Search Results

You are looking at 1 - 6 of 6 items for

  • Author: Jae-Sik Yoon x
Clear All Modify Search
Open access

Jae Jung, Hyun Sik Yoon, Ho Hwan Chun, Pham Anh Hung and Osama Ahmed Elsamni

ABSTRACT

The present study numerically investigates the aerodynamic characteristics of two-dimensional wings in the vicinity of the ground by solving two-dimensional steady incompressible Navier-Stokes equations with the turbulence closure model of the realizable k −ε model. Numerical simulations are performed at a wide range of the normalized ground clearance by the chord length ( 0.1 ≤ h / C ≤ 1.25 ) for the angles of attack ( 0° ≤α ≤10° ) in the prestall regime at a Reynolds number ( Re ) of 2×106 based on free stream velocity U∞ and the chord length. As the physical model of this study, a cambered airfoil of NACA 4406 has been selected by a performance test for various airfoils. The maximum lift-to-drag ratio is achieved at α = 4° and h / C = 0.1 . Under the conditions of α = 4° and h / C = 0.1 , the effect of the Reynolds number on the aerodynamic characteristics of NACA 4406 is investigated in the range of 2×105 ≤ Re≤ 2×109. As Re increases, l C and d C augments and decreases, respectively, and the lift-todrag ratio increases linearly.

Open access

Jae Hwan Jung, Hyun Sik Yoon and Chang Yeol Lee

Abstract

Liquid sloshing in two-dimensional (2-D) and three-dimensional (3-D) rectangular tanks is simulated by using a level set method based on the finite volume method. In order to examine the effect of natural frequency modes on liquid sloshing, we considered a wide range of frequency ratios (0.5 ≤ fr ≤ 3.2). The frequency ratio is defined by the ratio of the excitation frequency to the natural frequency of the fluid, and covers natural frequency modes from 1 to 5. When fr = 1 which corresponds to the first mode of the natural frequency, strong liquid sloshing reveals roof impact, and significant forces are generated by the liquid in the tank. The liquid flows are mainly unidirectional. Thus, the strong bulk motion of the fluid contributes to a higher elevation of the free surface. However, at fr = 2 the sloshing is considerably suppressed, resulting in a calm wave with relatively lower elevation of the free surface, since the waves undergo destructive interference. At fr = 2 the lower peak of the free surface elevation occurs. At higher modes of fr3, fr4, and fr5 the free surface reveals irregular deformation with nonlinear waves in every case. However, the deformation of the free surface becomes weaker at higher natural frequency modes. Finally, 3-D simulations confirm our 2-D results.

Open access

Mi Jeong Kim, Hyun Sik Yoon, Jae Hwan Jung, Ho Hwan Chun and Dong Woo Park

ABSTRACT

The present study numerically investigates the effect of the wavy leading edge on hydrodynamic characteristics for the flow of rectangular wings with the low aspect ratio of 1.5. Five different wave lengths at fixed wavy amplitude have been considered. Numerical simulations are performed at a wide range of the angle of attack ( 0° ≤ α ≤ 40° ) at one Reynolds number of 106 . The wavy wings considered in this study did not experience enough lift drop to be defined as the stall, comparing with the smooth wing. However, in the pre-stall region, the wavy wings reveal the considerable loss of the lift, compared to the smooth wing. In the post-stall, the lift coefficients of the smooth wing and the wavy wings are not much different. The pressure coefficient, limiting streamlines and the iso-surface of the spanwise vorticity are also highlighted to examine the effect of the wave length on the flow structures.

Open access

Jae Hwan Jung, Hyun Sik Yoon, Ho Hwan Chun, Inwon Lee and Hyun Park

ABSTRACT

The present study numerically models the interaction between a regular wave and the roll motion of a rectangular floating structure. In order to simulate two-dimensional incompressible viscous two-phase flow in a numerical wave tank with the rectangular floating structure, the present study used the volume of fluid method based on the finite volume method. The sliding mesh technique is adopted to handle the motion of the rectangular floating structure induced by fluid-structure interaction. The effect of the wave period on the flow, roll motion and forces acting on the structure is examined by considering three different wave periods. The time variations of the wave height and the roll motion of the rectangular structure are in good agreement with experimental results for all wave periods. The present response amplitude operator is in good agreement with experimental results with the linear potential theory. The present numerical results effectively represent the entire process of vortex generation and evolution described by the experimental results. The longer wave period showed a different mechanism of the vortex evolution near each bottom corner of the structure compared to cases of shorter wave periods. In addition, the x-directional and z-directional forces acting on the structure are analyzed.

Open access

Chan-Mi Kim, Peyala Dharmaiah, Hyo-Seob Kim, Jar-Myung Koo, Jae-Sik Yoon, Hyun-Seon Hong and Soon-Jik Hong

Abstract

The objective of this particular study was to recover valuable metals from waste plasma display panels using high energy ball milling with subsequent acid dissolution. Dissolution of milled (PDP) powder was studied in HCl, HNO3, and H2SO4 acidic solutions. The effects of dissolution acid, temperature, time, and PDP scrap powder to acid ratio on the leaching process were investigated and the most favorable conditions were found: (1) valuable metals (In, Ag, Mg) were recovered from PDP powder in a mixture of concentrated hydrochloric acid (HCl:H2O = 50:50); (2) the optimal dissolution temperature and time for the valuable metals were found to be 60°C and 30 min, respectively; (3) the ideal PDP scrap powder to acid solution ratio was found to be 1:10. The proposed method was applied to the recovery of magnesium, silver, and indium with satisfactory results.

Open access

Jae Hwan Jung, Mi Jeong Kim, Hyun Sik Yoon, Pham Anh Hung, Ho Hwan Chun and Dong Woo Park

ABSTRACT

We investigated the aerodynamic characteristics of a three-dimensional (3D) wing with an endplate in the vicinity of the free surface by solving incompressible Navier-Stokes equations with the turbulence closure model. The endplate causes a blockage effect on the flow, and an additional viscous effect especially near the endplate. These combined effects of the endplate significantly reduce the magnitudes of the velocities under the lower surface of the wing, thereby enhancing aerodynamic performance in terms of the force coefficients. The maximum lift-to-drag ratio of a wing with an endplate is increased 46% compared to that of wing without an endplate at the lowest clearance. The tip vortex of a wing-with-endplate (WWE) moved laterally to a greater extent than that of a wing-without-endplate (WOE). This causes a decrease in the induced drag, resulting in a reduction in the total drag.