Multi-Objective Optimisation of Aero-Engine Compressors

The design of a new aero-engine compressor is a complex task: design objectives are almost always conflicting, the design space is large, nonlinear and highly constrained, and the effects of some geometrical changes can be difficult to predict. Computational fluid dynamics (CFD) is now widely used in real-world applications and especially in the design of turbomachinery. However, the large design space and the time required for the numerical simulation of the whole turbomachine make the use of CFD in the early phases of the design process infeasible: preliminary design relies on a number of physical and empirical relations, still quite similar to those used in the early history of turbomachinery design. In this study, 87 independent parameters were used to define the geometry of a 7-stage compressor, the performance of which was evaluated using proprietary design codes for mean-line, multi-stage analysis. The effects on efficiency and surge margin of changing 44 design variables were analysed and their optimal values found by means of deterministic (gradient-based) and meta-heuristic (Tabu Search [TS]) optimisation methods. The results show clearly how the use of meta-heuristic optimisation tools can improve the preliminary design of turbomachinery, allowing a more thorough but still rapid exploration of the design space to identify the most promising regions that will then be verified and further analysed with higher fidelity tools. The results also reveal the impact of introducing various constraints into the design process, highlighting the effects of design decomposition

High resolution and high order methods for RANS modelling and aerodynamic optimization

With the optimisation of fixed aerodynamic shapes reaching its limits, the active flow control concept increasingly attracts attention of both academia and industry. Adaptive wing technology, and shape morphing airfoils in particular, represents a promising way forward. The aerodynamic performance of the morphing profiles is an important issue affecting the overall aerodynamic performance of an adaptive wing. A new concept of active flow, the Active Camber concept has been investigated. The actuator is integrated into the aerofoil and aerofoil morphing is realized via camber deformation. In order to identify the most aerodynamically efficient designs, an optimisation study has been performed using high resolution methods in conjunction with a two equation eddy viscosity model. Several different types of previously proposed compressible filters, including monotone upstream-centered schemes for conservation laws (MUSCL) and weighted essential non-oscillatory (WENO) filters, are incorporated and investigated in the present research. The newly developed CFD solver is validated and the effect that high resolution methods have on turbulent flow simulations is highlighted. The outermost goal is the development of a robust high resolution CFD method that will efficiently and accurately simulate various phenomena, such as shock/boundary layer interaction, flow separation and turbulence and thus provide the numerical framework for analysis and aerodynamic aerofoil design. With respect to the latter a multi-objective integrated design system (MOBID) has been developed that incorporates the CFD solver and a state-of-the-art heuristic optimisation algorithm, along with an efficient parametrization technique and a fast and robust method of propagating geometric displacements. The methodologies in the MOBID system resulted in the identification of the design vectors that revealed aerodynamic performance gains over the datum aerofoil design. The Pareto front provided a clear picture of the achievable trade-offs between the competing objectives. Furthermore, the implementation of different numerical schemes led to significant differences in the optimised airfoil shape, thus highlighting the need for high-resolution methods in aerodynamic optimisation.EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Interactive optimisation for high-lift design.

Interactivity always involves two entities; one of them by default is a human user. The specialised subject of human factors is introduced in the context of computational aerodynamics and optimisation, specifically a high-lift aerofoil. The trial and error nature of a design process hinges on designer’s knowledge, skill and intuition. A basic, important assumption of a man-machine system is that in solving a problem, there are some steps in which the computer has an advantageous edge while in other steps a human has dominance. Computational technologies are now an indispensable part of aerospace technology; algorithms involving significant user interaction, either during the process of generating solutions or as a component of post-optimisation evaluation where human decision making is involved are increasingly becoming popular, multi-objective particle swarm is one such optimiser. Several design optimisation problems in engineering are by nature multi-objective; the interest of a designer lies in simultaneous optimisation against two or more objectives which are usually in conflict. Interactive optimisation allows the designer to understand trade-offs between various objectives, and is generally used as a tool for decision making. The solution to a multi-objective problem, one where betterment in one objective occurs over the deterioration of at least one other objective is called a Pareto set. There are multiple solutions to a problem and multiple betterment ideas to an already existing design. The final responsibility of identifying an optimal solution or idea rests on the design engineers and decision making is done based on quantitative metrics, displayed as numbers or graphs. However, visualisation, ergonomics and human factors influence and impact this decision making process. A visual, graphical depiction of the Pareto front is oftentimes used as a design aid tool for purposes of decision making with chances of errors and fallacies fundamentally existing in engineering design. An effective visualisation tool benefits complex engineering analyses by providing the decision-maker with a good imagery of the most important information. Two high-lift aerofoil data-sets have been used as test-case examples; a multi-element solver, an optimiser based on swarm intelligence technique, and visual techniques which include parallel co-ordinates, heat map, scatter plot, self-organising map and radial coordinate visualisation comprise the module. Factors that affect optima and various evaluation criteria have been studied in light of the human user. This research enquires into interactive optimisation by adapting three interactive approaches: information trade-off, reference point and classification, and investigates selected visualisation techniques which act as chief aids in the context of high-lift design trade studies. Human-in-the-loop engineering, man-machine interaction & interface along with influencing factors, reliability, validation and verification in the presence of design uncertainty are considered. The research structure, choice of optimiser and visual aids adapted in this work are influenced by and streamlined to fit with the parallel on-going development work on Airbus’ Python based tool. Results, analysis, together with literature survey are presented in this report. The words human, user, engineer, aerodynamicist, designer, analyst and decision-maker/ DM are synonymous, and are used interchangeably in this research. In a virtual engineering setting, for an efficient interactive optimisation task, a suitable visualisation tool is a crucial prerequisite. Various optimisation design tools & methods are most useful when combined with a human engineer's insight is the underlying premise of this work; questions such as why, what, how might help aid aeronautical technical innovation.PhD in Aerospac