• 오토저널
• /
• 제15권2호
• /
• pp.92-104
• /
• 1993

In the present study, the velocity profiles and entrance length of developing transitional pulsating flows are investigated both analytically and experimentally in the entrance region of a square duct. The systems of conservation equations for transitional pulsating flows in a square duct are solved analytically by linearizing the non-linear convective terms. Analytical solutions are obtained in the form of infinite series for velocity pofiles. The experimental study for the air flow in a square duct(40mm*40mm*4000mm) is carried out to measure velocity profiles and other parameters by using a hot-wire anemometer with a data acquisition and processing system. The distribution of velocity profiles( $u_{ps}$ / $u_{m,ta}$) in the decelerating period is higher than in the accelerating period. The distribution of the axial component of the axial component of velocity in the transitional flow is nearly uniform in the central region of the duct, and decrease rapidly near the wall. The entrance length correlation of the transitional pulsating flows in a square duct is obtained to be $L_{e}$/ $D_{h}$=0.83 $A_{1}$R $e_{ta}$ /(.omega. sup+1)$^{2}$TEX>

• 한국해안·해양공학회논문집
• /
• 제31권1호
• /
• pp.9-16
• /
• 2019

유속의 크기와 블레이드의 기하학적 형상 변화에 따라 발생하는 조류발전용 쉬라우드 시스템 내 유속 변화를 분석하기 위하여 수리모형실험과 수치해석적 방법을 이용하였다. 모형실험을 통해 시스템의 유입부에서 유속 변화와 블레이드 형상변화에 따른 고유 회전수를 계측하였으며, 수치해석을 통해 쉬라우드내 유속 변화를 분석하였다. 실험 유속이 약 28% 증가하고, 익형의 형상을 적용하였을 때, 쉬라우드 유입부에서 계측된 유속은 최대 약 56% 증가하는 경향을 보였다. 한편, 익형 형상을 적용한 블레이드가 설치된 경우 유입부에서의 유속은 일반 블레이드에 비해 최대 14% 증가하는 경향을 보였으며, 회전수 역시 동일 조건에서 가장 높은 수치를 보였다. 수리실험과 수치해석 결과는 약 13%의 오차를 보였으며, 각각의 결과에서 보이는 유속 변화에 대한 경향은 유사하다. 쉬라우드 내 유속 변화를 수치해석으로 분석한 결과 유입부 대비 블레이드 앞부분에서 유속은 최대 1.7배 증가하는 경향을 보였다. 본 연구를 통해 얻은 시스템 내 유속 변화 분석 결과는 효율적인 조류발전용 쉬라우드 시스템 개발에 필요한 기초 자료를 제시할 수 있을 것으로 판단된다.

• 한국유체기계학회 논문집
• /
• 제6권1호
• /
• pp.6-13
• /
• 2003

Variations of performance and NPSH of a turbo pump inducer were measured. The flows at the inlet and the outlet of the inducer were also experimentally investigated by measuring flow velocity and angle using a 3-hole Pilot tube. Performance and velocity profiles show a similarity for tested speeds, however not for efficiencies. Strong recirculating flows appears at the inlet of inducer even at the design condition. Cavitating flows were also visualized at several NPSH's.

• 한국정밀공학회:학술대회논문집
• /
• 한국정밀공학회 2011년도 춘계학술대회 논문집
• /
• pp.1275-1276
• /
• 2011

• 한국유체기계학회 논문집
• /
• 제5권3호
• /
• pp.54-59
• /
• 2002

A commercial CFD code is used to compute the 3-D viscous flow field within the inlet flow concentrator of the newly developed AHU (Air Handling Unit). To improve the performance of the AHU, the inlet air needs to be gradually accelerated to the fan's annular velocity without causing turbulence or flow separation. Three major geometric parameters were selected to specify the inlet shape of the AHU. The performance of the AHU could be measured by the inlet and outlet flow uniformity and the total pressure loss through the inlet flow concentrator. Several numerical calculations were carried out to determine the influence of the geometric parameters on the performance of the AHU. The best geometric values were decided to have efficient inlet shape with analyzing CFD calculation results.

