• Journal of the KSME
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• v.31 no.1
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• pp.68-79
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• 1991

이 글에서는 다음의 내용에 대하여 알아보았다. Duffing - holmes 방정식에서의 Chaos Logistic map에서의 Chaos 기타 시스템에서의 Chaos 1) Henon map 2) Bouncty bau map (standard map) 3) 진자에서의 Chaos 4) Taylor-Couette유동 5) Fluid drop Chaos 6) Surface wave Chaos Lyapunov 지수 (Exponent)

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.3
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• pp.540-546
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• 1992

Turbulent Couette flow between coaxial cylinders with inner one rotating has been investigated experimentally and numerically. The radius ratio of the coaxial cylinders is 0.43. Mean velocity and turbulent stresses have been measured by hot-wire anemometer in the range of Reynolds number based on the velocity at rotating wall and the radial distance between walls, 60,900-187,000. For the numerical computation, the Reynolds stress model has been used as a turbulence closure model. Measurements of mean velocity show that the velocity profile of wall layer largely deviates from universal logarithmic law due to the effect of streamline curvature, especially in the region near the stationary outer cylinder. The results computed with the Reynolds stress model agree well with the experimental data in the prediction of circumferential intensity of turbulent fluctuations. However, the computed level of radial intensity is much higher than the measurement. Curvature-corrected versions of the Reynolds stress model improves the prediction of turbulent intensities, but the results are not fully satisfactory.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.27 no.6
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• pp.766-772
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• 2003

The pseudospectral method for stability analysis was used to find the most influential disturbance mode for transition of plane channel flows and Blasius flow at their critical Reynolds numbers. A number of various oblique disturbance waves were investigated for their pseudospectra and resolvent norm contours in each flow, and an exhaustive search method was employed to find the disturbing waves to which the flows become most unstable. In plane Poiseuille flow an oblique disturbance with a wavelength of 3.59h (where h is the half channel width) at an angle $28.7^{\circ}$ was found to be the most influential for the flow transition to turbulence, and in plane Couette flow it is an oblique wave with a wavelength of 3.49h at an angle of $19.4^{\circ}$. But in Blasius flow it was found that the most influential mode is a normal wave with a wavelength of $3.44{\delta}_{999}$. These results imply that the most influential disturbance mode is closely related to the fundamental acoustic wave with a certain shear sheltering in the respective flow geometry.

• Journal of the Society of Naval Architects of Korea
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• v.36 no.4
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• pp.21-27
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• 1999

A low order panel method based on the perturbation potential is applied for prediction of performance of blown-flap rudders. In order to improve the solution behavior at the large angle of attacks, the geometry of the trailing wake sheet is computed by aligning freely with the local flow. The effect of the wake sheet roll-up is also included with use of a high order panel method. The flow in the gap between the main component and the flap of the rudder is modeled as Couette flow. The effects of the gap and the flow jet are included in application of a kinematic and a dynamic boundary condition on the inlet and the outlet of the gap as well as on the flap and the wake. The results with the present method are compared with existing experimental data. The method is shown to be capable of determining accurately the flow characteristics even for large flap angles.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.7
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• pp.877-884
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• 2001

A theoretical analysis is conducted on the Stokes flow in a narrow channel. A vertical fin is mounted on the bottom plate and the flow is induced by uniformly sliding top plate. The governing harmonic equation was solved in the transformed ζ-plane, which is obtained by applying conformal mappings to the physical plane. By using well-known transformation technique, closed-form expressions for velocity and skin frictional stress on the top and bottom plates were obtained.

• Journal of the Korean Society for Aviation and Aeronautics
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• v.23 no.3
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• pp.8-17
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• 2015

In this research, low fidelity air/heat load analysis was conducted for the intake of high speed vehicle. For air/heat load calculations, aerodynamic properties at the surface and the boundary layer edge were estimated using Taylor-Maccoll equation for conical flow, shockwave relation and Prandtl-Meyer expansion equation for internal and external flow. Couette flow assumption and Reynolds analogy were used in order to calculate convective heat transfer coefficient. In order to calculate skin friction coefficient for heat transfer coefficient analysis, Van Driest method II and Reference Enthalpy method were considered. An axis symmetric SCRAMJET model was selected as a reference configuration for verifying the proper implementation of the present method. Comparison of the results using the present method and Computational Fluid Dynamic analysis showed that the present method is valuable for efficiently providing pressure and heat loads for air-intake structure design of the high speed air vehicle.

