• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.1
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• pp.82-91
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• 1999

A numerical analysis based on the three-dimensional Reynolds-averaged Navier-Stokes equation has been conducted to investigate the flow within a NASA rotor 67 transonic fan. General coordinate transformations are used to represent the complex blade geometry and an H-type grid is used. The governing equations are solved using implicit LU-SGS scheme for the time-marching integration and a standard ${\kappa}-{\varepsilon}$ model is used with wall functions for the turbulence modeling. The computations are compared with the experimental data and a detailed study of the flow structures near peak efficiency and near stall is presented. The calculated overall aerodynamic efficiency and three-dimensional shock system agree well with the laser anemometer data.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.4 no.4
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• pp.201-207
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• 1992

The averaged non-linear term in the turbulence equations, suggested by Yeo (1987), is analyzed theoretically and experimentally. It was formulated by applying the filtering concepts to the convolution integral average definition with the Gaussian response function. This filtering approach seems to be superior to the conventional averaging methods in which all four terms at the doubly average vol must be defined separately, and it also gives a very useful tool in understanding the turbulence structures. By theoretically analyzing the newly derived description for the averaged non-linear terms, it is found that the vortex stretching can be explicitly accounted for. Furthermore, comparisons of the correlation coefficients based on the experimental data show that the vortex stretching acts most significantly on the turbulence residual stress. Thus, it strongly supports the claim that the vortex stretching is essential in the transfer of turbulence. In addition. a general form of turbulent energy models in LES is derived, by which it is recognized that the Smagorinsky, the vorticity and the SGS energy models are not distinctive.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.34 no.10
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• pp.925-931
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• 2010

The paper describes a Large Eddy Simulation (LES) study of turbulent flow around a cavity. A series of three-dimensional cavities placed in a turbulent boundary layer are simulated at a Reynolds number of $1.0{\times}10^5$ by considering U and h, which represent the velocity at the top and the depth of the cavity, respectively. In order to obtain the appropriate solution for the filtered Navier-Stokes equation for incompressible flow, the computational mesh forms dense close to the wall of the cavity but relatively coarse away from the wall; this helps reduce computation cost and ensure rapid convergence. The Boussinesq hypothesis is employed in the subgrid-scale turbulence model. In order to determine the subgrid-scale turbulent viscosity, the Smagorinsky-Lilly SGS model is applied and the CFL number for time marching is set as 1.0. The results show the flow variations inside cavities of different sizes and shapes.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.8
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• pp.849-854
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• 2005

The laminar flame concept in turbulent reacting flow is considered applicable to many practical combustion systems For turbulent premixed combustion under widely used flamelet concept, the flame surface is described as an infinitely thin propagating surface that such a Propagating front can be represented as a level contour of a continuous function G. In this study, for the Purpose of validating the LES of G-equation combustion model. LES of turbulent Premixed combustion with dynamic SGS model of G-equation in turbulent channel flow are carried out A constant density assumption is used. The Predicted flame propagating speed is goof agreement with the DNS result of G. Bruneaux et al.

• Journal of Advanced Marine Engineering and Technology
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• v.30 no.3
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• pp.369-375
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• 2006

Large eddy simulation has been applied to simulate turbulent flow around a cubic obstacle mounted on a channel surface for a Reynolds number of 40000(based on the incoming bulk velocity and the obstacle height) using a Smagorinsky model and a Lagrangian dynamic model. In order to develop the LES to the practical engineering application, the effect of upwind scheme, turbulent sub-grid scale model were investigated. The computed velocities. turbulence quantifies, separation and reattachment length were evaluated by compared with the previous experimental results.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.30 no.5 s.248
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• pp.438-445
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• 2006

