|
|
|
Simulating Flow
Software – Wind tunnels are well established in design – at least on a computer.
One way to achieve optimised products is to use numerical flow simulation. After all, knowledge of the physical
flow processes is a clear advantage. But how can flows be simulated without laboratory experiments?
Dr. Ivo Weinhold, Product Manager, NIKA GmbH
|
|
Flow paths with speed represented in colour.
Picture: NIKA
|
It is only in the last decade that mathematical flow simulation (Computational Fluid Dynamics – CFD) has broken through into
development departments in industry. The crucial impetus came from the availability of low-cost computing power and modern
mathematical algorithms. Further impetus came from model-based 3D design. In line with the trend towards integrated digital
product development, high-quality 3D product models can be used for physical and technical simulations. This idea leads on
to the concept of Product Lifecycle Management (PLM), under which all product-related data, from development, use and disposal
of a product is consistently used and managed. An important element of the PLM concept is the seamless integration of simulations
of physical functions. This includes the traditional strength calculations using finite elements, as well as acoustic and
lighting simulations. There is an almost complete range of simulation software for these tasks, for example for the PLM
system based around CATIA V5. Only almost, however, as suppliers of flow simulation software were previously very reticent.
It is only recently that the Frankfurt company NIKA has closed this gap with EFD.V5, the world’s first software package for
calculating flows and heat transfer. What is so difficult about integrating flow calculations into a PLM concept? Actually,
a range of technical and conceptual requirements need to be met for this to happen, from integration into the user interface
through to consistent use of common product data. The simulation program must be completely integrated into the PLM system’s
user interface. This is normally supported by the PLM provider using an open software architecture based on a development
environment such as CAAV5 from Spatial Inc. Specialised companies can integrate their technology directly and use the existing
3D product data within CATIA V5 for calculations. However, flow simulations have the problem that the (empty) flow space to be
analysed for the calculation is not modelled as a separate component or assembly for grid generation in the original CAD design.
A special method, such as NIKA’s “Direct CAD to CFD” technology is therefore needed to allow a grid to be generated for the
flow space without separate CAD modelling. The normal method of deriving this calculation space from the CAD model and creating
the grid externally with a separate pre-processor is unacceptable from the perspective of the PLM concept. The links to the
original data and thus the advantages of integration into the CAD systems, such as feature-based model history and parameterisation,
are lost.
‘Direct CAD to CFD’ generates the flow grid without separate CAD modelling.
Picture: NIKA
|
Numerical methods for CFD calculations, which have become established in practice today, are mathematically based on discretisation
methods and require a calculation grid in the flow space. The time required to manually create a high quality CFD grid for
industrial applications is often the decisive variable in the total processing time for a simulation calculation. However,
this total processing time is in turn the critical factor that determines the benefit of flow simulations alongside development.
The entire project, starting with the first access to the 3D CAD model through to presentation of the verified calculation
results in the decision-making meeting, must keep pace with the internal development cycles. If results are delivered too late
or are of inadequate quality, they are worthless.
Access to CAD Data
Flow simulations integrated into PLM therefore need an automatic grid generator that delivers high-quality grids
optimised for flow calculations without excessive user input. The ability to directly access the original CAD data
plays a major role, as this is the only way to guarantee a high level of accuracy in mapping the flow geometry using
the calculation grid. The RAM (Rectangular Adaptive Mesh) grid technology included in the EFD.V5 simulation package
for CATIA V5 meets all of these requirements. Historically, CFD programs have often required extensive inputting of
parameters to completely define the available physical models. The terminology used also historically comes from
academic language and demands considerable “translation” before the values can actually be entered.
Flow calculation simplifies the design of a catalytic converter.
Picture: NIKA
|
Such models are useless for PLM-integrated flow simulations. Engineers have certain working methods that the simulation
software needs to adapt to. This includes limiting the required entries to important engineering data and clear use of
standard terminology. As well as being based on the familiar Windows standard, the engineering user interface in EFD.V5
provides assistance in creating a targeted model definition and identifying errors as early as possible.
Representation of flows in a ball valve.
Picture: NIKA
|
In most cases, the primary objective of the simulation calculations is to find the optimum solution to take account
of the flow processes in the design. As a consequence, a large number of alternatives are simulated, which include
modifications to the geometric parameters and to the physical input variables and flow conditions. One of the major
advantages of computer-based simulation is that alternatives can be studied and parameter studies performed with no
risk, economically and without using any actual materials. A modern PLM environment is the ideal platform for this,
as the components and assemblies are already parameterised and structured and it is therefore very easy to make
targeted changes to the parameter values. Of course, the simulation software must be consistent with feature concept
and offer the corresponding flow parameters as object-oriented features in addition to the geometric parameters and
manage them directly in the CAD system’s feature tree. EFD.V5 also supports a link to alternatives from design tables,
which allows a series of projects to be defined and then automatically processed.
|
|
