• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.285-288
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• 2008

The Present Study describes the numerical investigations concerning a fuel(Hydrogen), inert gas (Nitrogen) or supersonic air stream issued between each other. The basic flow configuration consists of a plane, double shear/mixing layer flow. For the numerical solution, a fully conservative unsteady $2^{nd}$ order time accurate sub-iteration method and a $2^{nd}$ order Total Variation Diminishing(TVD) scheme are used with the finite volume method(FVM). The results are consist of three categories ; single shear layer consist of fuel and supersonic air stream, inert gas stream issued between supersonic air and fuel stream, fuel gas stream issued between supersonic air and fuel stream. The numerical calculations has been carried out in case of 1,2, and 4mm thickness of center stream. The width of total gas stream is 4cm.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.8
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• pp.18-25
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• 2005

This paper describes a supersonic separation of air-launching rocket from the mother plane. Three dimensional Euler equations were numerically solved to analyze steady/unsteady state fluid flows. The results of simulation clearly demonstrate effect of shock-expansion wave interaction between the rocket and the mother plane. Moreover, important influential factors at separating stage of the rocket were extracted with a comprehensive analysis. Finally, from the consideration of supersonic-separation, a guideline to safety-separation is given to the design of supersonic air-launching rocket.

• International Journal of Aeronautical and Space Sciences
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• v.13 no.3
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• pp.296-306
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• 2012

A series of numerical simulations are carried out to analyze a supersonic inlet buzz, which is an unsteady pressure oscillation phenomenon around a supersonic inlet. A simple but efficient geometry, experimentally adopted by Nagashima, is chosen for the analysis of unsteady flow physics. Among the two sets of simulations considered in this study, the effects of various throttling conditions are firstly examined. It is seen that the major physical characteristic of the inlet buzz can be obtained by inviscid computations only and the computed flow patterns inside and around the inlet are qualitatively consistent with the experimental observations. The dominant frequency of the inlet buzz increases as throttle area decreases, and the computed frequency is approximately 60Hz or 15% lower than the experimental data, but interestingly, this gap is constant for all the test cases and shock structures are similar. Secondly, inviscid calculations are performed to examine the effect regarding angle of attack. It is found that patterns of pressure oscillation histories and distortion due to asymmetric (or three-dimensional) shock structures are substantially affected by angle of attack. The dominant frequency of the inlet buzz, however, does not change noticeably even in regards to a wide range of angle of attacks.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.05a
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• pp.36-40
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• 2006

An analysis is made of flow and rocket motion during a supersonic separation stage of air-launching rocket(ALR) from the mother plane. Three-dimensional compressible Navier-Stokes equations is numerically solved to analyze the steady/unsteady flow field around the rocket which is being separated from the mother plane configuration(F-4E Phantom). The simulation results clearly demonstrate the effect of shock-expansion wave interaction between the rocket and the mother plane. To predict the behavior of the ALR according to the change of the C.G., three cases of numerical analysis are performed. As a result, a design-guideline of supersonic air-launching rocket for the safe separation is proposed.

• International Journal of Aeronautical and Space Sciences
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• v.4 no.1
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• pp.53-62
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• 2003

In this study, nonlinear aeroelastic characteristics of an supersonic missile wing with strong shock interferences are investigated. The missile wing model has a freeplay structural nonlinearity at its pitch axis. To practically consider the effects of freeplay structural nonlinearity, the fictitious mass method is applied to structural vibration analysis based on finite element method. Nonlinear aerodynamic flows with unsteady shock waves are also considered in supersonic flow regions. To solve the nonlinear aeroelastic governing equations including the freeplay effect, a modal-based coupled time-marching technique based on the fictitious mass method is used in the time-domain. Various aeroelastic computations have been performed for the nonlinear wing structure model. Linear and nonlinear aeroelastic analyses have been conducted and compared with each other in supersonic flow regions. Typical nonlinear limit cycle oscillations and phase plots are presented to show the complex vibration phenomena with simultaneous fluid-structure nonlinearities.

