• 제목/요약/키워드: Rarefied gas

검색결과 43건 처리시간 0.019초

희박기체 상태의 라디오미터릭 효과에 의해 구동되는 선형 마이크로 액추에이터의 성능해석 (Performance Analysis of a Linear Micro-actuator Operated by Radiometric Phenomena in Rarefied Gas Flow Field)

  • 황영규;허중식
    • 대한기계학회논문집B
    • /
    • 제26권10호
    • /
    • pp.1394-1405
    • /
    • 2002
  • The performance of micro-actuators utilizing radiometric forces are studied numerically. The Knudsen number based on gas density and characteristic dimension is varied from near-continuum to highly rarefied conditions. Direct simulation Monte Carlo(DSMC) calculations have been performed to estimate the performance of the micro-actuators. In the present DSMC method, the variable hard sphere molecular model and no time counter technique are used to simulate the molecular collision kinetics. For simulation of diatomic gas flows, the Borgnakke-Larsen phenomenological model is adopted to redistribute the translational and internal energies.

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

  • 최서원
    • 대한기계학회논문집B
    • /
    • 제21권4호
    • /
    • pp.509-517
    • /
    • 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.

헬리컬 채널내부의 3차원 희박기체유동 (Three-dimensional Rarefied Flows in Rotating Helical Channels)

  • 황영규;허중식
    • 대한기계학회:학술대회논문집
    • /
    • 대한기계학회 2000년도 춘계학술대회논문집B
    • /
    • pp.625-630
    • /
    • 2000
  • Numerical and experimental investigations are peformed for the rarefied gas flows in pumping channels of a helical-type drag pump. Modern turbomolecular pumps include a drag stage in the discharge side, operating roughly in $10^{-2}{\sim}10Torr$. The flow occurring in the pumping channel develops from the molecular transition to slip flow traveling downstream. Two different numerical methods are used in this analysis: the first one is a continuum approach in solving the Navier-Stokes equations with slip boundary conditions, and the second one is a stochastic particle approach through the use of the direct simulation Monte Carlo(DSMC) method. The flow in a pumping channel is three-dimensional(3D), and the main difficulty in modeling a 3D case comes from the rotating frame of reference. Thus, trajectories of particles are no longer straight lines. In the Present DSMC method, trajectories of particles are calculated by integrating a system of differential equations including the Coriolis and centrifugal forces. Our study is the first instance to analyze the rarefied gas flows in rotating frame in the presence of noninertial effects.

  • PDF

화학반응을 수반하는 극초음속 희박류 유동의 직접모사법 개발 (A DSMC Technique for the Analysis of Chemical Reactions in Hypersonic Rarefied Flows)

  • 정찬홍;윤성준
    • 한국전산유체공학회지
    • /
    • 제4권3호
    • /
    • pp.63-70
    • /
    • 1999
  • A Direct simulation Monte-Carlo (DSMC) code is developed, which employs the Monte-Carlo statistical sampling technique to investigate hypersonic rarefied gas flows accompanying chemical reactions. The DSMC method is a numerical simulation technique for analyzing the Boltzmann equation by modeling a real gas flow using a representative set of molecules. Due to the limitations in computational requirements. the present method is applied to a flow around a simple two-dimensional object in exit velocity of 7.6 km/sec at an altitude of 90 km. For the calculation of chemical reactions an air model with five species (O₂, N₂, O, N, NO) and 19 chemical reactions is employed. The simulated result showed various rarefaction effects in the hypersonic flow with chemical reactions.

  • PDF

평판 주위의 저속 희박기체 유동장 해석 (Simulation of Low-Speed Rarefied Gas Flows Around a Flat Plate)

  • 정찬홍
    • 한국전산유체공학회지
    • /
    • 제9권3호
    • /
    • pp.1-7
    • /
    • 2004
  • A kinetic theory analysis is made of low-speed rarefied gas flows around a flat plate. The Boltzmann equation simplified by a collision model is solved by means of a finite difference approximation with the discrete ordinate method. The method does not suffer from statistical noise which is common in particle based methods and requires much less amount of computational effort. Calculations are made for flows around a micro-scale flat plate with a finite length of 20 microns. The method is assessed by comparing the results with those from several different methods and available experimental data.

