• International Journal of Naval Architecture and Ocean Engineering
• /
• 제2권1호
• /
• pp.1-13
• /
• 2010

A comparative study between a computation and an experiment has been conducted to predict the performance of a Pod type waterjet for cm amphibious wheeled vehicle. The Pod type waterjet has been chosen on the basis of the required specific speed of more than 2500. As the Pod type waterjet is an extreme type of axial flow type waterjet, theoretical as well as experimental works about Pod type waterjets are very rare. The main purpose of the present study is to validate and compare to the experimental results of the Pod type waterjet with the developed CFD in-house code based on the RANS equations. The developed code has been validated by comparing with the experimental results of the well-known turbine problem. The validation also extended to the flush type waterjet where the pressures along the duct surface and also velocities at nozzle area have been compared with experimental results. The Pod type waterjet has been designed and the performance of the designed waterjet system including duct, impeller and stator was analyzed by the previously mentioned m-house CFD Code. The pressure distributions and limiting streamlines on the blade surfaces were computed to confirm the performance of the designed waterjets. In addition, the torque and momentum were computed to find the entire efficiency and these were compared with the model test results. Measurements were taken of the flow rate at the nozzle exit, static pressure at the various sections along the duct and also the nozzle, revolution of the impeller, torque, thrust and towing forces at various advance speed's for the prediction of performance as well as for comparison with the computations. Based on these measurements, the performance was analyzed according to the ITTC96 standard analysis method. The full-scale effective and the delivered power of the wheeled vehicle were estimated for the prediction of the service speed. This paper emphasizes the confirmation of the ITTC96 analysis method and the developed analysis code for the design and analysis of the Pod type waterjet system.

• Journal of Biosystems Engineering
• /
• 제33권6호
• /
• pp.384-389
• /
• 2008

Three prototype chestnut harvesters were constructed and evaluated their chestnut collection ability and field efficiency. Air-lock paddle system successfully picked up all loose material, and pick up efficiency was about 56 kg/h. Power required to operate this system was evaluated to be 8.7 kW with an air flow rate of $32.6\;m^3/min$. A radial blade type blower with 0.41 m impeller diameter was considered to be a minimum size for this system. For the auger system, air was sucked into the cylinder as the hinged flat cover began to be opened by the material pushed by the auger, and the empty burrs flew back to the container through the space between auger flights and collected in the bottom of the container. It was considered to add a device to prevent air from flowing back or to use the back flowing air for separation of burrs and nuts inside the container. The venturi system could not pick up chestnuts, as they only carried part way up to the suction hose. Consideration was given to an idea that the venturi could be used as a cleaning and separation mechanism for containers filled with both empty burrs and good nuts. A minimum vacuum of 129 mm wg was required to pick up chestnuts, and the corresponding inlet air velocity was 19.3 m/s. 104 mm of vacuum, which was about 81 % of that required for nuts, was enough to pick up burrs with nuts inside. Also, empty burrs with higher moisture content recorded the same pressure as for the burrs with nuts.

• International Journal of Fluid Machinery and Systems
• /
• 제7권1호
• /
• pp.34-41
• /
• 2014

Computational fluid dynamics (CFD) and particle image velocimetry (PIV) are commonly used techniques to evaluate the flow characteristics in the development stage of blood pumps. CFD technique allows rapid change to pump parameters to optimize the pump performance without having to construct a costly prototype model. These techniques are used in the construction of a bi-ventricular assist device (BVAD) which combines the functions of LVAD and RVAD in a compact unit. The BVAD construction consists of two separate chambers with similar impellers, volutes, inlet and output sections. To achieve the required flow characteristics of an average flow rate of 5 l/min and different pressure heads (left - 100mmHg and right - 20mmHg), the impellers were set at different rotating speeds. From the CFD results, a six-blade impeller design was adopted for the development of the BVAD. It was also observed that the fluid can flow smoothly through the pump with minimum shear stress and area of stagnation which are related to haemolysis and thrombosis. Based on the compatible Reynolds number the flow through the model was calculated for the left and the right pumps. As it was not possible to have both the left and right chambers in the experimental model, the left and right pumps were tested separately.

