• Title/Summary/Keyword: rarefied regime

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Analysis of rarefied compressible boundary layers in transition regime (천이영역의 희박기체 압축성 경계층 해석)

  • Choe, Seo-Won
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.21 no.4
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    • pp.509-517
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    • 1997
  • Results of flat plate compressible boundary layer calculation, based on discrete formulation of DSMC method, are presented in low Mach number and low Knudsen number range. The free stream is a uniform flow of pure nitrogen at various Mach numbers in low pressures (i.e. rarefied gas). Complete thermal accommodation and diffuse molecular reflections are used as the wall boundary condition, replacing unreal no-slip condition used in continuum calculations. In the discrete formulation of DSMC method, there is no need to use ad hoc assumptions on transport properties like viscosity and thermal conductivity, instead viscosity is calculated from values of other field variables (velocity and shear stress). Also the results are compared with existing self-similar continuum solutions. In all Mach number cases computed, velocity slip is most pronounced in regions near the leading edge where continuum formulation renders the solution singular. As the boundary layer develops further downstream, velocity slips asymptote to values that are between 10 to 20% of the magnitude of free stream velocity. When the free stream number density is reduced, so the gas more rarefied, the velocity slip increases as expected.

Studies on Flowfields Around Axisymmetric Bodies in the Rarefied Gas Regime Using the Direct Simulation Monte Carlo Method (희박기체영역에서의 직접모사법에 의한 축대칭 형상 주위의 유동장 해석에 관한 연구)

  • Lee Dong-Dae;Park Hyeong-Gu
    • 한국전산유체공학회:학술대회논문집
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    • 1998.11a
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    • pp.71-77
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    • 1998
  • In this study we calculated the flowfields around the axisymmetric bodies in the rarefied gas regime by using the DSMC. A flat-ended cylinder was selected as a representative axisymmetric body and the gas used for all calculations was nitrogen. With zero angle of attack, an increasingly rapid rise in density and the effect of shock waves near the flat-ended face were examined. And on the cylinder surface velocity slips and boundary layers could be observed in the results. Larsen-Borgnakke model was used for the energy redistribution in inelastic collisions. And by considering all internal energy modes, the distributions of translational, rotational and vibrational temperatures were plotted. The calculations were peformed for various Knudsen numbers, Especially the rotational temperatures calculated for a case were compared with the experimental results. And the simulation results show good agreements with the experimental ones.

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A Numerical Analysis of Rarefied Flow of Cylinder Using FDDO (FDDO를 이용한 실린더를 지나는 희박기체의 해석)

  • Ahn M. Y.;Chang K. S.
    • 한국전산유체공학회:학술대회논문집
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    • 1998.05a
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    • pp.138-144
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    • 1998
  • The BGK equation, which is the kinetic model equation of Boltzmann equation, is solved using FDDO(finite difference with the discrete-ordinate method) to compute the rarefied flow of monatomic gas. Using reduced velocity distribution and discrete ordinate method, the scalar equation is transformed into a system of hyperbolic equations. High resolution ENO(Essentially Non-Oscillatory) scheme based on Harten-Yee's MFA(Modified Flux Approach) method with Strang-type explicit time integration is applied to solve the system equations. The calculated results are well compared with the experimental density field of NACA0012 airfoil, validating the developed computer code. Next. the computed results of circular cylinder flow for various Knudsen numbers are compared with the DSMC(Direct Simulation Monte Carlo) results by Vogenitz et al. The present scheme is found to be useful and efficient far the analysis of two-dimensional rarefied gas flows, especially in the transitional flow regime, when compared with the DSMC method.

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DSMC Analysis of Low Thruster Nozzle (저추진력 추력기의 DSMC 해석)

  • 박재현;백승욱;김정수
    • Proceedings of the Korean Society of Propulsion Engineers Conference
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    • 2000.11a
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    • pp.3-3
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    • 2000
  • 저추진력 추력기라는 것은 추력이 수 N 정도, 노즐출구직경이 수 mm 정도의 소형추력기를 의미하며, 주로 인공위성을 비롯한 우주 비행체의 자세제어, 궤도천이 등의 목적을 위해 사용된다. 따라서, 저추진력 추력기의 일반적인 작동환경은 연속체 영역, 천이영역(transition flow regime), 희박영역(rarefied flow regime)을 모두 포함하므로, 기존의 연속체 유체역학에서 사용되는 Navier-Stokes 방정식을 사용할 수 없고, 분자들의 미시적인 움직임과 내부 에너지 분포를 고려한 Boltzmann 방정식을 이용한 해석을 수행하여야 한다.(중략)

