• 유체기계공업학회:학술대회논문집
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• 2006.08a
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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.

• Journal of Advanced Marine Engineering and Technology
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• v.31 no.6
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• pp.681-686
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• 2007

The flow analysis was made by applying the turbulent models in the scroll volume of centrifugal compressor. The $k-{\varepsilon}.\;k-{\omega}$, Spalart-Allmaras and reynolds stress models are used in which the hybrid grid is applied for the simulation. The velocity vector the Pressure contour. the change of residual along the iteration number. and the dynamic head are simulated by solving the Navier-Stokes equations for the comparison of four example cases.

• 한국전산유체공학회:학술대회논문집
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• 1997.10a
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• pp.149-154
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• 1997

Based on the full Navier-Stokes solutions, the thermohydrodynamic performance of a long journal bearing is investigated. A numerical method based on Galerkin's procedure and B-spline test functions has been presented for solving two-dimensional problems involving fluid flow and heat transfer. For numerical stability the artificial compressibility is employed to the conservation of mass. The discretized algebraic equations are solved by Newton's method. Effects of varying the speed of an inner cylinder to load carrying capacity are investigated. The results indicated that the increase of the speed of an inner cylinder has a significant effect on the temperature profile and ultimately on the performance.

• Journal of Advanced Marine Engineering and Technology
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• v.14 no.2
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• pp.48-65
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• 1990

Numerical solutions of the Navier-Stokes equations, governing 2-dimensional, time-dependent, viscous, incompressible fluid flow past a square cylinde in an infinite region, are presented for Reynolds numbers $10^2$, $10^3$and $10^4$. Finite-difference scheme, based on SOLA-VOF is adopted and a discretization of the convection term for irregular grid is newly suggested by altering the original nonconservation form into conservation one. Distribution of finer grids around the body reveals fairly reasonable consistency with the experimental variables : drag coefficient, lift coefficient, Strouhal number, fluctuating pressure coefficient, etc.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.359-363
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• 2005

In SCRamjet engine, combustion occurs in supersonic flow with airbreathing. SCRamjet is characterized by very short combustion time in combustor, so it is very important to be mixing the air and fuel in short duration. Several methods are suggested for mixing enhancement. Among these, cavity is selected to study for enhancement of mixing. The numerical simulation is performed in the case of freestream Mach number of 2.5 and cavity located in front of fuel jet injection. CFD-Fastran, commercial code with three-dimensional Navier-Stokes equation with the Menter SST turbulence model were used. The results are obtained validate experiment results for same condition. Therefore, the numerical results show the mixing enhancement characteristics with a cavity.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.20 no.5
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• pp.671-680
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• 2007

The objective of this work is to reduce drag on a bluff body within a viscous flow by applying suction or injection of fluid along the surface of the body. In addition to minimizing drag, the optimal solution tends to reduce boundary layer separation and flow recirculation. When discretized by finite elements, the optimal control problem can be posed as a large-scale nonlinearly-constrained optimization problem. The constraints correspond to the discretized form of the Navier-Stokes equations. Unfortunately, solving such large-scale problems directly is essentially intractable. We developed several Sequential Quadratic Programming methods that are tailored to the structure of the control problem. Example problems of laminar flow around an infinite cylinder in two dimensions are solved to demonstrate the methodology. We use these optimal control techniques to study the influence of number of suction/injection holes and location of holes on the resulting optimized flow. We compare the proposed SQP methods against one another, as well as against available methods from the literature, from the point of view of efficiency and robustness. The most efficient of the proposed methods is two orders of magnitude faster than existing methods.

• Journal of Mechanical Science and Technology
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• v.16 no.10
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• pp.1303-1313
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• 2002

Effects of the reduced frequency of upstream wake on downstream unsteady boundary layer flow were simulated by using a Wavier-Stokes code. The Wavier-Stokes code is based on an unstructured finite volume method and uses a low Reynolds number turbulence model to close the momentum equations. The geometry used in this paper is the MIT flapping foil experimental set-up and the reduced frequency of the upstream wake is varied in the range of 0.91 to 10.86 to study its effect on the unsteady boundary layer flow. Numerical solutions show that they can be divided into two categories. One is so called the low frequency solution, and behaves quite similar to a Stokes layer. Its characteristics is found to be quite similar to those due to either a temporal or spatial wave. The low frequency solutions are observed clearly when the reduced frequency is smaller than 3.26. The other one is the high frequency solution. It is observed for the reduced frequency larger than 7.24. It shows a sudden shift of the phase angle of the unsteady velocity around the edge of the boundary layer. The shift of phase angle is about 180 degree, and leads to separation of the boundary layer flow from corresponding outer flow. The high frequency solution shows the characteristics of a temporal wave whose wave length is half of the upstream frequency. This characteristics of the high frequency solution is found to be caused by the strong interaction between unsteady vortices. This strong interaction also leads to destroy of the upstream wake strips inside the viscous sublayer as well as the buffer layer.

• Journal of computational fluids engineering
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• v.20 no.2
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• pp.37-45
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• 2015

A parametric study on the shapes of bobsleigh bumpers has been performed to reduce the aerodynamic drag. Effects of geometric parameters, such as leading angle of leading bumper, the ratio of minimum width to maximum width of leading bumper, the ratio of leading bumper length to trailing bumper length, trailing angle of trailing bumper, and the ratio of bumper height to installation location of bumper from the bottom of bobsleigh, on the aerodynamic performance of the bobsleigh were estimated using 3-D Reynolds-averaged Navier-Stokes equations. The turbulence was analyzed using the shear stress turbulence model. Reynolds number based on the hydraulic diameter of the external flow channel was in the range of 150,000~1,000,000. Numerical results for drag coefficient were validated compared to experimental data. Ranges of the five geometric parameters were determined according to the rule of Federation Internationale de Bobsleigh et de Tobaganning. The aerodynamic performance of the bobsleigh sled was most sensitive to the leading angle of leading bumper and the ratio of minimum width to maximum width of leading bumper.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.399-402
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• 2005

The present numerical study describes the flow physics on the interaction between the supersonic freestream and jet plume. The compressible flow past a simplified afterbody model with a sonic nozzle is investigated using mass-averaged Navier-Stokes equations, discretized by a fully implicit finite volume scheme, and the standard $k-{\omega}$ turbulence model. The results obtained through the present study are discussed specifically regarding the effect of the plume pressure ratio, freestream Mach number and base dimensions on the location of the plume-induced shock wave generated on the afterbody by the underexpansion of the jet plume.

• Journal of the Society of Naval Architects of Korea
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• v.40 no.5
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• pp.36-42
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• 2003

A CFD simulation technique has been developed to handle the unsteady body motion with large amplitude by use of overlapping multi-block grid system. The three-dimensional, viscous and incompressible flow around body is investigated by solving the Navier-Stokes equations, and the motion of body is represented by moving effect of the grid system. Composite grid system is employed in order to deal with both the body motion with large amplitude and the condition of numerical wave maker in convenience at the same time. The governing equations, Navier-Stokes (N-S) and continuity equations, are discretized by a finite volume method, in the framework of an O-H type boundary-fitted grid system (inner grid system including test model) and a rectangular grid system (outer grid system including simulation equipments for generation of wave environments). If this study, several flow configurations, such as an oscillating cylinder with large KC number, are studied in order to predict and evaluate the hydrodynamic forces. Furthermore, the motion simulation of a Series 60 model advancing in a uniform flow under the condition of enforced roll motion of angle 20$^{\circ}$ is performed in the developed numerical wave tank.