• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 추계학술대회논문집
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• pp.27-33
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• 2009

In this paper, the flow past a rotary oscillating circular cylinder is simulated. The high-order and high-resolution numerical schemes with the characteristic boundary conditions are used for the compressible Navier-Stokes equation. The frequencies of rotating oscillation are $0.19\;{\leq}\;S_f\;{\leq}\;0.25$ for the maximum angular $\theta_{max}=10^{\circ}$ and $17^{\circ}$. The flow conditions are Mach number of 0.3 and Reynolds number of 1000. At Lock-on and Non-lock-on region which are defined by the relation between the vortex shedding frequency and the oscillating frequency, the drag and lift coefficient are analyzed.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 춘계학술대회논문집
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• pp.75-80
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• 2009

The present paper focuses on the analysis of aero-acoustics characteristic by several boundary conditions. In this simulation, a high-order and high-resolution numerical schemes are used for the accurate computation of compressible flow with several boundary conditions including characteristic boundary conditions as well as extrapolation and zonal characteristic boundary condition. These boundary conditions are applied to the computation of two dimensional circular cylinder flows with Mach number of 0.3 and Reynolds number of 400. The computation results are validated with measurement datum and other computation results for the Strouhal frequency of vortex shedding, the mean drag coefficient and root-mean-square lift for the unsteady periodic flow regime. Secondary frequency is predicted by three kinds of boundary conditions characteristic.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2002년도 유체기계 연구개발 발표회 논문집
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• pp.337-345
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• 2002

The present study addresses a computational result of unsteady gas flow through a critical nozzle. The axisymmetric, unsteady, compressible, Wavier-Stokes equations are solved using a finite volume method that makes use of the second order upwind scheme for spatial derivatives and the multi-stage Runge-Kutta integral scheme for time derivatives. The steady solutions of the governing equation system are validated with the previous experimental data to ensure that the present computational method is valid to predict the critical nozzle flows. In order to simulate the effects of back pressure fluctuations on the critical nozzle flows, an excited pressure oscillation with an amplitude and frequency is assumed downstream of the exit of the critical nozzle. The results obtained show that for low Reynolds numbers, the unsteady effects of the pressure fluctuations can propagate upstream of the throat of critical nozzle, and thus giving rise to the applicable fluctuations in mass flow rate through the critical nozzle, while for high Reynolds numbers, the pressure signals occurring at the exit of the critical nozzle do not propagate upstream beyond the nozzle throat. For very low Reynolds number, it is found that the sonic line near the throat of the critical nozzle remarkably fluctuateswith time, providing an important mechanism for pressure signals to propagate upstream of the nozzle throat, even in choked flow conditions. The present study is the first investigation to clarify the unsteady effects on the critical nozzle flows.

• 대한기계학회논문집
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• 제8권3호
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• pp.185-194
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• 1984

본 연구에서는 2차원 정상 층류 유동을 지배하는 극좌표계로 표시된 Navier- Stokes 방정식을 유한해석법으로 전개하여 극좌표계에서의 그 수치계산적 성질을 검토 하고 유한해석법의 적용 좌표계 범위를 확장하는 한편, 2차원 부채꼴 캐비티 유동에 응용하여 공학적 해석도구로서의 그 가능성을 확인하고 아직 연구가 불충분한 부채꼴 캐비티 유동을 고찰하는데 그 목적이 있다.

• 설비공학논문집
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• 제17권12호
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• pp.1161-1168
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• 2005

A Multi-Sectional 3D-PTV algorithm was developed to reduce the calculation time of the conventional GA-3D-PTV. The hardware system of the constructed 3D-PTV system consists of two high-speed cameras ($1,024\times1,018$ pixels, 60 fps), a metal halogen lamp (400W) and a host computer. The sphere(D=30mm) is suspended in a circulating water channel $(300mm\times300mm\times1,200m)$ and Reynolds number is 1,130. About 5,000 instantaneous three-dimensional velocity vectors have been obtained by the constructed 3D-PTV system. Turbulent properties such as turbulent intensity, Reynolds stress and turbulent kinetic energy were obtained. An eigenvalue analysis was carried out using the obtained instantaneous 3D velocity vectors to get the topological relations of the asymptotically stable critical point. Two structured shells, inner shell and outer shell, were found in the sphere wake and their motions were clarified by the measured data.

