• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.21 no.2
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• pp.137-141
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• 1985

In this paper, the author investigate viscous effects on the characteristics of TP620 hydrofoil. The pressure distribution on the foil section in non-cavitating flow should be considered its characteristics of displacement thickness due to viscous effects. Theoretical potential theory, which neglects viscous effects do not agree with this analysis, especially at leading edge region of the foil. And, the efficiency of TP620 hydrofoil considering viscous effects is a little lower than that of the foil, which neglected viscous effects.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.1
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• pp.1-7
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• 2003

The aerodynamic optimization method for airfoil design was described in this paper. The Navier-Stokes equations were solved to consider the viscous flow information around an airfoil. The Modified Method of Feasible Direction(MMFD) was used for sensitivity analysis and the polynomial interpolation was used for distance calculation of the minimization. The Message Passing Interface(MPI) library of parallel computation was adopted to reduce the computation time of flow solver by decomposing the entire computational domain into 8 sub-domains and one-to-one allocating 8 processors to 8 sub-domains. The parallel computation was also used to compute the sensitivity analysis by allocating each search direction to each processor. The present optimization reduced the drag of airfoil while the lift is maintained at the tolerable design value.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.37 no.6
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• pp.527-536
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• 2009

A cascade apparatus was designed with only one blade. Its passage is a 160% width of the cascade pitch. This kind of apparatus can give more accurate experimental result than those applying multi-blades even though the apparatus is small. However, this causes difficulties to make the periodic condition along the pitchwise direction. In this study, sidewalls were designed to satisfy the periodic condition based on the flow structure using a gradient based optimization and a genetic algorism. The objective function was adopted the surface Mach number obtained on the cascade and fourteen design variables were selected for controlling sidewall shapes. The designed sidewalls using the genetic algorism shows better result.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.2
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• pp.141-147
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• 2016

Underwater cavitation is one of the most important issues because it causes not only vibration and erosion of submerged bodies but also significant flow noise problems. In this paper, flow noise due to cavitation flows around the NACA66 MOD hydrofoil is numerically investigated. The cavitation flow simulation is conducted using the Reynolds-Averaged Navier-Stokes equations based on finite difference methods. To capture the cavitation phenomena accurately and effectively, the homogeneous mixture model with the Merkle's cavitation model is applied. The predicted results are compared with available experimental data in terms of pressure coefficients and volume fraction, which confirms the validity of numerical results. Based on flow field analysis results, hydro-acoustic noise field due to the cavitation flow is predicted using the Ffowcs-Williams and Hawkings equation derived from the Lighthill's acoustic analogy. The typical lift dipole propagation patterns are identified.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.8
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• pp.661-669
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• 2007

Study on the feasibility assessment for applying the overlap grid method to numerical calculations on the ground effect has been performed. The objective of the present study is to settle the problem in the grid generation process. A low Mach number preconditioned turbulent flow solver using the overlap grid and the multi-block grid methods has been developed and applied to the ground effect simulation around the RAE 101 airfoil. It has been verified that the overlap grid method not only can provide sufficiently accurate solutions but also work out the grid generation problem in the ground effect simulations.

• Journal of computational fluids engineering
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• v.17 no.4
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• pp.93-102
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• 2012

Once the condensation of water vapor in moist air around a thin airfoil occurs, liquid droplets nucleate. The condensation process releases heat to the surrounding gaseous components of moist air and significantly affects their thermodynamic and flow properties. As a results, variations in the aerodynamic performance of airfoils can be found. In the present work, the effects of upstream Mach number and thickness ratio of airfoil on the transonic flow of moist air around a thin airfoil are investigated by numerical analysis. The results shows that a significant condensation occurs as the upstream Mach number is increased at the fixed thickness ratio of airfoil($\epsilon$=0.12) and as the thickness ratio of airfoil is increased at the fixed upstream Mach number($M_{\infty}$=0.80). The condensate mass fraction is also increased and dispersed widely around an airfoil as the upstream Mach number and thickness ratio of airfoil are increased. The position of shock wave for moist air flow move toward the leading edge of airfoil when it is compared with the position of shock wave for dry air.

• Transactions of the Korean Society of Mechanical Engineers
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• v.15 no.1
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• pp.229-240
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• 1991

The large camber angle theory of turbomachine blade of compressor has been developed recently for the two-dimensional flow by Hawthorn, et al. However, in the above theory it was assumed that the fluid was incompressible and inviscid, and the blades had no thickness. In this study, the flow in a blade cascade being mounted in parallel fashion with blade of arbitrary thickness is studied in order to determine the effects of the camber angle on the performance characteristic of the blade section under the consideration of compressibility and viscosity of fluid. The panel method is used for potential flow analysis. The flow in the boundary-layer is obtained by solving the integral boundary-layer structure through the laminar, transitional , and turbulent flow using the pressure field determined from the potential flow. And then the viscous-inviscid interaction scheme is used for interaction of these two flows. For the determination of the variation in the outlet fluid angle influenced by deviation in cascade flow, the superposition method which is used for single foil is introduced in this analysis. By the introduction of this method, the effects of the deviation on outlet fluid angle and the resulting fluid angle are made to adjust for oneself through the calculation. As the result of this study, the blade of large camber angle, large incidence angle, large pitch-chord ratio has large viscous and compressible effect than those of small camber angle. Lift force increase as camber angle increases, but above 60.deg. of camber angle, lift force decrease as camber angle increases. But drag force increases linearly with camber angle increases in the entire region.

• 한국전산유체공학회:학술대회논문집
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• 2009.04a
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• pp.51-56
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• 2009

Optimization with metamodel is one of numerical optimization methods. Response surface method is performed for making metamodel. The Hcks-Henne function is used for designing 2D shape of the airfoil and spring analogy is used to change the grid according to the change in shape of the airfoil. Aerodynamic coefficient required for response surface method are obtained by using Navier-Stokes solver with $\kappa-\omega$ shear stress transport turbulence model. For the baseline airfoils, OA 312, OA 309, and OA 407 airfoils select and optimize to improve aerodynamic performance.

• Journal of computational fluids engineering
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• v.3 no.1
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• pp.46-53
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• 1998

An inverse method for the subsonic and transonic airfoil design was developed using the Euler equations. Two testcases were performed. One was a verification of the method using the supercritical airfoil of the Korean mid-sized (100 passengers class) transport aircraft. The other was the design of an airfoil showing a good cruising performance (L/D ratio) in the high subsonic flow regime. These testcases demonstrated the efficiency and the robustness of the design method in the present study.

• 한국전산유체공학회:학술대회논문집
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• 2006.10a
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• pp.199-205
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• 2006

Two dimensional turbulent flow simulations on the low Mach number - high Reynolds number flow about the NACA 4412 airfoil are carried out as the airfoil approaches a ground. It has been turned out that angle of attack between 2 and 8 is recommended for the airfoil to utilize the benefit of ground effect. For the large angle of attack, the increment of lift due to the ground effect is eliminated and negative aerodynamic effect such as destabilizing aspect in static longitudinal stability are occurred as the airfoil approaches a ground.