DS2V version 3
The current release is 3.8.04 dated February 5, 2007
When run this produces the executable program DS2V.EXE that
can be freely used to run eight integrated demonstration examples.
The setting of new data or the modification of existing requires
a password for the first run in a new directory. The password
is e-mailed to purchasers of the DS2Vprogram who then become license
holders. The same password is used for all versions.
Evaluation copies will be supplied
upon request.
Further enquiries should be addressed to Graeme Bird
at gab@gab.com.au
Description of the DS2V (Version 3.7) Program
The flowfield limits are specified by the minimum and maximum
values of the x and y co-ordinates. These four boundaries may
be stream boundaries, planes if symmetry, vacuum boundaries or
the axis of an axially symmetric flow, although the minimum y
coordinate may be at any radius. This basically rectangular flowfield
may be modified by the definition of one or more separate "surfaces".
Each of these must be either a closed surface or an open surface
that starts and finishes on a boundary of the basic rectangle.
Each surface is specified either by a combination of straight
line and circular arc segments . Most importantly with regard
to the flexibility of the program, each of the surfaces may be
a combination of solid surface segments, stream entry boundaries
and specified flow entry boundaries. The surfaces may be set to
move in the plane of the flow or normal to it. The latter boundary
in the axially symmetric case permits the study of rotating flows.
The flow input boundaries permit the study of a wide range
of problems that involve jets and plumes. A secondary stream may
be set to occupy part of the initial flowfield and this permits
the study of unsteady shock tube type flows and shear flows. Alternatively,
shock waves may be generated by a moving "piston" type
boundary for diffraction studies. Special "constant pressure"
boundaries are available for the generation of steady internal
flows that are driven by a pressure differential. Periodic boundary
conditions are also available.
The flowfield grid consists of a background
rectangular grid that is uniformly spaced in each direction. Each
division is further subdivided into a large number of elements.
The total number of elements is of the order of the number of
simulated molecules. There is a restriction on the geometry in
that the size of the elements sets the minimum thickness of bodies
within the flow. The computational cells comprise those elements
that are nearer to a particular cell node than to any other node.
The nodes for the sampling cells
are initially comprised of the centers
of the divisions that are within the flow plus the points that
define the sampling intervals along any surfaces. Separate cell systems are employed for collisions
and the sampling of flow properties, the former being much smaller. At
any time during the calculation, the cells may be adapted
to the flow densities and density gradients that exist at that
time. The user selects the desired number of simulated molecules
within each adapted cell.
The gas may be chosen from a menu that includes ideal air,
real air with vibration and chemical reactions, nitrogen, argon
and a hard sphere gas. Alternatively, a custom non-reacting or
reacting gas may be specified. Surface reactions are included.
The program employs the physical gas models that have been
described and validated in Bird (1994). The gas is a mixture of
the VHS or VSS models and the cross-sections,
the viscosity-temperature index (which determines the way in which
the cross-section changes with the relative velocity), are set
separately for every molecular species. The
VSS is to be preferred for gas mixtures because it allows the
correct Schmidt number to be set. A classical Larsen-Borgnakke
model is employed for the rotational degrees of freedom, while
a quantum model is used for the vibrational modes.
The chemical reaction model calculates reactive cross-sections
that are consistent with the measured rate constants.
The classical diffuse reflection model with complete accommodation
of the gas to the surface temperature is appropriate to "engineering
surfaces" that have not been exposed for a long period to
ultra-high vacuum. The CLL model is now
included for a better representation of ultra-clean surfaces.
A fraction of specular reflection may still
be specified, but the specular option is recommended only for
the setting of symmetry surfaces. A set temperature distribution
may be specified for the surface or it may be specified as an
adiabatic surface with zero heat transfer. The temperature distribution
on the surface is one of the output quantities for adiabatic surfaces.
The adiabatic surface may be either insulated
with zero thermal conductivity or perfectly conducting with infinite
thermal conductivity. Thermal radiation at a specified surface
emissivity is included.
Files of the molecules crossing specified
lines may be generated and these may be used as part of the molecules
entry flux to the DS3V program. This facilitates the computation
of floews that are part two-dimensional or axially symmetric and
part three-dimensional.