During the course of the experiment the post-processing system builds up its own data base which is stored independently of the data base created by the wind tunnel data acquisition system. This data base contains identifiers for data points, sets and series as well as time stamps for each entry and experimental parameters. This allows to process series of data entries according to a variety of selection criteria. This may be done by specifying some of the parameters, such as Mach number and angle of attack and using wildcard symbols for other criteria.
The data evaluation system is made of two major components, a graphical user interface and a modular toolkit based on Unix-style filters.
Figure 8 Information flow between wind tunnel, control and data acquisition system, data evaluation system and engineers.
The graphical user interface is created by a GUI-builder 11. This CASE tool allows to create the user interface interactively. The advantage of using a GUI builder is the rapid creation of the user interface without any programming work. A user interface tailored to meet the requirements of a given wind tunnel experiment is easily created. Acceptance of the evaluation system is improved because the user interface may be kept simple and restricted to the functions needed for the test.
Due to the simplicity of this method, changes to the user interface may be performed with minimal effort. This also holds for extensions of the system and incorporation of new methods or algorithms.
All calculations are done outside the user interface in separate Unix programs. For complex operations these may be combined as pipes. The programs or modules to be called by the user interface are specified interactively inside the user interface. For this purpose, the interface has built-in configuration menus.
Methods or algorithms to be applied to the data may be selected from a large suite of tools developed earlier at the DLR 5. This toolkit (GRTools) comprises a variety of mathematical functions, filters, data converters and graphic tools. Only a few tools were needed for the F9-tests. The large variety of available tools offers great flexibility when building a data evaluation for any future wind tunnel test.
The toolkit also offers a well-defined application programming interface API. This allows to easily implement further methods if needed. Programming may be limited to the mathematical part of the new algorithm while all system access is provided by predefined functions.
The modularity of the system with all programs providing only a small functionality guarantees that the tools are re-usable for many applications.
The data processing system is not limited to tools taken from the GRTools toolkit or new modules. As the tools communicate through the standard Unix pipe mechanisms the whole world of filters, converter and tools available in a Unix environment is easily integrated into the system.
(c) by DLR, Institute for Fluid mechanics - 8 Oct 1997, hgp