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Influence of partial accommodation coefficients on the aerodynamic parameters of an airfoil in hypersonic, rarefied flow

  • Zuppardi, Gennaro
    • Advances in aircraft and spacecraft science
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    • v.2 no.4
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    • pp.427-443
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    • 2015
  • The present paper is the follow-on of a former work in which the influence of the gas-surface interaction models was evaluated on the aerodynamic coefficients of an aero-space-plane and on a section of its wing. The models by Maxwell and by Cercignani-Lampis-Lord were compared by means of Direct Simulation Monte Carlo (DSMC) codes. In that paper the diffusive, fully accommodated, semi-specular and specular accommodation coefficients were considered. The results pointed out that the influence of the interaction models, considering the above mentioned accommodation coefficients, is pretty strong while the Cercignani-Lampis-Lord and the Maxwell models are practically equivalent. In the present paper, the comparison of the same models is carried out considering the dependence of the accommodation coefficients on the angle of incidence (or partial accommodation coefficients). More specifically, the normal and the tangential momentum partial accommodation coefficients, obtained experimentally by Knetchel and Pitts, have been implemented. Computer tests on a NACA-0012 airfoil have been carried out by the DSMC code DS2V-64 bits. The airfoil, of 2 m chord, has been tested both in clean and flapped configurations. The simulated conditions were those at an altitude of 100 km where the airfoil is in transitional regime. The results confirmed that the two interaction models are practically equivalent and verified that the use of the Knetchel and Pitts coefficients involves results very close to those computed considering a diffusive, fully accommodated interaction both in clean and flapped configurations.

Aerodynamic control capability of a wing-flap in hypersonic, rarefied regime

  • Zuppardi, Gennaro
    • Advances in aircraft and spacecraft science
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    • v.2 no.1
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    • pp.45-56
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    • 2015
  • The attitude aerodynamic control is an important subject in the design of an aerospace plane. Usually, at high altitudes, this control is fulfilled by thrusters so that the implementation of an aerodynamic control of the vehicle has the advantage of reducing the amount of thrusters fuel to be loaded on board. In the present paper, the efficiency of a wing-flap has been evaluated considering a NACA 0010 airfoil with a trailing edge flap of length equal to 35% of the chord. Computational tests have been carried out in hypersonic, rarefied flow by a direct simulation Monte Carlo code at the altitudes of 65 and 85 km, in the range of angle of attack 0-40 deg. and with flap deflection equal to 0, 15 and 30 deg.. Effects of the flap deflection have been quantified by the variations of the aerodynamic force and of the longitudinal moment. The shock wave-boundary layer interaction and the shock wave-shock wave interaction have been also considered. A possible interaction of the leading edge shock wave and of the shock wave arising from the vertex of the convex corner, produced on the lower surface of the airfoil when the flap is deflected, generates a shock wave whose intensity is stronger than those of the two interacting shock waves. This produces a consistent increment of pressure and heat flux on the lower surface of the flap, where a thermal protection system is required.

NUMERICAL STUDY OF WEDGE FLOW IN RAREFIED GAS FLOW REGIME USING A SLIP BOUNDARY CONDITION (희박기체 영역에서 미끄럼 경계조건을 적용한 쐐기 형상 주위의 유동 해석)

  • Choi, Y.J.;Kwon, O.J.
    • Journal of computational fluids engineering
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    • v.19 no.2
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    • pp.40-48
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    • 2014
  • For rarefied gas flow regimes, physical phenomena such as velocity slip and temperature jump occur on the solid body surface. To predict these phenomena accurately, either the Navier-Stokes solver with a slip boundary condition or the direct simulation Monte Carlo method should be used. In the present study, flow simulations of a wedge were conducted in Mach-10 flow of argon gas for several different flow regimes using a two-dimensional Navier-Stokes solver with the Maxwell slip boundary condition. The results of the simulations were compared with those of the direct simulation Monte Carlo method to assess the present method. It was found that the values of the velocity slip and the temperature jump predicted increase as the Knudsen number increases. Also, the results are comparatively reasonable up to the Knudsen number of 0.05.

