• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2009.10a
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• pp.241-242
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• 2009

There are marry ships and marine structures and also has marry differences on according to the shape and the interval of hulls to the purpose. the multi-submerged body needs appropriate distance between the hulls because of the optimum hull form. thus, through this paper, the flow characteristics behind the multi-submerged body according os the distance ration between the hulls and various angles of attack was conducted.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.2
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• pp.11-16
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• 2006

An experimental study of the transonic flows over NACA and double wedge airfoils was conducted with a shock tube. The configuration of test section with a slotted wall and chamber was designed and tested to minimize wall and reflected shock wave effects and use the shock tube as simple and less costly wind tunnel generating the relatively high Reynolds numbers transonic flow. Transonic airfoil flows at hot gas Mach numbers of 0.80~0.84, Reynolds number of about $1.2{\times}10^6$ on airfoil chord length and angles of attack of $0^{\circ}$ and $2^{\circ}$ were visualized with the shadowgraph method. The shock wave profiles on the airfoils were compared with the corresponding results from the conventional transonic wind tunnel tests. The experimental results showed that present shock tube exhibited the proper performance characteristics as transonic wind tunnel for tested Mach number range and airfoils.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.6
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• pp.475-484
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• 2012

Numerical investigation is performed to understand the effects of thickness uncertainty of a supporting airfoil due to manufacturing processes on the aerodynamic characteristics of an airfoil used for measuring data in a wind tunnel testing. This is done by comparing the coefficients of lift, drag and moment of the airfoils. In this work, the airfoil model consists of three parts, one located in the center for measuring and two outer parts used for supporting. The study is carried out with a NACA64-418 airfoil and the turbulence model of Transition SST. It is found that the effect of thickness uncertainty of the airfoils used for supporting is not significant to the performance of the test airfoil at various angles of attack and Reynolds numbers.

• Journal of Ship and Ocean Technology
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• v.12 no.3
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• pp.36-54
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• 2008

A jet stream applied tangential to a curved surface in fluid increases lift force by strengthening circulation around the surface and this phenomenon is known as the Coanda effect. Many experimental and numerical studies have been performed on the Coanda effect and the results found to be useful in various fields of aerodynamics. Recently, preliminary studies on Coanda control surface are in progress to look for practical application in marine hydrodynamics since various control surfaces are used to control behaviors of ships and offshore structures. In the present study, the performance of a Coanda control surface with different geometries of the jet injection nozzle was surveyed to assess applicability to ship rudders. A numerical simulation was carried out to study flow characteristics around a section of a horn type rudder subjected to a tangential jet stream. The RANS equations, discretized by a cell-centered finite volume method were used for this computation after verification by comparing to the experimental data available. Special attentions have been given to the sensitivity of the lift performance of a Coanda rudder to the location of the slit (outlet) and intake of the gap between the horn and rudder surface at the various angles of attack. It is found that the location of the water intake is important in enhancing the lift because the gap functions as a conduit of nozzle generating a jet sheet on the rudder surface.

• International Journal of Naval Architecture and Ocean Engineering
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• v.4 no.2
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• pp.151-161
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• 2012

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-${\varepsilon}$ model. Numerical simulations are performed at a wide range of the normalized ground clearance by the chord length ($0.1{\leq}h/C{\leq}1.25$) for the angles of attack ($0^{\circ}{\leq}{\alpha}{\leq}10^{\circ}$) in the prestall regime at a Reynolds number (Re) of $2{\times}10^6$ based on free stream velocity $U_{\infty}$ 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 ${\alpha}=4^{\circ}$ and h / C = 0.1. Under the conditions of ${\alpha}=4^{\circ}$ and h / C = 0.1, the effect of the Reynolds number on the aerodynamic characteristics of NACA 4406 is investigated in the range of $2{\times}10^5{\leq}Re{\leq}2{\times}10^9$. As Re increases, $C_l$ and $C_d$ augments and decreases, respectively, and the lift-to-drag ratio increases linearly.

• Advances in aircraft and spacecraft science
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• v.10 no.2
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• pp.107-125
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• 2023

Drag reduction is significant research in aircraft design due to its effect on the cost of operation and carbon footprint reduction. Aircraft currently use conventional solid winglets to reduce the induced drag, adding extra structural weight. Fluidic on-demand winglets can effectively reduce drag for low-speed flight regimes without adding any extra weight. These utilize the spanwise airflow from the wingtips using hydraulic actuators to create jets that negate tip vortices. This study develops a computational model to investigate fluidic on-demand winglets. The well-validated computational model is applied to investigate the effect of injection velocity and angle on the aerodynamic coefficients of a rectangular wing. Further, the turbulence parameters such as turbulent kinetic energy (TKE) and turbulent dissipation rate are studied in detail at various velocity injections and at an angle of 30°. The results show that the increase in injection velocity shifted the vortex core away from the wing tip and the increase in injection angle shifted the vortex core in the vertical direction. Further, it was found that a 30° injection is efficient among all injection velocities and highly efficient at a velocity ratio of 3. This technology can be adopted in any aircraft, effectively working at various angles of attack. The culmination of this study is that the implementation of fluidic winglets leads to a significant reduction in drag at low speeds for low aspect ratio wings.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.12
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• pp.1-8
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• 2006

