Multi-disciplinary optimisation of a compressor rotor subjected to ice impact

Abstract

Compressors of gas turbine engines are multi-disciplinary systems whereas the different disciplines are largely considered separately. In order to produce feasible designs, the components need to be re-designed several times which is time consuming. A multi-disciplinary design process enabling an integrated approach for all discipline is described in this paper. The main disciplines considered are aerodynamics and ice impact-worthiness for the front stage intermediate pressure compressor (IPC) rotor of a modern three-spool jet-engine. Due to long lead times, ice impact analyses are usually not carried out until the aerodynamic design is reasonably mature. Only small changes to the rotor are usually allowed in order to satisfy the impact requirements that may lead to sub-optimal designs. Therefore, the introduction of ice impact analysis in the earlier design stages provides higher flexibility for the designers and leads to an overall better compressor performance. A fast thick-shell approach has been developed to model the transient dynamics of the compressor rotor impacted by crystalline ice cuboids released from upstream stators. The disciplines are linked using surrogate models which are based on the Kriging method. An adaptive multi-objective, multi-disciplinary optimisation approach has been used in order to increase the accuracy of the surrogate model iteratively in the areas of interest. It allows to optimise the performance of each discipline individually. The obtained Pareto front shows design trends in order to improve each discipline individually or both together. NOMENCLATURENumber of baldes/vanesNon-dimensional wall distance 1Copyright 2017 c by Rolls-Royce plc INTRODUCTIONAircraft fly through cold and moist air during take-off and landing where the liquid water droplets are super-cooled which means that the water temperature is below −15• C. The super-cooled water droplets are entering the core engine and are freezing instantaneously when hitting cold engine surfaces such as stators and casings. The ice accretes to thick crystalline ice shells and eventually shed in presence of vibrations and warmed-up components. The ice cuboids will then travel downstream impacting the compressor rotor. Due to the high rotor speeds, the ice impact cause severe mechanical damage. Hence, it is important to consider the impact-worthiness during the design process. Only the front stages of the compressor are typically affected by the ice impact threat as the rear stages are warmer. However, recent incidents shows that also melting ice particles can accrete on rear stages (Saxena et al. (2015)). In addition, the ice ingestion can affect the compressor aerodynamics causing a shift of the working line and stall margin when the ice melts and evaporates as shown by Saxena et al. (2015).Numerical impact analysis is common for many aircraft structures such as wings and windscreens and also fan blades. Most commonly, two kinds of foreign object damage (FOD), bird strike (softbody) and impact from foreign object debr...