• Journal of Advanced Marine Engineering and Technology
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• v.22 no.1
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• pp.16-20
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• 1998

The critical reynolds number in a square-sectional straight duct is investigated experimentally. The experimental study for the air flow in a square-sectional straight duct is carried out to calssify critical Reynolds number on steady flow and unsteady flow. To calssify the critical Reynolds number we obtained velocity waveform by using a hot-wireanemometer and data acquisition system with photocorder.

• Proceeding of EDISON Challenge
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• 2016.11a
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• pp.27-34
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• 2016

본 연구에서는 EDISON CFD의 2D_Incomp_P 해석자를 이용하여 0.16부터 1,000,000까지 다양한 레이놀즈수에서 실린더의 유동 특성을 연구하였다. 임계 레이놀즈수 이하에서 실험값과 유사한 압력분포도를 제작하여 해석 결과의 타당성을 검증하였다. 레이놀즈수에 따른 항력계수의 그래프를 제작하여 항력계수의 값이 레이놀즈수의 변화에 대해 선형적으로 변화하는 것을 연구하였다. 같은 속도장일 때 특성길이에 따른 유동장의 차이점도 연구하기 위하여 특성길이에 변화를 주어 해석을 진행하였고, 특성길이가 길수록 박리가 빠르게 발생하는 것을 알게 되었다.

• Journal of Ocean Engineering and Technology
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• v.11 no.4
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• pp.122-129
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• 1997

Flow characteristics of two-dimensional closed square cavities near unsteady critical Reynolds numbers were studied numerically at five Reynolds numbers : 8${\times}10^3$, 8.5${\times}10^3$, 9${\times}10^3$, 9.5${\times}10^3$ and $10^4$ were investigated. A convection conservative difference scheme based upon SOLA to maintain the nearly 2nd-order spatial accuracy was adopted on irregular grid formation. Irregular grid number is 80${\times}$80 and its minimum size is about 1/400 of the cavity height(H) and its maximum is about 1/53 H. The result shows that the critical Reynolds number indicating the emergence of flow unsteadiness exists near Re=8.5${\times}10^3$ and their flow patterns reveal periodic fluctuation during transient and fully-developed stages.

• Journal of Advanced Marine Engineering and Technology
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• v.20 no.5
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• pp.22-29
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• 1996

Flow characteristics of two-dimensional closed square cavities near unsteady critical Reynolds numbers were studied numerically at four Reynolds numbers : $8{\times}10^3,\;8.5{\times}10^3,\;9{\times}10^3\;and\;9.5{\times}10^3.$ A convection conservative difference scheme based upon SOLA to maintain the nearly 2nd-order spatial accuracy is adopted on irregular grid formation. Irregular grid number is $80{\times}80$ and its minimum size is about 1/400 of the cavity height(H) and its maximum is about 1/53 H. The result shows that the critical Reynolds number indicating the emergence of flow wnsteadiness is ranging from Re=$8{\times}10^3\;to\;8.5{\times}10^3$ and their flow patterns reveal periodic fluctuation during transient and fully developed stages. But macroscopic flow behavior in terms of instantaneous and time-mean characteristics represent remarkable difference.

• Proceeding of EDISON Challenge
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• 2015.03a
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• pp.547-552
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• 2015

이번 연구에서는 Ali & Ramadhayni[2]에 의해 실험된 corrugated fin에 Cross-Cutting을 하여 압력강하를 2-D Laminar 영역에서 분석하였다. 분석 지표로는 Pressure drop의 무차원화된 지표인 friction factor를 사용하였고, corrugation angle을 $10^{\circ}$, $20^{\circ}$, $30^{\circ}$로 변화 시켜가며 진행하였다. Cross-Cutting의 길이는 $0.3D_h$길이로 고정시켜 계산하였고, 모든 값은 $D_h=2l$로 무차원화 하였다. Corrugated Fin의 경우, Corrugation Angle에 따라 층류영역에서 주기성을 가진 vortex shedding이 일어나는데, 그 때의 레이놀즈 수를 본 연구에서는 임계 레이놀즈 수라 하고, Vortex Shedding이 일어나기 시작하는 $Re_{cr}$ 이하에서 연구를 진행하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.820-823
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• 2017