An experimental study was carried out in order to investigate the influence of Reynolds number on the near-wake of an oscillating airfoil. An NACA 0012 airfoil was sinusoidally pitched at the quarter chord point, and is oscillated over a range of instantaneous angles of attack of $\pm$6$^{\circ}$. An X-type hot-wire probe was employed to measure the near-wake of an oscillating airfoil, and the smoke-wire visualization technique was used to examine the flow properties of the boundary layer. The free-stream velocities were 1.98, 2.83 and 4.03 m/s and the corresponding chord Reynolds numbers were 2.3${\times}10^4$, 3.3$\times$104 and 4.8${\times}10^4$, respectively. The frequency of airfoil oscillation was adjusted to fix a reduced frequency of K=0.1. The results show that the properties of the boundary layer and the near-wake can dramatically be distinguished in the range of Reynolds numbers between 2.3${\times}10^4$ and 3.3${\times}10^4$, on the other hand, it is similar in the cases of Re=3.3$\times$104 and 4.8$\times$104. This is caused by that the unsteady separation point is dramatically delayed in case of Re= 2.3${\times}10^4$.

• Journal of the Society of Naval Architects of Korea
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• v.28 no.2
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• pp.159-173
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• 1991

This paper describes a potential-based panel method formulated for the analysis of a super-cavitating two-dimensional hydrofoil. The method employs normal dipoles and sources distributed on the foil and cavity surfaces to represent the potential flow around the cavitating hydrofoil. The kinematic boundary condition on the wetted portion of the foil surface is satisfied by requiring that the total potential vanish in the fictitious inner flow region of the foil, and the dynamic boundary condition on the cavity surface is satisfied by requiring thats the potential vary linearly, i.e., the tangential velocity be constant. Green's theorem then results in a potential-based integral equation rather than the usual velocity-based formulation of Hess & Smith type. With the singularities distributed on the exact hydrofoil surface, the pressure distributions are predicted with improved accuracy compared to those of the linearized lilting surface theory, especially near the leading edge. The theory then predicts the cavity shape and cavitation number for an assumed cavity length. To improve the accuracy, the sources and dipoles on the cavity surface are moved to the newly computed cavity surface, where the boundary conditions are satisfied again. This iteration process is repeated until the results are converged. Characteristics of iteration and discretization of the present numerical method are much faster and more stable than the existing nonlinear theories. The theory shows good correlations with the existing theories and experimental results for the super-cavitating flow. In the region of small angles of attack, the present prediction shows and excellent comparison with the Geurst's linear theory. For the long cavity, the method recovers the trends of the Wu's nonlinear theory. In the intermediate regions of the short super-cavitation, the method compares very well with the experimental results of Parkin and also those of Silberman.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.2
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• pp.95-106
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• 2021

Side-jets enable the immediate maneuver of a missile compared to control surfaces; however, they may cause adverse effects on aerodynamic coefficients, for they interfere with freestream. To find out the impact of side-jets on aerodynamic coefficients, we simulate side-jets as air gas and utilize multi-fidelity models to evaluate differences between aerodynamic coefficients obtained with and without side-jets. We computed differences in aerodynamic coefficients to investigate side-jet effects for the changes of a Mach number, a bank angle, and an angle of attack. As a result, asymmetrically developed side-jets affect the longitudinal force and moment coefficients, and the lateral force and moment coefficients drastically change in-between -30 and 30 degrees of bank angles. In contrast, side-jets hardly influence the axial force coefficients. As for the axial moment coefficient, we could not determine the side-jet effect due to a lack of aerodynamic coefficient samples in the Mach number. All in all, we confirm that side-jets lead to the change of a missile attitude as they considerably vary the longitudinal and lateral aerodynamic coefficients.

• Journal of Navigation and Port Research
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• v.46 no.3
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• pp.168-178
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• 2022

In this study, the resistance test, the vertical static angle of the attack test and VPMM test will be conducted to estimate the maneuverability of underwater vehicles with ahead propeller. The vertical static test will be conducted within the range of -40deg to 40deg, to investigate the cross-flow drag at high incidence angles. The tests will be conducted by dividing the propeller rotation into a case in which the propeller rotates at a specific rpm, and a case in which the propeller rotates naturally, according to the towing speed. Hydrodynamic coefficients of vertical direction will be estimated by the captive model tests. Additionally, the vertical dynamic stability index based on estimated hydrodynamic coefficients will be calculated and the impact of the propeller revolution state on the index will be investigated. The results are expected to be used as reference test data for underwater vehicles with ahead propeller.