1,406 research outputs found
Numerical simulation of moving rigid body in rarefied gases
In this paper we present a numerical scheme to simulate a moving rigid body
with arbitrary shape suspended in a rarefied gas. The rarefied gas is simulated
by solving the Boltzmann equation using a DSMC particle method. The motion of
the rigid body is governed by the Newton-Euler equations, where the force and
the torque on the rigid body is computed from the momentum transfer of the gas
molecules colliding with the body. On the other hand, the motion of the rigid
body influences the gas flow in its surroundings. We validate the numerical
results by testing the Einstein relation for Brownian motion of the suspended
particle. The translational as well as the rotational degrees of freedom are
taken into account. It is shown that the numerically computed translational and
rotational diffusion coefficients converge to the theoretical values.Comment: 16 pages, 8 figure
An immersed boundary method for the fluid--structure--thermal interaction in rarefied gas flow
An immersed boundary method for the fluid--structure--thermal interaction in
rarefied gas flow is presented. In this method, the slip model is incorporated
with the penalty immersed boundary method to address the velocity and
temperature jump conditions at the fluid--structure interface in rarefied gas
flow within slip regime. In this method, the compressible flow governed by
Navier-Stokes equations are solved by using high-order finite difference
method; the elastic solid is solved by using finite element method; the fluid
and solid are solved independently and the fluid--structure--thermal
interaction are achieved by using a penalty method in a partitioned way.
Several validations are conducted including Poiseuille flow in a 2D pipe, flow
around a 2D NACA airfoil, moving square cylinder in a 2D pipe, flow around a
sphere and moving sphere in quiescent flow. The numerical results from present
method show good agreement with the previous published data obtained by other
methods, and it confirms the the good ability of the proposed method in
handling fluid--structure--thermal interaction for both weakly compressible and
highly compressible rarefied gas flow. To overcome the incapability of
Navier-Stokes equations at high local Knudsen numbers in supersonic flow, an
artificial viscosity is introduced to ease the sharp transition at the shock
wave front. Inspired by Martian exploration, the application of proposed method
to study the aerodynamics of flapping wing in rarefied gas flow is conducted in
both 2D and 3D domains, to obtain some insights for the flapping-wing aerial
vehicles operating in Martian environment
Monte Carlo direct simulation technique user's manual
User manual for Monte Carlo direct simulation techniqu
DNS of dispersed multiphase flows with heat transfer and rarefaction effects
We propose a method for DNS of particle motion in non-isothermal systems. The method uses a shared set of momentum and energy balance equations for the carrier- and the dispersed phases. Measures are taken to ensure that non-deformable entities (solid particles) behave like rigid bodies. Moreover, deformable entities (e.g. bubbles) as well as rarefaction effects can be accommodated. The predictions of the method agree well with the available data for isothermal solid particles motion in the presence of walls and other particles, natural convection around a stationary particle, solid particles motion accompanied with heat transfer effects and isothermal solid particles motion under rarefied conditions. The method is used to investigate the simultaneous effects of heat transfer and rarefaction on the motion of a solid catalyst particle in an enclosure, the interaction of a solid particle and a microbubble in a flotation cell and a case with more than 1000 particles
Thermophoresis of Janus particles at large Knudsen numbers
The force and torque on a Janus sphere moving in a rarefied gas with a
thermal gradient are calculated. The regime of large Knudsen number is
considered, with the momenta of impinging gas molecules either obtained from a
Chapman-Enskog distribution or from a binary Maxwellian distribution between
two opposing parallel plates at different temperature. The reflection
properties at the surface of the Janus particle are characterized by
accommodation coefficients having constant but dissimilar values on each
hemisphere. It is shown that the Janus particle preferentially orients such
that the hemisphere with a larger accommodation coefficient points towards the
lower temperature. The thermophoretic velocity of the particle is computed, and
the influence of the thermophoretic motion on the magnitude of the torque
responsible for the particle orientation is studied. The analytical
calculations are supported by Direct Simulation Monte Carlo results, extending
the scope of the study towards smaller Knudsen numbers. The results shed light
on the efficiency of oriented deposition of nanoparticles from the gas phase
onto a cold surface
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