Adaptive multi-objective aerofoil optimisation : impact of surface contamination and degradation

• Main Author: Cameron, Lee Stewart William.
• Published: Queen's University Belfast 2013
• Subjects: 629.13432
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.602451

The preliminary design of aerofoils for use in versatile air vehicles is considered, with a view to addressing the sensitivity of the boundary layer transition to surface imperfections arising through surface contamination and degradation. An efficient multi-objective optimisation framework has been developed, enabling optimal trade-offs between key flight conditions to be quantified which include the impact of surface contaminants on the evolution of the design space. The impact of surface contamination and degradation on the design of optimal profiles is assessed through the reduction in the critical amplification factor of boundary layer disturbances at the point of transition onset and the resulting Pareto front compared with comparative 'clean' surface cases. A meta-model assisted global search alleviates the expense of coupling the algorithms with expensive CFD solvers, with an adaptive Kriging -based strategy adopted. The surrogate is iteratively refined in promising regions of the design space according to a probablistic adaptive sampling algorithm. Optimal solutions identified using the global multi-objective search are further improved using a novel local search and reparameterisation scheme. Additional degrees of freedom are iteratively introduced into the parameterisation resulting in an increasingly flexible geometry description. The proposed framework is benchmarked against traditional approaches and found to be superior in both accuracy and efficiency. The requirement that take-off be insensitive to contamination effects proves to be a key consideration and the physical mechanisms by which this robustness in design is achieved are discussed.