• 한국전산유체공학회:학술대회논문집
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• 1998.05a
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• pp.117-122
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• 1998

A numerical study is carried out to investigate the transient process of combustion phenomena associated with hypersonic propulsion devices. Reynolds averaged Navier-Stokes equations for reactive flows are used as governing equations with a detailed chemistry mechanism of hydrogen-air mixture and two-equation SST turbulence modeling. The governing equations are discretized by a high order accurate upwind scheme and solved in a fully coupled manner with a fully implicit time accurate method. At first, oscillating shock-induced combustion is analyzed and the comparison with experimental result gives the validity of present computational modeling. Secondly, the model ram accelerator experiment was simulated and the results show the detailed transient combustion mechanisms. Thirdly, the evolution of oblique detonation wave is simulated and the result shows transient and final steady state behavior at off-stability condition. Finally, shock wave/boundary layer interaction in combustible mixture is studied and the criterion of boundary layer flame and oblique detonation wave is identified.

• 한국전산유체공학회:학술대회논문집
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• 2000.05a
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• pp.39-44
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• 2000

Two-dimensional Navier-Stokes codes are used to simulate the shock tunnel in Konkuk university. In order to design experiments in impulse facilities properly and to interpret data from such facilities, it is necessary to understand how the flow approaches steady state. This is done by determining the transient flow field and flow establishment time around a given model. This will be accomplished by developing appropriate CFD codes which solve the Navier-Stokes equations, and simulating the starting process and resulting unsteady viscous flow phenomena. The starting process in a shock tunnel consists of multiple shock interactions and contact discontinuities, which are difficult to solve with the classical shock capturing schemes. A recently developed high resolution scheme is adapted for resolving the unsteady phenomena of those multiple shock interactions and contact surfaces during the starting process. The bifurcation phenomenon due to the interactions of the reflected shock from the end of the shock tube with the boundary layer generated by the incident shock becomes of particular interest. By comparing with the experiment results, the accuracy of the numerical analysis is validated and it is demonstrated that the properties which can hardly be obtained through the experiment can be estimated.

• 한국전산유체공학회:학술대회논문집
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• 2004.03a
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• pp.139-145
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• 2004

A numerical study of underexpanded jet and impingement on a wall mounted at various distances from the nozzle exit is presented. The 3-dimensional Navier-Stokes equations and $\kappa-\omega$ turbulence equations are solved. The grids are constructed as overlapped grid systems to examine the distance effect. The DADI method is applied to obtain steady-state solutions. To avoid numerical instability such as the carbuncle that sometimes accompany approximate Riemann solver, the HLLE+ scheme is employed for the inviscid flux at the cell interfaces. A goal of this work is to apply a number of two-equation turbulence models based on the $\omega$ equation to the impinging jet problem.

• Journal of computational fluids engineering
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• v.3 no.1
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• pp.30-36
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• 1998

The three dimensional Navier-Stokes equations in rotational coordinate are solved using a multigrid algorithm for the calculations of turbulent flows in centrifugal compressor impellers. Some numerical studies are made in applying the multigrid algorithm for the turbulent flow calculations with the standard κ-ε equations. The present method is used to calculate the flow fields of Mizuki's B-type and Niigata Ms. 350 centrifugal compressor impellers. Fast convergent steady-state solutions are carefully examined, comparing the static pressure distributions along the impeller flow passage and also in the diffuser with experimental data. Performance of a centrifugal compressor system is also numerically validated by comparing the performances of the impeller and the diffuser individually.

• 한국연소학회:학술대회논문집
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• 2006.04a
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• pp.32-38
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• 2006

A premixed flame propagating in a tube suffers strong variation in its shape and structure depending on boundary conditions. The effects of thermal boundary conditions and flow fields on flame propagation are numerically investigated. Navier-Stokes equations and species equations are solved with a one-step irreversible global reaction model of methane-air mixture. Finite volume method using an adaptive grid method is applied to investigate the flame structure. In the case of an adiabatic wall, friction force on the wall significantly affected the flame structure while in the case of an isothermal wall, local quenching near the wall dominated flame shapes and propagation. In both cases, variations of flow fields occurred not only in the near field of the flame but also within the flame itself, which affected propagation velocities. This study provides an overview of the characteristics of flames in small tubes at a steady state.

