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Rarefied gas dynamics - kinetic theory, solutions of boltzmann equation, molecular beams and surface interactions
Rarefied gas dynamics - transition flow in gases of simple, nonreacting, electrically neutral molecules
Rarefied gas dynamics - molecular beams and surface interactions, free-molecular flow, fluid mechanics, kinetic theory
Rarefied gas dynamics - gas flow
Non-equilibrium rarefied flows are frequently encountered in a wide range of applications, including atmospheric re-entry vehicles, vacuum technology, and microscale devices. Rarefied flows at the microscale can be effectively modeled using the ellipsoidal statistical Bhatnagar–Gross–Krook (ESBGK) form of the Boltzmann kinetic equation. Numerical solutions of these equations are often based on the finite volume method (FVM) in physical space and the discrete ordinates method in velocity space. However, existing solvers use a sequential solution procedure wherein the velocity distribution functions are implicitly coupled in physical space, but are solved sequentially in velocity space. This leads to explicit coupling of the distribution function values in velocity space and slows down convergence in systems with low Knudsen numbers. Furthermore, this also makes it difficult to solve multiscale problems or problems in which there is a large range of Knudsen numbers. In this paper, we extend the coupled ordinates method (COMET), previously developed to study participating radiative heat transfer, to solve the ESBGK equations. In this method, at each cell in the physical domain, distribution function values for all velocity ordinates are solved simultaneously. This coupled solution is used as a relaxation sweep in a geometric multigrid method in the spatial domain. Enhancements to COMET to account for the non-linearity of the ESBGK equations, as well as the coupled implementation of boundary conditions, are presented. The methodology works well with arbitrary convex polyhedral meshes, and is shown to give significantly faster solutions than the conventional sequential solution procedure. Acceleration factors of 5–9 are obtained for low to moderate Knudsen numbers on single processor platforms.
Not Available
A detailed model of the tidal disruption events (TDEs) has been constructed using stellar dynamical and gas dynamical inputs that include black hole (BH) mass M{sub •}, specific orbital energy E and angular momentum J, star mass M{sub ⋆} and radius R{sub ⋆,} and the pericenter of the star orbit r{sub p}(E, J, M{sub •}). We solved the steady state Fokker–Planck equation using the standard loss cone theory for the galactic density profile ρ (r) ∝ r{sup −γ} and stellar mass function ξ(m) where m = M{sub ⋆}/M{sub ⊙} and obtained the feeding rate of stars to the BH integrated over the phase space as N-dot {sub t}∝M{sub ∙}{sup β}, where β=−0.3±0.01 for M{sub •} > 10{sup 7}M{sub ⊙} and ∼6.8 × 10{sup −5} Yr{sup −1} for γ = 0.7. We use this to model the in-fall rate of the disrupted debris, M-dot (E,J,m,t), and discuss the conditions for the disk formation, finding that the accretion disk is almost always formed for the fiduciary range of the physical parameters. We also find the conditions under which the disk formed from the tidal debris of a given star with a super Eddington accretion phase. We have simulated the light curve profiles in the relevant optical g band and soft X-rays for both super and sub-Eddington accretion disks as a function of M-dot (E,J,t). Using this, standard cosmological parameters, and mission instrument details, we predict the detectable TDE rates for various forthcoming surveys as a function of γ.
Recent research in CO 2 photocatalysis has largely focused on exploring new catalysts; however, details of the relationship between charge carrier dynamics and gas dynamics on the surface of nanomaterials often remain unclear. Knowledge of these processes will allow one to rationally design highly efficient catalysts for solar CO 2 conversion. This project aimed to develop state-of-the-art techniques and establish new capabilities in SRNL to enable the study of photocatalysts and other materials in detail. In FY21, we developed two new in situ techniques that are unique to SRNL, allowing the study of reaction intermediates and adsorbed gases during photocatalysis at various wavelengths of excitation. We also established a new in-house capability for catalyst synthesis and product evaluation which enables a deep understanding of how catalyst preparation methodologies impact product generation. In FY22, we gained in-house expertise and knowledge on the newly constructed a physical vapor deposition device, i.e. glancing angle deposition (GLAD) system, and constructed a flow photoreactor system for CO 2 photoconversion and other photocatalytic studies.
Galactic gas dynamics, spiral structure, and star formation are discussed in relation to N-body computational studies based on a cloud-particle model of the interstellar medium. On the small scale, the interstellar medium is seen as cloud-dominated and supernova-perturbed. It is noted that the cloud-particle model simulates cloud-cloud collisions, the formation of stellar associations, and supernova explosions as dominant local processes. On the large scale, in response to a spiral galactic gravitational field, global density waves and galactic shocks develop having large-scale characteristics similar to those found in continuum gas dynamical studies. Both the system of gas clouds and the system of young stellar associations forming from the clouds figure in the global spiral structure. However, with the attributes of neither assuming a continuum of gas (as in continuum gas dynamical studies) or requiring a prescribed equation of state (such as the isothermal condition), the cloud-particle picture retains much of the detail lost in earlier work. By detail is meant the small-scale features and structures so important in understanding the local, turbulent state of the interstellar medium as well as the degree of raggedness often seen to be superposed on the global spiral structure.
Second international symposium on rarefied gas dynamics totaling 40 individually abstracted papers on related topics, edited by l. talbot
For the determination of aerodynamic characteristics such as lift, drag, and moment coefficients, it is crucial to compute the properties of steady flow past an airfoil. This investigation provides a set of flow dependent grid systems and initial flowfield guesses which substantially improve convergence rates when applied to the Euler equations for flows past an airfoil. The basic equations are examined, taking into account nonlinear equations which are difficult to solve. A good approximation to these equations under certain conditions can be obtained by introducing the so-called 'tangent gas approximation' considered by Woods (1961), in which the isentropic relation between rho and p is replaced by a tangent to a curve. Attention is given to the solution procedure, the analysis (direct) problem, and a comparison of the tangent gas solution with the converged Euler solution.
Molecular approach to rarefied gas dynamics
The principle types of silencers are discussed for gas dynamic noise of free steam and gas expansions, as well as the results of research in gas dynamics of jets and applied acoustics. Gas dynamic noise attenuation by means of the Coanda effect is due to fluid decompression in a Coanda ejector of the external type, where a structural change takes place in the acoustic frequency spectrum and in its direction, as well as a substantial decrease in the fluid's velocity, temperature and concentration. This process is continued in the second phase with absorption of the acoustic waves by means of an active structure.
Shock tube for gas dynamics studies
Dynamic gas velocity and pressure effects on breakdown potential of argon flow between flat parallel plate electrodes
Carbon dioxide gas dynamic layer in shock tube facility, measuring shape, time, output energy, beam diameter, etc
Carbon monoxide gas dynamic laser oscillation generation, observing maximum power and vibrational exchange among single diatomic species states
Magnetohydrodynamics, fourth biennial gas dynamics symposium