• Journal of the korean Society of Automotive Engineers
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• v.14 no.3
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• pp.109-114
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• 1992

The purpose of this study is to experimentally research the effects of polymer additives on turbulent transition of Couette flow between concentric cylinders when outer one is rotating and inner one is at rest; the diameter ratio being 0.2. Aqueous polymer solution generate the degradation phenomena in machine forming work, but this is not effected in about 10 minute at 5ppm. aqueous polymer solution testing. The Reynolds number, referred to the gap distance and rotation velocity of the outer cylinder, of turbulent transition is about 20000 for water flow. In the laminer region, the torque value is as same as theoretical one in the region of low Reynolds number, but becomes high with an increase in the Reynolds number. The polymer additives reduce the Reynolds number for turbulent transtition. In the turbulent region, the torque is remarkably reduced by the polymer additives, soluble polymer take down effect of turbulent transition boundary torque.

• Journal of the Korean Society for Precision Engineering
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• v.11 no.4
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• pp.148-157
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• 1994

A multi-cylindrical hydraulic valve incorporating with an electro-rheological(ER) fluid is developed in this study. Field-dependent Bingham properties of the ER fluid are exploited to devise the valve system which features fast system response as well as simple mechanism. The fast response is accrued from almost instant response characteristics of the ER fluid itself, and the mechanism configuration is simplified since no nechanically moving parts are required. The material properties of the ER fluids to be utilized for modeling of the proposed valve system are firstly tested with a couette-type electroviscometer. The design and manufacturing processes are then undertaken on the basis of model parameters. The performance characteristics of the valve system are evaluated in terms of pressure variations with respect to the intensity of employed electric fields and flow rates.

• Applied Chemistry for Engineering
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• v.28 no.4
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• pp.448-453
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• 2017

We conducted the three-dimensional fluid flow analysis in a Taylor reactor using computational fluid dynamics (CFD). The Taylor flow can be categorized into five regions according to Reynolds number, i.e., circular Couette flow (CCF), Taylor vortex flow (TVF), wavy vortex flow (WVF), modulated wavy vortex flow (MWVF), and turbulent Taylor vortex flow (TTVF), and we investigated the flow characteristics at each region. For each region, the shape, number and length of vortices were different and they influenced on the bypass flow. As a result, the Taylor vortex was found at TVF, WVF, MWVF and TTVF regions. The highest number of Taylor vortex was observed at TVF region, while the lowest at TTVF region. The numerical model was validated by comparing with the experimental data and the simulation results were in good agreement with the experimental data.

• Journal of the Korean Society of Visualization
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• v.15 no.3
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• pp.27-33
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• 2017

Direct numerical simulations of turbulent channel flows with moving wall conditions on the top wall are performed to examine the effects of the moving wall on the turbulent characteristics. The moving wall velocity only applied to the top wall with the opposite direction to the main flow is systematically varied to reveal the sustained-mechanism for turbulence. The turbulence statistics for the Couette-Poiseuille flow, such as mean velocity, root mean square of the velocity fluctuations, Reynolds shear stress and pre-multiplied energy spectra of the velocity fluctuations, are compared with those of canonical turbulent channel flows. The comparison suggests that although the turbulent activity on the top wall increases with increasing the Reynolds number, that on the bottom wall decreases, contrary to the previous finding for the canonical turbulent channel flows. The increase of the turbulent energy on the top wall is attributed to not only the increase of the Reynolds number but also elongation of the logarithmic layer due to increase of the wall layer on the top wall. However, because the logarithmic layer is shortened on the bottom wall due to the decrease of the wall layer, the turbulence energy on the bottom wall decreases despite of the increase of the Reynolds number.