More Powerful CFD Tools in SVU Wang Junhong
(SVU/Academic Computing, Computer Centre, NUS)
Computational Fluid Dynamics simulation is one of the major applications in HPC. In May 2003, SVU upgraded the FLUENT computational fluid dynamics (CFD) software to its latest version 6.1. At the same time, a special-purpose CFD software, POLYFLOW, was installed and made available to the users. Together with two other CFD softwares, CFX and FIDAP, researchers now have a more comprehensive range of software to choose from for their CFD simulation and analysis work.
A brief introduction to four CFD softwares that is
available for use in SVU: FLUENT: a generic CFD software and can be applied to
various areas. It is the leading CFD software in the market so far. The advantage is its user-friendly GUI and plenty & advanced physic models.
POLYFLOW: a special-purpose CFD software, which is
good at handling non-Newtonian and viscoelastic flows for problems like extrusion die design, blow molding, and fiber spinning.
CFX: a generic CFD software and can be applied to
wide range of areas. It is very powerful in solving highly coupled problems, such as cases in turbomachinery and combustion.
FIDAP: a special-purpose CFD software for materials
processing applications, such as polymer processing, thin film coating, bio-medical, semi-conductor crystal growth.
What Can POLYFLOW Do ? POLYFLOW (current version 3.9) is a finite-element
based CFD package for the analysis of polymer
processing, including extrusion die design, blow molding, and fiber spinning as well as other materials processing applications. POLYFLOW is particularly well-known for its extensive library of viscoelastic fluid models. GAMBIT is the preferred pre-processor of POLYFLOW for geometry creation and mesh generation.
A major feature of POLYFLOW is its ability to predict
three-dimensional free surfaces in the extrusion of non-Newtonian and viscoelastic fluids. This is very useful for die lip section design that can reduce the time and cost to obtain the desired extrudate shape.
Using POLYFLOW, the extrusion blow molding or
injection blow molding process, which is used to make hollow product such as bottles, gas tanks or car bumpers, can be simulated. This is achieved by its ability in dealing with different phases, boundary condition change and remeshing technique implemented to match the large deformation. POLYFLOW is also a very powerful tool for problems such as thermoforming, stamping, viscoelastic fluids and fiber spinning, etc.
Figure 1. die-extrusion using POLYFLOW Figure 2. blow molding & fiber spinning in POLYFLOW
Internet Webpage for four softwares: CFX: www.cfx.aeat.com FLUENT: www.fluent.com FIDAP: www.fluent.com/software/fidap/index.htm POLYFLOW: www.fluent.com/software/polyflow/index.htm
Whats New in FLUENT 6.1 ? FLUENT 6.1 deliveries many exciting new features and
capabilities in several focus areas, such as dynamic mesh, heat transfer and phase change, multiphase flow, rotating equipment, and reacting flow. Among those new features, dynamic mesh and heat transfer & phase change in multiphase flow are of most challenge and user expected.
The dynamic mesh model officially released in FLUENT
6.1 offers users to more complex CFD problems with a wide range of motion types. Because this kind of unsteady state simulation always takes huge computing time to complete, the model was delivered to be fully parallelized. The dynamic mesh model includes three modes of mesh deformation: dynamic layering, spring smoothing, and local remeshing. Dynamic mesh is useful for parts having linear motion like in-cylinder movement using quadrilateral, prismatic, and hexahedral elements. The spring smoothing method can only be applied in relatively small deformations using triangular and tetrahedral
elements. The local remeshing approach, of course, offers a greater flexibility in motion types. Those regions need to remesh will be automatically detected by the solver. The remeshing process is automatic carried out by the solver too and then the simulation will continue on.
Piston and vibromixer with linear motion are examples to
apply dynamic layering method. Spring smoothing approach can be utilized to hydro valve analysis. While the applications like launch of a rocket, store separation and internal combustion engines with moving pistons and valves, for which cases have complex and irregular motions, all three dynamic mesh approaches may be used.
Heat and mass transfer is now allowed in the Eulerian
multiphase model. Mass transfer can be calculated in VOF simulations. This significantly extends Eulerian multiphase model applications available in complex geometry or irregular computational domains. Users are able to use FLUENT 6.1 to do those simulations that they could not do in FLUENT 6.0, for instant, liquid boiling process.
Which CFD Software to Use ? Obviously, if you are going to solve a die extrusion or
crystal growth problem, you should consider using the special-purpose software, either POLYFLOW or FIDAP. This may save a lot of your efforts by using some build-in capabilities and models.
FLUENT and CFX are generic CFD codes. Ideally, they
should not have much difference because they
solve exactly the same governing equations (N-S eqs.). The GUI and the calculation algorithm lead to the major difference of the two packages. So for common applications, e.g. HVAV or mixing, you can chose to use whichever depending on your preference of the graphics interface and familiarity of software. However, for some special simulations like transient analyses of fan, pump or turbine, you should use CFX due to its strong advantages in this kind of application.
Figure 3. dynamic mesh model in FLUENT: instantaneous contours of exhaust gas mass fraction during the launch of a rocket.
Figure 4. liquid volume fraction in a boiling simulation.