• 제목/요약/키워드: Turbulent structure

검색결과 571건 처리시간 0.037초

순 산소 연소기 개발을 위한 노즐직경변화에 따른 화염길이 특성 (Flame Length Characteristic for Varying Nozzle Diameter to Develop Oxy-Fuel Combustor)

  • 김호근;김용모
    • 대한기계학회논문집B
    • /
    • 제29권7호
    • /
    • pp.861-867
    • /
    • 2005
  • In order to develop oxy-fuel combustor, the Flame length characteristic of $CH_4$ with oxidizer of air and oxygen has been experimentally investigated for tile nozzle diameters of 1.6mm, 2.7mm, 4.4mm and 7.7mm. The structure of $CH_4$ flame with oxidizer of oxygen was sharp in contrast with the $CH_4$ flame with oxidizer of air. The stability of $CH_4$ flame with oxidizer of oxygen was higher than $CH_4$ flame with oxidizer of air. In all $CH_4$ flames with oxidizer of air and oxygen, the flame length were dependent on the flowrate in laminar flame regime, and in turbulent flame dependent on the initial jet diameter. Using correlation equation of Delichatsios, the flame length has been expected exactly for $CH_4$ flame with oxidizer of air, but underestimated for $CH_4$ flame with oxidizer of oxygen. This paper proposed correlation equation of $CH_4$ flame with oxidizer of oxygen.

청평호 및 팔당호 어류군집 비교 연구 (The Comparative Study on the Fish Community in Lake Chungpyung and Lake Paldang)

  • 박혜경;이장호;윤석환;최명재
    • 한국물환경학회지
    • /
    • 제29권1호
    • /
    • pp.7-18
    • /
    • 2013
  • We compared the structure of fish community and condition of major fish species in Lake Chungpyung and Lake Paldang, which are relatively shallow, meso-eutrophic, cascading dam reservoirs on the North Han River. Two lakes have wide littoral zone in the lakeside providing similarly good habitat for fishes, whereas fishery and water recreational activities such as motorboating, water skiing are allowed in Lake Chungpyung but are prohibited in Lake Paldang. The average lengths of large size fishes in Lake Chungpyung are shorter than those of same species in Lake Paldang, resulting in the slight distortion of generation distribution of those species in Lake Chungpyung, possibly owing to the active fishery such as fixed shore net fishing, gill net fishing and angling. Meanwhile the condition of fishes represented by the length-weight relationship of fish species did not show the significant differences between two lakes and showed normal condition. To evaluate the impact of physical disturbance such as loud noise and turbulent wave from water recreational activities to fishes precisely, further studies including physiological responses to stress an spawing activity should be needed.

식생수로의 유속분포에 관한 실험적 연구 (An Experimental Study on Velocity Profile in a Vegetated Channel)

  • 권도현;박성식;백경원;송재우
    • 한국수자원학회:학술대회논문집
    • /
    • 한국수자원학회 2004년도 학술발표회
    • /
    • pp.957-960
    • /
    • 2004
  • From a water-environmental point of view, with a change of understanding and concern about vegetation, it changes that vegetation acts as stability of channel and bed, providing habitats and feed for fauna, and means improving those with appreciation of the beautiful but resistant factor to the flow So, it becomes important concern and study subjects that turbulent structure by vegetation, shear stress and transport as well as roughness and average velocity by vegetation. But from a hydraulic point of view, vegetation causes resistance to the flow and can increase the risk of flooding, Therefore, this thesis concern the flow characteristics in vegetated open channels. According to the experimental results, $z_0$ was on an average $0.4h_p$ in a vegetated open channel. So, the elevation corresponding to zero velocity in a vegetated channel was the middle of roughness element. The limit for logarithmically distributed profile over the roughness element was from $z_0$ to $0.80h_{over}$ for a vegetated channel. Among the existing theory, the method of Kouwen et al.(1969), Haber(1982), and El-Hakim and Salama(1992) except Stephan(2001) gave a very good value compared to the measured velocity profile.