• Transactions of the Korean Society of Mechanical Engineers
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• v.19 no.11
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• pp.3031-3040
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• 1995

Two-dimensional incompressible Navier-Stokes equations have been solved by the node-centered finite volume method with the unstructured triangular meshes. The pressure-velocity coupling is handled by the artificial compressibility algorithm due to its computational efficiency associated with the hyperbolic nature of the resulting equations. The convective fluxes are obtained by the Roe's flux difference splitting scheme using edge-based connectivities and higher-order differences are achieved by a reconstruction procedure. The time integration is based on an explicit four-stage Runge-Kutta scheme. Numerical procedures with local time stepping and implicit residual smoothing have been implemented to accelerate the convergence for the steady-state solutions. Comparisons with experimental data and other numerical results have proven accuracy and efficiency of the present unstructured approach.

• Journal of Mechanical Science and Technology
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• v.20 no.10
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• pp.1730-1740
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• 2006

A nodeless variables finite element method for analysis of two-dimensional, steady-state viscous incompressible flow is presented. The finite element equations are derived from the governing Navier-Stokes differential equations and a corresponding computer program is developed. The proposed method is evaluated by solving the examples of the lubricant flow in journal bearing and the flow in the lid-driven cavity. An adaptive meshing technique is incorporated to improve the solution accuracy and, at the same time, to reduce the analysis computational time. The efficiency of the combined adaptive meshing technique and the nodeless variables finite element method is illustrated by using the example of the flow past two fences in a channel.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 1997.04a
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• pp.43-51
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• 1997

Steady and unsteady numerical simulations are conducted for the experiments performed to investigate the ram accelerator flow field by using the expansion tube facility in Stanford University. Navier-Stokes equations for chemically reacting flows are analyzed by fully implicit and time accurate numerical methods with Jachimowski's detailed chemistry model for hydrogen-air combustion involving 9 species and 19 reaction steps. Although the steady state assumption shows a good agreement with the experimental schlieren and OH PLIF images for the case of $2H_2$+$O_2$+$17N_2$, it fails in reproducing the combustion region behind the shock intersection point shown in the case of $2H_2$+$O_2$+$12N_2$, mixture. Therefore, an unsteady numerical simulation is conducted for this case and the result shows all the detailed flow stabilization process. The experimental result is revealed to be an instantaneous result during the flow stabilization process. The combustion behind the shock intersection point is the result of a normal detonation formed by the intersection of strong oblique shocks that exist at early stage of the stabilization process. At final stage, the combustion region behind the shock intersection point disappears and the steady state result is retained. The time required for stabilization of the reacting flow in the model ram accelerator is found to be very long in comparison with the experimental test time.

• Journal of computational fluids engineering
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• v.16 no.4
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• pp.1-6
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• 2011

Aerodynamic characteristics depending on the shape of an internal motor in a small-size sirocco fan for residential ventilation have been investigated. For the aerodynamic analyses of the sirocco fan, three-dimensional Reynolds-averaged Navier-Stokes equations are solved with the shear stress transport model for turbulence closure. The flow analyses are performed on hexahedral grids using a finite-volume solver. The validation of the numerical results at steady-state is performed by comparing with experimental data for the pressure and efficiency. In order to investigate the aerodynamic characteristics depending on shape of an internal motor in a sirocco fan, the reference shape is analyzed compared to the case without internal motor. Additionally, two shape parameters, height and width of the internal motor in a sirocco fan, are tested to investigate their effects on the aerodynamic characteristics. The results show that the shape of the internal motor in a sirocco fan is an important factor to improve the aerodynamic performances.

• Transactions of the Korean Society of Mechanical Engineers
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• v.16 no.6
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• pp.1163-1170
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• 1992

A computer program was developed to analyze the two-dimensional unsteady incompressible viscous flow behind a rectangular bluff body between two parallel plates. The Peaceman-Rachford alternating direction implicit numerical method and Wachspress parameter were adopted to solve the governing equations in vorticity-transport and stream function formulation. The steady state flow and the vortex flow behind a rectangular bluff body in a chemical were investigated for Reynolds numbers of 200 and 500. The vortex shedding was generated by a physical pertubation numerically imposed at the center of the flow field for a short time. It was observed that the perturbed flow became periodic after a transient period.