|
|
|
Flow Simulations
Software Solutions for Simulations with NIKA
The trend towards using digital product data across the entire development and life cycle of a product
increasingly includes flow simulations. Suitable software solutions for simulating flow and heat transfer
processes allow engineers to deliver usable results in an acceptable timeframe based solely on their own
specialist knowledge.
Dr. Ivo Weinhold, Product Manager for NIKA GmbH
|
|
Figure 1: Speeds and temperatures in a control unit
Picture: NIKA
|
The acceptable timeframe for practical simulation alongside development in an industrial environment is normally
determined directly by the frequency of design modifications in the development process. The simulation results
for one design version must be available in a good quality sufficiently quickly to allow the findings to be
incorporated into the next round of modifications. This is the critical criterion for practical simulation
alongside development in industry. NIKA’s Engineering Fluid Dynamics software family enables complex flow and
heat transfer calculations to be efficiently incorporated into the development cycle for industrial products.
“We have been successfully using the EFD.Lab simulation tool for three years now. The software has become an
indispensable tool in our product development. It provides visualisations of fluid flow effects that previously
would have been very time consuming or downright impossible. This opportunity to visualise the effects opens up
totally new dimensions for designers developers in product design and optimisation”. This ringing endorsement
of the concept comes from Rocco Kemnitz, an engineer in the Research and Development department at RAPA Rausch & Pausch GmbH.
Handling the Geometry
In the digital engineering age, the initial version of the geometry to be analysed normally exists as a 3D CAD data record.
It therefore makes sense to make direct use of this data by integrating the simulation software into the relevant CAD environment.
However, for flow simulations we are faced with the problem that the (empty) flow space to be considered in the calculation is
not modelled as an independent part or assembly for subsequent use in the original CAD design. A special method such as the
“Direct CAD to CFD” EFD technology is therefore required to allow analysis of the flow space without separate CAD modelling.
Figure 2: Speed distribution in a connecting element
Picture: NIKA
|
Grid Generation
The established practical numerical methods for flow calculations are based mathematically on discretisation methods
and require a calculation grid in the flow space. The requirements in terms of the quality of this calculation grid
are particularly high for flow simulations, as it has a direct impact on the quality of the results and the efficiency
of the simulation calculations. EFD software therefore features an integrated automatic grid generator, which requires
at most a few user actions to function, even with extremely complex CAD geometries. The result is a special grid for
flow calculations, which uses a numerically very favourable cell form and features adaptive local refinement based
on geometric and physical criteria to allow analyses that make efficient use of resources. The “Direct CAD to CFD”
technology mentioned above allows a grid to be created over the flow area to be analysed using the original CAD data.
Calculation
The quality of the physical models and numerical solution algorithms has top priority. Here too, basic technologies such
as Modified Wall Functions (MWF) describing the special physical flow processes close to walls or the ACC convergence
control system for a stable solution in non-linear differential equation systems, provide the necessary framework for
high-quality, meaningful calculation results. In practice, this aspect is often neglected, but in many cases it is
decisive for the success or failure of a calculation and as such is a critical productivity factor in every simulation
project.
Evaluation and Documentation of Results
Every simulation result must be subjected to a plausibility and accuracy test by the engineer. EFD software provides a
variety of graphical and numerical evaluation functions closely related to the original 3D geometry. This means that
graphical representations are very clear and can often be easily understood even by non-technical staff. A direct link
to Office applications for numerical evaluation in tables and charts or to generate an automated results report enables
presentation-ready documentation to be produced extremely efficiently.
Analysing Alternatives
In most instances, the aim is not merely to perform calculations for a single model. The focus of interest is normally
on systematically identifying methods to improve the function and design of a product. In practice, this means calculations
need to be performed for a variety of geometrically and/or physically different alternatives, starting from an initial
version. Computer-based development methods such as EFD allow numerous alternatives, including unusual concepts, to be
“run through” with no risk. As an object-oriented simulation system, EFD software is based on the versions of the
parameterised CAD model organised using configurations, allowing corresponding versions of an EFD calculation project
to be created with minimum input from the user.
|
|