This study experimentally investigate how the Reynolds number affect cavitation performance in a turbopump inducer using water. Cavitation performance has been determined by the static pressure measured at the inlet of the inducer. Reynolds number has been varied by varying water temperature and inducer rotational speed to maintain constant non-dimensional thermal parameter. At low non-dimensional thermal parameter, the critical cavitation number is insensitive to Reynolds number. However, at high non-dimensional thermal parameter, the critical cavitation number increased as Reynolds number increases. Thus, cavitation performance is deteriorated as Reynolds number increases when thermal effect exists.

• Economic and Environmental Geology
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• v.52 no.4
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• pp.291-297
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• 2019

Fluid flow through rock fractures has been quantified using equations such as Stokes equations, Reynolds equation (or local cubic law), cubic law, etc. derived from the Navier-Stokes equations under the assumption that linear flow prevails. Therefore, these simplified equations are limited to linear flow regime, and cause errors in nonlinear flow regime. In this study, causal mechanism of nonlinear flow and critical Reynolds number were presented by carrying out fluid flow modeling with both the Navier-Stokes equations and the Stokes equations for a three-dimensional rough-walled rock fracture. This study showed that flow regimes changed from linear to nonlinear at the Reynolds number greater than 10. This is because the inertial forces, proportional to the square of the fluid velocity, increased enough to overwhelm the viscous forces. This tendency was also shown for the unmated (slightly sheared) rock fracture. It was found that nonlinear flow was caused by the rapid increase in the inertial forces with increasing fluid velocity, not by the growing eddies that have been ascribed to nonlinear flow.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.8
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• pp.2051-2063
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• 1995

An improved version of nonlinear low-Reynolds-number k-.epsilon. model is developed. In this model, the limiting near-wall behavior and nonlinear Reynolds stress representations are incorporated. Emphasis is placed on the adoption of Ry(.iden. $k^{1}$2/y/.nu.) instead of $y^{[-10]}$ (.iden. $u_{{\tau}/y/{\nu}}$) in the low-Reynolds-number model for predicting turbulent separated and reattaching flows. The non-equilibrium effect is examined to describe recirculating flows away from the wall. The present model is validated by doing the benchmark problem of turbulent flow behind a backward-facing step. The predictions of the present model are cross-checked with the existing measurements and DNS data. The model performance is shown to be generally satisfactory.

• Applied Chemistry for Engineering
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• v.16 no.5
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• pp.698-704
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• 2005

Power consumption for paddle impeller in spherical and cylindrical agitated vessel was measured over a wide range of Reynolds number from laminar to turbulent flow regions. The power correlation was obtained for both spherical and cylindrical vessels, where the apparent diameter of the spherical vessel was equal to the diameter of the cylindrical vessel (height equal to its diameter and had the same volume as the spherical vessel). The power consumption well correlated with the experimental results of Nagata, et al. and Hixson-Baum. Also the critical Reynolds numbers was directly related to the transition coefficient $C_{tr}$ characterizing the transition from a laminar to a turbulent flow region in the correlation proposed here.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.8
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• pp.2039-2050
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• 1995

The nonlinear low-Reynolds-number k..epsilon. model of park and Sung is extended to predict the turbulent heat transports in separated and reattaching flows. The equations of the temperature variance( $k_{\theta}$ and its dissipation rate(.epsilon.$_{\theta}$ are solved, in concert with the equations of the turbulent kinetic energy(k) and its dissiation rate(.epsilon). In the present model, the near-wall effect and the non-equilibrium effect are fully taken into consideration. The validation of the model is then applied to the turbulent flow behind a backward-facing step and the flow over a blunt body. The predicted results of the present model are compared and evaluated with the relevant experiments.