• 한국유체기계학회 논문집
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• 제3권2호
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• pp.44-49
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• 2000

Small sonic nozzles (throat diameter $0.28{\~}4.48mm$) were tested in the gas flow standard system. This standard system is composed of two bell provers and 5 column piston provers, compressor, filters, and dehumidifier. The discharge coefficients of small some nozzles are obtained and correlated as a function of throat Reynolds numbers with $0.316\%$ uncertainty at a confidence level $95\%$. The tested high Reynolds number was the lower limit of ISO 9300 specifications. The data are useful as data base for revision of ISO 9300.

• Journal of Advanced Marine Engineering and Technology
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• 제24권1호
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• pp.127-133
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• 2000

A numerical study of the flow of incompressible fluid in a polar cavity is presented. Irregular grids is proposed by applying the interior division principle to the variables on polar coordinate grid formation. Stability analysis and the pressure correction method of SOLA algorithms were discussed in detail on cylindrical coordinates. The results present that unsteady flow behavior appears over $Re=3{\times}10^4$ on polar cavities but nearly steady state at $Re=10^4$. Furthermore, with increasing Reynolds numbers, vortices behaviors indicate more complicated flow phenomena and more severe temporal fluctuation of total kinetic energy and time variation of velocity components at arbitrary pick-up points are detected in case of $Re=5{\times}10^4$.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2001년도 추계 학술대회논문집
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• pp.44-50
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• 2001

A numerical study was made to choose the better turbulence model for the flow in the discharge flow path from a diffuser to a wall. In this study standard $\kappa-\epsilon$ model(SKE), RNG $\kappa-\epsilon$ model(RNG), and Reynolds stress model(RSM) were applied. In case of the flow with relatively high Reynolds number at a diffuser inlet, the pressure loss coefficients by RNG have a tendency to be near to those by SKE at small ratio(below about 0.35) of $h/D_o$, but to those by RSM at large ratio(above about 0.35). At large ratio RNG begins to enlarge the effects of rapid strain and streamline curvature. RNG & RSM are recommended as the appropriate turbulence models for this case. But it is noticeable that the velocity gradient pattern in RNG is same as in SKE, and also that the total pressure distribution in RNG is same as in RSM only at swirling flow area, same as in SKE only at main flow area.

• Journal of Mechanical Science and Technology
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• 제17권11호
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• pp.1628-1637
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• 2003

The vortex-induced vibrations of a circular cylinder at low Reynolds (Re) numbers are simulated by applying a method of the two-dimensional computational fluid dynamics coupled with the structural dynamics based on the multi-physics. The fluid solver is first tested on the case of a fixed cylinder at Re$\leq$160, and shows a good agreement with the previous high-resolution numerical results. The present study then reports on the detailed findings concerning the vibrations of an elastic cylinder with two degrees of translational freedom for a number of cases in which Re is fixed at 200, a reduced damping parameter Sg=0.01, 0.1, 1.0, 10.0 and the mass ratio M$\^$*/ = 1, 10.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2004년도 추계학술대회 논문집
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• pp.68-71
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• 2004

The experiments for NACA airfoils are conducted as the preliminary study for the aerodynamic characteristics of the transonic airfoil flow in the shock tube. The test section configurations were designed to use shock tube as simple and less costly experimental facility generating transonic flow at relatively high Reynolds numbers. Experiments at hot gas Mach numbers of 0.80, 0.82 and 0.84, Reynolds numbers of about $1.2\times10^6$ on airfoil chord length and angle of attack of $0^{\circ}\;and\;2^{\circ}$ were carried out by means of shadowgraph visualization method and static pressure measurements. Visualization results were compared with the corresponding results from the conventional transonic wind tunnel tests. The results of study showed that present shock tube facility is useful to study the proper performance characteristics in transonic Mach number range.