  • PDF

입구 및 출구 형상 변화에 따른 촉매 삽입형 머플러 내부의 유동 해석 (A Numerical Study on the Flow Characteristics in the Catalytic Muffler with Different Inlet and Outlet Configurations)

  • 안태현;이승엽;박윤범;김만영
    • 한국자동차공학회논문집
    • /
    • 제21권5호
    • /
    • pp.59-66
    • /
    • 2013
  • Lack of the space in many diesel vehicles make it difficult to design and install the catalytic muffler to reduce emissions. For this reason, inlet part of the catalytic muffler is made of L-type which has lower flow uniformity than conventional I-type, and catalytic muffler has complex internal structure by various insertions, which affect the flow uniformity and pressure drop of the systems. In this work, the flow characteristics such as flow uniformity and pressure drop have been numerically investigated by changing such various geometries as inlet shape, porosity, and outlet shape inside the muffler with the three-dimensional turbulent incompressible flow solver. Total 4 different cases are considered in order to find optimal configurations of the catalytic muffler in view of high flow uniformity and low pressure drop. The results show that Case 2 which has no induction cone and outlet perforated pipe has higher uniformity index and lower pressure drop than others considered in this work.

풍하중이 농업시설물의 구조적 안정성에 미치는 영향 -수치해석에 의한 풍력계수분포 산정- (The Effect of Wind Force on Stability of Agricultural Structures - Numerical Calculation of Wind Pressure Coefficients -)

  • 최홍림;손정익
    • 생물환경조절학회지
    • /
    • 제3권1호
    • /
    • pp.10-19
    • /
    • 1994
  • Wind load is known to be one of major forces to influence the stability of agricultural structures. General flow fields were calculated to determine flow characteristics over the envelop of the following three types of greenhouses with arched roof : single span, twin span greenhouses, and two single span greenhouses apart 3m inbetween. Pressure coefficients along the envelop of greenhouse were numerically calculated by the k-$\varepsilon$ turbulence model, which lead to determine wind forces on it. Curvilinear coordinate for an arched roof and the upwind scheme were adopted for the study. The calculated pressure coefficients were validated with the avaliable data of Japanese Standard and NGAM Standard. The Magnitude of calculated forces over the envelop was not in good accordance with data except the windward wall. Even tile data of Japanese and NGAM Standard for validation deviated a lot from each other in quantity and quality. Such discrepancy may be attributed to different geometric and/or flow configuration conditions for experiments, or the insenstivity of the k-$\varepsilon$ turbulence model to recirculation flow.

  • PDF

유한요소법을 이용한 버클링 마이크로 밸브의 유동특성 해석 및 최적 설계 (Analysis of Flow Characteristics and Optimum Design of a Buckling Microvalve Using the Finite Element Method)

  • 김재민;이종춘;정귀상;윤석진
    • 한국전기전자재료학회:학술대회논문집
    • /
    • 한국전기전자재료학회 2002년도 추계학술대회 논문집 Vol.15
    • /
    • pp.383-386
    • /
    • 2002
  • This paper reports on the fluid flow simulation results of an active microvalve. The mechanical and fluidic analysis are done by finite element method. The designed structure is normally closed microvalve using buckling effect, which is consist of three separate structures; a valve seat die, an actuator die and a small piezoelectric actuator. It is confirmed that the complete laminar flow and the lowest flow leakage are strongly depend on the valve seat geometry. In addition, turbulent flow was occurs in valve outlet according to increase seat dimension, height and inlet pressure. From this, we was deducts the optimum geometry of the valve seat and diaphragm deflection that have an great influence fluid flow in microvalve. Thus, it is expected that our simulation results would be apply for constructing integrated chemical analyzing system or drug delivery system.

  • PDF

Rectangular prism pressure coherence by modified Morlet continuous wavelet transform

  • Le, Thai-Hoa;Caracoglia, Luca
    • Wind and Structures
    • /
    • 제20권5호
    • /
    • pp.661-682
    • /
    • 2015
  • This study investigates the use of time-frequency coherence analysis for detecting and evaluating coherent "structures" of surface pressures and wind turbulence components, simultaneously on the time-frequency plane. The continuous wavelet transform-based coherence is employed in this time-frequency examination since it enables multi-resolution analysis of non-stationary signals. The wavelet coherence quantity is used to identify highly coherent "events" and the "coherent structure" of both wind turbulence components and surface pressures on rectangular prisms, which are measured experimentally. The study also examines, by proposing a "modified" complex Morlet wavelet function, the influence of the time-frequency resolution and wavelet parameters (i.e., central frequency and bandwidth) on the wavelet coherence of the surface pressures. It is found that the time-frequency resolution may significantly affect the accuracy of the time-frequency coherence; the selection of the central frequency in the modified complex Morlet wavelet is the key parameter for the time-frequency resolution analysis. Furthermore, the concepts of time-averaged wavelet coherence and wavelet coherence ridge are used to better investigate the time-frequency coherence, the coherently dominant events and the time-varying coherence distribution. Experimental data derived from physical measurements of turbulent flow and surface pressures on rectangular prisms with slenderness ratios B/D=1:1 and B/D=5:1, are analyzed.