We performed the simulation of the unsteady three dimensional flow over a square cylinder in a wind tunnel in moderate Reynolds number range, $100{\sim}2500$ by using LBM. SGS model was applied for the turbulent flow. Frist of all we compared LBM(Lattice Boltzmann Method) solution of Poiseuille flow applied Farout and bounce back boundary conditions with the analytical and FOAM solutions to verify the applicability of the boundary conditions. For LBM simulation the calculation domain was formed by structured grids and prescribed uniform velocity and density inlet and Farout boundary conditions were imposed on the in-out boundaries. Bounceback and wind tunnel boundary conditions were applied to the cylinder walls and the boundaries of calculation domain respectively. The maximum Strouhal number of the vortex shedding is 0.2025 at Re = 750. and the number maintains the constant value of 0.18 when Re>1000. We also predicted that the critical reynolds number of the turbulent flow is in the range of $250{\sim}500$.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.34 no.1
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• pp.24-31
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• 2006

In the present study, a strongly coupled analysis code is developed for transonic flutter analysis. For aerodynamic analysis, two dimensional Reynolds-Averaged Navier-Stokes equation was used for governing equation, and ε-SST for turbulence model, DP-SGS(Data Parallel Symmetric Gauss Seidel) Algorithm for parallelization algorithm. 2 degree-of-freedom pitch and plunge model was used for structural analysis. To obtain flutter response in the time domain, dual time stepping method was applied to both flow and structure solver. Strongly coupled method was implemented by successive iteration of fluid-structure interaction in pseudo time step. Computed results show flutter speed boundaries and limit cycle oscillation phenomena in addition to typical flutter responses - damped, divergent and neutral responses. It is also found that the accuracy of transonic flutter analysis is strongly dependent on the methodology of fluid-structure interaction as well as on the choice of turbulence model.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1999.10a
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• pp.18-18
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• 1999

IRR형태의 액체 램제트 추진기관의 공기 흡입구 유동과 내부 연소 유동을 파악하기 위한 수치적 해석을 수행하였다. 해석은 다원 혼합기체에 대한 압축성 Navier-Stoke 방정식과 공기/Kerosene에 대한 화학 반응을 고려하였으며, 결합된 형태의 k-$\omega$/k-$\varepsilon$ 2 방정식 난류모델을 이용하였다. 기본 유동 해법으로는 고차의 시간 및 공간 정확도를 가지는 근사 Riemann 해법과 LU-SGS 방법을 이용하였다.

• Journal of the Korean Society of Propulsion Engineers
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• v.3 no.3
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• pp.31-39
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• 1999

In this paper, numerical experiment is attempted to analyze and compare the combustion efficiency of the burning sprays due to OFO, FOF triplet / FOOF split doublet injectors. Preconditioned Wavier-Stokes equation system with low Reynolds number $\kappa$-$\varepsilon$ model for turbulence closure, is LU-SGS time-integrated. Spray processes are modeled by DSF analysis with experimentally determined injection characteristics. n-heptane/air global reaction model approximates the combustion for simplicity, and the influence of turbulence on the chemical reaction is included using eddy dissipation model. The results showed the FOF triplet injector of highest combustion efficiency, whereas the OFO type of poet performance. It was also observed that the droplet mean diameter and the average gas temperature due to the mixing efficiency, are the representative parameters for the performance design of combustion.

• Journal of computational fluids engineering
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• v.4 no.1
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• pp.53-61
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• 1999

Two-dimensional, unsteady, incompressible and compressible Navier-Stokes codes are developed for the computation of the viscous turbulent flow over high-lift airfoils. The compressible code involves a conventional upwind-differenced scheme for the convective terms and LU-SGS scheme for temporal integration. The incompressible code with pseudo-compressibility method also adopts the same schemes as the compressible code. Three two-equation turbulence models are evaluated by computing the flow over single and multi-element airfoils. The compressible and incompressible codes are validated by predicting the flow around the RAE 2822 transonic airfoil and the NACA 4412 airfoil, respectively. In addition, both the incompressible and compressible code are used to compute the flow over the NLR 7301 airfoil with flap to study the compressible effect near the high-loaded leading edge. The grid systems are efficiently generated using Chimera overlapping grid scheme. Overall, the κ-ω SST model shows closer agreement with experiment results, especially in the prediction of adverse pressure gradient region on the suction surfaces of high-lift airfoils.