• 유체기계공업학회:학술대회논문집
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• 2002.12a
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• pp.337-345
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• 2002

The present study addresses a computational result of unsteady gas flow through a critical nozzle. The axisymmetric, unsteady, compressible, Wavier-Stokes equations are solved using a finite volume method that makes use of the second order upwind scheme for spatial derivatives and the multi-stage Runge-Kutta integral scheme for time derivatives. The steady solutions of the governing equation system are validated with the previous experimental data to ensure that the present computational method is valid to predict the critical nozzle flows. In order to simulate the effects of back pressure fluctuations on the critical nozzle flows, an excited pressure oscillation with an amplitude and frequency is assumed downstream of the exit of the critical nozzle. The results obtained show that for low Reynolds numbers, the unsteady effects of the pressure fluctuations can propagate upstream of the throat of critical nozzle, and thus giving rise to the applicable fluctuations in mass flow rate through the critical nozzle, while for high Reynolds numbers, the pressure signals occurring at the exit of the critical nozzle do not propagate upstream beyond the nozzle throat. For very low Reynolds number, it is found that the sonic line near the throat of the critical nozzle remarkably fluctuateswith time, providing an important mechanism for pressure signals to propagate upstream of the nozzle throat, even in choked flow conditions. The present study is the first investigation to clarify the unsteady effects on the critical nozzle flows.

• International Journal of Aeronautical and Space Sciences
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• v.13 no.2
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• pp.210-220
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• 2012

The model-free control of aeroelastic vibrations of a non-linear 2-D wing-flap system operating in supersonic flight speed regimes is discussed in this paper. A novel continuous robust controller design yields asymptotically stable vibration suppression in both the pitching and plunging degrees of freedom using the flap deflection as a control input. The controller also ensures that all system states remain bounded at all times during closed-loop operation. A Lyapunov method is used to obtain the global asymptotic stability result. The unsteady aerodynamic load is considered by resourcing to the non-linear Piston Theory Aerodynamics (PTA) modified to account for the effect of the flap deflection. Simulation results demonstrate the performance of the robust control strategy in suppressing dynamic aeroelastic instabilities, such as non-linear flutter and limit cycle oscillations.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.344-352
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• 2006

Evacuation performance, starting transient, and plume blowback at diffuser breakdown of a straight cylindrical supersonic exhaust diffuser with no externally supplied secondary flow are investigated. Pressure records in the transitional periods are measured by a small-scale cold-gas simulator. Flow-fields evolving in the diffuser-type ejector are solved by preconditioned Favre-averaged Navier-Stokes equations with a low-Reynolds number $k-{\varepsilon}$ turbulence model edited for turbulence compressibility effects. The present RANS method is properly validated with measured static wall pressure distributions and evacuation level at steady operation as well as the pressure records during the transition regime.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2003.10a
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• pp.108-113
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• 2003

The numerical research has been done for the transverse jet behind a rearward- facing step in turbulent supersonic flow without chemical reaction. The purpose of transverse jet is used to improve mixing of the fuel in the combustor. Two- dimensional unsteady flowfields generated by slot injection into supersonic flow are numerically simulated by the integration of Navier-Stokes equation with two-equation k - $\varepsilon$ turbulence model. Numerical methods are used high-order upwind TVD scheme. Eight cases are computed, comprising slot momentum flux ratios and slot position at downstream of the step. The flow is very similar to the cavity flow, because the jet is like an obstacle. Therefore, the numerical results show the periodic phenomenon.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.06a
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• pp.1198-1203
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• 2000

In this study, a nonlinear aeroelastic analysis system for the fighter wing with tip-store has been developed additionally in the transonic and supersonic flow region. The unsteady CFD code based on the transonic small disturbance theory has been incorporated to consider the numerical capability for the aerodynamic nonlinear effects. The coupled time-integration method is used to observe the detailed nonlinear aeroelastic responses for elastic wings in their flight. condition. A conservative wing-box model of a fighter wing with tip-store is modeled by MSC/PATRAN and the corresponding free vibration analysis has been performed by MSC/NASTRAN. The results of flutter analyses are presented in the subsonic, transonic and supersonic flow regime.