• 한국항공우주학회지
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• 제46권9호
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• pp.703-711
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• 2018

본 연구에서는 실기체 환경 모사(고도 모사)가 가능한 극초음속 Ludwieg tube 개념설계 도구를 개발하고, 전산유체해석을 통해 Ludwieg tube 개념설계 도구의 성능을 검증하였다. 극초음속 Ludwieg tube 개념설계 도구를 개발하기 위해 Ludwieg tube의 작동원리를 연구하였고, 도구를 활용하여 목표 성능을 만족하기 위한 Ludwieg tube의 제원을 결정하였다. 마하수 4에서 10의 유동을 모사할 수 있고, 특히 마하수 4 유동은 고도 모사가 가능하다.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2004년도 제22회 춘계학술대회논문집
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• pp.15-25
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• 2004

This paper outlines a new convergence acceleration de-signed to solve scramjet flowfields with zones of re-circulation. Named the “marching-window”, the algorithm consists of performing pseudo-time iterations on a minimal width subdomain composed of a sequence of cross-stream planes of nodes. The upstream boundary of the subdomain is positioned such that all nodes upstream exhibit a residual smaller than the user-specified convergence threshold. The advancement of the downstream boundary follows the advancement of the upstream boundary, except in zones of significant streamwise ellipticity where a streamwise ellipticity sensor ensures its continuous progress. Compared to the standard pseudo-time marching approach, the march-ing-window is here seen to decrease the work required for convergence by up to 24 times for supersonic flows with little streamwise ellipticity and by up to 8 times for supersonic flows with large streamwise separated regions. The memory requirements are observed to be reduced sixfold by not allocating memory to the nodes not included in the computational subdomain. The marching-window satisfies the same convergence criterion as the standard pseudo-time stepping methods, hence resulting in the same converged solution within the tolerance of the user-specified convergence threshold. The extension of the marching-window to the weakly-ionized Navier-Stokes equations is also discussed.

• 한국전산유체공학회지
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• 제19권2호
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• pp.49-57
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• 2014

In the present study, 2-D gas-kinetic flow solver on unstructured meshes was developed for flows from continuum to transitional regimes. The gas-kinetic BGK scheme is based on numerical solutions of the BGK simplification of the Boltzmann transport equation. In the initial reconstruction, the unstructured version of the linear interpolation is applied to compute left and right states along a cell interface. In the gas evolution step, the numerical fluxes are computed from the evaluation of the time-dependent gas distribution function around a cell interface. Two-dimensional compressible flow calculations were performed to verify the accuracy and robustness of the current gas-kinetic approach. Gas-kinetic BGK scheme was successfully applied to two-dimensional steady and unsteady flow simulations with strong contact discontinuities. Exemplary hypersonic viscous simulations have been conducted to analyze the performances of the gas-kinetic scheme. The computed results show fair agreement with other standard particle-based approaches for both continuum part and transitional part.

• International Journal of Aeronautical and Space Sciences
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• 제17권1호
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• pp.1-7
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• 2016

The influence of boundary condition of the bodies with gas flows is one of the most important problems in high-altitude aerodynamics. In this paper presents the results of the calculation of aerodynamic characteristics of aerospace vehicle using Monte-Carlo method based on three different gas-surface interaction models - Maxwell model, Cercignani-Lampis-Lord (CLL) model and Lennard-Jones (LJ) potential. These models are very sensitive for force and moment coefficients of aerospace vehicle in the hypersonic free molecular flow. The models, method and results can be used for new generation aerospace vehicle design.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2000년도 춘계 학술대회논문집
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• pp.166-171
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• 2000

A two-dimensional/axisymmetric CSCM upwind flux difference splitting Wavier-Stokes method has been developed to study the finite rate chemically react-ing invisicd and viscous hypersonic flows over blunt-body. A upwind method was chosen due to its robustness in capturing the strong bow shock waves. For the nonequilibrium chemically reacting air, NS-I species conservation equations were strongly coupled with flowfield equations through convection and species production terms. The nonequilibrium wall pressure and heat transfer rate distributions along the vehicle were compared with those from equilibrium and perfect gas calculations. The nonequilibrium species distribution shows the reduced concentrations of O and N species when compared with equilibrium species distribution. The solutions resolved strong bow shock waves md heat transfer rate very accurately when compared with central difference schemes.

