후향 계단 주위 난류 박리 유동에 대한 비정상 후류의 영향

전세종,성형진,Chun, Se-Jong,Sung, Hyung-Jin 대한기계학회 2003 大韓機械學會論文集B Vol.27 No.12

An experimental study was made of turbulent separated and reattaching flow over a backward-facing step, where unsteady wake was generated by a spoked-wheel type wake generator with cylindrical rods in front of the separated flow. The influence of unsteady wake was scrutinized in terms of the rotating speed of the wake generator (0$\leq$S $t_{H}$$\leq$0.4). A conditional averaging technique in corporation with SBF was employed to elucidate the influence of the unsteady wake on the large-scale vortical structures of the separated flow. Special attention was made during two-dimensional measurements of wall-pressure with or without unsteady wake. The wall-pressure fluctuations were used to predict dipole sound source by Curie's integral formula. It was found that the reduction of the dipole sound source was due to the reduction of turbulent kinetic energy by unsteady wake in the recirculation region.n.

KOLAS 교정기관의 측정동등성 확립을 위한 물유량 숙련도 시험

전세종,윤병로,김수진,Chun, Sejong,Yoon, Byung-Ro,Kim, Soo-Jin 대한기계학회 2017 대한기계학회 논문집. Transactions of the KSME. C, 산업기술과 혁신 Vol.5 No.2

KOLAS (KOrea Laboratory Accreditation Scheme) belongs to APLAC (Asia Pacific Laboratory Accreditation Cooperation). KOLAS manages the accreditation scheme for measurement traceability to SI units. As per June 2016, there are 22 KOLAS laboratories for liquid flow metering. Among them, 12 laboratories participated in the proficiency test (PM2015-08) for water flow metering, organized by KASTO (Korea Association of Standards and Testing Organizations). This proficiency test was performed with three kinds of flow ranges ($3.6m^3/h{\sim}12m^3/h$, $40m^3/h{\sim}80m^3/h$, $40m^3/h{\sim}200m^3/h$) considering the CMC (calibration and measurement capability) of the participating laboratories. The purpose of the proficiency test was to find out measurement equivalence of the CMC's between each participating laboratory and the reference testing laboratory (KRISS). The measurement equivalence was tested by the number of equivalence ($E_n$). If ${\mid}E_n{\mid}$ < 1, the measurement equivalence was established. All the participating laboratories passed this proficiency test. 한국인정기구(KOLAS)는 아시아태평양인정협의체(APLAC)에 소속되어 있으며, 측정 결과를 SI 단위로 소급하고 이를 유지시키기 위해 교정기관 인정제도를 운영하고 있다. 2016 년 6 월 현재, 22 개의 기관이 KOLAS 물유량 분야 교정기관으로 지정되어 있다. 이 중 12 개 KOLAS 교정기관들이 한국계량측정협회(KASTO)가 2015 년에 주관한 물유량 숙련도 시험(PM2015-08)에 참가했다. 이번 숙련도 시험은 KOLAS 교정기관들의 교정측정능력(CMC)을 고려하여 3 가지의 유량 범위($3.6m^3/h{\sim}12m^3/h$, $40m^3/h{\sim}80m^3/h$, $40m3/h{\sim}200m^3/h$)에서 실시되었다. 숙련도 시험의 목적은 참가기관들의 CMC 가 기준시험소(KRISS)의 CMC 와 비교하여 측정동등성이 성립하는지 여부를 판단하기 위한 것이다. 측정동등성은 측정동등성지수(number of equivalence; $E_n$)를 산출하여 평가했다. ${\mid}E_n{\mid}$ < 1 일 때, 측정동등성이 확립된다고 판단했다. 이번 시험에서 12 개 KOLAS 교정기관 모두 기준시험소와 측정동등성이 성립함을 확인했다.

Implementation of unscented transform to estimate the uncertainty of a liquid flow standard system

전세종,최해만,윤병로,강웅 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.3

First-order partial derivatives of a mathematical model are an essential part of evaluating the measurement uncertainty of a liquid ow standard system according to the Guide to the expression of uncertainty in measurement (GUM). Although the GUM provides a straightforward method to evaluate the measurement uncertainty of volume flow rate, the first-order partial derivatives can be complicated. The mathematical model of volume flow rate in a liquid flow standard system has a cross-correlation between liquid density and buoyancy correction factor. This cross-correlation can make derivation of the first-order partial derivatives difficult. Monte Carlo simulation can be used as an alternative method to circumvent the difficulty in partial derivation. However, the Monte Carlo simulation requires large computational resources for a correct simulation because it considers the completeness issue whether an ideal or a real operator conducts an experiment to evaluate the measurement uncertainty. Thus, the Monte Carlo simulation needs a large number of samples to ensure that the uncertainty evaluation is as close to the GUM as possible. Unscented transform can alleviate this problem because unscented transform can be regarded as a Monte Carlo simulation with an infinite number of samples. This idea means that unscented transform considers the uncertainty evaluation with respect to the ideal operator. Thus, unscented transform can evaluate the measurement uncertainty the same as the uncertainty that the GUM provides.

