Abstract
The inherent mathematical smoothness of intuitive class shape transformation (iCST) curves has been shown to be suitable for the design of aerodynamic shapes. However, this property means that any changes to a constraint are not local but will result in a modification to the whole curve. This poses a problem to the aerodynamic designer when different parts of the curve are required to fulfil particular design requirements. A Hybrid iCST (HiCST) parameterisation approach is proposed which allows two sections of a single aero-line curve to be decoupled, without geometric discontinuity, whilst maintaining the dimensionality of a design problem. The HiCST approach has been tested on two key aerodynamic components of an aero-engine. Firstly, a design space exploration and optimisation were carried out for an aero-engine fan cowl. A comparison of Pareto fronts showed a 3.9% reduction in the minimum achievable nacelle drag from the iCST to the HiCST parameterisation. Secondly, aero-engine intakes were designed with both the iCST and HiCST parameterisations. The HiCST intake showed improved aerodynamic performance in terms of DC60 and IPR and proved more insensitive to changes in massflow and incidence. This development of the method for an aero-engine fan cowl and intake highlights the potential aerodynamic benefit from the proposed HiCST method.
Highlights
Aerodynamic shapes can be represented in a number of ways
Of the 71 designs which had an inflection in the intuitive class shape transformation (iCST) formulation, only 3 had inflections on the fore-body when created with Hybrid iCST (HiCST)
This considerable improvement in the response to Mach number indicates that the use of HiCST to remove inflections from the designs allows a much improved design space and enables designs which would be poorly performing with an iCST formulation
Summary
The most basic approach is to construct the shape from a point cloud of co-ordinates. This method requires a large number of design variables to guarantee a smooth and accurate shape [1]. An alternative approach is free-form deformation (FFD) [13] which allows smooth global deformations of the reference shape and can reduce the overall number of design variables [14]. Two key considerations for the aerodynamic designer are the number of and intuitiveness of the design variables. The PARSEC parameterisation method is an aerodynamically intuitive approach it is unable to provide the required flexibility for airfoil design [16]. It is unable to provide high flexibility because it fails in the inverse design for some airfoils [17]
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