending upon the species of ginseng and their growth stage, some variations in the quantity and number of amino acids were recognized. 2. In all, 19 kinds of ninhydrin sensitive substances including two amides were detected from PQ. The identified amino acids and amides were: alanine, valine, valine, leucine, phenylalanine, proline, hydroxyproline, serine, threonine, histidine, tyrosine, aspartic acid, glutamic ac id, lysine, γ-amino butyric acid, arginine, cysteic acid, tryptophan, asparagine and glutamine. From PJ, 21 kinds of ninhydrin sensitive substances were detected. Compared with PQ, β-alanine, pipecolic acid and one unknown substance were detected while histidine was not. 3. After flowering time γ-amino butyric acid was detected in PQ a nd PJ. Through the formation of the flower organ and seed of PQ and PJ, β-alanine, lysine and arginine were dected in smaller amounts than in PG. 4. The change of praline in PQ and PJ was similar to that in PG. At the microspore stage, pollen mature stage and flowering time it was detected in large amounts (+~+++) but after the falling of the petals it was hardly detected. Therfore, proline could be presumed to be closely related to the formation of the flower organ of the ginseng plant. 5. As in PG, alanine, aspartic acid, glutamic acid and cysteic acid were generally the main amino acids while valine, leucine and tyrosine appeared as comparatively distinct spots. This phenomenon seems to be common in all species of the ginseng plant. 6. Since the sulfur-containing amino acids, cysteine and cystine, are scarce in the reproductive organ of other plants, it was interesting that cysteine and cystine were always detected in large quantity in the form of cysteic acid through the formation of ginseng seeds and during the stratification period. To discover whether these sulfur containing amino acids are related to the formation of ginseng seeds and to embryo development, further studies are required.

人蔘 種子形成에 對한 生理化學的 硏究. Ⅱ. 催芽 科程에 있어서의 遊離아미노酸의 消長

J. K. Hwang(黃鍾奎),H. C. Yang(梁熙天) 한국육종학회 1973 한국육종학회지 Vol.5 No.2

Ginseng seeds were sampled every 10 days after humid stratification in sand from August 1, 1972 to February 10, 1973 and changes of free amino acids in the seeds were investigated by thin layer chromatography employing a mixed layer of silicagel and micro-crystalline cellulose. The results are summarized as follows: 1. The quantity and quality of amino acids varied with the stratification period. As a result of the experiment 23 kinds of ninhydrin positive substances were detected. They were (1) 20 amino acids: alanine, valine, leucine, leucine phenylalanine, proline, hydroxyproline, serine, pipecolic acid, histidine, γ-amino butyric acid, threonine, tyrosine, aspartic acid, methionine sulfoxide, lysine, glutamic acid, arginine, β-alanine, cysteic acid and tryptophan; (2) two amides: asparagine and glutamine, and one unknown. 2. During seeding time at the end of November, a greater number of ninhydrin positive substances-(22 kinds excluding β-alanine) than at any other time were observed during the experiment. At this atage alanine, aspartic acid and glutamic acid were detected in large amounts compared with the other amino acids. If one reflects upon the close relationship of these amino acids with the TCA cycle it would seem as if they play an important role in the embryo development metabolism of ginseng seeds at this stage. 3. Valine increased gradually after stratification especially from the middle of October to the middle of November. On the contrary, tyrosine, which had been more abundant than valine decreased gradually after stratification. 4. Cysteic acid was detected in the largest spot (冊) until the beginning of September but decreased gradually to the smallest spot (+) at the seeding time. At this stage some other main amino acids appeared large spots. 5. Two amides, asparagine and glutamine were detected in large and distinct spots after seeding time. After seeding time aspartic acid and glutamic acid decreased while asparagine and glutamine increased. The other amino acids had little changes. 6. During the stratification period tryptophan was always detected. Since tryptophan is a precursor of auxin further studies of tryptophan related to the growth hormone and on its relation to embryo development are required. 7. The changes of amino acids during the stratification are regarded as physiological interchanges which influence the embryo development. For a study of the metabolism of each amino acid and of the relation of amino acids to the metabolism of the other compounds, further experiments are required.

[論文] 보올형상과 선회비에 따른 디젤기관 실린더내의 유동장 해석

최영진(Y. J. Choi),양희천(H. C. Yang),유홍선(H. S. Ryou),최영기(Y. K. Choi) 한국자동차공학회 1991 오토저널 Vol.13 No.2

There are many factors which influence on the performance of a diesel engine. The piston bowl shape and swirl ratio are important factors to enhance the fuel-air mixing and flame pro­pagation.<br/> In this study, calculations of the flow field in the cylinder of the diesel engine were carried out using the CONCHAS-SPRAY code for different bowl shapes and swirl ratios.<br/> In the case of constant swirl ratio, vortices which affect fuel-air mixing, evaporation and flame propagation are generated more strongly and consistently in the bowl-piston type com­bustion chamber than in the flat piston type. With this strong squish effect, injected fuel droplets are widely diffused and rapidly evaporated in the bowl-piston type combustion chamber. Especi­ally a strong squish is developed and large and strong vortices are generated in the edge cutted bowl piston chamber.<br/> As the swirl ratio increases, it is found that a large and strong squish and vortices are generat­ed in the combustion chamber and also fuel droplets are diffused into the entire combustion chamber.