• International Journal of Fluid Machinery and Systems
• /
• 제5권1호
• /
• pp.30-37
• /
• 2012

A two dimensional Darrieus-type turbine has been proposed for the hydropower utilization of extra-low head less than 2m. In a practical use of Darrieus-type hydro-turbine, head and flow rate may be varied temporally and seasonally. Considering that the cost advantage is required for the low head hydro turbine system, the Darrieus turbine should be operated with high efficiency in the wider range of flow rate possibly by using an additional device with simpler mechanism. In the present paper, an adjustment of inlet nozzle section by lowering the inlet nozzle height is proposed to obtain the preferable inlet velocity in low flow rate conditions. Effects of resulting spanwise partial inlet flow are investigated. Finally, an effective modification of inlet nozzle height over flow rate variation is shown.

• 한국군사과학기술학회지
• /
• 제5권2호
• /
• pp.195-206
• /
• 2002

The conjugate heat transfer from the simulated module in a horizontal channel with the variation of inlet air temperature is experimentally investigated. The aim of this study is to estimate temperature difference between a module and inlet air. This study is performed with the variation of parameters that are inlet air temperature(Ti=25~$55^{\circ}C), thermal resistance( $R_c$=0.05, 4.11, 158 K/W), inlet air velocity(Vi=0.1~1.5m/s), and input power(Q=3, 7 W). The results show that the effect of inlet air temperature is little, at the case of using conductive board. And input power was most effective parameter on the temperature difference between module and Inlet air.

• International Journal of Aeronautical and Space Sciences
• /
• 제6권1호
• /
• pp.1-7
• /
• 2005

The inlet boundary condition of computations about the supersonic turbine flow is commonly applied as far-field inlet boundary condition with specified velocity. However, the inflow condition of supersonic turbine is sometimes affected by the shocks or expansion waves propagated from leading edges of blade. These shocks and expansion waves alter the inlet boundary condition. In this case, the inlet boundary condition can not be specified Therefore, in this paper, numerical analyses for three different inlet conditions - fa-field inlet boundary condition, inlet boundary condition with a linear nozzle and inlet boundary condition with a converging-diverging nozzle - have been performed and compared with experimental results to solve the problem. It is found that the inlet condition with a linear nozzle or a converging-diverging nozzle can prevent changing of inlet boundary condition, and thus predict more accurately the supersonic flow within turbine cascade than a far-field inlet boundary condition does.

• Journal of Advanced Marine Engineering and Technology
• /
• 제35권7호
• /
• pp.914-920
• /
• 2011

For a hydro turbine electricity generation system in river or bay, a venturi system could be applied to accelerate flow speed at the inlet of the turbine system in a flow field. In this study, a steady flow simulation was conducted to understand the effect of venturi system on the acceleration of current speed at the inlet of a hydro turbine system. According to the continuity equation, the flow speed is inversely proportional to the cross-section area in a conduit flow; however, it would be different in an open region because the venturi system would be an obstruction in the flow region. As the throat area is 1/5 of the inlet area of the venturi, the flow velocity is accelerated up to 2.1 times of the inlet velocity. It is understood that the venturi system placed in an open flow region gives resistance to the upcoming flow and disperses the flow energy around the venturi system. The result of the study should be very important information for an optimum design of a hydro turbine electricity generation system.

• 한국추진공학회:학술대회논문집
• /
• 한국추진공학회 2009년도 춘계학술대회 논문집
• /
• pp.295-298
• /
• 2009

Bent duct 는 손실을 가중시키고, 효율을 저하시킨다. 지금까지 bent duct에 대한 많은 연구가 진행되었지만, 입구와 출구가 같은 형상에 대해서 연구가 되어왔다. 이번 연구에서는 입구는 환형이지만, 출구는 원형을 가진 bent duct에 대해서 진행되었다. 입구 속도 54 m/s, 레이놀즈수 238,000에서 수행된 이번 연구에서는 bent duct 바깥에 태핑홀을 배치하여 정압분포를 확인하고, 입구와 출구에서 5공 프로브로 유동을 측정하여 스트림 방향 속도 프로파일과 전압 손실 계수를 얻었다. 본 연구에서는 전압 손실 계수, 0.243를 얻었다.