회전하는 선박 프로펠러 전방 유입류에 대한 PIV 속도장 해석 (PIV Velocity Field Analysis of Inflow ahead of a Rotating Marine Propeller)

  • 이상준;백부근
    • 대한조선학회논문집
    • /
    • 제41권4호
    • /
    • pp.30-37
    • /
    • 2004
  • Flow characteristics of the inflow ahead of a rotating propeller attached to a container ship model were investigated using a two-frame PIV (Particle Image Velocimetry) technique. Ensemble-averaged mean velocity fields were measured at four different blade phases. The mean velocity fields show the acceleration of inflow due to the rotating propeller and the velocity deficit in the near-wake region. The axial velocity distribution of inflow in the upper plane of propeller is quite different from that in the lower plane due to the thick hull boundary layer. The propeller inflow also shows asymmetric axial velocity distribution in the port and starboard side. As the inflow moves toward the propeller, the effect of phase angle variation of propeller blade on the inflow becomes dominant. In the upper plane above the propeller axis the inflow has very low axial velocity and large turbulent kinetic energy, compared with the lower plane. The boundary layer developed along the bottom surface of stern hull forms a strong shear layer affecting vortex structure of the propeller near-wake.

초임계 압력상태의 기체메탄/액체산소 연소과정 해석 (Modeling for gaseous methane/liquid oxygen combustion processes at supercritical pressure)

  • 김태훈;김용모;김성구
    • 한국추진공학회:학술대회논문집
    • /
    • 한국추진공학회 2010년도 제35회 추계학술대회논문집
    • /
    • pp.85-88
    • /
    • 2010
  • 본 연구에서는 액체로켓 분사기에서 임계압력 이상의 추진제의 혼합과 연소과정을 수치적으로 모사하여 분석하고자 하였다. 이 과정에서 확장된 $k-{\varepsilon}$ 난류 모델을 이용하여 난류 속도장을 예측하였고 고압에서의 실제 유체 효과를 고려하기 위하여 혼합 추진제의 물성치는 SRK 상태 방정식을 이용하여 계산하였다. 또한 난류 확산 화염에서의 좀 더 정확한 난류와 화학반응의 상호작용을 고려하기 위하여 실제 유체 효과를 고려할 수 있는 층류 화염편 모델을 이용하였다. 수치적인 계산을 바탕으로 이상기체 가정을 사용한 결과와 비교하여 실제 유체의 효과와 기체메탄/액체산소 동축 전단 분사기의 제트화염 구조를 상세하게 살펴보았다.

  • PDF

연속 생산 공정상의 유동장 계측 및 공기유입에 관한 연구 (Research on the Airflow and Air Entrainment on Roll-to-Roll System)

  • 김성균;박준형;휜쾅림
    • 대한기계학회:학술대회논문집
    • /
    • 대한기계학회 2008년도 추계학술대회B
    • /
    • pp.2718-2722
    • /
    • 2008
  • The Roll-to-Roll system including continuous flexible thin materials and roller has its wide range of applications especially in the electronic printing industry. The industry is growing rapidly and the printing speed is also improving. However, the printing machine based on web and roller system has it own problem. As the web speed increases, the failure to wet the surface may occur and the air entrains between the liquid and the paper web. Air bubbles may remain attached to the paper web causing defects on product surface. With the development of image processing technique, the air airflow around the web and rolls can be visualized and calculated by PIV method. In our experiment, the simple web and rolls system is used to R2R simulator. The flow field is studied at various web speeds and positions. The result shows that the flow field has complicated structure with turbulent characteristic and the main trend of flow is obtained by taking time average of flow field.

  • PDF