Flexibility or Performance? Modularity and Aero Engine Design

Year: 2008
Author: Bell, Theo A.
Supervisor: Jarrett, Jerome
Institution: University of Cambridge
Page(s): 218

Abstract

The design of aero engines is difficult, expensive and time-consuming. Consequently the industry typically follows a modular evolutionary design process to minimise the technological and business risks and maximise the return on invested design resources. A modular approach has much to commend it and has indeed been successful for many decades. Modularity of both the product and the design process facilitates the development of product families with varying thrust requirements and division of labour within the organisational structure. However, modularity can be a double-edged sword: to enable flexibility in the modules, there must be inflexibility in their interfaces. The interfaces form process-intrinsic constraints which are non-physical and purely artefacts of the decomposition into modules. While modularity improves the commercial return of a given architecture, the inflexibility of the architecture limits performance improvements as it matures. Not only is the aero engine industry showing signs of architectural maturity as asymptotes in performance are reached, improving environmental performance in particular is increasingly important for commercial success. Thus despite the advantages of modularity, it is appropriate to measure the impact of product flexibility on environmental performance. This work aims to measure the effects of modularity and process-intrinsic constraints on performance and product flexibility. By varying the number of fixed interfaces and the number of constraints fixed across them, the trade-offs between performance improvement and flexibility loss can be quantified. The hypothesis is that removing constraints and changing interfaces will reduce the design time needed to obtain the same performance and enable larger performance gains. The results of the four studies indicate support for the hypothesis: removing constraints and sacrificing product flexibility results in higher performance in less time. The effect is increased as more constraints are softened but the observed behaviour is bi-modal with large performance gains costing significantly more. Although integration of the design process while maintaining the original fixed interfaces was also found to improve performance without any loss of architectural flexibility, the benefits of changing interface values were much larger. As environmental impact brings performance improvements into the spotlight, transferring flexibility from the product to the design process could be part of the solution.