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Flow Analysis – Not Just for Rocket Engines
Computational fluid dynamics is becoming increasingly important industry. Formerly the domain of a few highly
qualified computation specialists, new modelling tools are making it accessible to a wider group of users. The
new products speak the language of engineers. Products such as the software from NIKA described in this user
report are gaining ground, above all in areas where meaningful and presentation-ready results are required in
a short timeframe.
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Figure 1: Schematic representation of rocket engine
Picture: NIKA
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NIKA, a specialist in fluidic and thermal simulation programs, launched the world’s first CAD-integrated flow simulation
system back in 1999. It was designed exclusively for use on a PC under Windows NT. The software developers wanted to make
a CFD (Computational Fluid Dynamics) tool accessible to product developers outside major high-tech companies, as they had
previously only existed in the form of very complex and expensive programs.
It was not just companies in the automotive, aerospace and space industries that had a need for fluidic optimisation of
their products. Engineers in medical technology, building technology and production of all types of electronic equipment
and building services systems needed time and cost-saving tools to develop new products. Relying on colleagues’ experience,
laboriously obtained empirical data and expensive prototypes alone was no longer enough to keep up with the demands of our
fast-paced society.
The software manufacturer NIKA responded to these market requirements by developing the “FloWorks” flow analysis software,
which is based on EFD (Engineering Fluid Dynamics) technology, delivers clear data and is easy to operate.
Calculation for Ramjets
The benefits of the system convinced the engine and power train manufacturer Bayern-Chemie at Aschau am Inn. There,
development engineer Ralf Stierle performed calculations on air inlets on ramjets. “Air inlets are components of
controllable ramjets, whose thrust is varied by active regulation of the fuel delivery rate in line with mission
requirements”, he said, as an outline of the function. “Air breathing engines like this are used in supersonic and
hypersonic missiles.”
In previous years, Stierle performed the necessary FEM (finite element method) calculations using high-end tools and
software developed in-house. To supplement the programs used in the past, he needed an uncomplicated tool to obtain
quick estimates of fluid mechanics issues and to easily produce graphical representations of data for pre-development
studies and presentations. As part of a test installation of the SolidWorks CAD system, he also had the opportunity to
get to know FloWorks.
An initial demonstration of the software aroused Bayern’s curiosity. They followed this by using a test version, during
which time meaningful examples were used to test the software’s suitability for Bayern-Chemie. FloWorks impressed them
with its user-friendliness, the high level of compatibility with the SolidWorks CAD software and the excellent value for
money.
Figure 2: Ramjet on test bench
Picture: NIKA
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Simulating Flow Behaviour
With the programs he was previously using, Stierle had modelled the flow space himself and had to manually create
the corresponding calculation grids. Generating the calculation grid calls for a great deal of know-how and work.
Despite this, it was absolutely essential, as it is vital for the developer to understand which flow conditions
exist in the corresponding engine components.
This step is much simpler these days: FloWorks uses the CAD geometry to identify the cavity and automatically
generates the grid for it using hexahedron elements, an innovation in this area. The more complex the geometry,
the finer the grid, particularly in critical areas of the model such as boundary layers, turbulence zones, narrow
apertures, sharp edges or recirculation areas. The developer first uses the IDI (Intelligent Driver Interface) to
define the engineering calculation objective for the requested computer simulation. This objective then forms the
basis for the analysis process. There is no source of errors due to multiple entry of individual items of data.
FloWorks continuously improves the grid and automatically adjusts the grid points to the physical conditions.
IDI generates the results using isoplots, vector plots, particle tracks, intersections etc. Focusing on the objective
reduces the cycle times to a level that was previously impossible. During the automatically controlled process, a preview
function and graphical representation of the calculation progress allows constant monitoring of the processing status.
Once the calculation objectives defined by the user have been achieved, FloWorks automatically stops the program.
Maximum Results from Minimal Settings
Back to the missile engines. In the case of the ramjets, the developers at Bayern-Chemie evaluate the calculation
results on a phenomenological basis. They are more interested in the nature of the flow field than in the exact
numerical values. The observations made allow them to draw conclusions about the design and act as specifications
for design modifications. Stierle decides the accuracy of the results himself: “I use a minimal setting, which
allows me to achieve a reasonable result in a reasonable time. The advantage of FloWorks is that you can get what
you need quickly.” Of course, the accuracy can be increased to meet other requirements, ultimately providing stable
figures.
