• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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• pp.387-390
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• 2006

Numerical study has been conducted in two dimensions about a NACA0012 airfoil with an oscillating microflap on the surface. We show that this microflap is effective in controlling the unsteady stall at high angles of attack. We solve the compressible Navier-Stokes equations for the Reynolds numbers with an extensible chimera grid fitted to the oscillatory microflap. For turbulent calculation, we adopt the SST $k-{\omega}$ model. We investigate the parametric effect of angle of attacks, Reynolds number, and the location where the microflap is installed.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2003년도 The Fifth Asian Computational Fluid Dynamics Conference
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• pp.75-76
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• 2003

Direct numerical simulation results of aeolian tones generated by a two-dimensional obstacle (circular cylinder, square cylinder, NACA0012 airfoil) in a uniform flow are presented and the generation and propagation mechanisms of the sound are discussed. The unsteady compressible Navier-Stokes equations are solved by a highly-accurate finite difference scheme over the entire region from near to far fields. The direct numerical simulation results are also compared with the results obtained by Curle's acoustic analogy.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2006년도 PARALLEL CFD 2006
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• pp.382-384
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• 2006

• 한국항공우주학회지
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• 제31권6호
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• pp.23-29
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• 2003

얇은 익형 주위에 다양한 응축 과정을 수반하는 상대 습도가 100%인 포화 습공기 천음속 이상 유동에 대하여 연구하였다. 본 연구는 Rusak 과 Lee[11, 12]가 발전시킨 그리고 응축에 의한 열 증가의 효과를 포함하는 확장된 천음속 미 교란 모델을 사용하였고, 응축 과정은 서로 다른 두 가지 형태의 응축 과정을 고려한다. 먼저, 비 평형 균질 과정(nonequilibrium and homogeneous process)에서의 응축 질량비는 고전적 핵형성 이론과 작은 물방울 성장이론에 따라 계산되고, 평형과정(equilibrium process)에서의 응축 질량비는 등엔트로피 가정으로부터 계산된다. 유동 방정식과 응축 방정식들은 반복수치 계산법을 사용하여 그 해를 구하였다. 상류 유동 조건을 같게 하여 얻은 수치계산 결과들은 유동구조, 응축장, 그리고 익형 표면에서의 압력분포 등을 묘사한다. 유동특성, 즉 충격파의 위치와 강도 그리고 익형의 압력분포 등은 서로 다른 두 응축과정에서 각각 다른 유동특성을 나타냈다. 하지만, 각각의 응축과정에서 응축 결과로 생긴 열 증가는 유동거동에 상당한 변화를 야기 시키고 익형의 공력 성능에도 상당한 영향을 미친다.

• 한국전산유체공학회지
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• 제10권1호
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• pp.51-55
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• 2005

For proper installation, operation and performance of axial flow jet engines in aircrafts, the impacts and effects of inlet flow distortion in axial compressors have to be understood. Inlet distortion conditions may cause component-mismatch and instability problems known as rotating stall, and severe oscillations of mass flow rate called surge or a combination of both. Typical effects of this phenomenon include stresses and wear on the compressor blading, destruction of entire jet engines due to the failure of airfoil and mechanical failure or interruption of the combustion process. Therefore, it is important to study inlet flow distortion and its propagation effects to minimize and hence to prevent the occurrence of such calamity. The current novel integral method with parametric analysis signifies its validity to this field of research and offers much potential for further improvements. The present effort further indicates that this simple method may be flourishing in the problems of strongly distorted flow and propagating stall in axial compressor. It is therefore believe that using a more realistic and flexible velocity and pressure profiles could develop this approach further.