PREDICTION OF THE AERODYNAMIC CHARACTERISTICS OF AN ORBITAL BLOCK OF A LAUNCH VEHICLE IN THE RAREFIED FLOW REGIME USING DSMC APPROACH (DSMC 해석기법을 이용한 희박유동 환경에서의 발사체 Orbital Block 공력특성 예측)

  • Kim, Young-Hoon;Ok, Ho-Nan;Choi, Young-In;Kim, In-Sun
    • 한국전산유체공학회:학술대회논문집
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    • 2007.04a
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    • pp.79-82
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    • 2007
  • The aerodynamic coefficients of Apollo capsule are calculated using a DSMC solver, SMILE, and the results agree very well with the data predicted by NASA. The aerodynamic characteristics of an orbital block which operates at high altitudes in the free molecule regime are also predicted. For the nominal flow conditions, the predicted aerodynamic force is very small since the dynamic pressure is extremely low. And the additional aerodynamic coefficients for the analysis of the attitude control are presented as the angle of attack and the side slip angle vary from $+45^{\circ}\;to\;-45^{\circ}$ of the nominal angle.

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Simulations of Axisymmetric Transition Flow Regimes Using a CFD/DSMC Hybrid Method (CFD/DSMC 혼합해석기법을 이용한 축대칭 천이영역 유동 해석)

  • Choi, Young-Jae;Kwon, Oh-Joon
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.47 no.3
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    • pp.169-176
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    • 2019
  • In the present study, a CFD/DSMC hybrid method performed by a coupled analysis between the CFD method and the DSMC method was developed to obtain the flow information on the rarefied gas flows effectively. Flow simulations around the high speed vehicles on the transition flow regimes were conducted by using the developed method. The FRESH-FX vehicle made of cone and cylinder shapes was considered for the simulations. The results of the hybrid method were compared with the results of the pure CFD and the pure DSMC method to confirm the reliability and efficiency of the hybrid method. It was found that the gradient and the intensity of the shock waves were weakened due to the relatively low density on the transition flow regime. It was confirmed that the results of the hybrid analysis were different to those of the pure CFD analysis and almost identical to those of the pure DSMC analysis. In addition, the computational time of the hybrid method was reduced than that of the pure DSMC method. As a result, it was obtained that the validity and the efficiency of the CFD/DSMC hybrid method.

Aerodynamic control capability of a wing-flap in hypersonic, rarefied regime: Part II

  • Zuppardi, Gennaro;Vangone, Daniele
    • Advances in aircraft and spacecraft science
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    • v.4 no.5
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    • pp.503-514
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    • 2017
  • The attitude control of an aircraft is usually fulfilled by means of thrusters at high altitudes. Therefore, the possibility of using also aerodynamic surfaces would produce the advantage of reducing the amount of fuel for the thrusters to be loaded on board. For this purpose, Zuppardi already considered some aerodynamic problems linked to the use of a wing flap in a previous paper. A NACA 0010 airfoil with a trailing edge flap of 35% of the chord, in the range of angle of attack 0-40 deg and flap deflections up to 30 deg was investigated. Computer tests were carried out in hypersonic, rarefied flow by a direct simulation Monte Carlo code at the altitudes of 65 and 85 km of Earth Atmosphere. The present work continues this subject, considering the same airfoil and free stream conditions but two flap extensions of 45% and 25% of the chord and two flap deflections of 15 and 30 deg. The main purpose is to compare the influence of the flap dimension with that of the flap deflection. The present analysis is carried out in terms of: 1) percentage variation of the global aerodynamic coefficients with respect to the no-flap configuration, 2) increment of pressure and heat flux on the airfoil lower surface due to the Shock Wave-Shock Wave Interaction (SWSWI) with respect to the same quantities with no SWSWI or in no-flap configuration, 3) flap hinge moment. Issues 2) and 3) are important for the design of the mechanical and thermal protection system and of the flap actuator, respectively. Under the above mentioned test and geometrical conditions, the flap deflection is aerodynamically more effective than the flap extension, because it involves higher variation of the aerodynamic coefficients. However, tests verify that a smaller deflection angle involves the advantage of a smaller increment of pressure and heat flux on the airfoil lower surface, due to SWSWI, as well as a smaller hinge moment.