• 대한기계학회논문집A
• /
• 제35권10호
• /
• pp.1211-1222
• /
• 2011

일반적으로 회전체나 초기 하중 하의 구조물 또는 열변형된 파이프 등의 프리스트레스 구조물은 이러한 프리스트레스 효과로 인하여 고유진동수 및 고유진동모드가 변화되기 때문에 정확한 고유진동해석을 위해서는 프리스트레스 고유진동해석을 수행해야 한다. 시스템에 따라서는 그 복잡성으로 인하여 수십만~수백만의 큰 자유도를 갖는 대형 유한요소모델이 요구되어 이러한 대형 모델의 프리스트레스 영향을 파악하기 위한 프리스트레스 고유진동해석을 주어진 설계시간 내에 반복적으로 수행하기에는 여전히 시간적 어려움이 많은 형편이다. 따라서, 본 논문에서는 크리로프 부공간에 근거한 축소기법으로 시스템의 초기 유한요소모델에 대하여 고유진동 특성을 정확하게 나타내면서도 작은 차수의 축소모델로 표현하여 프리스트레스 고유진동해석에서의 계산시간 문제를 감소하였다. 초기 시스템과 축소 시스템의 모멘트를 일치하는 수치계산에는 아놀디 과정을 이용하였다. 적용예제로 휠과 컴프레서 임펠러를 선택하여 제안한 방법을 통한 회전에 따른 프리스트레스 고유진동해석의 정확성과 효율성을 보였다.

• 한국유체기계학회 논문집
• /
• 제7권1호
• /
• pp.17-23
• /
• 2004

Aeroacoustic characteristics of sirocco fan used in Over-The-Range (OTR) has been analyzed in this paper. A microwave hood combination over the gas range is short for the OTR. The flow phenomena of the double-sided sirocco fan was analyzed numerically and experimentally by using commercial code and three dimensional PIV for flow visualization. Also, microphone array is used in order to understand acoustic characteristics of OTR. Two dimensional unsteady flow and acoustic simulation is tried to qualitatively estimate the effects of tonal noise and broadband noise on the overall sound pressure level. It is found that tonal sound is generated from the strong interaction between the impeller and cutoff while broadband sound is generated from the strong secondary flows along the scroll surface. To reduce the noise level, the V-shape cut-off was applied to improve the sound quality by reducing tonal noise. So the peak noise at BPF (Blade Passing Frequency) was almost reduced. The shape of flow-guide to suppress the secondary flow over the scroll surface was carefully checked. It is found that this affects flow pattern at the fan exit and reduces the broad band noise. Through this numerical and experimental study, the sound pressure level was lowered by 4dBA compared to that of the previous fan at the operating point.

• International Journal of Fluid Machinery and Systems
• /
• 제2권2호
• /
• pp.165-171
• /
• 2009

We developed a 'multi-point vibration acceleration method' for accurately predicting the cavitation intensity in pumps. Pressure wave generated by cavitation bubble collapse propagates and causes pump vibration. We measured vibration accelerations at several points on a casing, suction and discharge pipes of centrifugal and mixed-flow pumps. The measured vibration accelerations scattered because the pressure wave damped differently between the bubble collapse location and each sensor. In a conventional method, experimental constants are proposed without evaluating pressure propagation paths, then, the scattered vibration accelerations cause the inaccurate cavitation intensity. In our method, we formulated damping rate, transmittance of the pressure wave, and energy conversion from the pressure wave to the vibration along assumed pressure propagation paths. In the formulation, we theoretically defined a 'pressure propagation coefficient,' which is a correlation coefficient between the vibration acceleration and the bubble collapse pressure. With the pressure propagation coefficient, we can predict the cavitation intensity without experimental constants as proposed in a conventional method. The prediction accuracy of cavitation intensity is improved based on a statistical analysis of the multi-point vibration accelerations. The predicted cavitation intensity was verified with the plastic deformation rate of an aluminum sheet in the cavitation erosion area of the impeller blade. The cavitation intensities were proportional to the measured plastic deformation rates for three kinds of pumps. This suggests that our method is effective for estimating the cavitation intensity in pumps. We can make a cavitation intensity map by conducting this method and varying the flow rate and the net positive suction head (NPSH). The map is useful for avoiding the operating conditions having high risk of cavitation erosion.

