• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2000.11a
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• pp.33-33
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• 2000

고압의 공기를 노즐을 통하여 가속시켜. 노즐 출구로부터 방출하는 경우 제트 경계부근에서 발생하는 강한 전단작용과 제트 내부에서 발생하는 압력강하로 인하여 주변의 기체가 제트유동으로 유입하게 된다. 이러한 원리를 응용한 대표적 유체기계로 이젝터를 들 수 있다. 최근 이젝터 시스템은 각종 플랜트 시설, 냉공조 시설, 고도시뮬레이션 장치뿐만 아니라 건설장비 등에까지 다양하게 응용되고 있다.(중략)

• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.534-541
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• 2010

A high-order accurate Euler flow solver based on a discontinuous Galerkin method has been developed for the numerical simulation of unsteady flows on unstructured meshes. A multi-level solution-adaptive mesh refinement/coarsening technique was adopted to enhance the resolution of numerical solutions efficiently by increasing mesh density in the high-gradient region. An acoustic wave scattering problem was investigated to assess the accuracy of the present discontinuous Galerkin solver, and a supersonic flow in a wind tunnel with a forward facing step was simulated by using the adaptive mesh refinement technique. It was shown that the present discontinuous Galerkin flow solver can capture unsteady flows including the propagation and scattering of the acoustic waves as well as the strong shock waves.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.123-126
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• 2002

Very frequently the compressible flow in an extinction nozzle of gas circuit breaker is simulated under no arc assumption, which can be reasonable for both high and low current breakings. In the present study, computations are performed to investigate the major features of the compressible flows inside the arc extinction nozzle of gas circuit breaker. A fully implicit finite volume scheme is applied to solve the two-dimensional, steady, compressible, Wavier-Stokes equations. The computed results are validated with the previous experimental data available. Several types of turbulence models are explored to reasonably predict the complicated flows inside the arc extinction nozzle. The obtained results show that the shock wave boundary layer interaction inside the nozzle significantly influences the whole performance of the gas breaker.

• 한국전산유체공학회:학술대회논문집
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• 2007.04a
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• pp.142-147
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• 2007

The realizability condition has been applied to modern turbulence models, Simulations are performed to compare ${\kappa}-{\omega}$ turbulence models imposing the realizability condition. An improvement to the ${\kappa}-{\varepsilon}$ turbulence model is also presented and shown to lead to better agreement with data for supersonic base flows. The improvement is achieved by imposing a grid-independent realizability constraint in the Launder-Sharma ${\kappa}-{\varepsilon}$ model. Numerical results for several test problems show a critical role of the realizability constraint in the prediction of separated flows.

• 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.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.477-482
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• 2009

Though rocket nozzle flow is very important to the rocket performance, the direct measurement is very difficult because of high temperature and high pressure gas flow. Then the experiment utilizing the hydraulic analogy has been developed for such a problem. Supersonic flows through an axisymmetric De Laval nozzle of solid rocket motor was simulated in a 2-D sluice-type water-table designed and manufactured utilizing hydraulic analogy. Methods to minimize or account for non-analogous effects in the hydraulic system must be reviewed for the quantitative application of the hydraulic analogy. In this application the water table is inclined slightly, so that gravity acceleration has a small component in the direction of motion, thus compensating for the effect of friction. Flow visualization leads to better understanding of the analogous system. Within the experimental errors, it is shown that the hydraulic analogy can be used as an effective tool for the study of two dimensional isentropic flows of gases in many fields.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.30 no.6
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• pp.61-68
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• 2002

Combustion characteristics of dual transverse injection of hydrogen in supersonic air flows were studied using computational methods. Three-dimensional Navier-Stokes with a non-equilibrium chemical reaction model and the k-$\omega$ SST turbulence model were used. A parametric study was conducted with the variation of the distance between two injectors. Combustion characteristics of dual injection are very different from those of single injection. The combustion characteristics of two injection flows are very different from each other, and the ignition and combustion characteristics of the rear injection flow are strongly influenced by those of the front injection flow. The increase of the distance between two injectors up to a specific distance results in the increase of burning rate. However, the increase of the distance over the specific distance gives no increase of burning rate but makes more losses of stagnation pressure. From the results it can be stated that there exists a distance between two injectors for optimum combustion characteristics.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.5
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• pp.375-384
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• 2012

This paper presents numerical results comparing the performance of the 2008 Wilcox $\mathcal{k}-{\omega}$ turbulence model to the one of the 1988 Wilcox $\mathcal{k}-{\omega}$ model for supersonic flows. A comparison with experimental data is offered for a shock wave/turbulent boundary layer interaction case and two ramp injector mixing cases. Furthermore, a comparison is performed with empirical correlations on the basis of skin friction for flow over a flat plate and shear layer growth for a free shear layer. It is found that the maximum injectant mass fraction of some ramp injector cases is better predicted using the 1988 Wilcox model. On the other hand, the 2008 model performs better in simulating shock-boundary layer cases.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2005.11a
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• pp.86-89
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• 2005

A computational work has been performed to investigate the aerodynamics of a projectile which is launched from the two-stage light gas gun. A moving coordinate method for a multi-domain technique is employed to simulate unsteady projectile flows with a moving boundary. The effect of a virtual mass is added to the axisymmetric unsteady Euler equation system. The computed results reasonably capture the major flow characteristics which we generated in launching the projectile supersonically, such as the interaction between the shock wave and the blast wave, the interaction between the vortical flow and the barrel shock, and the steady under-expanded jet. The present computational results properly predict the velocity, acceleration, and drag histories of the projectile.

• Journal of computational fluids engineering
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• v.14 no.3
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• pp.76-85
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• 2009

The shock wave is deformed and the vortex is elongated simultaneously during the shock-vortex interaction. More precisely, the shock wave is deformed to a S-shape, consisting of a leading shock and a lagging shock by which the corresponding local vortex flows are accelerated and decelerated, respectively: the vortex flow swept by the leading shock is locally expanded and the one behind the lagging shock is locally compressed. As the leading shock escapes the vortex in the order of microseconds, the expanded flow region is quickly changed to a compression region due to the implosion effect. An induced shock is developed here and propagated against the vortex flow. This happens for a strong vortex because the tangential flow velocity of the vortex core is high enough to make the induced-shock wave speed supersonic relative to the vortex flow. For a weak shock, the vortex is basically subsonic and the induced shock wave is absent. For a vortex of intermediate strength, an induced shock wave is developed in the supersonic region but dissipated prematurely in the subsonic region. We have expounded these three shock-vortex interaction patterns that depend on the vortex flow regime using a third-order ENO method and numerical shadowgraphs.