• 한국전산유체공학회지
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• 제5권1호
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• pp.43-59
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• 2000

Characteristic boundary conditions are discussed in conjunction with a flux-difference splitting formulation as modified from Roe's linearization. Details of how one can implement the characteristic boundary conditions which are made compatible with the interior point formulation are described for different types of boundaries including subsonic outflow and adiabatic wall. The validity of boundary conditions are demonstrated through computation of transonic airfoil, supersonic ogive-cylinder, hypersonic cylinder, and S-duct internal flows. The computed wall pressure distributions are compared with published experimental and computed data. Objectives of this paper are thus to give insight of formulation procedure of a flux-difference splitting method and to pave ways for other users to adopt present boundary procedure on their numerical methods.

• 한국전산유체공학회지
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• 제18권3호
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• pp.87-93
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• 2013

A computational study has been performed to examine the effects of catalytic walls on the stagnation region heat transfer. The boundary conditions for none, finite, and fully catalytic walls have been incorporated into a multi-block compressible Navier-Stokes solver. In the present study, both chemical and thermal non-equilibrium effects were included. The flows over a blunt body model were simulated by varying surface catalytic recombination rates. A full range of catalycities was explored in the context of a constant wall temperature assumption. Detailed information on species concentrations, temperature, and surface heat flux are presented. Comparison with available flight data of surface heat flux is also made.

• 한국항공우주학회지
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• 제46권8호
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• pp.652-661
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• 2018

고속 고온 유동에서 나타나는 고온 기체 현상을 모사하기 위해서는 마하수뿐 아니라 절대속도도 재현할 수 있어야 한다. 이러한 유동을 초음속 유동과 구분하여 극고속 유동이라 부르며, 충격파 터널과 같은 고엔탈피 시험 장치를 통해 연구가 이루어지고 있다. 그러나 이러한 고엔탈피 시험 장비는 높은 온도와 압력 때문에 노즐에서 열화학적 비평형 현상을 경험하게 되며 기존의 이론적 방법으로 그 실험 조건을 규정하기 어렵다. 이에 본 연구에서는 알려진 비평형 노즐 코드의 단점들을 보완하고 충격파 터널의 운용 조건에서 시험부 유동 특성을 빠르게 예측하기 위하여 열화학적 비평형을 고려한 준 1차원 노즐 해석 코드를 개발하였다. 개발된 코드는 시험 결과 및 2차원 축대칭 해석 결과와 비교를 통하여 충격파 풍동 시험부 유동 조건 예측을 위한 활용성 및 한계를 살펴보았다.

• International Journal of Aeronautical and Space Sciences
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• 제17권4호
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• pp.455-466
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• 2016

Chemical-kinetic parameters of the equilibrium constants to evaluate the reverse rate coefficients in the shock layer of a blunt body and the expanding flows are derived for the temperature range from 300 K to 20,000 K. The expanded equilibrium constants for the chemical reactions of the dissociation, ionization, associative ionization, and neutral and charge exchange reactions of the atmospheric species and carbon materials are proposed in the present work. In evaluating the equilibrium constants, the inter-nuclear potential energies of the molecular species are calculated by the analytical potential function of the Hulburt-Hirschfelder model, and the parameters of the analytical model are determined from the semi-classically calculated RKR potentials. The electronic states and energies of the atoms are calculated by the electronic energy grouping model, and the rovibrational states and energies of each electronic states of the molecules are evaluated by the WKB method. The expanded equilibrium constants for 31 types of the reactions are provided for the best curve-fit functions, and the recombination reaction rate coefficients evaluated from the present equilibrium constants are compared with existing measured values.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2008년 영문 학술대회
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• pp.346-357
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• 2008

Endothermic fuels are known as a probable fuel for hypersonic atmospheric flight vehicles and advanced propulsion systems, as well as cryogenic fuels. Especially, from the standpoint of the advanced regenerative cooling use, they are quite useful as a coolant fuel because of their large heat sink due to their chemical decompositions; so-called endothermic cooling effect. However, no heat transfer equations have been proposed taking into account such endothermic reactive behaviors concretely. This paper describes an analytical method for evaluation of the heat transfer rates between endothermic reacting coolant fuel and coolant-side wall in the regenerative cooling passages. Heat transfer mechanism is indicated based on a classical transport-phenomenological approach. A new relational expression of Nusselt number ratio for forcedconvective heat transfer with such endothermic reactions is also proposed by theoretical approaches using some classical hypotheses. Its applicability is assessed provisionally by comparison with confirmed results of heated tube tests for supercritical JP-7 fuel carried out at NASA Lewis Research Center, using its heat sink characteristics evaluated by United Technologies Research Center(UTRC). As a result, it has been suggested that the proposed relational equation is applicable to the evaluation of enhancement of Nusselt numbers due to such reactions in developed turbulent flows such as in the regenerative cooling passages.