Towards a Robust Design Methodology for Growth Engine Concepts

Development of a clean sheet engine program can be finalized after many years of internal strategic decisions and plans, but the success of such a time- and cost-investing initiative cannot be guaranteed. For that reason, the concept of growth engines becomes crucial, mitigating potential risks through the idea of geometric core commonality. Specifically, it is an engine family program, deploying geometrically the same engine core (or high-pressure system); the most expensive, thermodynamically critical and most technologically advanced part of an aircraft engine. Although geometrically same, the engine core might have substantially different performance between the baseline and the growth engine configuration. Engine core performance might be optimal either for the baseline engine, or for any potential growth engine variant, thus imposing performance penalties when not optimal. On the other hand, low- and intermediate-pressure (if applicable) systems design can be modified to meet any thrust or power requirements imposed by aircraft manufacturers. Eventually, the growth engine family will need to take into consideration potential market criteria and demands in order for each variant to come to the best performance compromise.

The main part of this work focuses on developing a comprehensive methodology for defining the design space of possible engine cores that will sufficiently power a family of engines of different thrust and airframe requirements. Different time-frames of development are also considered through technology improvement factors. Potential performance trade-offs between optimal growth engine design and non-optimal baseline engine design are investigated (and vice versa), employing an in-house engine conceptual design framework. Thus, the framework targets at exploring the design space of best performance for the variants that need it the most, while ensuring that all variants are competitive among their rivals.

However, real engine designs and operations are always subject to uncertainties during any stage of the design phase. Production scatter, measurement uncertainty and performance deterioration are taken into account within the growth engine design methodology by performance deltas and factors. Probability distribution functions are also used to simulate component level uncertainty. Consequently, a robust growth engine design methodology is presented, considering real engine design uncertainty scenarios, and making the first step towards a robust optimal conceptual design framework for growth engine concepts.