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전산해석을 활용한 풍동 Diffuser의 익형 공력특성 분석
김철완,조태환 한국항공우주학회 2013 한국항공우주학회 학술발표회 논문집 Vol.2013 No.11
Mylar 표면을 갖는 장기체공 무인기 날개의 풍동시험이 Diffuser에서 수행되었고 그 결과에 대한 분석을 위해 동일한 특성을 갖는 풍동 Diffuser에 익형에 대한 전산해석이 수행되었다. 2차원 해석결과 시험부내의 익형에 비해 Diffuser내의 익형은 양력이 증가하고 항력이 감소하였고 3차원 익형에 대한 전산해석결과도 비슷한 결과를 도출하였다. Diffuser내 한 단면의 유동속도가 동일하지 않아 3차원익형의 양력분포는 중심부가 높고 Diffuser 벽면으로 갈수록 양력이 감소하였다. The wing of an unmanned aerial vehicle which is capable of flying for long time, was tested at the wind tunnel diffuser. The wing was covered with mylar and very flexible. To assist the analysis of the wind tunnel test, CFD simulation was performed for 2D and 3D airfoils in the diffuser geometry and compared with the results of test section. 2D simulation revealed that the lift of airfoil in the diffuser was increased and the drag was decreased. 3D simulation also showed the similar trend to the 2D results. The velocity distribution of the diffuser cross section was not uniform and the lift distribution was high at the center and decreased at the diffuser wall area.
능동형 리어 디퓨져 장치를 이용한 고속 주행 시 승용차의 공기저항 감소 기법에 관한 연구
조준호(Jun-Ho Cho),강승은(Seung-On Kang),박훈일(Hoon-Il Park),송기선(Ki-Sun Song),기정도(Jung-Do Ki),김규홍(Kyu-Hong Kim),이동호(Dong-Ho Lee) 한국자동차공학회 2011 한국자동차공학회 학술대회 및 전시회 Vol.2011 No.11
This paper suggests a technique that reduces aerodynamic drag of a fast cruising passenger car using actively translating rear diffuser. Actively translating rear diffuser is hidden under the trunk when a passenger car is parked and is driven slowly. And it slides out from under rear car body only at high speed driving condition not to ruin the external design of the car. 5 types of rear diffuser devices whose slid out lengths are ranging from 200mm to 450mm were installed under the car body and Computational Fluid Dynamics (CFD) analyses were performed under moving ground and rotating wheel conditions. The main purpose of this study is to explain the aerodynamic drag reduction mechanism of a passenger car cruising at a high speed via an actively translating rear diffuser device and find a length which shows the best aerodynamic performance. The diffuser device raises pressure of underbody flow with diffusing process and then underbody flow and upperbody flow mix strongly. They make strong vortices and the vortices hit the rear surface of the trunk, bringing about an aerodynamic drag reduction. Finally, aerodynamic drag of the passenger car is reduced by an average of more than 5%, which helps to improve the fuel efficiency.
고고도 환경 모사용 Center Body Diffuser의 형상 변화에 따른 성능특성에 관한 연구
김준철(Junechul Kim),이현섭(Hyunseob Lee),박진(Jin Park),김홍집(Hongjip Kim) 한국추진공학회 2016 한국추진공학회 학술대회논문집 Vol.2016 No.5
고고도에서 작동하는 로켓의 작동 환경을 지상에서 모사하기 위한 방법 중에 하나로 사용할 수 있는 Center Body Diffuser (CBD)의 유동 특성을 파악하기 위하여 상온 실험과 수치해석을 병행하였다. 본 연구의 목적은 CBD의 설계 변수 중에 Diffuser 2차목 길이와 2차 목의 직경비 (L/D)st의 변화에 따른 고공환경 모사성능과 Diffuser의 시동특성을 확인하기 위함이다. 연구 결과 2차목의 직경비가 커질수록 시동압력이 낮아지는 것을 확인하였다. To elucidate the flow characteristics of center-body diffuser which has been used to simulate a high altitude for rocket at sea level, cold flow experiments were conducted with sub-scaled equipment with numerical analyses through ANSYS FLUENT. Objective of this study is to evaluate the performance characteristic of high altitude pressure by varying the ratio of second throat length and second throat diameter (L/D)st. The study results show that present diffuser with the bigger ratio of second throat length and second throat diameter has had the lower startup pressure.
하류 유동제어에 의한 에젝터의 효율상승 방법에 관한 연구
김세현(S. H. Kim),이상철(S. C. Lee),신유식(Y. S. Shin),최석천(S. C. Choi),정효민(H. M. Jeong),정한식(H. S. Chung) 한국동력기계공학회 2004 한국동력기계공학회 학술대회 논문집 Vol.- No.-
The ejector system is used for making a low pressure in industrial field. The ejector is consists of nozzle, mixing section and diffuser. The diffuser is influenced in low pressure of ejector system. The diffuser is an important fluid-mechanical equipment to convert kinetic energy into pressure energy. Many of the experimental and theoretical researches have been done in a diffuser but the understanding of energy transfer and detailed mechanism of energy dissipation is unclear. In this study, computations were performed using a numerical method with SIMPLE algorithm for conical diffuser with various diffuser angles and Reynolds number. Also, we investigated the pressure recovery coefficient in conical diffuser by inserting strut. In this paper, we showed that the strut can cause a rising pressure recovery.
