Rate-Based Model Predictive Control of Turbofan Engine Clearance

An innovative model predictive control strategy is developed for a rapid-response, closed-loop active clearance control application, in which the objectives are to tightly regulate turbine blade tip clearances and also anticipate and avoid detrimental blade-shroud rub occurrences by optimally maintaining a predefined minimum clearance. At the heart of the controller is a rate-based linear parameter-varying model of a turbofan engine that extends performance to transient regimes in which conventional controllers begin to degrade. Engine-in-the-loop simulations of this rate-critical tip clearance control system with a variety of different actuators and uncertainty modes are presented, demonstrating the efficacy and versatility of this approach. Comparisons are made with a conventional linear quadratic control approach, where it is shown that substantial clearance gap reductions are possible by incorporating the strategy explored in this paper, thereby maximizing the cycle benefits that the tip clearance actuation/sensing hardware is capable of producing. Based on the results, it is concluded that the new strategy has promise for this and other nonlinear aerospace applications that place high importance on attaining strict control objectives during transient regimes.