• 대한기계학회논문집B
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• 제21권12호
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• pp.1608-1614
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• 1997

The fluidic flow meter detects the gas flow rate based on the principle of fluidic oscillation instead of the conventional displacement method. It has many merits: wide rangeability, no moving mechanical parts and calibration insensitive to physical properties of fluids. The width of nozzle, size of oscillation chamber, size of target, width of outlet are tested to obtain the effects of jet oscillation on the fluidic flow meter. As the width of nozzle is too wide compared with the size of target, jet oscillation is unstable. The oscillation frequency decreases as the distance between the nozzle and target increases and also as the distance between target and outlet contraction increases. Two different vortexes exist in the front and the rear regions of the target, and they affect the oscillation frequency. The outlet contraction is very important, because the feedback flow is generated by the blocking of the flow. As the width of outlet increases, the jet oscillation frequency decreases. The linearity of this tested flow meter is quite good.

• Design & Manufacturing
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• 제15권2호
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• pp.56-62
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• 2021

In this study, design technology of a non-mechanical flow meter using fluidic oscillation generated during the fluid flow in the chamber was investigated. To with respect to design a splitter, which is the most important factor in fluid oscillation, a transient flow simulation analysis was performed for three types of shapes and changes in inlet flow velocity. The oscillation characteristics with respect to the time in each case were compared, and it was confirmed that the SM03 model was the best among the presented models. In addition, the FFT analysis of the fluid oscillation results for the SM03 model was used to obtain a linear correlation between the flow velocity change and the maximum frequency, and a frequency of 20.957 (Hz/m/s) per unit flow velocity was obtained. Finally, injection molding simulation and molding experiment of the chamber with the designed splitter were performed.

• Journal of Mechanical Science and Technology
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• 제17권10호
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• pp.1507-1519
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• 2003

The two-phase flow patterns for both non-loop and loop type oscillating capillary tube heat pipes (OCHPs) were presented in this study. The detailed flow patterns were recorded by a high-speed digital camera for each experimental condition to understand exactly the operation mechanism of the OCHP. The design and operation conditions of the OCHP such as turn number, working fluid, and heat flux were varied. The experimental results showed that the representative flow pattern in the evaporating section of the OCHP was the oscillation of liquid slugs and vapor plugs based on the generation and growth of bubbles by nucleate boiling. As the oscillation of liquid slugs and vapor plugs was very speedy, the flow pattern changed from the capillary slug flow to a pseudo slug flow near the annular flow. The flow of short vapor-liquid slug-train units was the flow pattern in the adiabatic section. In the condensing section, it was the oscillation of liquid slugs and vapor plugs and the circulation of working fluid. The oscillation flow in the loop type OCHP was more active than that in the non-loop type OCHP due to the circulation of working fluid in the OCHP. When the turn number of the OCHP was increased, the oscillation and circulation of working fluid was more active as well as forming the oscillation wave of long liquid slugs and vapor plugs in the OCHP. The oscillation flow of R-142b as the working fluid was more active than that of ethanol and the high efficiency of the heat transfer performance of R -142b was achieved.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1996년도 추계학술발표회논문집(1)
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• pp.242-247
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• 1996

Flow oscillations in boiling channels induces a drastic reduction of the (critical heat flux) CHF or premature burnout. However, most of CHF works and correlations have been focused on stable flow conditions without considering flow oscillation. Therefore to improve the understanding on flow oscillation CHF, in this paper a new CHF correction factor to predict the CHF values under flow oscillation conditions has been developed from 126 experimental data. Also to investigate the dominant factor on flow oscillation CHF parametric trends are analyzed by using the developed correction factor. The overall mean accuracy ratio of the developed correction factor is 1.033 with a standard deviation of 0.195. The RMS errors 0.198. Its assessment shows that the predictions agree well with the experimental data within 25% error bounds.