마이크로 펌프용 디퓨져/노즐의 유동 특성에 관한 CFD 해석
김동환,한동석,정시영,허남건,윤석진 대한설비공학회 2005 설비공학 논문집 Vol.17 No.6
The flow characteristics have been numerically investigated for various shapes of the diffuser/nozzles which are used for a valveless micro-pump. The important parameters considered in this study are the throat width(15~120m), the taper angle(3.15~25.2°), and the diffuser length(600~4,800m), and the size of the middle chamber(1~16mm2). To find the optimal values for these parameters, steady state calculations have been performed assuming the constant pressure difference between the inlet and exit of the flow. For the taper angle and the throat width, it is found that there exists an optimum at which the net flow rate is the greatest. The optimal taper angle is in the range of 10~20° for all the pressure differences; and the throat width indicates an optimal value near 75m for the case of 35 kPa pressure difference. The net flow rate is also influenced by the size of the middle chamber. With decreasing chamber size, the net flow rate is reduced because of the interference between two streams flowing into the middle chamber. The unsteady pulsating flow characteristics for a micro-pump with a given diffuser/nozzle shape have been also investigated to show the validity of the steady state parametric study.
직관부와 디퓨져 길이 변화에 따른 Side-type 이젝터의 유동특성
김문오(M. O. Kim),김창구(C. G. kim),안주하(Jooha. An),이영호(Y. H. Lee) 한국동력기계공학회 2009 한국동력기계공학회 학술대회 논문집 Vol.2009 No.11
Ejector is a device that uses the energy of a fluid to move another fluid. This device works like a vacuum pump without usage of piston, rotor of any other moving components. An ejector contains an active nozzle, a passice nozzle, a mixing chamber and a diffuser. Mainly, the ejector performance directly affects the water performance, therfore, an investigation on the characteristics and an efficient design of the ejector are importants to improve ejector water systems. In the present study the effect of the throat and diffuser length on flow characteristics in a side type ejector. A computational fluid dynamics (CFD) code, ANSYS-CFX, is employed to predict the flow phenomena and performance of side-type ejector. In addition to this the CFD results is compared with the experimental data. It was found from the study that case 3-1 had the highest efficiency of 23.4%.
CFD 시뮬레이션 시 디퓨져 유형에 따른 모델링 및 해석 방법에 관한 연구
석호태(Seok Ho-Tae),최동호(Choi Dong-Ho),김호진(Kim Ho-Jin),양정훈(Yang Jeong-Hoon) 대한건축학회 2010 대한건축학회논문집 Vol.26 No.1
Because people spend most of their time indoors nowadays, various technical systems are required to efficiently maintain comfortable indoor temperatures. Diffusers play an important role in air conditioners; therefore, the selection of the diffuser is crucial to the efficiency of the air conditioner. Currently, predictive assessments of the ideal indoor thermal environment are made using CFD(Computational Fluid Dynamics); however, the CFD method rarely carefully considers the importance of diffusers. Diffusers affect the result of the air flow and distribution of heating and cooling, so we must carefully consider diffusers in CFD. With more accurate CFD models of diffusers, the energy load can more efficiently be predicted in the architectural design step. To keep adequate IAQ(Indoor Air Quality), a result of restriction of excessive air flow and preferable limitation to the occupancy zone, the air flow pattern should be projected and adjusted as well. Among numerical analysis models, the CFD model is currently being used to predict air flow distribution. However, various results of the CFD analysis method have caused some errors, proving that a more accurate calculation method is required. The purpose of this study is to suggest the CFD calculation method to simulate diffusers in order to minimize the errors between results of the predicted energy performance and ventilation efficiency and the actual physical condition.
디퓨져/노즐을 이용한 압전형 마이크로 펌프의 입ㆍ출구 형상 차이에 따른 유동특성에 관한 수치해석적 연구
김창녕(Chang Nyung Kim),김진욱(Chin Uck Kim) 대한기계학회 2007 대한기계학회 춘추학술대회 Vol.2007 No.5
The present study has been carried out to investigate the pumping characteristics for different figures of inlet and outlet in diffuser/nozzle based on piezoelectric micropump. Piezoelectric micropump system consists of several parts like a pumping chamber, diffuser/nozzle, piezoelectric element and tubes. Parts of the micropump connected with diffuser/nozzle and tubes have been analyzed.. The magnified parts have been classified into two different models based on their resistance. These models have been further classified into six models with each one having three different angles at the magnified parts. Each model has been compared and analyzed using the simulation tool, namely, CFD- ACE depending on their flow rates and characteristics.
윤상규(SangKyu Yoon),염효원(Hyo-Won Yeon),김진곤(Jinkon Kim),성홍계(Hong-Gye Sung),김용욱(YongWook Kim),오승협(SeungHyup Oh) 한국추진공학회 2008 한국추진공학회지 Vol.12 No.4
Theoretical and numerical approaches were conducted in order to study supersonic exhaust diffusers to simulate high altitude performance of rockets on the ground. A physical model of concern includes a rocket motor, vacuum chamber, and diffuser, which have axisymmetric configurations. An analysis was conducted to investigate operation characteristics of supersonic exhaust diffusers from a flow-development point of view. Emphasis was placed on theoretical formulation to predict the starting pressure of diffusers, the effect of the vacuum chamber size, and the minimum starting pressure of the rocket motor to start the diffuser.
최영석(Young-Seok Choi),이경용(Kyoung-Yong Lee),김준형(Joon-Hyung Kim),김성(Sung Kim) 한국유체기계학회 2008 유체기계 연구개발 발표회 논문집 Vol.2008 No.-
In this paper, design optimization for mixed-flow pump impellers and diffusers has been studied by using a commercial CFD code. Geometric design variables were defined with the meridional shape and the vane plane development which is derived from the frontal view of the impeller and diffuser, The influences of selected design variables on the impeller and diffuser performance are also examined as a result of the optimization process. The results showd that the newly defined design variables are successful in optimizing the mixed-flow pump impellers and diffusers. In addition, the optimized models satisfied the performance requirement of the pump based on the CFD results and will be verified by experiments in the next study.