• 대한기계학회논문집B
• /
• 제38권12호
• /
• pp.1065-1072
• /
• 2014

본 연구에서는 양흡입 원심블로어의 성능향상을 위하여 임펠러 스플리터의 형상 최적화 연구를 수행하였다. 두 개의 스플리터 형상 설계 변수(스플리터 코드 및 피치)를 선정하여 블로어 성능 및 내부 유동장 특성을 평가하였다. 수치해석에 의한 블로어 성능은 설계유량 조건에서 실험결과와 최대 4 % 이내로 잘 일치하였다. 스플리터 형상 최적화를 통하여 설계조건에서의 블로어 효율 및 압력은 기준 블로어 보다 3.65 % 및 1.14 % 각각 향상되었다. 스플리터 최적설계로 임펠러 날개 부압면의 유동박리를 억제시켜 익간 저속 유동에 의한 압력손실을 줄임으로써 블로어 전체의 성능이 향상되었다. 익간 내부유동 균일화는 임펠러 출구속도 분포에도 영향을 주어 볼류트케이싱 출구압력도 향상되었다.

• 한국추진공학회지
• /
• 제22권4호
• /
• pp.61-67
• /
• 2018

액체로켓엔진용 산화제펌프의 캐비테이션 시험 중 입출구 배관과 펌프 케이싱에서 계측된 고주파 신호를 분석하였다. 각각의 데이터의 RMS 값을 캐비테이션 수에 따라 표현하였다. 또한 회전수 동기 주파수와 날개 개수 성분, 캐비테이션 불안정성 주파수의 크기를 검토하였다. 입출구 배관의 압력섭동은 캐비테이션 불안정성의 영향을 받았다. 출구 배관의 신호에서는 인듀서 날개 주파수인 3x 성분이 탁월하였다. 이러한 현상은 임펠러의 날개 개수가 인듀서의 날개 개수의 배수인 것과 관계가 있는 것으로 추정된다. 케이싱에 부착된 가속도계에서도 캐비테이션 불안정성 주파수가 확인되었다.

• Nuclear Engineering and Technology
• /
• 제54권7호
• /
• pp.2491-2509
• /
• 2022

As an important device in the nuclear island, the nuclear coolant pump can continuously provide power for medium circulation. The vane is one of the stationary parts in the nuclear coolant pump, which is installed between the impeller and the casing. The shape of the vane plays a significant role in the pump's overall performance and stability which are the important indicators during the safety serve process. Hence, the bionic concept is firstly applied into the design process of the vane to improve the performance of the nuclear coolant pump. Taking the scaled high-performance hydraulic model (on a scale of 1:2.5) of the coolant pump as the reference, a united bionic design approach is proposed for the unique structure of the guide vane of the nuclear coolant pump. Then, a new optimization design platform is established to output the optimal bionic vane. Finally, the comparative results and the corresponding mechanism are analyzed. The conclusions can be gotten as: (1) four parameters are introduced to configure the shape of the bionic blade, the significance of each parameter is herein demonstrated; (2) the optimal bionic vane is successfully obtained by the optimization design platform, the efficiency performance and the head performance of which can be improved by 1.6% and 1.27% respectively; (3) when compared to the original vane, the optimized bionic vane can improve the inner flow characteristics, namely, it can reduce the flow loss and decrease the pressure pulsation amplitude; (4) through the mechanism analysis, it can be found out that the bionic structure can induce the spanwise velocity and the vortices, which can reduce drag and suppress the boundary layer separation.