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Why
STAR-CCM+ is the next step for CFD
Milovan
Peric, CD-adapco
After four years of intensive work, the first version of CD-adapco's software package STAR-CCM+ has been recently released, and a free version (with some restrictions) is available on request, for everyone! The aim of this article is to explain what is new in this next-generation software compared to contemporary packages on the market.
The major and probably the most important distinction from all currently available simulation software in the fields of computational continuum mechanics (CCM) is the way that STAR-CCM+ is used. Designed with a view to future, when computational points in a mesh will be counted in billions, it offers a novel user interface that provides ultimate ease of use and functionality. Although the currently released version starts by importing a mesh, extensions are already under way to include a solid modeler and meshing tools, thus making STAR-CCM+ a complete environment for computational continuum mechanics – from geometry definition to post-processing of solutions.
Computations on large meshes are usually not performed on the user's desktop machine; in most cases a cluster of compute nodes is doing the number crunching, and such jobs are executed in batch mode. This means that the user can check the progress of the simulation only by post-processing the solutions at pre-defined break points.
STAR-CCM+ has been designed to change this paradigm: the user is given full interactive access to the simulation data at all times. This is achieved by splitting the software into a client that handles the user interface, and a server which performs the compute operations. When executing a large job on a parallel computer (which may be at a different location than user's environment), only the server will be running on that machine; the client (a light-weight java code) can be at any time connected to the server from any networked computer, disconnected for a while, and re-connected again from another host.
Whenever a client connects to a server, the user obtains full access to all monitoring, analysis and visualization functionality. Many kinds of reports and monitors can be defined by the user (e.g. forces over certain boundary regions, area or mass averaged quantities, residual norms, variable values at a given point or line in space, etc.), and any or a combination of them can be used to define the convergence criterion. However, by monitoring the variation of selected quantities as the simulation is running, the user can intervene in many ways, e.g. by changing control parameters (like time-step size or underrelaxation factors), boundary conditions, or particular models.
In
addition to the visualiztion of solution on boundary regions, the
user can create any number of derived parts – coordinate and
iso-surfaces, lines, points, streamlines, etc. – and create
visualization scenes using an arbitrary number of such parts. The
important novelty is that the work of creating images is performed
by the server concurrently with simulation; the client only displays
the images. Thus, the analysis and visualization of results is fully
parallelized and runs seamlessly on any parallel platform. Impressive
also is the list of quantities that can be visualized: it includes
not only the solution variables, but also a large number of pre-defined
derived scalar and vector field functions, plus any number of user-defined
field functions.
Even
the users who like creating scripts for repetitive simulations with
parameter variations will have an easy go with STAR-CCM+: all steps
from one simulation, including not only the case set-up, but also
the analysis (creation of monitors and reports, derived parts and
functions, plot scenes, etc.), can be recorded in a java-script.
This can be edited (e.g. to change the inlet velocity or another
boundary condition) and automatically re-played, thus enabling a
set of jobs to be executed in batch mode.
The
user interface of STAR-CCM+ offers many novel features, like positioning
of different visualization scenes on the screen (behind or next
to each other), selection of functions to be plotted (one mouse
click or one drop operation), creation of plots based on monitoring
values, etc. Its design ensures not only an ultimate ease of use
(by making it look and feel similar to other common graphical user
interfaces), but alsoultimate flexibility when it comes to future
multi-component, multiphase, multi-physics extensions of STAR-CCM+
capabilities.
Restarting
an existing simulation or performing some additional postprocessing
has never been easier: just click on the simulation file in an explorer
and it “opens”, i.e. STAR-CCM+ starts up and offers the user access
to all menu options. All simulation data is stored in a database,
which is seen as a single file; it is independent of the computing
platform and the number of processors used. The data is written
in binary format and loaded only on demand, making the software
extremely fast and memory-efficient with respect to data handling.
STAR-CCM+ also comes with a new presentation of user manuals. All the documentation is browsable and searchable, providing a fast and easy-to-use context-sensitive on-line help
system. With the provision of extensive user-coding options – which can be either in C, C++ or FORTRAN – STAR-CCM+ is meeting the demands of all present and future users of CFD and CCM software.
STAR-CCM+ comes not only with a novel user interface, but also with a novel architecture of the solver and state-of-the-art numerics. The data structure and code architecture are designed to handle meshes made of arbitrary polyhedra, with arbitrary interfaces between grid blocks (sliding, cyclic, etc.), and to solve a large variety of continuum mechanics problems. An already available addition to the methods available in STAR-CD is the coupled solver (both an implicit version with an algebraic-multigrid solver and an explicit version with a multistage Runge-Kutta solver), which is especially robust and accurate when dealing with shocks, natural convection and other problems involving a strong coupling between velocity, pressure, and temperature (in both compressible and incompressible flows). Currently released features cover a wide range of external and internal flows including conjugate heat transfer and porous media modeling, a comprehensive suite of turbulence models, and a variety of boundary conditions.
Future extensions of STAR-CCM+ models will include several options for solid-body deformation, fluid-structure interaction, phase change, electro-static, electro-chemistry and electro-magnetics effects, multicomponent multi-phase flows, combustion, etc. On the numerics side, a fully automatic mesh generation, mesh adaptation and mesh motion, including re-meshing and overlapping grid options, will be available. Many of these models and numerical features have already been presented in various prototypes and have proved their fitness for practical applications. STAR-CCM+ is the optimum environment for implementing these multi-physics features for numerical simulation in engineering practice – a truly new-generation software for computational continuum mechanics.
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