극초음속 희박유동 해석을 위한 축대칭 다화학종 GH 방정식의 개발 (EVELOPMENT OF AXISYMMETRIC MULTI-SPECIES GH EQUATION FOR HYPERSONIC RAREFIED FLOW ANALYSES)

  • 안재완;김종암
    • 한국전산유체공학회:학술대회논문집
    • /
    • 한국전산유체공학회 2008년도 학술대회
    • /
    • pp.84-91
    • /
    • 2008
  • Generalized hydrodynamic (GH) theory for multi-species gas and the computational models are developed for the numerical simulation of hypersonic rarefied gas flow on the basis of Eu's GH theory. The rotational non-equilibrium effect of diatomic molecules is taken into account by introducing excess normal stress associated with the bulk viscosity. The numerical model for the diatomic GH theory is developed and tested. Moreover, with the experience of developing the dia-tomic GH computational model, the GH theory is extended to a multi-species gas including 5 species; O$_2$, N$_2$, NO, O, N. The multi-species GH model includes diffusion relation due to the molecular collision and thermal phenomena. Two kinds of GH models are developed for an axisymmetric flow solver. By compar-ing the computed results of diatomic and multi-species GH theories with those of the Navier-Stokes equations and the DSMC results, the accuracy and physical consistency of the GH computational models are examined.

  • PDF

극초음속 희박유동 해석을 위한 축대칭 다화학종 GH 방정식의 개발 (EVELOPMENT OF AXISYMMETRIC MULTI-SPECIES GH EQUATION FOR HYPERSONIC RAREFIED FLOW ANALYSES)

  • 안재완;김종암
    • 한국전산유체공학회:학술대회논문집
    • /
    • 한국전산유체공학회 2008년 추계학술대회논문집
    • /
    • pp.84-91
    • /
    • 2008
  • Generalized hydrodynamic (GH) theory for multi-species gas and the computational models are developed for the numerical simulation of hypersonic rarefied gas flow on the basis of Eu's GH theory. The rotational non-equilibrium effect of diatomic molecules is taken into account by introducing excess normal stress associated with the bulk viscosity. The numerical model for the diatomic GH theory is developed and tested. Moreover, with the experience of developing the dia-tomic GH computational model, the GH theory is extended to a multi-species gas including 5 species; $O_2,\;N_2$, NO, O, N. The multi-species GH model includes diffusion relation due to the molecular collision and thermal phenomena. Two kinds of GH models are developed for an axisymmetric flow solver. By compar-ing the computed results of diatomic and multi-species GH theories with those of the Navier-Stokes equations and the DSMC results, the accuracy and physical consistency of the GH computational models are examined.

  • PDF

Heat Transfer in a Micro-actuator Operated by Radiometric Phenomena

  • Heo Joong-Sik;Hwang Young-Kyu
    • Journal of Mechanical Science and Technology
    • /
    • 제19권2호
    • /
    • pp.664-673
    • /
    • 2005
  • The heat transfer characteristics of rarefied flows in a micro-actuator are studied numerically. The effect of Knudsen number (Kn) on the heat transfer of the micro-actuator flows is also examined. The Kn based on gas density and characteristic dimension is varied from near-continuum to highly rarefied conditions. Direct simulation Monte Carlo calculations have been performed to estimate the performance of the micro-actuator. The results show that the magnitude of the temperature jump at the wall increases with Kn. Also, the heat transfer to the isothermal wall is found to increase significantly with Kn.

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

  • 안무영;장근식
    • 한국전산유체공학회:학술대회논문집
    • /
    • 한국전산유체공학회 1998년도 춘계 학술대회논문집
    • /
    • pp.138-144
    • /
    • 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.

  • PDF

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

  • 최영재;권오준
    • 한국전산유체공학회지
    • /
    • 제19권2호
    • /
    • pp.40-48
    • /
    • 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.