비정상 후류가 난류박리기포의 응집구조에 미치는 영향

전세종,성형진,Jeon, Se-Jong,Seong, Hyeong-Jin 대한기계학회 2002 大韓機械學會論文集B Vol.26 No.9

Large-scale vortical structure of a turbulent separation bubble affected by unsteady wake is essential to understand flow mechanisms in various fluid devices. A spoked-wheel type of wake generator provides unsteady wake, which modifies the turbulent separation bubble significantly by changing rotation directions and passing frequencies. A detailed mechanism of vortex shedding from the separation bubble with unsteady wake is analyzed by taking a conditional average with spatial box filtering, which spatially integrates measured signals at pre-determined wavelength. A convecting nature of the large-scale vortical structure is analyzed carefully. Spatial evolution of the large-scale vortical structure with frequency variance is also exemplified.

난류박리기포에 대한 비정상 후류의 영향

전세종,성형진,Jeon, Se-Jong,Seong, Hyeong-Jin 대한기계학회 2002 大韓機械學會論文集B Vol.26 No.2

An experimental study was made of turbulent separated and reattaching flow over a blunt body, where unsteady wake was generated by a spoke wheel-type wake generator with cylindrical rods. The influence of unsteady wake was scrutinized by altering the rotating direction (CW and CCW) and the normalized passing frequency (0 St$\_$H/ 0.20). The Reynolds number based on the cylindrical rod was Re$\_$d/=375. A phase-averaging technique was employed to characterize the unsteady wake. The effect of different rotating directions was examined in detail, which gave a significant reduction of x$\_$R/. The wall pressure fluctuations on the blunt body were analysed in terms of the spectrum and the coherence.

유량계 및 밸브분야 연구동향

전세종,박경암,Jun, Se-Jong,Park, Kyung-Am 한국유체기계학회 2005 한국유체기계학회 논문집 Vol.8 No.1

Correction of flow metering coefficients by using multi-dimensional non-linear curve fitting

전세종,Byung-Ro Yoon,Duck-Ki Lee,Hae-Man Choi 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.11

Flow disturbances can significantly affect flow metering because the downstream flow of flow disturbances can become unstable and asymmetric, thus resulting in measurement errors in the flow meter. A clamp-on type ultrasonic flow meter is an example of a flow meter that is susceptible to flow disturbances given its diametrical configuration of ultrasonic paths. Several flow rate correction formulas have been suggested to mitigate the effect of flow disturbance for improved flow metering. As a novel method, a multi-dimensional non-linear correction formula is suggested to overcome limitations in flow metering that are attributed to the non-linearity of flow disturbances. The non-linear correction formula comprises n-th order polynomials with multiple variables. To validate the usefulness of the non-linear correction formula, the standard error of estimate (SEE) is introduced. Four types of flow configurations, namely, downstream of a contraction pipe, an expansion pipe, a single elbow joint, and a tee joint, are used to show the effect of the non-linear correction formula. The expanded uncertainty based on the SEE indicates estimated values of 1.29%, 11.14%, 1.07%, and 6.31% for the four upstream flow configurations,respectively. Thus, the effect of the non-linear correction formula is limited according to the upstream flow conditions. In the downstream flow of the contraction pipe and of the single elbow joint, the non-linear correction formula not only harmonizes the distribution of the flow rate deviations but also removes the biases of flow rate deviations with respect to the flow velocity, the installation location, and the diameter ratio.

Use of Wigner-Ville transformations for fluid particles in laser Doppler flow accelerometry

전세종,권휴상 대한기계학회 2012 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.26 No.3

Flow acceleration with Lagrangian description is crucial to understanding particle movements in turbulent jet flows or dissipation statistics in isotropic turbulence. Laser Doppler anemometry is regarded as a suitable experimental tool for measuring flow acceleration,because scattering particles generate trajectories in the measurement volume, which process gives rise to flow acceleration at a fixed measuring point with the Lagrangian description. The most useful algorithm for processing Doppler signals is either the quadrature demodulation technique (QDT) or the iterative parametric method (alternatively, the minimization of least squares, LSM) as in the literature. In the present study, another algorithm using the Wigner-Ville transform (W-V) is introduced to give more accurate estimation of flow acceleration than the QDT or the LSM. Five signal-processing algorithms, including the QDT, the LSM, the MC (maximization of correlation),and the W-V, were compared with each other in experiments with an impinging air jet flow with a cylindrical rod and a round free-air jet flow. Mean flow acceleration distribution in the streamwise direction was mainly investigated. Processing speeds for the above-mentioned signal-processing algorithms were checked to find the best algorithm, which has best performance with short processing time. Although QDT was found to be an accurate algorithm with short processing time, it has limited applications to flows with large acceleration and high SNR. The MC was also found to be a good algorithm with moderate processing speed, which can be useful in flows with low SNR because the MC is an iterative parametric method. The W-V gave the most accurate values for flow acceleration;however, the processing time for this method was the slowest among the signal-processing algorithms.

가스괴저 치험 1례

전세종,김동호,오정일,정우구 최신의학사 1980 最新醫學 Vol.23 No.11

난류박리기포에 대한 비정상 후류의 영향 ( Influence of Unsteady wake on a Turbulent separation bubble )

전세종,성형진 대한기계학회 2001 대한기계학회 춘추학술대회 Vol.2 No.2