31,324 research outputs found
Recommended from our members
Advances and Challenges in Computational Research of Micro and Nano Flows
This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.This paper presents a collective overview of recent studies regarding the computational modelling
of micro- and nano-fluidic systems. The review provides an introduction to atomistic, mesoscale and hybrid
methods for simulating micro and nano-flows, as well as discusses recent applications and results from the
application of such methods
A high order compact scheme for hypersonic aerothermodynamics
A novel high order compact scheme for solving the compressible Navier-Stokes equations has been developed. The scheme is an extension of a method originally proposed for solving the Euler equations, and combines several techniques for the solution of compressible flowfields, such as upwinding, limiting and flux vector splitting, with the excellent properties of high order compact schemes. Extending the method to the Navier-Stokes equations is achieved via a Kinetic Flux Vector Splitting technique, which represents an unusual and attractive way to include viscous effects. This approach offers a more accurate and less computationally expensive technique than discretizations based on more conventional operator splitting. The Euler solver has been validated against several inviscid test cases, and results for several viscous test cases are also presented. The results confirm that the method is stable, accurate and has excellent shock-capturing capabilities for both viscous and inviscid flows
A Hybrid Godunov Method for Radiation Hydrodynamics
From a mathematical perspective, radiation hydrodynamics can be thought of as
a system of hyperbolic balance laws with dual multiscale behavior (multiscale
behavior associated with the hyperbolic wave speeds as well as multiscale
behavior associated with source term relaxation). With this outlook in mind,
this paper presents a hybrid Godunov method for one-dimensional radiation
hydrodynamics that is uniformly well behaved from the photon free streaming
(hyperbolic) limit through the weak equilibrium diffusion (parabolic) limit and
to the strong equilibrium diffusion (hyperbolic) limit. Moreover, one finds
that the technique preserves certain asymptotic limits. The method incorporates
a backward Euler upwinding scheme for the radiation energy density and flux as
well as a modified Godunov scheme for the material density, momentum density,
and energy density. The backward Euler upwinding scheme is first-order accurate
and uses an implicit HLLE flux function to temporally advance the radiation
components according to the material flow scale. The modified Godunov scheme is
second-order accurate and directly couples stiff source term effects to the
hyperbolic structure of the system of balance laws. This Godunov technique is
composed of a predictor step that is based on Duhamel's principle and a
corrector step that is based on Picard iteration. The Godunov scheme is
explicit on the material flow scale but is unsplit and fully couples matter and
radiation without invoking a diffusion-type approximation for radiation
hydrodynamics. This technique derives from earlier work by Miniati & Colella
2007. Numerical tests demonstrate that the method is stable, robust, and
accurate across various parameter regimes.Comment: accepted for publication in Journal of Computational Physics; 61
pages, 15 figures, 11 table
High speed corner and gap-seal computations using an LU-SGS scheme
The hybrid Lower-Upper Symmetric Gauss-Seidel (LU-SGS) algorithm was added to a widely used series of 2D/3D Euler/Navier-Stokes solvers and was demonstrated for a particular class of high-speed flows. A limited study was conducted to compare the hybrid LU-SGS for approximate Newton iteration and diagonalized Beam-Warming (DBW) schemes on a work and convergence history basis. The hybrid LU-SGS algorithm is more efficient and easier to implement than the DBW scheme originally present in the code for the cases considered. The code was validated for the hypersonic flow through two mutually perpendicular flat plates and then used to investigate the flow field in and around a simplified scramjet module gap seal configuration. Due to the similarities, the gap seal flow was compared to hypersonic corner flow at the same freestream conditions and Reynolds number
Radiation hydrodynamics including irradiation and adaptive mesh refinement with AZEuS. I. Methods
Aims. The importance of radiation to the physical structure of protoplanetary
disks cannot be understated. However, protoplanetary disks evolve with time,
and so to understand disk evolution and by association, disk structure, one
should solve the combined and time-dependent equations of radiation
hydrodynamics.
Methods. We implement a new implicit radiation solver in the AZEuS adaptive
mesh refinement magnetohydrodynamics fluid code. Based on a hybrid approach
that combines frequency-dependent ray-tracing for stellar irradiation with
non-equilibrium flux limited diffusion, we solve the equations of radiation
hydrodynamics while preserving the directionality of the stellar irradiation.
The implementation permits simulations in Cartesian, cylindrical, and spherical
coordinates, on both uniform and adaptive grids.
Results. We present several hydrostatic and hydrodynamic radiation tests
which validate our implementation on uniform and adaptive grids as appropriate,
including benchmarks specifically designed for protoplanetary disks. Our
results demonstrate that the combination of a hybrid radiation algorithm with
AZEuS is an effective tool for radiation hydrodynamics studies, and produces
results which are competitive with other astrophysical radiation hydrodynamics
codes.Comment: 15 pages, 10 figures, accepted for publication in A&
- ā¦