• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 1995년도 추계 학술대회논문집
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• pp.154-159
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• 1995

Numerical optimization technique with Navier-Stokes code has been used to reduce the drag of conventional ogival nose. Forebody optimizations are performed for supersonic laminar and turbulent flow conditions. To alleviate the computing time of aerodynamic drag calculation, axisymmetric boundary condition is implemented in the 3-dimensional Navier-Stokes code. The automated optimization procedure with gradient based method results in a drag reduction of $4\;\%$.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2010년 춘계학술대회논문집
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• pp.214-220
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• 2010

This article described that a high Reynolds number version of a turbulence model was modified by using drag reduction to analyze the turbulent flows of non-Newtonian fluid with visco-elastic viscosity and it was applied hemodynamics which was representative of visco-elastic fluid. The turbulence characteristics of visco-elastic fluid was expanded viscous sublayer region and buffer layer region by drag reduction phenomenon and also Newtonian turbulence models does not predict because viscosity was related with shear rate of fluid flow. Hence numerical simulation using a modified turbulence model was conducted under the same conditions that were applied to obtain the experiment results and previous turbulence models and then the numerical investigation of turbulent blood flow in the stenosed artery bifurcation under periodic acceleration of the human body.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년도 학술대회
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• pp.321-326
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• 2008

The engineering use of CFD is recently extending to the prediction of maneuvering characteristics, response to waves, propeller performance, and so on. The focus of the research is shifting to simulation of more complex processes. Typical examples of such processes are bow or stern slamming, green water problem, propeller cavitation, hull-propeller interaction, or drag reduction by bubble injection. Those processes are characterized by keywords such as high nonlinearity, unsteadiness, multiphase flow. In this paper, two new attempts which have been recently made by the author's research grop are presented. One is the prediction of propeller cavitation and its effect to the ship hull. The others is the application to the drag reduction by use of air bubbles.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2008년 추계학술대회논문집
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• pp.321-326
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• 2008

The engineering use of CFD is recently extending to the prediction of maneuvering characteristics, response to waves, propeller performance, and so on. The focus of the research is shifting to simulation of more complex processes. Typical examples of such processes are bow or stern slamming, green water problem, propeller cavitation, hull-propeller interaction, or drag reduction by bubble injection. Those processes are characterized by keywords such as high nonlinearity, unsteadiness, multiphase flow. In this paper, two new attempts which have been recently made by the author's research group are presented. One is the prediction of propeller cavitation and its effect to the ship hull. The other is the application to the drag reduction by use of air bubbles.

• Journal of Advanced Marine Engineering and Technology
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• 제30권3호
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• pp.389-395
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• 2006

The fluid force reduction of a square prism having fences on the corner was studied by the measuring the drag and lift acting on the prism and by the visualization experiment of the flow around the prism. The height of the fence was 10% of the square width and the range of Reynolds number considered was from $Re=0.9{\times}104$ to $Re=2.1{\times}104$. The drag of the prism was reduced about 6.8% and the amplitude of the lift was reduced by attaching two normal fences on the rear corners of the prism. In this case, the separated flow at the front corners was reattached on the upper and lower sides of the prism and the vortex streets at the wake region were appeared more slowly than that of the prototype prism.

• 대한기계학회논문집B
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• 제25권9호
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• pp.1227-1236
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• 2001

A systematic analysis is made of suboptimal control for drag reduction. The influence of the amplitude of actuation (A) and the time scale of actuation ($\Delta$t(sub)a(sup)+) is evaluated. Two wall sensing variables are employed (∂w/∂y│(sub)w and ∂p/∂z│(sub)w) with two wall actuations (${\Phi}$$_2$and ${\Phi}$$_3$). To test the suboptimal control, direct numerical simulations of turbulent channel flow at Re(sub)$\tau$=100 are performed in a spectral domain. It is found that the effect of A and $\Delta$t(sub)a(sup)+∼1. The near-wall behaviors of flow structure are analyzed to characterize the drag reduction. The size effect of the sensor/actuator is examined.

• 태양에너지
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• 제19권3호
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• pp.1-11
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• 1999

Previous researchers have studied how to reduce a pumping power in order to save energy in the fluid transporting system. Especially, it has been studied a lot about reducing the pressure drop among parameters related to the energy saving for fluid transport. This study is to investigate the effect of a substantial drag reduction caused by the polymer(A611P, A601P) when the working fluids flow to the vertical and horizontal direction in the vertical cylindrical equipment of closed flow system. In this experiment, we mount a visualization equipment on the test section and take pictures. With using the PIV system, instrument and analyzing the movement of bubble for different polymer concentration are observed and some mechanism of the drag reduction effect is clarified.

• 대한조선학회논문집
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• 제41권2호
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• pp.70-78
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• 2004

The present study numerically investigates two-dimensional laminar flow past a circular cylinder in an aligned magnetic field using the spectral method. Numerical simulations are performed for flow fields with Re=100 and 200 in the range of 0$\leq$N$\leq$10, where Ν is the Stuart number that is the ratio of electromagnetic force to inertial force. The present study reports the detailed information of flow quantities on the cylinder surface at different Stuart numbers. It is shown that the vortex shedding can be controlled by the magnetic force representing the Stuart number. As Ν increases, the vortex shedding becomes weaker, resulting in drag reduction whose magnitude is the largest at a critical value. In addition, as the magnetic force increases, the lift amplitude decreases, reaching zero at the critical number.

• Nuclear Engineering and Technology
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• 제38권8호
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• pp.763-778
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• 2006

Injection of microbubbles within the turbulent boundary layer has been investigated for several years as a method to achieve drag reduction. However, the physical mechanism of this phenomenon is not yet fully understood. Experiments in a channel flow for single phase (water) and two phase (water and microbubbles) flows with various void fraction values are studied for a Reynolds number of 5128 based on the half height of the channel and bulk velocity. The state-of-the art Particle Tracking Velocimetry (PTV) measurement technique is used to measure the instantaneous full-field velocity components. Comparisons between turbulent statistical quantities with various values of local void fraction are presented to elucidate the influence of the microbubbles presence within the boundary layer. A decrease in the Reynolds stress distribution and turbulence production is obtained with the increase of microbubble concentration. The results obtained indicate a decorrelation of the streamwise and normal fluctuating velocities when microbubbles are injected within the boundary layer.

• 수산해양교육연구
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• 제10권1호
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• pp.63-68
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• 1998

The microbubble splits injection system are improved for the enhancement efficiency of viscous frictional drag reduction. It was confirmed that the experimental results is effective more than Mercle's[7] using the present system in the comparisons. And the new experimental equation is derived to get viscous frictional drag reduction useful for the present experimental data. The new experimental equation approaches Mercle's[7] experimental data wel.