• Journal of Advanced Marine Engineering and Technology
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• 제33권6호
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• pp.903-911
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• 2009

During the past three or four decades, the characteristics of turbulent swirling flow have been studied extensively because of their scientific and academic importance. This research deal with the periodic flow oscillation with and without swirling flow in a 180 degree circular tube using hot wire anemometry, microphone and accelerometer. The frequency regions are observed through the structured oscillation from spectrum. This work carried out to measure the sound level by using hot wire anemometry, microphone and accelerometer for each Reynolds number, $6{\times}10^4$, $8{\times}10^4$ and $1{\times}10^5$ respectively at the entry of the test tube with and without swirl flow.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.3009-3014
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• 2007

The effectiveness of passive control techniques for alleviating the pressure oscillation generated in a supersonic cavity flow was investigated numerically and experimentally, respectively. The control device includes a sub-cavity installed near the leading edge of a rectangular cavity. Time-dependent supersonic cavity flow characteristics with turbulent features were examined by using the three-dimensional, mass-averaged Navier-Stokes computation based on a finite volume scheme and large eddy simulation. The results show that the pressure oscillation near the trailing edge dominates overall time-dependent cavity pressure variations. Such an oscillation can be attenuated more significantly in the presence of the sub-cavity compared with the cavity without sub-cavity, and a larger sub-cavity leads to better control performance.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.141-142
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• 2003

When the under-expanded supersonic jet impinges on the perpendicular plate, it is well known that the self-induced flow oscillation occurs at the specific conditions. This phenomenon is related with the noise problems of aeronautical and other industrial engineering. But, the very complicated flow field is formed and it is difficult to clear the flow structure and the mechanism of oscillation. This paper aims to clear the characteristics of flow field and the wave pattern during the under-expanded supersonic jet impinges on the plate. The numerical calculation was carried out using the TVD numerical method. In this paper, the flow visualization, the pressure fluctuation on the surface of plate and the mechanism of oscillation are discussed.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2006년도 제26회 춘계학술대회논문집
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• pp.310-313
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• 2006

본 연구에서는 sub-cavity를 적용한 경우 얻어지는 압력진동의 제어효과를 수치계산 방법을 사용하여 조사하였으며, 삼각돌기와 블로잉제트를 사용하여 얻어진 결과들과 비교하여 그 효율성을 검토하였다. 사각형의 공동을 지나는 유동장은 3차원 비정상 압축성 Wavier-Stokes 방정식에 완전 내제적 유한체적법 및 다단계 Runge-Kutta 방법을 적용하여 수치모사하였으며, 공동유동의 난류상태량들을 적절히 예측하기 위하여 large eddy simulation(LES)을 수행하였다. 본 연구의 결과로부터, 공동후단 부근에서 발생하는 압력진동이 전체 공동유동의 비정상 거동을 지배하며, sub-cavity를 사용하여 압력진동의 폭을 감소시킬 수 있음을 알았다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2009년도 제33회 추계학술대회논문집
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• pp.359-362
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• 2009

유체 공급 배관 내에 오리피스를 설치하여, 압력진동의 감쇠효과를 수치해석 및 실험을 통하여 조사하였다. 압력진동이 작다는 가정에 기초하여 오리피스의 음향학적 감쇠 효과를 실험적으로 확인 하였으며, 평균 유동이 있을 경우 관찰되는 감쇠 특성을 수치적으로 조사하였다. 오리피스의 위치에 따른 압력진동의 마디, 즉 속도 진동의 배가 되는 위치에 오리피스를 설치할 때 가장 효과적인 압력 진동이 감쇠 되었다. 배관 내 평균 유속이 있을 경우 공진주파수가 감소하였고, 이에 따라 최적 감쇠 효과를 갖는 오리피의의 위치도 변화함을 알 수 있었다.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2004년도 유체기계 연구개발 발표회 논문집
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• pp.748-753
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• 2004

The performance of a valveless micropump driven by chamber wall oscillation was numerically investigated for various frequency and amplitude of the oscillation. The numerical study was performed in the range of oscillation frequency from 200Hz to 1000Hz and amplitude from $1{\mu}m$ to $15{\mu}m$. And optimal values for the parameters are found. At the oscillation frequency 600Hz, the net flow rate of micropump shows a maximum value. Also the results show good agreement with the experimental results. The total flow rate was increased with the oscillation amplitude. However, the net flow rate was found to be decreased over $7{\mu}m$.