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Engineering Edge

Marrying Test & Simulation

The Whole is Greater Than the Sum of the Parts for Fuel Systems

Modern Design Engineers have at their disposal a variety of ways to help them in their work. The art lies in ensuring each method complements the others to ensure deadlines are met and costly reworking is avoided. Fábrica Argentina de Aviones have integrated Flowmaster fluid system simulation into their design process in a manner which maximises the return from their test programs and provides additional insight from the earliest possible stage in their design process.

Figure 1 Increasing Cost of Change in Design Process

It is widely acknowledged that there is a direct correlation between the cost to make a change in a design and the time since work on it commenced. As the process develops and more man-hours and resources are committed, the relationship becomes decidedly non-linear and even small changes can have large repercussions. Integrating simulation into the design process is a proven and established way of minimizing the risk of having to make a late change to any element of the design.

This principle works best when used in conjunction with 'traditional' experimental methods utilizing test results to validate simulation models, and applying simulation models to help focus experimental programs. The result is a streamlined design process that allows the strengths of all available methods to be brought to bear on a given problem in a cost effective manner.

Figure 2 IA 58 Pucará

Guillermo Robíglio, an engineer at Fábrica Argentina de Aviones (FAdeA) explains further, "When designing a new system, or modifying an existing one, we begin by creating 'virtual prototypes' in Flowmaster®. We can enhance the component models with our own test data and then begin the design process on this digital mock-up. This allows us to save a great deal of time and significantly reduce the risk of unexpected problems occurring later on when the design is at an advanced stage."

This principle was demonstrated during the re-engineering of the aircraft and the design stage of the adaptation of the fuel system of the IA-58 Pucará, a twin-engine turbo-propeller aircraft that has been in continuous service with the Argentinian Air Force since 1975. The ultimate goal was to produce a Flowmaster model that could provide information not only for steady state operation, but also on the transient response of the network under differing scenarios. For example, the design team may wish to know the time taken to fill or empty the inverted flight accumulators at different pneumatic pressures, the behavior of the system at different altitudes and attitudes or its performance following the failure of one or more components. In working toward this goal, FAdeA followed an extremely rigorous procedure which took maximum advantage of all the tools at their disposal. Where test results from individual components were available, or made available, they could be used to add an extra degree of reliability to the virtual prototype. In addition, having access to test facilities could be used to supply an extra degree of confidence in the model as a whole. "FAdeA has an extremely capable and high precision test facility at its disposal. This allowed us to validate almost all the simulations we made in Flowmaster. In every case the results were satisfactory and for that reason Flowmaster became an extremely valuable and trusted partner in the design process." explains Martin Blank, Manager of the Systems Team.

Figure 3 Pressure drop calculation in the fuel system of IA-58 Pucará

Knowing that he had a virtual prototype of such proven accuracy at his disposal allowed Guillermo to confidently deploy Flowmaster across a range of scenarios in order to generate a comprehensive picture of the system behavior. Not only was this achievable in a more cost effective and timely manner than would be possible using physical testing alone (like an 'iron bird' test), it also provided the design team an insight into areas of the system inaccessible to instrumentation. "We were able to identify a localized zone of high pressure in the Flowmaster model of the hydraulic system which was 'invisible' to our system indicator or the relief valves. However, with a virtual prototype at our disposal, discovering the location of this problem was as simple as noting a nodal pressure in the Flowmaster model." explains Guillermo Robiglio.


The integration of Flowmaster into the design loop has allowed FAdeA to increase the efficiency of their extensive test facilities. In turn, the test facilities have allowed the Systems Team to validate their virtual prototypes and so have confidence in using them to predict and understand system behavior across the design envelope. This method of working has proven itself so valuable that it is now the standard for the team, "Actually, every time we need to evaluate or design a fluid system we run lots of Flowmaster simulations," says Martin Blank, "this allows us to understand the behavior of that system very well." By taking full advantage of all the facilities and tools available to them, the Systems Team at FAdeA have been able to generate validated virtual system models that afford them the ability to test and interrogate their fluid systems to a degree and within timescales that wouldn't previously have been possible, This is also substantially cheaper to set up and run and virtual prototypes have the additional advantage that simulations can be run in seconds or minutes and without supervision.

Hence, batches of simulations can be run over lunch breaks or overnight. Furthermore, the advantages of working in this manner will only increase and become more apparent with time. As the library of test data and simulation results grows, the Systems Team will be in an even better place to predict the performance of new or redesigned systems.

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