Although the development of a rocket involves warranty periods that go far beyond those that we are used to in the
fast-paced consumer society, the maxim “Time is money” still applies. Depending on the task, a program cycle can take
two to three days, excluding any extension. Simulating a symmetrical incoming flow reduces the cycle time as in this
case only a model reduced to the symmetrical axes has to be calculated.
However, if the angle of incidence is taken into account or spiralling flight with lateral and transverse incoming
flow is simulated, the complete model is essential. There are also other physical conditions that require very complex
calculations, for example the occurrence of compression waves in the supersonic range, the best know example of which
is the sonic boom.
Regardless of whether there is laborious calculation or a conclusion based on trends, the customer does not want
to receive column upon column of figures. The developers therefore present the results of their work in the form of
representative graphics. User Stierle demonstrates the graphical capabilities of the NIKA program using the examples shown.
Figure 3: Clear: The FloWorks software shows the pressure relationships in a missile at Mach 3
Picture: NIKA
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Practical Test Passed
Bayern-Chemie chose FloWorks around eighteen months ago. Once the program had been installed, they only needed
one day of training from NIKA. “Most of the functions were self-explanatory and every upgrade has brought genuine
improvements so far”, reports Stierle. His experiences with the NIKA Hotline have also been very positive, and he
has always received quick and expert assistance: “To date, I have not had to sit and wait for a solution to any of
my problems.”
As well as excellent service, the software manufacturer’s credo includes in-depth dialogue with its customers,
so that any problems or issues they have raised can be reflected in new developments. This was the basis for
FloWorks PE, the Professional Edition (PE) of the established FloWorks package. The PE version was extended with
additional functions to meet needs established by the manufacturer through dialogue with its customers. These special
functions include semi-automatic grid generation and solution monitoring, as well as network-based evaluation of results.
The advanced version of FloWorks also supports multi-processor computers, allowing it to deliver even demanding
calculation results in a short timeframe.
To solve specific analysis problems, the developers have added EFD Zooming, which allows simulation results for a large
calculation model to be used as general conditions for calculating smaller extracts of that model. Because of these
features, FloWorks PE has already been introduced as a useful upgrade version at Bayern-Chemie. For the future, Stierle
would like to see extensions in single-phase and multi-phase flows in subsequent programs to tackle some of his own specific
issues.
Development Continues
With the development of its EFD.Lab flow simulation program, NIKA is going in a completely new direction. While FloWorks was
primarily tailored to work with the SolidWorks CAD system, EFD.Lab is designed as a stand-alone solution and is independent
of specific CAD systems. The system exchanges data with CAD systems via import and export interfaces. This enables existing
CAD geometries to be transferred and processed with no problems.
This development will be of particular interest to companies that use different CAD systems. This is true of Bayern-Chemie.
“We mainly use CATIA. This makes using EFD.Lab an interesting option, which we are currently investigating”,
reports Stierle.
EFD.Lab Prefers Complexity
Based on positive experiences with FloWorks, the specialists at NIKA developed the EFD.Lab software as a flow simulation
tool specially designed for medium-sized industrial companies. The virtual prototypes it creates provide a variety of
options for varying different physical variables. Depending on the objectives of the simulation, users can either have
the flow space modelled automatically or set the grid parameters completely or partly themselves.
With automatic grid generation, EFD.Lab takes account of critical points in the model geometry and constantly adapts the
initial grid to the physical conditions during the calculation process. This adaptation principle based on the analysed
values is known as RAM (Rectangular Adaptive Mesh) results in increased accuracy at problematic points while simultaneously
reducing the required computer resources in less demanding areas. It is an extremely efficient method.
EFD.Lab creates virtual prototypes quickly and very cost effectively. Trying out various design solutions, for hydraulic or
pneumatic components or for the housing of electrical equipment, for example, is no longer the privilege of the “big boys” –
medium-sized companies can do it too. NIKA believes that there are applications for EFD.Lab in many industries. These include
manufacturers of engines, hydraulic and pneumatic components, computer housings, electronic equipment, refrigeration and air
conditioning systems and building technology.
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