1,720,991 research outputs found
Cubic Fokker-Planck-DSMC hybrid method for diatomic rarefied gas flow through a slit and an orifice
No full textFokker-Planck kinetic models have been devised as an approximation of the Boltzmann collision operator. Cubic Fokker-Planck-DSMC hybrid method is employed to simulate the diatomic gas flow through a thin slit and a thin orifice. Pressure driven nitrogen expansion gas flows with two different pressure ratios are investigated at Knudsen number 0.001. The DSMC method is physically accurate for all flow regime; however it is computationally expensive in high density or near continuum regions. The Fokker-Planck-DSMC hybrid scheme employs DSMC in rarefied regions and Fokker-Planck method in near continuum flow regions for an efficient and accurate solution. Numerical procedures of the cubic Fokker-Planck method are implemented within the framework of an existing DSMC-solver, SPARTA. The Fokker-Planck-DSMC hybrid solution reproduces pure DSMC solution with improved computational efficiency up to a factor of five for vacuum flow through a thin orifice. In addition, breakdown of translational equilibrium is investigated. Domain criterion of FP-DSMC is safely smaller than Bird's breakdown criterion
Fokker–Planck-Based Kinetic Models for Rarefied Gas Flows: Extending to Diatomic Mixtures and Achieving Second-Order Accuracy
No full textNumerical Analysis of Ground Testing for the Intake Device of an Atmosphere-Breathing Electric Propulsion
No full textCharacterization of Atmosphere-Breathing Electric Propulsion Intake Performance
No full textSatellite deployment at lower altitudes is increasing due to the benefits of payload operation. The payload performances, such as optical resolution, communication latency, and transmission power efficiency, are inversely proportional to the altitude [1]. In Very-Low-Earth-Orbit (VLEO), which indicates an altitude of less than 500 km, deorbit of the satellite is intensified by the drag of the rarefied atmosphere [2]. Atmosphere-Breathing-Electric-Propulsion (ABEP) has been proposed for continuous drag compensation maneuvers without onboard propellants [3]. The ABEP system is designed to intake and compress the upper atmosphere as a propellant of electric propulsion. The captured atmosphere is ionized and accelerated by the electromagnetic field to obtain thrust. Mechanisms of the ABEP system consist of four stages; intake, ionization, acceleration, and plume. The intake device is a component that sets it apart from conventional electric propulsion. As intake performance is directly re
A Comparative Study of Fokker-Planck Models for Rarefied Gas Flows
No full textThe Boltzmann equation accurately describes the flow behavior of a dilute gas from a continuum to the free molecular regime. The Direct Simulation Monte Carlo (DSMC) method is commonly used to obtain the numerical solution of the Boltzmann equation [1]. In the DSMC method, each particle evolves through the probabilistic binary collision dynamics. Although the DSMC method has achieved great success in rarefied gas dynamics, it becomes prohibitively expensive in the continuum regime due to a large number of collisions. In order to reduce the computational cost of the DSMC method, the particle-based Fokker-Planck (FP) method has been suggested [2]. In the FP method, each particle evolves under Brownian dynamics. Since Brownian motion is a macroscopic movement produced by many microscopic random effects, the computational cost of the FP method is independent of the number of collisions. Various FP models have been proposed in the last decade, but a comprehensive comparative study to assess their performance is still scarce. In this study, three FP models that is the Cubic-FP model [3], the Ellipsoidal-Statistical FP (ES-FP) model [4], and the Quadratic Entropic FP (Quad-EFP) model [5] are numerically investigated to assess their efficiency and accuracy
Radiative equilibrium boundary condition and correlation analysis on catalytic surfaces in DSMC
No full textThis study integrates radiative equilibrium boundary conditions on a catalytic surface within the Direct Simulation Monte Carlo (DSMC) method. The radiative equilibrium boundary condition is based on the principle of energy conservation at each surface element, enabling the accurate capture of spatially varying surface temperatures and heat fluxes encountered during atmospheric re-entry. The surface catalycity is represented through the finite-rate surface chemistry (FRSC) model, specifically focusing on the heterogeneous recombination of atomic oxygen on silica surfaces. Both the FRSC model and the radiative equilibrium boundary conditions within the DSMC framework are validated through comparison to analytical solutions. Numerical simulations are conducted for rarefied hypersonic flow around a two-dimensional cylinder under representative re-entry conditions for both non-catalytic and catalytic surfaces. The results demonstrate significant discrepancies in computed surface properties between the radiative equilibrium and conventional isothermal boundary conditions. Furthermore, linear interpolation between results from two independent isothermal boundary conditions is shown to be inadequate for accurately predicting surface heat flux, particularly when surface reactions are considered. The observed discrepancies originate from a non-linear correlation between surface temperature and heat flux, influenced by factors such as surface catalycity and local geometric variations along the cylinder. These findings highlight the necessity of implementing radiative equilibrium boundary conditions within DSMC to ensure physically accurate aerothermodynamic computations.
A stochastic Fokker-Planck-Master model for diatomic rarefied gas flows
No full textThe direct simulation Monte Carlo (DSMC) method is widely used for numerical solutions of the Boltzmann equation. However, the associated computational cost becomes prohibitive in the nearcontinuum regime. To address this limitation, the particle-based Fokker-Planck (FP) method has been extensively studied in the past decade. The FP equation, which describes Brownian motion, does not require resolution of the collisional time and length scales. While several monatomic FP models have been proposed, the modeling of diatomic gases within the FP framework has received limited attention. In this paper, we propose a new diatomic kinetic model, named the Fokker-Planck-Master (FPM) model, which can accurately describe energy exchanges between translational-rotational and translational-vibrational modes. The FPM model combines the FP equation to describe the evolution of translational and rotational modes, and the master equation to describe the evolution of the vibrational modes. The numerical test cases include relaxation problems, Couette flows, and hypersonic flows past a vertical flat plate. The results demonstrate that the FPM model shows good agreement with both analytical and DSMC solutions.
Velocity-dependent surface corrugation in gas-surface scattering
No full textGas-surface scattering transitions from the thermal to the structure scattering regime as incident energy increases, with the dominant mechanism shifting from surface thermal motion to surface corrugation. Conventional models such as the Maxwell and Cercignani-Lampis-Lord (CLL) models incorporate thermal motion but neglect explicit corrugation effects, while the washboard model accounts for corrugation yet violates reciprocity. To overcome these limitations, the washboard-CLL hybrid approach has been proposed. In this approach, the surface is represented using a washboard model with random local tilts, while velocity updates are performed via the CLL model to ensure reciprocity. However, this approach assumes an energy-independent distribution of surface tilts, while in reality high-energy incident particles penetrate deeper into the surface and experience enhanced corrugation. To address this, this study proposes a corrugated CLL model incorporating a velocity-dependent corrugation factor. Building on the washboard-CLL hybrid approach, the model represents surface corrugation as a function of incident velocity and employs a Metropolis-Hastings acceptance to preserve reciprocity. Validation against molecular beam scattering experiments demonstrates that the model successfully reproduces the nonmonotonic angular distribution, which narrows in the thermal regime and broadens in the structural regime with increasing incident energy. Additionally, it captures the gradual inversion of the energy distribution slope from negative to positive as incident energy increases. Overall, the corrugated CLL model provides a unified and physically consistent description of gas-surface scattering over a wide range of incident energies and scattering angles.
- …