• Wind and Structures
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• 제26권6호
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• pp.355-367
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• 2018

This paper studies the aerodynamic stability of a tensioned, geometrically nonlinear orthotropic membrane structure with hyperbolic paraboloid in sag direction. Considering flow separation, the wind field around membrane structure is simulated as the superposition of a uniform flow and a continuous vortex layer. By the potential flow theory in fluid mechanics and the thin airfoil theory in aerodynamics, aerodynamic pressure acting on membrane surface can be determined. And based on the large amplitude theory of membrane and D'Alembert's principle, interaction governing equations of wind-structure are established. Then, under the circumstance of single-mode response, the Bubnov-Galerkin approximate method is applied to transform the complicated interaction governing equations into a system of second-order nonlinear differential equation with constant coefficients. Through judging the frequency characteristic of the system characteristic equation, the critical velocity of divergence instability is determined. Different parameter analysis shows that the orthotropy, geometrical nonlinearity and scantling of structure is significant for preventing destructive aerodynamic instability in membrane structures. Compared to the model without considering flow separation, it's basically consistent about the divergence instability regularities in the flow separation model.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.161-164
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• 2002

In the present study, a passive control method, using the porous wall and cavity system, is applied to the shock wave/boundary layer interactions in transonic moist air flow. The two-dimensional, unsteady, compressible Navier-Stokes equations, which are fully coupled with a droplet growth equation, are solved by the third-order MUSCL type TVD finite difference scheme. Baldwind-Lomax turbulence model is employed to close the governing equations. In order to investigate the effectiveness of the present control method, the total pressure losses of the flow and the time-dependent behaviour of shock motions are analyzed in detail. The computed results show that the present passive control method considerably reduces the total pressure losses due to the shock/boundary layer interaction in transonic moist air flow and suppresses the unsteady shock wave motions over the airfoil, as well. It is also found that the location of the porous ventilation significantly influences the control effectiveness.

• 한국전산유체공학회지
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• 제19권2호
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• pp.99-107
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• 2014

The aim of the present study is to investigate the flow interference between two adjacent undulating fish-like body, and its effect on the undulating propulsion. For this purpose, unsteady two dimensional incompressible flow calculations were conducted using an unstructured mesh flow solver, coupled with an overset mesh technique. To deal with mesh deformation due to fish locomotion, spring analogy is utilized. The fish body used in the simulation is constructed from the NACA0012 airfoil. The study indicates that the propulsion of undulating fish is proportional to frequency and wavelength of the midline oscillation when there is no adjacent fish. It also reveals that average thrust was increased when the vortex shedding from the tail was conserved well and pressure difference between upper and lower sides of the fish was magnified due to flow interference. From this study, which relative position and phase difference of locomotion between two fishes can generate maximum thrust was known among six different cases.

• 한국가시화정보학회지
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• 제18권3호
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• pp.69-76
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• 2020

In the present study, we investigate the flow separation characteristics of a paraglider canopy model by tuft visualization. The experiment is conducted at Re = 3.3×105 in a wind tunnel large enough to contain the three-dimensional paraglider canopy model, where Re is Reynolds number based on the mean chord length and the free-stream velocity. The flow separation characteristics of the canopy model near the wing root are similar to those of a two-dimensional airfoil with a cross-section similar to the model. On the other hand, near the wingtip region, the flow separation is suppressed by the downwash induced by the wingtip vortex. As a result, as the angle of attack increases, the flow separation occurs from the wing root region of the canopy model and develops toward the wingtip.

• 공학교육연구
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• 제13권5호
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• pp.8-14
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• 2010

This study intends to study about the blade performance loss occurred due to the variation in the shape of an airfoil from attachment/non-attachment of an erosion shield for the hovercraft. The model in this study has used NACA44XXseries, has designed NACA44XX-series by using the Auto CAD, and it designed the shape that has attached an erosion shield to this model according to the thickness and length. By using these models, a grid was generated by GAMBIT and the lift coefficient ($C_l$) and the drag coefficient ($C_d$) were calculated FLUENT code for flow analysis. Through this, the $C_l$ and $C_d$ have calculated and compared the lift-to-drag ratio that an indicator of airfoil performance according to the shape and attachment/non-attachment of erosion shield.